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1
Strauss, Toby Anthony Lavery. "The geology of the Proterozoic Haveri Au-Cu deposit, Southern Finland." Thesis, Rhodes University, 2004. http://hdl.handle.net/10962/d1015978.
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The Haveri Au-Cu deposit is located in southern Finland about 175 km north of Helsinki. It occurs on the northern edge of the continental island arc-type, volcano-sedimentary Tampere Schist Belt (TSB) within the Palaeoproterozoic Svecofennian Domain (2.0 – 1.75 Ga) of the Fennoscandian Shield. The 1.99 Ga Haveri Formation forms the base of the supracrustal stratigraphy consisting of metavolcanic pillow lavas and breccias passing upwards into intercalated metatuffs and metatuffites. There is a continuous gradation upwards from the predominantly volcaniclastic Haveri Formation into the overlying epiclastic meta-greywackes of the Osara Formation. The Haveri deposit is hosted in this contact zone. This supracrustal sequence has been intruded concordantly by quartz-feldspar porphyries. Approximately 1.89 Ga ago, high crustal heat flow led to the generation and emplacement of voluminous synkinematic, I-type, magnetite-series granitoids of the Central Finland Granitoid Complex (CFGC), resulting in coeval high-T/low-P metamorphism (hornfelsic textures), and D₁ deformation. During the crystallisation and cooling of the granitoids, a magmatic-dominated hydrothermal system caused extensive hydrothermal alteration and Cu-Au mineralisation through the late-D₁ to early-D₂ deformation. Initially, a pre-ore Na-Ca alteration phase caused albitisation of the host rock. This was closely followed by strong Ca-Fe alteration, responsible for widespread amphibolitisation and quartz veining and associated with abundant pyrrhotite, magnetite, chalcopyrite and gold mineralisation. More localised calcic-skarn alteration is also present as zoned garnetpyroxene- epidote skarn assemblages with associated pyrrhotite and minor sphalerite, centred on quartzcalcite± scapolite veinlets. Post-ore alteration includes an evolution to more K-rich alteration (biotitisation). Late D₂-retrograde chlorite began to replace the earlier high-T assemblage. Late emanations (post-D₂ and pre-D₃) from the cooling granitoids, under lower temperatures and oxidising conditions, are represented by carbonate-barite veins and epidote veinlets. Later, narrow dolerite dykes were emplaced followed by a weak D₃ deformation, resulting in shearing and structural reactivation along the carbonate-barite bands. This phase was accompanied by pyrite deposition. Both sulphides and oxides are common at Haveri, with ore types varying from massive sulphide and/or magnetite, to networks of veinlets and disseminations of oxides and/or sulphides. Cataclastites, consisting of deformed, brecciated bands of sulphide, with rounded and angular clasts of quartz vein material and altered host-rock are an economically important ore type. Ore minerals are principally pyrrhotite, magnetite and chalcopyrite with lesser amounts of pyrite, molybdenite and sphalerite. There is a general progression from early magnetite, through pyrrhotite to pyrite indicating increasing sulphidation with time. Gold is typically found as free gold within quartz veins and within intense zones of amphibolitisation. Considerable gold is also found in the cataclastite ore type either as invisible gold within the sulphides and/or as free gold within the breccia fragments. The unaltered amphibolites of the Haveri Formation can be classified as medium-K basalts of the tholeiitic trend. Trace and REE support an interpretation of formation in a back-arc basin setting. The unaltered porphyritic rocks are calc-alkaline dacites, and are interpreted, along with the granitoids as having an arc-type origin. This is consistent with the evolution from an initial back-arc basin, through a period of passive margin and/or fore-arc deposition represented by the Osara Formation greywackes and the basal stratigraphy of the TSB, prior to the onset of arc-related volcanic activity characteristic of the TSB and the Svecofennian proper. Using a combination of petrogenetic grids, mineral compositions (garnet-biotite and hornblendeplagioclase thermometers) and oxygen isotope thermometry, peak metamorphism can be constrained to a maximum of approximately 600 °C and 1.5 kbars pressure. Furthermore, the petrogenetic grids indicate that the REDOX conditions can be constrained at 600°C to log f(O₂) values of approximately - 21.0 to -26.0 and -14.5 to -17.5 for the metasedimentary rocks and mafic metavolcanic rocks respectively, thus indicating the presence of a significant REDOX boundary. Amphibole compositions from the Ca-Fe alteration phase (amphibolitisation) indicate iron enrichment with increasing alteration corresponding to higher temperatures of formation. Oxygen isotope studies combined with limited fluid inclusion studies indicate that the Ca-Fe alteration and associated quartz veins formed at high temperatures (530 – 610°C) from low CO₂, low- to moderately saline (<10 eq. wt% NaCl), magmatic-dominated fluids. Fluid inclusion decrepitation textures in the quartz veins suggest isobaric decompression. This is compatible with formation in high-T/low-P environments such as contact aureoles and island arcs. The calcic-skarn assemblage, combined with phase equilibria and sphalerite geothermometry, are indicative of formation at high temperatures (500 – 600 °C) from fluids with higher CO₂ contents and more saline compositions than those responsible for the Fe-Ca alteration. Limited fluid inclusion studies have identified hypersaline inclusions in secondary inclusion trails within quartz. The presence of calcite and scapolite also support formation from CO₂-rich saline fluids. It is suggested that the calcic-skarn alteration and the amphibolitisation evolved from the same fluids, and that P-T changes led to fluid unmixing resulting in two fluid types responsible for the observed alteration variations. Chlorite geothermometry on retrograde chlorite indicates temperatures of 309 – 368 °C. As chlorite represents the latest hydrothermal event, this can be taken as a lower temperature limit for hydrothermal alteration and mineralisation at Haveri.The gold mineralisation at Haveri is related primarily to the Ca-Fe alteration. Under such P-T-X conditions gold was transported as chloride complexes. Ore was localised by a combination of structural controls (shears and folds) and REDOX reactions along the boundary between the oxidised metavolcanics and the reduced metasediments. In addition, fluid unmixing caused an increase in pH, and thus further augmented the precipitation of Cu and Au. During the late D₂-event, temperatures fell below 400 °C, and fluids may have remobilised Au and Cu as bisulphide complexes into the shearcontrolled cataclastites and massive sulphides. The Haveri deposit has many similarities with ore deposit models that include orogenic lode-gold deposits, certain Au-skarn deposits and Fe-oxide Cu-Au deposits. However, many characteristics of the Haveri deposit, including tectonic setting, host lithologies, alteration types, proximity to I-type granitoids and P-T-X conditions of formation, compare favourably with other Early Proterozoic deposits within the TSB and Fennoscandia, as well as many of the deposits in the Cloncurry district of Australia. Consequently, the Haveri deposit can be seen to represent a high-T, Ca-rich member of the recently recognised Fe-oxide Cu-Au group of deposits.
2
Swift, Peter Norton. "EARLY PROTEROZOIC TURBIDITE DEPOSITION AND MELANGE DEFORMATION, SOUTHEASTERN ARIZONA." Dissertation-Reproduction (electronic), The University of Arizona, 1987. http://hdl.handle.net/10150/187544.
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Greenschist-facies, Lower Proterozoic metasedimentary rocks of the Johnny Lyon Rills and Little Dragoon Mountains of southeastern Arizona were deposited prior to the intrusion of an approximately 1690 Ma rhyodacite pluton. Well-preserved primary structures indicate deposition by turbidity currents in an intermediate to neardistal setting. Sandstone compositions suggest derivation from either a complex, heterogeneous source or multiple source terranes that provided mature, quartzose sediment as well as lesser quantities of volcaniclastic detritus. Earliest deformation, predating both intrusion of the rhyodacite and metamorphism, produced sections of melange composed primarily of dismembered turbidite beds, but also incorporating large (up to several km long) blocks of deformed basalt. Subsequent deformation, in part post-dating intrusion of the rhyodacite and in part coinciding with metamorphism, affected both melange and coherent strata, and involved isoclinal folding and layerparallel faulting and shearing. It is proposed that turbidite deposition occurred in a trench associated with a north-dipping subduction zone or on ocean floor outboard of such a trench. Melange formed primarily by ductile disruption of unlithified sediments within the subduction zone. Basalt blocks incorporated within the melange represent fragments of oceanic crust or seamounts detached from the lower plate during subduction. Later deformation and intrusion of the rhyodacite occurred within an accretionary prism above the subduction zone. Deformation within the prism ended prior to intrusion of the 1625 ± 10 Ma posttectonic Johnny Lyon Granodiorite.
3
Li, Longming, and 李龙明. "The crustal evolutionary history of the Cathaysia Block from the paleoproterozoic to mesozoic." PG_Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2010. http://hub.hku.hk/bib/B45693596.
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4
Wang, Wei, and 王伟. "Sedimentology, geochronology and geochemistry of the proterozoic sedimentary rocks in the Yangtze Block, South China." PG_Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2003. http://hdl.handle.net/10722/196033.
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The South China Craton comprises the Yangtze Block in the northwest and Cathaysia Block in the southeast. Located in the southeastern Yangtze Block, the Jiangnan Orogen formed through the amalgamation between the Yangtze and Cathaysia Blocks. The Yangtze Block has sporadically exposed Archean rocks in the north, Paleoproterozoic to Mesoproterozoic volcano-sedimentary sequences in the southwest and widespread Neoproterozoic sedimentary sequences accompanied by syn-sedimentary igneous rocks on the western and southeastern margins. The late Paleoproterozoic to early Mesoproterozoic Dongchuan, Dahongshan and Hekou groups in the southwestern Yangtze Block formed in a series of fault-controlled, rift-related basins associated with the fragmentation of the supercontinent Columbia. These sedimentary sequences were deposited between 1742 and 1503 Ma, and recorded continuous deposition from alluvial fan and fluvial sedimentation during the initial rifting to deep marine sedimentation in a passive margin setting. Sedimentation during initial rifting received felsic detritus mainly from adjacent continents, whereas sedimentation in a passive margin basin received detritus from felsic to intermediate rocks of the Yangtze Block. Paleoproterozoic to Mesoproterozoic rift basins in the southwestern Yangtze Block are remarkably similar to those of north Australia and northwestern Laurentia in their lower part (1742-1600 Ma), but significantly different after ca. 1600 Ma. The southwestern Yangtze Block was likely connected with the north Australia and northwestern Laurentia in Columbia but drifted away from these continents after ca. 1600 Ma. Traditionally thought Mesoproterozoic sedimentary sequences in the southeastern Yangtze Block are now confirmed to be Neoproterozoic in age and include the 835-830 Ma Sibao, Fanjingshan and Lengjiaxi groups, and 831-815 Ma Shuangqiaoshan and Xikou groups. These sequences are unconformably overlain by the ~810-730 Ma Danzhou, Xiajiang, Banxi, Heshangzheng, Luokedong and Likou groups. The regional unconformity likely marked the amalgamation between the Yangtze and Cathaysia Blocks and thus occurred at ~815-810 Ma. The lower sequences (835-815 Ma) received dominant Neoproterozoic (~980-820) felsic to intermediate materials in an active tectonic setting related to continental arc and orogenic collision, whereas the upper sequences represent sedimentation in an extensional setting with input of dominant Neoproterozoic granitic to dioritic materials (~740-900 Ma). The upper parts of the Shuangqiaoshan and Xikou groups, uncomfortably underlain by lower units, are molasse-type assemblages with additional input of pre-Neoproterozoic detritus, representing accumulation of sediments in a retro-arc foreland basin associated with the formation of the Jiangnan Orogen. Stratigraphic correlation, similarly low-δ18O and tectonic affinity of igneous rocks from different continents suggest that the Yangtze Block should be placed in the periphery of Rodinia probably adjacent to northern India. Paleoproterozoic (~2480 Ma and ~2000 Ma) and Early Neoproterozoic (711-997 Ma) were the most important periods of crustal and magmatic events of the southeastern Yangtze Block, but there is a lack of significant Grenvillian magmatism. Early Neoproterozoic magmatism highlights the contribution from both juvenile materials and pre-existing old crust, whereas ~2480 Ma and ~2000 Ma events are marked by reworking of pre-existing continental crust. Magmatism at 1600-1900 Ma was dominated by reworking of pre-existing crust, whereas the 1400-1600 Ma magmatic event recorded some addition of juvenile materials.
published_or_final_version
Earth Sciences
Doctoral
Doctor of Philosophy
5
Zhao, Junhong, and 趙軍紅. "Geochemistry of neoproterozoic arc-related plutons in the Western margin of the Yangtze Block, South China." PG_Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2008. http://hub.hku.hk/bib/B40203748.
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6
Harris, Charles William. "A sedimentological and structural analysis of the Proterozoic Uncompahgre Group, Needle Mountains, Colorado." Dissertation, Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/79644.
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Siliciclastic sediments of the Proterozoic Uncompahgre Group can be subdivided into stratigraphic units of quartzite (Q) and pelite (P); these units include a basal, fining- and thinning-upward retrogradational sequence (Q1-P1) that records the transition from an alluvial to a shallow-marine setting. Overlying the basal sequence are three thickening- and coarsening-upward progradational sequences (P2-Q2, P3-Q3 and P4-Q4) that were influenced by tide-, storm- and wave-processes. The progradational units are subdivided into the following facies associations in a vertical sequence. Outer-to inner-shelf mudstones, Bouma sequence beds and storm beds of association A are succeeded by inner-shelf to shoreface cross-stratified sandstones of association B. Conglomerates and cross-bedded sandstones of upper association B represent alluvial braid-delta deposits. Tidal cross-bedded facies of the inner shelf/shoreface (association C) gradationally overlie association B. Interbedded within the tidal facies in upper association C are single pebble layers or <1 m-thick conglomerate beds and trough cross-bedded pebbly sandstones. Single pebble layers could be due to storm winnowing whereas conglomerates and pebbly sandstones may record shoaling to an alluvial/ shoreface setting. A temporally separated storm/alluvial and tidal shelf model best explains the origin and lateral distribution of facies in the progradational sequences. The presence of smaller progradational increments in the mudstone dominated units (P3) and the recurrence of facies associations in the thick quartzite/conglomerate units (Q2, Q3, Q4) suggests that external cyclic factors controlled sedimentation. A composite relative sea level curve integrating glacio-eustatic oscillations and long-term subsidence may account for the evolution of the thick progradational sequences of the Uncompahgre Group. Sedimentary rocks of the Uncompahgre Group have been subjected to polyphase deformation and greenschist facies metamorphism. Phase 1 structures (localized to the West Needle Mountains) include bedding-parallel deformation zones, F₁ folds and an S₁ cleavage. Phase 2 coaxial deformation resulted in the development of upright, macroscopic F₂ folds and an axial-planar crenulation cleavage, S₂. In addition basement-cover contacts were folded. Phase 3 conjugate shearing generated strike-parallel offset in stratigraphic units, a macroscopic F₃ fold, and an S₃ crenulation cleavage. In addition, oblique-slip, reverse faults were activated along basement-cover contacts. The Uncompahgre Group unconformably overlies and is inferred to be parautochthonous upon ca. 1750 Ma gneissic basement that was subjected to polyphase deformation (DB) and amphibolite facies metamorphism. Basement was intruded by ca. 1690 Ma granitoids. Deformation of gneissic and plutonic basement together with cover (DBC) postdates deposition of the Uncompahgre Group. The structural evolution of the Uncompahgre Group records the transition from a ductile, north-directed, fold-thrust belt to the formation of a basement involved “megamullion" structure which was subjected to conjugate strike-slip faulting to accommodate further shortening. DBC deformation may be analogous to the deep foreland suprastructure of an orogenic belt that developed from ca. 1690 to 1600 Ma in the southwestern U.S.A ..
Ph. D.
7
Saylor, Beverly Z. (Beverly Zella). "Sequence stratigraphic and chemostratigraphic constraints on the evolution of the terminal Proterozoic to Cambrian Nama Basin, Namibia." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/10668.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1996.
Includes bibliographical references (p. 117-124).
by Beverly Z. Saylor.
Ph.D.
8
Gibson, R. G. "Structural studies in a Proterozoic gneiss complex and adjacent cover rocks, west Needle Mountains, Colorado." Dissertation, Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/76096.
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Proterozoic rocks in the Needle Mountains include ca. 1750 Ma amphibolite-grade, metavolcanic and metaplutonic gneisses and ca. 1690 Ma granitoids that comprise the basement to the siliciclastic Uncompahgre Group. The mafic and felsic gneisses underwent synkinematic metamorphism and two phases of isoclinal folding and foliation development during DB, prior to emplacement of the ca. 1690 Ma plutons. DBC deformation caused folding of DB fabrics in the gneisses, development of a subvertical, east-striking foliation in the granitoids, and generation of a macroscopic sigmoidal foliation pattern throughout the area prior to 1430 Ma. DBC structures in the basement are correlated with macroscopic structures in the Uncompahgre Group, which was deformed into an east-trending cuspate synclinorium during this event. Gently plunging mineral lineations and asymmetric kinematic indicators in the basement record a component of dextral strike-slip shearing in domains of east-striking foliation and sinistral shearing in areas of northeast-striking foliation. A model for DBC involving the development of conjugate strike-slip shear zones in response to north-northwest shortening is most consistent with the kinematic and fabric orientation data. A zone of phyllite, derived largely from basement, occurs everywhere along the basement-cover contact. Kinematic indicators along and near the contact record upward movement of the cover relative to the basement on each side of the synclinorium and imply that the cover rocks are parautochthonous. Stratigraphic facing of the cover rocks away from the basement supports the interpretation of this contact as an unconformity at the base of the Uncompahgre Group. Alteration of the basement rocks along this contact involved hydration and the loss of CaO, MgO, SiO₂, and Na₂O. The phyllite zone is interpreted as a metamorphosed and deformed regolith that localized out-of-synform movement while the basement and its parautochthonous cover were folded together during DBC. Rocks in the Needle Mountains comprise part of the Colorado Province, one of several terranes that were possibly accreted to the Archean Wyoming Craton during the Proterozoic. Age constraints on the timing of deformation indicate that DB and DBC are representative of two regionally extensive deformational episodes. Pre-1700 Ma deformation is attributed to the assembly of volcanogenic terranes and their accretion to the Wyoming Craton along the Cheyenne Belt. Post-1700 Ma deformation resulted from regional north-northwest crustal shortening induced by tectonic interactions along the southern margin of the Colorado Province. These results support the hypothesis that terrane accretion was important in the Proterozoic crustal evolution of southwestern North America.
Ph. D.
9
Hill, Robert E. (Robert Einar). "Stratigraphy and sedimentology of the Middle Proterozoic Waterton and Altyn Formations, Belt-Purcell Supergroup, southwest Alberta." Electronic Thesis or Dissertation, McGill University, 1985. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=63330.
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10
Lane, Robert Andrew. "Geologic setting and petrology of the Proterozoic Ogilvie Mountains breccia of the Coal Creek inlier, southern Ogilvie Mountains, Yukon Territory." Thesis/Dissertation, University of British Columbia, 1990. http://hdl.handle.net/2429/29196.
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Ogilvie Mountains breccia (OMB) is in Early (?) to Late Proterozoic rocks of the Coal Creek Inlier, southern Ogilvie Mountains, Yukon Territory. Host rocks are the Wernecke Supergroup (Fairchild Lake, Quartet and Gillespie Lake groups) and lower Fifteenmile group. Distribution and cross-cutting relationships of the breccia were delineated by regional mapping. OMB was classified by clast type and matrix composition. Ogilvie Mountains breccia crops out discontinuously along two east-trending belts called the Northern Breccia Belt (NBB) and the Southern Breccia Belt (SBB). The NBB extends across approximately 40 km of the map area, and the SBB is about 15 km long. Individual bodies of OMB vary from dyke- and sill-like to pod-like. The breccia belts each coincide with a regional structure. The NBB coincides with a north side down reverse fault—an inferred ruptured anticline—called the Monster fault. The SBB coincides with a north side down fault called the Fifteenmile fault. These faults, at least in part, guided ascending breccia. The age of OMB is constrained by field relationships and galena lead isotope data. It is younger than the Gillespie Lake Group, and is at least as old as the lower Fifteenmile group because it intrudes both of these units. A galena lead isotope model age for the Hart River stratiform massive sulphide deposit that is in Gillespie Lake Group rocks is 1.45 Ga. Galena from veinlets cutting a dyke that cuts OMB in lower Fifteenmile group rocks is 0.90 Ga in age. Therefore the age of OMB formation is between 1.45 and 0.90 Ga. Ogilvie Mountains breccia (OMB) has been classified into monolithic (oligomictic) and heterolithic (polymictic) lithologies. These have been further divided by major matrix components—end members are carbonate-rich, hematite-rich and chlorite-rich. Monolithic breccias with carbonate matrices dominate the NBB. Heterolithic breccias are abundant locally in the NBB, but are prevalent in the SBB. Fragments were derived mainly from the Wernecke Supergroup. In the SBB fragments from the lower Fifteenmile group are present. Uncommon mafic igneous fragments were from local dykes. OMB are generally fragment dominated. Recognized fragments are up to several 10s of metres across and grade into matrix sized grains. Hydrothermal alteration has locally overprinted OMB and introduced silica, hematite and sulphide minerals. This mineralization has received limited attention from the mineral exploration industry. Rare earth element chemistry reflects a lack of mantle or deep-seated igneous process in the formation of OMB. However, this may be only an apparent lack because flooding by a large volume of sedimentary material could obscure a REE pattern indicative of another source. The genesis of OMB is significantly similar to modern mud diapirs. It is proposed that OMB originated from pressurized, underconsolidated fine grained limey sediments (Fairchild Lake Group). These were trapped below and loaded by turbidites (Quartet Group) and younger units. Tectonics and the initiation of major faults apparently triggered movement of the pressurized fluid-rich medium. The resulting bodies of breccia are sill-like and diapir-like sedimentary intrusions. Fluid-rich phases may have caused hydrofracturing (brittle failure) of the surrounding rocks (especially in the hanging wall). Breccia intrusion would have increased the width of the passage way while encorporating more fragments. Iron- and oxygen-rich hydrothermal fluids apparently were associated with the diapirism. Presumably these fluids are responsible for the high contents of hematite and iron carbonate in fragments, and especially, in the matrix of the breccias. Exhalation of these fluids may have formed the sedimentary iron formations that are spatially associated with the breccias.
Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate
11
Teitz, Martin W. "Late proterozoic Yellowhead and Astoria Carbonate Platforms, southwest of Jasper, Alberta." Electronic Thesis or Dissertation, McGill University, 1985. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=63371.
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12
Simpson, Edward L. "Sedimentology and tectonic implications of the Late Proterozoic to Early Cambrian Chilhowee Group in southern and central Virginia." Dissertation, Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/53660.
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Few detailed facies analyses of rift to passive-margin transitions have been undertaken in exhumed orogenic belts. In the central Appalachians, the Chilhowee Group records such an evolution. The Unicoi and basal Hampton Formations record the transition from rifting to opening of the Iapetus Ocean. The majority of the Hampton Formation and the overlying Erwin Formation represent an overall regressive sequence punctuated by five progradational packages that accumulated along a passive margin. The rift to passive·margin phases of sedimentation in the central Appalachians reflect a continuum from fault·influenced to thermotectonic subsidence. Alluvial sediments and intercalated basalts of the lower Unicoi Formation developed in a rift setting. Paleontological data indicate that rifting continued into lower Cambrian time. The upper Unicoi Formation represents the incipient phase of passive-margin sedimentation related to a first-order, sea level rise. Differences in degree of crustal attenuation controlled the distribution of sedimentary environments during transgression. On the most attenuated crust to the east, initial transgressive facies consist of tidal sandwave and sandridge deposits intercalated with proximal and medial braid-pIain deposits. As transgression progressed cratonwards onto less attenuated crust, tidal sedimentation was supplanted by tide- and wave-influenced sedimentation characterized by sandwave complexes, tidal inlets and longshore bedforms. Drowning at the top of the Unicoi Formation is indicated by outer-shelf black mudstones. Deepening may have been enhanced by continued movement along listric faults throughout the incipient phase of passive-margin development. Examination of outcrops of the Hampton and Erwin Formations on different thrust sheets has permitted an across-strike reconstruction of the Early Cambrian Chilhowee shelf in space and time. Progradational packages developed under storm- and fair·weather wave conditions. Coarsening· and thickening-upward sequences on westerly thrust sheets were generated during progradation of shoreface, inner-shelf and outer-shelf environments. Outer-shelf facies predominate on easterly thrust sheets. Intertidal-flat deposits on the most westerly thrust sheet erosively overlie progradational shoreface sediments and developed during transgression in an embayment in which the tidal wave was amplified. More distal transgressive deposits consist of fining- and thinning·upward sequences with glauconitic horizons, and condensed sections in mudstones.
Ph. D.
13
Sun, Weihua, and 孙卫华. "The neoproterozoic Yanbian group and associated plutons in the westernYangtze block, SW China." PG_Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2009. http://hub.hku.hk/bib/B41897158.
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14
Johnson, Shannon D. "Structural geology of the Usakos Dome in the Damara Belt, Namibia." Thesis, Stellenbosch : Stellenbosch University, 2008. http://hdl.handle.net/10019.1/50457.
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Thesis (MSc)--Stellenbosch University, 2005.
ENGLISH ABSTRACT: The northeast-trending south Central Zone (sCZ) of the Pan-African Damara belt in central Namibia is structurally characterized by kilometer-scale, northeast-trending dome structures developed in Neoproterozoic rocks of the Damara Sequence. A number of different structural models have been proposed for the formation of these domes in the literature. This study describes the structural geology of the Usakos dome. The study discusses the structural evolution of the dome within the regional framework of the cSZ that represents the high-grade metamorphic axis of the Damara Belt, characterized by voluminous Pan-African granitoids. The northeastern part of the Usakos dome is developed as an upright- to northwestverging anticlinorium containing a steep southeasterly-dipping axial planar foliation. The northeast fold trend persists into the southwestern parts of the Usakos dome. However, this southwestern core of the dome is inundated by synkinematic granitic sheets. Distinct marker horizons of the Damara Sequence outcrop as screens within the granite, preserving a ghost stratigraphy. These screens illustrate the position and orientation of second-order folds. Significantly, most of the stratigraphy of the Damara Sequence is overturned in these folds. For example, some second-order anticlines developed in the northeastern parts of the Usakos dome can be followed along their axial traces into the southwestern hinge of the dome, where they appear as synformal anticlines, i.e. synformal structures cored by older strata, plunging towards the northeast. The inverted stratigraphy and northeasterly fold plunges suggest the northeast-trending folds are refolded by second-generation, northwest-trending folds, thus, forming kilometer-scale Type-2 interference folds. The resulting fold geometries are strongly non-cylindrical, approaching southwest-closing sheath folds indicating a top-to-the-southwest material transport. Lower-order folds in this overturned domain show radial fold plunges, plunging away from the centre of the dome core, as well as a shallowly-dipping schistosity. The close spatial and temporal relationship between granite intrusion and the formation of the southwest-vergent, sheath-type folds, radial distribution of fold plunges and the subhorizontal foliation confined to the southwestern hinge of the Usakos dome are interpreted to signify the rheological weakening and ensuing collapse of the developing first-order Usakos dome immediately above the synkinematic granite intrusions. Orogenparallel, southwest-vergent sheath folds and top-to-the southwest extrusion of the southwestern parts of the Usakos dome and northwest-vergent folding and thrusting characterizing the northeastern extent of the Usakos dome are both responses to the northwest-southeast- directed contractional tectonics recorded during the main collisional phase in the Damara belt. On a regional scale, the Usakos dome represents the link between the foreland-vergent northeastern part of the sCZ and the southwest-vergent, high-grade southwestern parts of the sCZ. The results of this study illustrate how dramatic variations in structural styles may be caused by the localized and transient rheological weakening of the crust during plutonic activity.
AFRIKAANSE OPSOMMING: Die noordoos-strekkende, suidelike Sentrale Sone (sSS) van die Pan-Afrikaanse Damara gordel in sentraal Namibië word karakteriseer deur kilometer-skaal, noordoosstrekkende koepel strukture, ontwikkel in die Neoproterozoïkum gesteentes van die Damara Opeenvolging. 'n Aantal verskillende struktuur modelle is voorgestel in die literatuur vir die vorming van hierdie koepels. Hierdie ondersoek beskryf die struktuur geologie van die Usakos koepel. Die ondersoek bespreek die strukturele ontwikkeling van die koepel in die regionale konteks van die sSS, wat die hoë graadse metamorfe magmatiese as van die Damara Gordel verteenwoordig, en karakteriseer word deur omvangryke Pan-Afrikaanse granitoïede. Die noordoostelike gedeelte van die Usakos koepel is ontwikkel as 'n antiklinorium met 'n vertikale- tot noordwestelike kantelrigting. wat 'n steil hellende, suidoostelike asvlak planêre foliasie bevat. Die noordoos-strekkende plooiing kom voor tot in die suidwestelike kern van die Usakos wat ingedring is deur sinkinematiese granitiese plate. Die posisie en oriëntasie van tweede-orde plooie is afgebeeld in die graniete deur 'n skimstratigrafie wat preserveer is deur duidelike merker horisonne van die Damara Opeenvolging. Die stratigrafie van die Damara Opeenvolging is opmerklik meestal omgekeer in hierdie plooie. Byvoorbeeld, tweede-orde antikliene ontwikkel in die noordoostelike gedeelte van die Usakos koepel kan gevolg word langs hul asvlakspore tot in die suidwestelike skarnier van die koepel, waar dit voorkom as sinforme antikliene, d.w.s. sinforme strukture met ouer strata in die kern wat na die noordooste duik. Die omgekeerde stratigrafie en noordoostelike plooi duiking impliseer dat die noordoosstrekkende plooie weer geplooi is deur tweede-generasie, noordwes-strekkende plooie, wat dus aanleiding gegee het tot die vorming van kilometer-skaal, tipe-2 interferensie plooie. Die gevolglike plooi geometrieë is uitdruklik nie-silindries, en toon 'n oorgang na skede plooie met 'n sluiting na die suidweste, wat dui op 'n bokant-na-die-suidweste materiaal vervoer. Laer-orde plooie in die omgekeerde domein vertoon radiale duiking van die plooie, weg van die middelpunt van die koepel kern, sowel as 'n vlak hellende skistositeit. Die noue ruimtelike en temporele verwantskap tussen graniet intrusie en die vorming van skede-tipe plooie met 'n kantelrigting na die suidweste, die radiale verspreiding van plooi duiking, en die subhorisontale foliasie wat beperk is tot die suidwestelike skarnier van die Usakos koepel, word interpreteer as 'n aanduiding van die reologiese verswakking en die gevolglike ineenstorting van die ontwikkelende eerste-orde Usakos koepel, onmiddellik aan die bokant van die sinkinematiese graniet intrusies. Die orogeenparalleie skede plooie met kantelrigting na die suidweste en bokant-na-die-suidweste ekstrusie van die suidwestelike gedeelte van die Usakos koepel, en plooiing met kantelrigting na die noordweste en stootverskuiwing wat kenmerkend is van die noordoostelike gedeelte van die Usakos koepel, is beide 'n reaksie op die noordwessuidoos- gerigte vernouings tektoniek opgeteken gedurende die hoof botsings fase in die Damara gordel. Op 'n regionale skaal verteenwoordig die Usakos koepel die verbinding tussen die noordoostelike gedeelte van die sSS met 'n voorland kantelrigting. en die hoë graad suidwestelike gedeelte van die sSS met 'n kantelrigting na die suidweste. Die resultate van hierdie ondersoek toon aan hoe dramatiese variasies in struktuur style veroorsaak kan word deur die gelokaliseerde en kortstondige reologiese verswakking van die kors gedurende plutoniese aktiwiteit.
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Moodley, Jason Anthony. "Petrogenesis of the Bysteek and Koenap Formation Migmatites, Central Namaqualand." Thesis, Rhodes University, 2013. http://hdl.handle.net/10962/d1001574.
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The Mesoproterozoic rocks of the Bysteek and Koenap Formations of the Arribees Group are exposed within a NW-SE striking antiformal structure comprised of mafic granulites and metapelitic diatexites, and a number of marble and calc-silicate rock layers. The mafic granulites of the Bysteek Formation show a typological variety of anatectic features, including nebulitic, stromatitic mesosomes, melanosomes, quartz syenitic leucocratic vein networks and syenitic pools. Melanosomes consist of hedenbergitic to diopside-rich clinopyroxene (XMg: 0.40), anorthitic plagioclase (An90), with some quartz, minor apatite and titanite. Anatexis was caused by biotite dehydration melting and formed a melt of probably granitic composition. The leucosome composition ranges from either alkali-feldspar-granitic to plagioclase rich or granitic. This variation is interpreted as a result of variable extraction of melt from the source to granitic pools. The diatexites of the Koenap Formation are most likely of metapelitic or meta-greywacke origin. They are texturally variable but always contain high modal contents of alkali feldspar and quartz which generally form magmatic textures. Almandine-rich garnet (XMg: 0.18-0.25), cordierite (XMg: 0.71) form secondary biotite, sillimanite and magnetite during retrograde breakdown. Thermodynamic modelling of mafic granulite compositions suggests peak P-T conditions of ~865 °C and 8.6 kbar. Occasionally, garnet rich in ferric iron (XAdr: 0.55) forms by plagioclase-clinopyroxene breakdown under oxidising conditions at ~6 kilobar and ~ 800 °C. At the same stage amphibole forms in some melanosomes. P-T estimations for the diatexites based on thermodynamic modelling suggest the equilibration of the assemblage garnet, cordierite, alkali feldspar and melt at ~860 °C and 5.5 kbar. Conditions comparable to the peak pressure in the mafic granulites could not be established. However, since the diatexites and the mafic granulites are closely related in the field and no evidence of juxtaposition after the thermal peak exists, the P-T record of the diatexites might be incomplete
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Greentree, Matthew Richard. "Tectonostratigraphic analysis of the Proterozoic Kangdian iron oxide - copper province, South-West China." University of Western Australia. Tectonics Special Research Centre, 2007. http://theses.library.uwa.edu.au/adt-WU2009.0054.
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The Cenozoic Ailaoshan – Red River shear zone marks the present day western margin of the South China Block. Along this margin are well preserved late Paleoproterozoic to early Neoproterozoic sedimentary and volcanic successions. This work examines the ages and tectonic environments for the formation of the successions, as well as significance of the regional tectono-magmatic events on the formation of widespread iron oxide-copper deposits. The oldest succession is the Paleoproterozoic Dahongshan Group. A new SHRIMP UPb age of 1675 ± 8 Ma for a tuffaceous schist unit confirms its Paleoproterozoic age. Detrital zircon ages of the Dahongshan Group range between Archean to Paleoproterozoic (ca. 2780 – 1860 Ma). They include a population of ca. 2400 – 2100 Ma grains, which have no known source region on the exposed Yangtze Block. Previous geochemical studies of metavolcanic rocks from the Dahongshan Group have suggested that these rocks were erupted in an oceanic setting. However, this study shows that the metavolcanics are extremely altered and cannot be used for reliable tectonic discrimination. Based on the characteristics of sedimentary rocks in the Dahongshan Group, it is suggested that these rocks were deposited in a continental setting. Overlying the Dahongshan Group is a thick sedimentary sequence which has been variably termed the Kunyang, Dongchuan, Huili or Xide Groups. In the past, these rocks have been considered as a Mesoproterozoic rift succession. However, no precise age constraints were available for the succession. In this study, this sequence is found to contain at least two separate tectonostratigraphic units. The oldest (ca.1140 Ma) is comprised of alkaline basalt with a geochemical and isotopic character similar to that of modern intracontinental rift basalts. The presence of Cathaysia-derived sediments in this unit indicates sedimentary transportation from the southerly Cathaysia Block to the northerly Yangtze Block (in present coordinates) in South China at that time, which suggests an “impactogen” scenario. The thick sedimentary sequence of what has traditionally been defined as the Kunyang Group has been found to have significantly younger depositional age of ca.1000 – 960 Ma. The composition of sedimentary rocks and the provenance of detrital zircons from the Kunyang Group are consistent with a foreland basin setting. The depositional age of this sequence coincides with the timing of Sibao Orogeny as determined elsewhere in the South China Block. Summary Page ii Numerous iron oxide - copper (gold) deposits occur within the rocks of the Dahongshan and Kunyang Groups. Previous studies have classified these deposits into two deposit styles: the Dahongshan-type Paleoproterozoic VMS mineralisation hosted within the Dahongshan Group, and the Dongchuan-type diagenetic carbonate and shale-hosted deposits hosted within the Kunyang Group. However, both deposit types share similarities with the iron oxide – copper (gold) deposit class, such as stratabound disseminated and massive copper ores, abundance of iron oxide occurring mostly as low Ti - magnetite and haematite, and variable enrichments in Au, Ag, Co, F, Mo, P and REE. 40Ar/39Ar data from both deposit types indicate mineralisation ages of ca. 850 – 830 Ma and 780 – 740 Ma.
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He, Yanhong, and 何艷紅. "Ages and geochemistry of the Xiong'er volcanic rocks along the southern margin of the North China Craton: implications for the outgrowths of the paleo-mesoproterozoicsupercontinent Columbia (Nuna)." PG_Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2008. http://hub.hku.hk/bib/B4163424X.
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Booth, Peter William King. "Pan-African imprint on the early mid-proterozoic Richtersveld and Bushmanland sub-provinces near Eksteenfontein, Namaqualand, Republic of South Africa." Doctoral Thesis, University of Cape Town, 1990. http://hdl.handle.net/11427/26232.
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The present investigation examines the relationship between the Proterozoic Richtersveld and Bushmanland Subprovinces in the westernmost part of the Namaqua Province, near Eksteenfontein, Republic of South Africa. There is a controversy about this relationship because isotopic data contrast with field evidence. On a regional scale the Richtersveld Subprovince is separated from the Bushmanland Subprovince by the northward-dipping Groothoek Thrust. North of the thrust the Richtersveld Subprovince is comprised of low grade volcano/ plutonic rocks of the Vioolsdrif Terrane and medium grade volcano sedimentary sequences of the Pella Terrane. Medium grade rocks of the Steinkopf Terrane (Bushmanland Subprovince) lie immediately south of the thrust. Late Proterozoic strata of the Stinkfontein Formation (Gariep Group) overlie the Namaqua Province in the west; Cambrian Nama Group outliers occur east of the Stinkfontein Formation. Isotopic data show that lithologies of the Richtersveld Subprovince formed between 2000 - 1730 Ma, whereas those of the Bushmanland Subprovince are younger. It is not clear whether the Namaqua metamorphic imprint (at 1200 - 1100 Ma), which is manifest in terranes south of the Groothoek Thrust, extended as far as the Vioolsdrif Terrane in the north. Early Proterozoic structural and metamorphic imprints are inferred to have been obliterated during this event. The westernmost part of the Namaqua Province was overprinted for a distance of 100 km from the coast, during the Pan-African event at 700 Ma and 500 Ma. An area measuring nearly 500 km2 , traversing the western extremity of the boundary between the Richtersveld and Bushmanland Subprovinces was mapped on a scale of 1:36,000. Field mapping was carried out with the aid of aerial photographs, whereas laboratory techniques included map compilation, structural analysis, X-ray diffractometry, geochemical (XRF) and electron microprobe analyses. Supracrustal units of the Richtersveld Subprovince are composed of quartzo-feldspathic gneisses, schists, and minor meta-pelites. Supracrustals of the Bushmanland Subprovince are less diverse than those of the Richtersveld Subprovince and have a disconformable relationship with them. Most intrusive rock-types are thick granitic sheets, except the Early Proterozoic Vioolsdrif Granodiorite which forms part of a batholithic pluton in the north. The Sabieboomrante adamellite gneiss, Kouefontein granite gneiss and Dabbieputs granite gneiss could not be correlated with lithologies commonly occurring in the Richtersveld and Bushmanland Subprovinces. They have been given the new rock names. Mafic and ultramafic rocks of the Klipbok complex occur along the strike of the Groothoek Thrust. They form part of the Richtersveld Subprovince.
19
Vallini, Daniela Alessandra. "The formation of authigenic xenotime in Proterozoic sedimentary basins : petrography, age and geochemistry." University of Western Australia. Geology and Geophysics Discipline Group, 2006. http://theses.library.uwa.edu.au/adt-WU2006.0070.
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[Truncated abstract] The realization in 1999 that the authigenic phosphate, xenotime, could be used in geochronological studies to place age constraints on burial events that affected sedimentary basins has opened numerous opportunities for establishing timeframes for sedimentary basin analysis. Since then, the mineral has been used to place new and novel age constraints on diagenesis, metamorphism, and hydrothermal alteration and mineralization events. Whilst these studies were successful, they identified many complexities in xenotime growth and were restricted to specific areas or single basins: they do not convey, demonstrate or explore the immense variety of geological applications in which xenotime may provide unique geochronological constraints. This thesis explores the nature of authigenic xenotime, utilizing studies in three different Proterozoic sedimentary basins: two in Australia, southwestern Australia and the Northern Territory, and the third in the United States of America. The thesis includes a number of discrete studies demonstrating different aspects of xenotime growth, elucidated from detailed petrography, geochronology and geochemistry of authigenic xenotime. An integrated textural, geochemical and geochronological study of authigenic xenotime from the Mt Barren Group, SW Australia, establishes an absolute timescale on some of the many processes involved during the diagenesis of siliciclastic units. ... positions and trends and broadly confirm the chemical discrimination criteria established for an Archaean basin. However, the Proterozoic data are shifted to lower Gd-Dy values and extend beyond the original field outlines, causing more overlap between fields intended to discriminate xenotimes of different origin. The plots were revised to encompass the new data. This study has significantly extended our knowledge of the nature of authigenic xenotime. It was found that xenotime may form in (meta)sediments in response to a large number of post-depositional processes, including early- and latediagenesis, (multiple) basinal hydrothermal events and low-grade metamorphism. A combination of detailed petrography and in situ geochronology provides the best avenue to decipher complex growth histories in xenotime. With further development, it is likely that xenotime geochemistry will also prove diagnostic of origin and can be incorporated into the interpretation of age data. The number of potential applications for xenotime geochronology has been expanded by this study.
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Baldim, Maurício Rigoni 1983. "O domo gnáissico Alto Alegre, transição embasamento-greenstone belt do Rio Itapicuru : evolução e significado tectônico." PublishedVersion, [s.n.], 2008. http://repositorio.unicamp.br/jspui/handle/REPOSIP/286596.
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Orientador: Elson Paiva de Oliveira
Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Geociências
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Resumo: Domos gnáissicos são estruturas que podem estar associadas tanto aos orógenos extensionais quanto aos colisionais. Em orógenos colisionais, normalmente balizam os distintos terrenos dispondo-se em corredores estruturais. Na região nordeste do Cráton São Francisco, Bloco Serrinha, localiza-se o Greenstone Belt Paleoproterozoico do Rio Itapicuru, interpretado como arco continental acrecionado a um Complexo de alto grau mesoarqueano. Mapeamento geológico realizado no segmento norte da transiçao, embasamento-greenstone, revelou a ocorrência de um domo gnáissico-migmatítico que limita dois terrenos, um arqueano e outro paleoproterozoico, que destoa litoestruturalmente de outros domos reconhecidos a sul do greenstone (e.g. domos do Ambrósio, Salgadália e Pedra Alta). Além disso, dados estruturais mostram que a evolução tectônica da área ocorreu a partir de tectônica compressiva em D1 com direção E-W, seguido de transcorrência N-S em D2, possivelmente associados a transpressão. O domo, denominado Alto Alegre, possui núcleo granito-diatexítico, sendo delineado por faixas anfibolíticas concêntricas e preserva paragênese de alto grau metamórfico. Análises de elementos maiores e traços revelam que as faixas de anfibolitos do referido domo possuem características geoquímicas semelhantes aos diques máficos que cortam o embasamento, e destoam dos basaltos toleíticos do greenstone belt. Dados geocronológicos e de campo revelam idades de ca. 3080 Ma para o embasamento arqueano e para gnaisses do domo Alto Alegre, e idades de ca. 2080 Ma para o granito que intrude a porção central do domo. Os dados mostram que o domo Alto Alegre representa o embasamento arqueano retrabalhado tectonicamente e influenciado por atividade granítica, durante colisão continente-continente em ca. 2080 Ma
Abstract: Gneiss domes are structures that may be associated with both extensional and collisional orogens. In collisional orogens typically delimit distinct land forming structural corridors. In northeastern of São Francisco craton, Serrinha Block, is located the Paleoproterozoic Rio Itapicuru Greenstone Belt which is interpreted as a continental arc acrecionado to a Mesoarqueano high degree Complex. Geological mapping carried out in the northern segment of the greenstone-basement transition, revealed the occurrence of a gneissic-migmatitic dome that limits two lands, one Archean and another Paleoproterozoic. This dome is different both on litology as structuraly when comparing with other domes recognized in a south of the greenstone (e.g., domes of Ambrose, Salgadália and Pedra Alta). Furthermore, structural data show that the tectonic evolution of the area occurred from compressive tectonics E-W in D1, followed by transcurrent N-S in D2, possibly associated with transpression. The dome, called Alto Alegre, has granite-diatexítico core being outlined by concentric amphibolitic bands that preserves high metamorphic grade paragenesis. Results of major and trace elements analyzes reveal that the amphibolites bands of dome has geochemical characteristics similar to mafic dikes that cut the basement, and differ from Rio Itapicuru greenstone belt basalts. Geochronological and field data reveal ages ca. 3080 Ma for the Archean basement and the dome Alto Alegre gneisses, and ages of ca 2080 Ma for the granite that intrude the central portion of the dome. The data show that the dome Alto Alegre represents the tectonically reworked Archean basement and influenced by granite activity during continent-continent collision at ca 2080 Ma
Mestrado
Geologia e Recursos Naturais
Mestre em Geociências
21
Doyle, Katherine Audrey. "The chemical evolution of the Proterozoic biosphere." Electronic Thesis or Dissertation, University of Leeds, 2018. http://etheses.whiterose.ac.uk/22150/.
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The chemical evolution of the Proterozoic biosphere is not a well comprehended topic. Major gaps exist in the redox record which documents the ocean’s transition from a dominantly ferruginous state throughout most of the Proterozoic, to widespread deep ocean oxygenation during the Late Neoproterozoic. Between ~1.85 – 0.54 Ga, significant developments in biological evolution also occurred with the emergence of macroscopic eukaryotes followed by the radiation of metazoans. A strong link between stably oxygenated marine environments and the radiation of increasingly complex organisms is observed across the literature. However, there is little understood concerning nutrient availability during the Proterozoic, another major governing factor in biological development. Phosphorus is considered the ultimate limiting nutrient for oxygen production over geological timescales through organic carbon burial, and is thus vital to consider in discussing the chemical evolution of the Proterozoic biosphere. Through the application of multiple palaeoredox proxies (iron speciation and trace metal analyses) alongside a newly adapted phosphorus speciation method, this research aims to add to the current record of Proterozoic redox to assess if the chemical evolution of the ocean had a potential effect on the biogeochemical phosphorus cycle, and thus the development of complex organisms. The sedimentary successions from the ~1.8 – 1.4 Ga Yanshan Basin in North China, and the 1.6 – 1.0 Ga Bashkir Meganticlinorium in Russia uncovered dynamically evolving water column chemistry. Their palaeoredox signals contrast to other basins from this time period and highlight the significant spatial and temporal heterogeneity that occurred across the Proterozoic ocean. Analysis of phosphorus-bound phases within marine sediments from the Late Palaeoproterozoic Yanshan Basin and the Ediacaran White Sea (Kel’tma and Kostovo cores), Avalon Peninsula, Cariboo Mountains and the Upper Ungoolya Group, Officer Basin confirmed that water column redox, and a basin’s depositional environment, were the dominant controls on the Proterozoic phosphorus cycle. This is the first geochemical record of phosphorus burial mechanisms in Proterozoic marine sediments as all other studies have been modelling based, or focused on BIFs and total phosphorus content. The research presented here provides a crucial insight into the feedbacks between ocean redox and nutrient availability during a dynamic period of Earth’s history.
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Glendinning, Neil Robert William. "Sedimentology of Proterozoic, Moine rocks of west Scotland." Electronic Thesis or Dissertation, Royal Holloway, University of London, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.246211.
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23
Agić, Heda. "Palaeobiology and diversification of Proterozoic-Cambrian photosynthetic eukaryotes." Doctoral thesis, comprehensive summary, Uppsala universitet, Paleobiologi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-265229.
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One of the most important events in the history of life is the evolution of the complex, eukaryotic cell. The eukaryotes are complex organisms with membrane-bound intracellular structures, and they include a variety of both single-celled and multicellular organisms: plants, animals, fungi and various protists. The evolutionary origin of this group may be studied by direct evidence of past life: fossils. The oldest traces of eukaryotes have appeared by 2.4 billion years ago (Ga), and have additionally diversified in the period around 1.8 Ga. The Mesoproterozoic Era (1.6-1 Ga) is characterised by the first evidence of the appearance complex unicellular microfossils, as well as innovative morphologies, and the evolution of sexual reproduction and multicellularity. For a better understanding of the early eukaryotic evolution and diversification patterns, a part of this thesis has focused on the microfossil records from various time periods and geographic locations. Examination of microfossil morphology, cell wall microstructure and biochemical properties, reflect their intracellular complexity and function, and allow reconstructions of their life cycle, as well as observing the evolutionary pattern of change from Mesoproterozoic, to Cambrian-Ordovician transition. Several case studies included assemblages deriving from Mesoproterozoic, Neoproterozoic and early Paleozoic time intervals that show disparate morphotypes and innovative features indicative of algal clades. The Mesoproterozoic Ruyang Group in northern China has yielded a diverse microfossil assemblage that provides important clues about the diversification of different eukaryotic groups. Furthermore these microfossils contributed an additional evidence for the emergence of the crown group Eukarya by 1.7-1.4 Ga. In another part of this thesis, examination of wall microstructure and chemical properties via Raman spectroscopy has been used to assess the biological affinities of various Neoproterozoic problematic carbonaceous compression fossils. Studies on the early Phanerozoic (c. 545-485 Ma) assemblages from Estonia reconstructed patterns of the early radiations of phytoplankton and its evolutionary innovations. A continuing theme in this thesis has been using a combination of evidence of microfossils’ fine-scale morphology, ecology and chemical properties to determine their function in life, in addition to their systematic position.
Palaeobiology and diversification of Proterozoic-Cambrian photosynthetic eukaryotes
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Moore, Kelsey Reed. "Cyanobacterial evolution and interactions with the Proterozoic world." Thesis, Massachusetts Institute of Technology, 2009. https://hdl.handle.net/1721.1/127144.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, May, 2020
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Includes bibliographical references.
Our understanding of the biosphere prior to the rise of complex life is built largely upon microbial mat structures and some exceptionally well-preserved microbial fossils from the Proterozoic (2500 to 540 million years ago). Some of these exceptional fossils are identifiable as cyanobacteria that were preserved by pyrite, amorphous silica (SiO₂) and other minerals. Although a record exists of these organisms, the sparse nature of fossil assemblages and simplicity of many Proterozoic fossil morphologies makes it difficult to identify specific taxa or create a complete picture of the ancient biosphere and how it interacted with the early Earth. Cyanobacteria are thought to have evolved early in Earth history and played a large part in shaping the ancient biosphere and geosphere, but questions remain about their evolution and the ways in which cyanobacterial communities interacted with the Earth during the Proterozoic Eon.
In this thesis, I seek to build a more complete understanding the record of Proterozoic cyanobacteria, their responses to environmental perturbations and the chemical conditions and microbe-mineral interactions that characterized the Proterozoic marine realm. I begin by investigating the evolutionary relationships between different cyanobacterial lineages and their relationship to chloroplasts. I then analyze an assemblage of pyritized cyanobacteria that were preserved during the Cryogenian and provide a record of primary productivity in the oceans following a global glaciation. Finally, I investigate factors that enabled the fossilization of some exceptionally preserved cyanobacteria and implications of these mechanisms for cyanobacterial biochemistry, chemical conditions, and interactions between microbes and Proterozoic tidal environments.
The combined molecular, fossil and experimental insights allow us to go beyond morphological interpretations of microbial fossils and build a more complete understanding of the evolutionary history of cyanobacteria, the types of cyanobacteria that were preserved during the Proterozoic, the responses of these cyanobacteria to environmental stresses and the interactions of those cyanobacteria with the evolving seawater chemistry.
by Kelsey R. Moore.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences
25
Roth, Frances Ann. "Implications of stratigraphic completeness analysis for magnetic polarity stratigraphic studies." Thesis-Reproduction (electronic), The University of Arizona, 1985. http://hdl.handle.net/10150/558017.
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26
Sharma, Arvind Kumar. "Quantitative Stratigraphic Inversion." Dissertation, Virginia Tech, 2001. http://hdl.handle.net/10919/30172.
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We develop a methodology for systematic inversion of quantitative stratigraphic models. Quantitative stratigraphic modeling predicts stratigraphy using numerical simulations of geologic processes. Stratigraphic inversion methodically searches the parameter space in order to detect models which best represent the observed stratigraphy. Model parameters include sea-level change, tectonic subsidence, sediment input rate, and transport coefficients. We successfully performed a fully automated process based stratigraphic inversion of a geologically complex synthetic model. Several one and two parameter inversions were used to investigate the coupling of process parameters. Source location and transport coefficient below base level indicated significant coupling, while the rest of the parameters showed only minimal coupling. The influence of different observable data on the inversion was also tested. The inversion results using misfit based on sparse, but time dependent sample points proved to be better than the misfit based on the final stratigraphy only, even when sampled densely. We tested several inversion schemes on the topography dataset obtained from the eXperimental EarthScape facility simulation. The clustering of model parameters in most of the inversion experiments showed the likelihood of obtaining a reasonable number of compatible models. We also observed the need for several different diffusion-coefficient parameterizations to emulate different erosional and depositional processes. The excellent result of the piecewise inversion, which used different parameterizations for different time intervals, demonstrate the need for development or incorporation of time-variant parameterizations of the diffusion coefficients. We also present new methods for applying boundary condition on simulation of diffusion processes using the finite-difference method. It is based on the straightforward idea that solutions at the boundaries are smooth. The new scheme achieves high accuracy when the initial conditions are non vanishing at the boundaries, a case which is poorly handled by previous methods. Along with the ease in implementation, the new method does not require any additional computation or memory.
Ph. D.
27
Polteau, Stéphane. "The early proterozoic Makganyene glacial event in South Africa : its implication in sequence stratigraphy interpretations, paleoenvironmental conditions and iron and manganese ore deposition." Thesis, Rhodes University, 2005. http://hdl.handle.net/10962/d1007612.
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The Makganyene Formation forms the base of the Postmasburg Group in the Transvaal Supergroup in the Griqualand West Basin. It consists of diamictites, sandstones, banded iron-formations (BIFs), shales, siltstones and carbonates. It is generally accepted that the Makganyene Formation rests on an erosive regional unconformity throughout the Northern Cape Province. However this study demonstrates that this stratigraphic relationship is not universal, and conformable contacts have been observed. One of the principal aims of this study is to identify the nature of the Makganyene basal contact throughout the Griqualand West Basin. Intensive fieldwork was carried out from Prieska in the south, to Danielskuil in the north. In the Sishen and Hotazel areas, only borehole material was available to assess the stratigraphy. The Griquatown Fault Zone delimits the boundary between the deep basin and platform facies. The Koegas Subgroup is only present south of the Griquatown Fault Zone, where it pinches out. However, the transition Griquatown BIFs-Koegas Subgroup occurs in lacustrine deposits on the Ghaap platform (Beukes, 1983). The Griquatown Fault Zone represents the edge of the basin, which corresponds to a hinge rather than a fault zone. The Makganyene Formation rests with a conformable contact on the Koegas Subgroup south of the Griquatown Hinge Zone, and north of it the Makganyene Formation lies unconformably on the Asbestos Hills Subgroup. The Makganyene Formation displays lateral facies changes that reflect the paleogeography of the Griqualand West Basin, and the development of ice sheets/shelves. The Ghaap platform is characterised by coarse immature sand interbedded with the diamictites. The clasts in this area contain local Asbestos Hills material and no dropstones are present. Such settings are typical of sediments that are being deposited below a grounded ice mass. At the Griquatown Hinge Zone, the sandstone lenses are smaller, and the clasts consist of chert, of which a great number are striated and faceted. In the Matsap area, the presence of dropstones is strong evidence for the presence of a floating ice shelf that released its material by basal melting. Further south, the Makganyene Formation contains stromatolitic bioherms that only form if clastic contamination is minimal and therefore the ice that transported the detritus to the basin did not extend far into open sea conditions. The base of the Hotazel Formation also contains diamictite levels. Dropstones have been identified, implying a glacial origin. The Hotazel diamictites are interbedded with hyaloclastites and BIFs. The Makganyene glacial event, therefore, was not restricted to the Makganyene Formation, but also included the Ongeluk Formation, through to the base of the Hotazel Formation. Petrographic studies of the Makganyene Formation and the base of the Hotazel Formation reveal mineral assemblages that are diagnostic of early to late diagenetic crystallisation and of low-grade metamorphism not exceeding the very low green-schist facies. The facies identified display the same sense of basin deepening, from shallow high-energy Hotazel area on the Ghaap platform, to the deep basin in the Matsap area. Whole-rock geochemical analyses reveal that the elemental composition of the Makganyene Formation is very similar to that of the Asbestos Hills BIFs, which were the most important source of clastic detritus for the Makganyene Formation. However, minor amounts of carbonates of the Campbellrand Subgroup, as well as a felsic crustal input from the Archean granitoid basement, made contributions. On the Ghaap platform, the Makganyene diamictite is enriched in iron, calcium, and magnesium, while in the deeper parts of the basin the diamictites are enriched in detrital elements, such as titanium and aluminium, which occur in the fine clay component. The Hotazel diamictite displays a distinct mafic volcanic input, related to the extrusion of the Ongeluk basaltic andesites, which was incorporated in the glacial sediments. Sequence stratigraphy is based on the recognition of contacts separating the different systems tracts that compose a depositional sequence. However, because the basal contact of the Makganyene Formation has not been properly identified in previous work, no correct model has been proposed so far. Therefore correlations between the Griqualand West and the Transvaal basins, based on lithostratigraphic similarities and extrapolations of unconformities, have to be reviewed, especially since the publication of new radiometric ages contradict all previously proposed correlations. It is proposed here that the Transvaal Supergroup in the Griqualand West Basin represents a continuous depositional event that lasted about 200 Ma. The Makganyene glacial event occurred during changing conditions in the chemistries of the atmosphere and ocean, and in the continental configuration. A Snowball Earth event has been proposed as the causative process of such paleoenvironmental changes. However, evidence presented here of less dramatic glacial conditions, with areas of ice-free waters, implies an alternative to the Snowball Earth event. The paleoenvironmental changes are thought to represent a transition from an anaerobic to aerobic atmosphere, that was responsible for the global cooling of the surface of the Earth, Such a glacial event may have aided in the large-scale precipitation of iron and manganese in areas of intense upwellings.
28
Mitchell, Emily Geraldine Harmsworth. "Quantitative approaches to understanding ediacaran ecology." Electronic Thesis or Dissertation, University of Cambridge, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.664750.
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29
Barbeau, David Longfellow Jr. "Application of Growth Strata and Detrital-Zircon Geochronology to Stratigraphic Architecture and Kinematic History." Dissertation-Reproduction (electronic), The University of Arizona, 2003. http://hdl.handle.net/10150/244092.
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Growth strata analysis and detrital-zircon geochronology are useful applications of stratigraphy to tectonic problems. Whereas both tools can contribute to kinematic analyses of supracrustal rock bodies, growth strata are also useful for analyzing the influence of tectonics on stratigraphic architecture. This study reports: 1) a conceptual model for growth strata development; 2) stratigraphic and kinematic analyses of growth strata architectures from growth structures in southeastern Utah, the Gulf of Mexico, and northeastern Spain; and 3) the detrital-zircon geochronology of the Salinian block of central coastal California. Kinematic sequence stratigraphy subdivides growth strata into kinematic sequences that are separated by kinematic sequence boundaries. Kinematic sequences can be further partitioned into kinematic domains based on the termination patterns of strata within a kinematic sequence. Salt- related fluvial growth strata from the Gulf of Mexico and southeastern Utah contain stratigraphic architectures that are unique to different kinematic domains. Offlap kinematic domains contain fluvial strata indicative of high slopes, low accommodation rates, and strong structural influence on paleocurrent direction. Onlap kinematic domains contain fluvial strata indicative of moderate slopes, high accommodation rates, and decreased structural influence on paleocurrent direction. The stratigraphic architecture of alluvial -fan thrust -belt growth strata in northeastern Spain does not display a marked correlation with kinematic domain, and is most easily interpreted using existing models for autocyclic alluvial -fan evolution. Detrital- zircon (U -Pb) geochronologic data from basement and cover rocks of Salinia suggest that Salinia originated along the southwestern margin of North America, likely in the vicinity of the Mojave Desert. The presence of Neoproterozoic and Late Archean detrital zircons in Salinian basement rocks also suggest that Salinian sediments were recycled from miogeoclinal sediments of the western margin of North America.
30
Bullen, Dean S. "The petrology of proterozoic mafic sills in southern Africa." Electronic Thesis or Dissertation, University of Portsmouth, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.444345.
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31
Rooney, Alan. "Re-Os geochronology and geochemistry of Proterozoic sedimentary successions." Electronic Thesis or Dissertation, Durham University, 2011. http://etheses.dur.ac.uk/621/.
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The Re-Os organic-rich sedimentary rocks (ORS) geochronometer has the potential to provide precise depositional ages and vital information on the Os isotope composition of palaeo-seawater. This thesis presents new geochronology data from Proterozoic sedimentary successions and insights into Re-Os systematics of organic-rich sedimentary rocks and petroleum products such as bitumen and oil. New Re-Os ORS geochronology from two drill cores indicate that the Proterozoic Atar Group of the Taoudeni basin, Mauritania is ~200 Ma older than previous estimates (1107 ± 12 Ma, 1109 ± 22 Ma and 1105 ± 37 Ma). Furthermore, this data also provides precise Re-Os geochronology data from sedimentary rocks that have experienced flash pyrolysis and demonstrate that the Re-Os systematics are not disturbed by the effects of very rapid heating. Coupled with palaeomagnetic data the Re-Os geochronology suggests that a reassessment of the role of the West African craton during the assembly of Rodinia is required. New Re-Os geochronology for the Ballachulish Slate Formation of the Dalradian Supergroup, Scotland yields a depositional age of 659.6 ± 9.6 Ma. The Re-Os age represents a maximum age for the glaciogenic Port Askaig Formation and represents the first successful application of the Re-Os geochronometer in sedimentary rocks with low Re and Os abundances (<1 ppb and <50 ppt, respectively). This new age suggests that the Port Askaig Formation may be correlative with Sturtian glaciations rather than middle Cryogenian events. Laboratory-based hydrous pyrolysis experiments were employed to evaluate the complexation of Re and Os in ORS and their transfer behaviour into petroleum. The findings from these experiments demonstrate that the Re-Os geochronometer is not disturbed by thermal maturation of whole rocks. Furthermore, the data support the hypothesis that the isotope composition of oils and bitumens can be used to fingerprint petroleum to specific source rocks.
32
De, Waele Bert. "The Proterozoic geological history of the Irumide belt, Zambia." Curtin University of Technology, Department of Applied Geology, 2004. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=15789.
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The Irumide belt is an elongate crustal province characterised by Mesoproterozoic tectonism and magmatism that stretches over a distance of approximately 900 kilometers from central Zambia to the Zambia-Tanzania border and northern Malawi. It is bounded to the northwest by largely undeformed Palaeoproterozoic basement lithologies of the Bangweulu block and is truncated to the northeast by Mesoproterozoic and Neoproterozoic transcurrent shear zones within reactivated parts of the Palaeoproterozoic Ubendian belt. To the southeast and south, Irumide lithologies were reworked within the Neoproterozoic Lufilian and Zambezi belts, and to the east by the East African Orogen. Lithologies in the Irumide belt comprise a Palaeo- to Mesoproterozoic complex of gneisses and granitoids and a supracrustal succession of quartzites and pelites. A three-fold subdivision was accepted prior to this study; (1) Palaeoproterozoic granites and gneisses forming the Irumide basement, (2) a supracrustal succession of quartzites and metapelites called the Muva Supergroup, (3) various deformed and undeformed granitoids intruding both the Palaeoproterozoic basement and Muva Supergroup and considered to be pre-Irumide (1.4 Ga) and syn-, late- to post-Irumide (1.1-0.95 Ga). The age of Irumide tectonism itself was poorly constrained between 1.4 and 1.0 Ga. The basement units comprise the Mkushi Gneiss in the southwest and the Luwalizi Granite, Mwambwa River and Mulungwizi Gneisses in the northeast. These units have been correlated with the Palaeoproterozoic Bangweulu block and Ubendian belt in the past. These basement units are structurally and in places unconformably overlain by a metasedimentary succession of quartzites and metapelites, which in the southwest has been called the Kanona Group, and in the northeast the Manshya River Group.
Both sequences have been correlated with similar quartzite-pelite successions on the Bangweulu block, termed the Mporokoso Group, and, together with a second cycle reworked unit on the Bangweulu block called the Kasama Formation, were collectively grouped into the Muva Supergroup. Both basement and supracrustals have been deformed, metamorphosed and intruded by a host of granitoids which, based on structural fabrics, were subdivided into pre-, syn-, late- and post-tectonic suites with respect to Irumide tectonism. Due to the lack of reliable geochronological constraints, this subdivision had remained untested until now. All units in the Irumide belt have been strongly affected by compressional tectonics, resulting in northwest-directed thrusting onto the Bangweulu block basement and extensive crustal shortening. Minor southeast-verging structures form part of locally developed backthrusts within an overall northwest-vergent tectonic regime. At least parts of the Irumide basement were affected by Irumide tectonism, but large-scale thrusting was mainly accommodated along a basal decollement at the basement-cover interface. Extensive shortening is exemplified by tight- to isoclinal folding within the supracrustal sequence, ranging from upright to recumbent. Thrusts developed where shortening could not be accommodated by tight folding, which produced tectonic duplication within the metasedimentary pile, making formation-to-formation correlations across the belt tenuous at best. Irumide tectonism has been reported to affect the base of the Mporokoso Group on the Bangweulu block, where folding along the Luongo shear zone occurred contemporaneously with thermal resetting of biotite dated at ~1.0 Ga (K-Ar dates). Metamorphic parageneses record low- to medium-pressure/medium- to high-temperature conditions.
Metamorphic grades range from greenschist facies in the northwestern foreland, to upper amphibolite facies in the southeast, with local granulites. Peak Irumide metamorphism, recorded in metamorphic zircon rim overgrowths, has been dated in this study at 1.02 Ga. Metamorphism to the southeast, across the younger Karoo grabens, had previously been constrained at 1.05 Ga, indicating an across strike diachronous development of metamorphism for the Irumide belt. The lithological units identified and dated as part of this study in the Irumide belt include: (1) limited Neoarchaean rocks emplaced at 2.73 Ga and representing the oldest rocks in the Bangweulu block; (2) ca. 2.05-1.85 Ga volcano-plutonic complexes and gneisses representing the most important components in the Bangweulu block; (3) an extensive quartzite-metapelite succession with minor carbonate forming the Mporokoso, Kanona and Manshya River groups, and deposited at ca. 1.8 Ga; (4) granitoids emplaced between 1.65-1.55 Ga; (5) deposition of the Kasama Formation between 1.43 and 1.05 Ga (second-cycle reworking of the Mporokoso Group); (6) voluminous syn- to post-kinematic Irumide granitoids emplaced between 1.05-0.95 Ga. In addition, a minor suite of 1.36-1.33 Ga anorogenic plutons (nepheline syenite and biotite granite) have been identified in the far northeastern Irumide belt, but were not included in this study. Whole-rock geochemical data for magmatic rocks in northern Zambia, predominantly from within the Irumide belt, indicate uniform crust-dominated patterns. Overall high REE contents and trace element characteristics indicate the significant participation of older crust in the generation of all magmatic suites.
The data are insufficient to conclusively demonstrate that this crustal melting was associated with either intra-plate, volcanic arc or post-collisional/extensional collapse. A limited number of Sm/Nd isotopic data for the entire range of magmatic suites corroborate the highly reworked nature of parent magmas, with all samples characterised by strongly negative åNd(T) values and TDM model ages between 2.2 and 3.2 Ga. The geochronological data presented in this thesis show that the Irumide belt includes a Palaeoproterozoic basement complex comprising units as old as 2.73 Ga, but mostly made up of granitic gneisses ranging in age between 2.05 and 1.93 Ga, while granitic and volcanic units of the Bangweulu block to the northwest were dated at 1.87-1.86 Ga. Detrital zircon age data from quartzites and zircon crystallisation ages of interlayered tuffs within the Muva Supergroup indicate a depositional age of between 1.88 and 1.85 Ga, with local derivation from locally recognised basement units, although similarly aged rocks of the Tanzania craton to the northeast are also a possible source. The detrital record of the Muva Supergroup shows that the various components of the Bangweulu block, including 2.73, 2.05-1.93 and 1.87-1.86 Ga units, were assembled by the time of deposition of the Muva Supergroup at around 1.8 Ga. Both the basement units and the Muva Supergroup were intruded by a previously unknown magmatic suite of biotite granites between 1.65-1.55 Ga, the first record of such a magmatic event in central Africa. The new data presented in this thesis allow a critical assessment of previously proposed regional correlations between Mesoproterozoic teranes in central and southern Africa.
Significant temporal differences between the Irumide belt and the Kibaran belt, Choma-Kalomo block and Namaqua-Natal belts had previously not been detected due to the poor quality, low resolution or limited size of isotopic data sets. The new data set produced in this study indicates a distinct and separate tectono-magmatic history for each of these terranes, therefore precluding previously suggested correlations. In particular, the presumed southeastward continuation of the Irumide belt across the Neoproterozoic Zambezi belt into the Choma-Kalomo block is precluded by the data presented in this thesis. This new geochronological framework allows for significant spatial separation of the Kalahari and Congo cratons prior to the Neoproterozoic closure of the Damara-Lufilian-Zambezi ocean, and is therefore in support of palaeogeographic models of Rodinia which either place the Congo and Kalahari cratons as distinct and separate fragments within the supercontinent, or show one or both of the two cratons not to form part of it. Currently, available data are not able to determine the tectonic setting or the palaeogeographic location of the Irumide belt, and as a result it is unclear whether it developed within Rodinia as a collisional orogen, at its margin as an accretionary orogen, or was not associated with Rodinia at all.
33
Dong, Lin. "Contributions to the Proterozoic and Cambrian Evolution of Eukaryotes." Dissertation, Virginia Tech, 2003. http://hdl.handle.net/10919/26626.
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This thesis makes several contributions to improve our understanding of Proterozoic-Cambrian evolution of eukaryote life. Chapter 1 provides, for the first time, a quantitative characterization of the evolutionary trends of Proterozoic macroalgae. The analysis reveals that morphological disparity of Paleoproterozoic macroalgae was low but increased in the Mesoproterozoic and Ediacaran, with a plateau in between. There was also a significant increase in thallus surface/volume ratio and maximum canopy height of the Ediacaran macroalgal communities. The prolonged plateau between the Mesoproterozoic and Ediacaran may be related to either nutrient stress or the absence of animal grazing pressure. The Ediacaran increase in surface/volume ratio and morphological complexity may have been driven by decreasing pCO2 levels and increasing animal grazing pressure. Chapter 2 presents a systematic re-examination of the carbonaceous compression fossils Protoarenicola baiguashanensis Wang, 1982, Pararenicola huaiyuanensis Wang, 1982, and Sinosabellidites huainanensis Zheng, 1980, from the early Neoproterozoic Liulaobei and Jiuliqiao formations in northern Anhui, North China. These fossils were previously interpreted as worm-like metazoans. Our study reveals new morphological features that weaken the metazoan interpretation. Instead, the new data indicate that these fossils can be alternatively interpreted as erect epibenthic organisms, possibly coenocytic algae. Chapter 3 examines two important eukaryote fossils: Horodyskia Yochelson and Fedonkin, 2000, and Palaeopascichnus Palij, 1976, from the upper Ediacaran chert of the Liuchapo Formation in central Guizhou, South China. These exceptionally preserved fossils offer us a unique opportunity to investigate their body constructions and affinities. The morphologies of Horodyskia and Palaeopascichnus support a phylogenetic relationship with agglutinated foraminifers, shedding new light on the divergence of bikont eukaryotes, the rise of rhizarians, and the ecological importance of heterotrophic eukaryotes in Proterozoic ecosystems. Chapter 4 focuses on Cambrian microfossils that represent the primary producersâ cyanobacteria and eukaryotic phytoplankton (acritarchs). Careful investigation of the basal Cambrian Yanjiahe Formation in the Yangtze Gorges area and the Yurtus Formation in the Aksu area revealed abundant acanthomorphic acritarchs, clustered coccoidal microfossils, filamentous cyanobacteria, and tubular microfossils. This study confirms previous stratigraphic correlation between the Yanjiahe and Yurtus formations and suggests that animals and phytoplankton radiated in tandem during the Cambrian explosion.
Ph. D.
34
Magyarosi, Zsuzsanna. "Metamorphism of the Proterozoic rocks associated with the Sudbury Structure." Electronic thesis or dissertation, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0007/MQ32431.pdf.
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35
Fitzsimons, Ian Christopher William. "The metamorphic histories of some proterozoic granulites from East Antarctica." Electronic Thesis or Dissertation, University of Edinburgh, 1991. http://hdl.handle.net/1842/14863.
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The Proterozoic Complex of East Antarctica is an extensive metamorphic terrain, which comprises various outcrop areas preserving granulite-facies mineral assemblages ascribed to a 1000 Ma metamorphic event. This study has focused on two areas of this terrain: the Brattstrand Bluffs coastline of Prydz Bay, Princess Elizabeth Land, and the Nemesis Glacier region in the northern Prince Charles Mountains of Mac. Robertson Land. Both areas are composed of granulite-facies gneisses and migmatites of igneous and sedimentary origin, with a complex history of deformation, anatexis and intrusion at high grade. The structure of both areas is dominated by a flat-laying, layer-parallel, foliation. This foliation is locally overprinted by folds and shear zones which are flat lying in the Brattstrand Bluffs coastline, but upright in the Nemesis Glacier region. Pressure-temperature (P-T) estimates were derived through application of suitable barometers and thermometers to selected specimens of garnet-orthopyroxene-plagioclase-quartz gneiss from both areas. A spread of temperature data from garnet-orthopyroxene thermometers, and pressure data from a barometer based on the solubility of alumina in coexisting garnet and orthopyroxene, are attributed to a variable extent of retrograde Fe-Mg exchange. P-T estimates were corrected for this exchange by using the Fe-Mg distributon coefficient required to bring the pressures derived from the exchange-sensitive barometer into agreement with pressures derived from garnet-orthopyroxene-plagioclase-quartz barometers, which are relatively insensitive to Fe-Mg exchange. Correct peak P-T estimates are c. 6.0 kbar and 860oC for the Brattstrand Bluffs coastline and c. 6.5 kbar and 800oC for the Nemesis Glacier region. Zonation trends in garnet, orthopyroxene and plagioclase from the two areas are consistent with a retrograde P-T path gradient of c. 17 bar/oC in the Brattstrand Bluffs coastline, and c. 6 bar/oC in the Nemesis Glacier region. Well-layered and migmatitic metapelites in the Brattstrand Bluffs coastline exhibit abundant field evidence for the generation and extraction of leucocratic melts at the metamorphic peak, and metapelite mineral assemblages imply low values of αHSO (less than 0.2). Textural studies indicate that H2O was partitioned in the silicate melt phase as melting progressed, and that the final stages of melting proceeded through incongruent reactions such as biotite + sillimanite + quartz = garnet + cordierite + K-feldspar + melt, which require fluid absence. Mineral assemblage development subsequent to the melting, for example spinel-cordierite symplectites after garnet and sillimanite, indicates decompression from pressures over 5 kbar to c. 3 kbar. Integration of microtextures with the structural history indicates that some of this decompression was synchronous with localized development of flat-lying folds and shear fabrics. This combination of decompression and sub-horizontal shearing is attributed to progressive extension after the metamorphic peak. Hydrous fluids were released by the melts as they crystallized, and were transported along the shear zones, thus preserving anhydrous assemblages in most of the rocks.
36
Cadman, Andrew Christopher. "The petrogenesis and emplacement of Proterozoic dyke swarms in Labrador." Electronic Thesis or Dissertation, University of Leicester, 1992. http://hdl.handle.net/2381/34998.
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The Archaean Hopedale Block, in the southern Nain Province of Labrador, Canada, is host to three generations of mafic intrusions of Proterozoic age; the 2.2 Ga Kikkertavak, the 1.6 Ga Kokkorvik and the 1.3 Ga Harp dyke swarms. Also present are two ultrabasic dyke types: firstly pyroxenites interpreted as coeval with the Kikkertavak swarm, and secondly 'high titanium dykes' with opaque-rich compositions of uncertain age. Many Kikkertavak (and Harp) intrusions show highly differentiated phyric textures attributed to rhythmic changes in flow conditions during solidification. Modelling of intradyke geochemical variation shows this can be largely correlated with phenocryst differentiation processes. Other textures indicate more extreme flow variations associated with composite intrusion. Analysis of Kikkertavak dyke morphologies and measurements of magma palaeo-flow directions using anisotropy of magnetic susceptibility suggests that the crack propagation direction during dyke emplacement may be decoupled from the preserved flow direction. However similar measurements on the Kokkorvik sheets suggests that decoupling does not occur in shallow-angle intrusions. Approaching the southern boundary of the Hopedale Block, Kikkertavak dykes show increasing tectonic, petrographic and geochemical alteration. The principle effects are mobile element depletion and redistribution, notably on the dyke margins. Fractional crystallisation, crustal contamination and partial melting processes alone are inadequate at explaining primary geochemical variation in both Kikkertavak and Harp swarms. Instead variation occurs mainly due to the melting of heterogeneous mantle sources. The iron-rich compositions of many Kikkertavak dykes is postulated to result from the underplating into the subcontinental mantle during subduction of mafic ocean plateau material. The geochemical signature of many Harp dykes may result from mixing with similar iron-rich mantle sources with alkaline partial melts added to the continental lithosphere. The geochemistry and emplacement style of other Proterozoic dyke swarms suggest that the mafic underplating model may be more generally applicable.
37
Hall, Susan Margaret. "Geochemistry of Proterozoic carbonates, Belt Supergroup, Montana and Idaho, U.S.A." Thesis, University of Ottawa (Canada), 1990. http://hdl.handle.net/10393/5827.
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An increase in the degree of post-depositional alteration of Belt limestones is reflected in a diminution of Sr and Mg content, increase in Mn and by depletion in $\sp $C and $\sp $O. $\delta\sb1\sp8$O of limestones ranges from +13.4 to +22.9$\perthous$ SMOW and $\delta\sp $C from $-$5.6 to +2.4$\perthous$ PDB. Two diagenetic trends can be resolved for the limestones. One, affecting the presumed originally aragonite-rich sediments, comprises the Newland, Libby and perhaps the Snowslip Formations. The other trend is confined to the Middle Belt Carbonate and may have been controlled by high-Mg calcitic sediments. A regional westward depletion in $\sp $O of 8$\perthous$ and $\sp $C of 2.5$\perthous$ reflects a higher temperature of alteration (300$\sp\circ$C) and an increased contribution from CO$\sb2$ derived from thermal cracking of hydrocarbons in the western Belt basin. The $\delta\sp $O and $\delta\sp $C compositions of the Belt limestones are within the ranges of the values reported for coeval Proterozoic basins. If compared to the modern ocean, the $\delta\sp $O of the Belt sea may have been lighter by perhaps 7$\perthous$. $\delta\sp $C averages close to 2$\perthous$, similar to modern values. Dolostones in the Belt basin are dominantly micritic, with good preservation of depositional textures. $\delta\sp $O of dolomite ranges from 18.1 to 27.9$\perthous$ SMOW and $\delta\sp $C from $-$2.2 to 1.9$\perthous$ PDB. Post-depositional alteration of dolostone is indexed by a decrease in Sr and Na contents, increase in Mn and by depletion in $\sp $O and $\sp $C. Dolostones of the Mt. Shields and Altyn Formations have low Sr and heavy $\delta\sp $O and $\delta\sp $C (if compared to the bulk of Belt samples), show pervasive and destructive dolomitization and may have formed in a mixed water zone of the Dorag type. The remainder of the Belt dolostones resemble typical 'early' diagenetic micritic dolostones in their high Sr content and may have formed in an evaporative setting. Carbonates of mixed dolomite and calcite composition show depletion in $\sp $O and $\sp $C and increase in Mn content with progressive diagenetic alteration. Secular variations in $\delta\sp $C are superimposed on diagenetic trends in this population, showing that carbonates of the Spokane/Greyson, Libby and Newland Formations are $\approx$2$\perthous$ heavier than those of the Middle Belt Carbonate. $\sp‡$Sr/$\sp†$Sr of Belt carbonates range between 0.70484 and 0.74991. Progressive diagenesis, as indexed by decreasing elemental Sr and depletion in $\sp $O and $\sp $C, results in an increase in $\sp‡$Sr/$\sp†$Sr values. $\sp‡$Sr/$\sp†$Sr is better preserved in dolomitized rocks and rocks with initially high Sr content (the Newland and Greyson/Spokane Formations). The 'best', that is the least radiogenic values, are similar to those for previously published coeval Proterozoic carbonates and they are more radiogenic than the contemporaneous mantle. A comparison of $\sp‡$Sr/$\sp†$Sr for the dissolved vs. the suspended load of the Belt basin indicates that the rivers supplying strontium to the basin did not exclusively drain young volcanic or plutonic terrain, but this terrain must have contained a significant source of Sr with marine isotopic composition. Alternatively, the source of nonradiogenic Sr might have been marine waters. (Abstract shortened by UMI.)
38
Hemmingsson, Christoffer. "Phosphate and Arsenic Cycling under Experimental Early Proterozoic Marine Conditions." Licentiate thesis, comprehensive summary, Stockholms universitet, Institutionen för geologiska vetenskaper, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-148800.
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Nutrient dynamics in the Archean-Paleoproterozoic oceans strongly influenced primary productivity and the rise of atmospheric O2. Reconstructing the cycling of key nutrients such as dissolved inorganic phosphate (DIP) at this time is important for our understanding of the timing, rate and extent of atmospheric oxygenation at this time. Banded iron formations (BIF) can be used as proxies for global DIP content in Precambrian marine waters. Estimating Precambrian DIP requires understanding of the mechanisms by which Fe(III)(oxyhydr)oxides scavenge DIP which has come mainly from experimental studies using NaCl solutions that mimick Precambrian marine conditions with for example, elevated Si and Fe(II) concentrations. The two DIP binding modes suggested for Early Proterozoic marine waters are 1) Adsorption - surface attachment on pre-formed Fe(III) (oxyhydr)oxides, and 2) Coprecipitation - incorporation of P into actively growing Fe(III) (oxyhydr)oxides. It has been suggested that the elevated Si concentrations suggested for Precambrian seawater, strongly inhibit adsorption of DIP in Fe(III)(oxyhydr)oxides. However recent coprecipitation experiments show that DIP is strongly scavenged by Fe(III)(oxyhydr)oxides in the presence of Si, seawater cations and hydrothermal As. In this study we show that the DIP uptake onto Fe(III)(oxyhydr)oxides by adsorption is less than 5% of that by coprecipitation. The data imply that in the Early Proterozoic open oceans, the precipitation of Fe(III)(oxyhydr)oxides during mixing of deep anoxic Fe(II)-rich waters with oxygenated ocean surface waters caused DIP removal from surface waters through coprecipitation rather than adsorption. Local variations in DIP and perhaps even stratification of DIP in the oceans were likely created from the continuous removal of DIP from surface waters by Fe(III)(oxyhydr)oxides, and its partial release into the anoxic bottoms waters and in buried sediments. In addition to a DIP famine, the selectivity for DIP over As(V) may have led to As enrichment in surface waters both of which would have most likely decreased the productivity of Cyanobacteria and O2 production.
Näringscirkulationen i haven under arkeikum och paleoproterozoikum påverkade primärproduktionen och uppkomsten av atmosfärisk syrgas (O2). För att förstå när och hur fort koncentrationen av O2 i atmosfären ökade behöver vi rekonstruera hur viktiga näringsämnen, t.ex. löst oorganiskt fosfor (engelska “Dissolved Inorganic Phosphorous”, DIP) cirkulerade. Bandad järnmalm (engelska “Banded Iron Formations”, BIF) kan användas som en markör för DIP i de prekambriska haven. För att kunna använda DIP som markör måste man förstå hur prekambrisk DIP tas upp av järn(III)(oxyhydr)oxider. Hittills har detta studerats med natriumkloridlösningar som ska efterlikna förhållande i de prekambriska haven, med t.ex. förhöjda kisel- och järn(II)-koncentrationer. Ur sådana studier har två bindningsmekanismer föreslagits för paleoproterozoiskt havsvatten 1) Adsorption, d.v.s. DIP binds till ytan på redan bildade kristaller av järn(III)(oxyhydr)oxid, och 2) samutfällning, d.v.s. upptag av fosfor i kristaller av järn(III)(oxyhydr)oxid medan kristallerna bildas. Det har föreslagits att de höga kiselkoncentrationerna som tros ha funnits i de prekambriska havsvattnet hämmade adsorption av DIP på ytan av järn(III) (oxyhydr)oxidkristaller. Men de senaste samutfällningsexperimenten tyder på att järn(III) (oxyhydr)oxid effektivt tar upp DIP även i närvaro av kisel, arsenik från hydrotermala källor och de katjoner som dominerar i havsvatten. I här presenterad studie var mängden DIP som bands till järn(III)(oxyhydr)oxidkristaller genom adsorption mindre än 5 % av den DIP som togs upp av kristallerna via samutfällning. Våra data tyder på att när järn(III) (oxyhydr)oxid fälldes ut i tidiga-proterozoiska hav när järn(II)-rikt djupvatten blandades med syrerikt ytvatten, och att DIP avlägsnades från ytvattnet genom samutfällning snarare än adsorption. Lokala variationer av DIP-koncentrationer i haven, möjligen även skiktning, kan ha orsakats av kontinuerlig utfällning av järn(III)(oxyhydr)oxider ur ytvattnet följt av partiell frigörelse av DIP i syrefria djupvatten och sediment. Kristallisationsprocessen, som gynnar inbindning av DIP och misgynnar inbinding av arsenik (V) kan ha orsakat brist av DIP och anrikning av arsenik i ytvattnet, vilket troligen minskade tillväxten av cyanobakterier med lägre syrgasproduktion som följd.
CLAPO
39
Gruen, Danielle S. "Biogeochemical and phylogenetic signals of Proterozoic and Phanerozoic microbial metabolisms." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/119991.
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Thesis: Ph. D., Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2018.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 213-240).
Life is ubiquitous in the environment and an important mediator of Earth's carbon cycle, but quantifying the contribution of microbial biomass and its metabolic fluxes is difficult, especially in spatially and temporally-remote environments. Microbes leave behind an often scarce, unidentifiable, or nonspecific record on geologic timescales. This thesis develops and employs novel geochemical and genetic approaches to illuminate diagnostic signals of microbial metabolisms. Field studies, laboratory cultures, and computational models explain how methanogens produce unique nonequilibrium methane clumped isotopologue (1 3CH3D ) signals that do not correspond to growth temperature. Instead, [Delta]13CH3D values may be driven by enzymatic reactions common to all methanogens, the C-H bond inherited from substrate precursors including acetate and methanol, isotope exchange, or environmental processes such as methane oxidation. The phylogenetic relationship between substrate-specific methyl-corrinoid proteins provides insight into the evolutionary history of methylotrophic methanogenesis. The distribution of corrinoid proteins in methanogens and related bacteria suggests that these substrate-specific proteins evolved via a complex history of horizontal gene transfer (HGT), gene duplication, and loss. Furthermore, this work identifies a previously unrecognized HGT involving chitinases (ChiC/D) distributed between fungi and bacteria (~650 Ma). This HGT is used to tether fossil-calibrated ages from within fungi to bacterial lineages. Molecular clock analyses show that multiple clades of bacteria likely acquired chitinase homologs via HGT during the late Neoproterozoic into the early Paleozoic. These results also show that, following these HGT events, recipient terrestrial bacterial clades diversified ~400-500 Ma, consistent with established timescales of arthropod and plant terrestrialization. Divergence time estimates for bacterial lineages are broadly consistent with the dispersal of chitinase genes throughout the microbial world in direct response to the evolution and expansion of detrital-chitin producing groups including arthropods. These chitinases may aid in dating microbial lineages over geologic time and provide insight into an ecological shift from marine to terrestrial systems in the Proterozoic and Phanerozoic eons. Taken together, this thesis may be used to improve assessments of microbial activity in remote environments, and to enhance our understanding of the evolution of Earth's carbon cycle.
by Danielle S. Gruen
Ph. D.
40
Blake, Kevin L. "The petrology, geochemistry and association to ore formation of the host rocks of the Kiirunavaara magnetite-apatite deposit, northern Sweden." Electronic Thesis or Dissertation, Cardiff University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.321483.
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41
Diarra, Pobanou Hughes. "The geology and genesis of the Syama gold deposit, Mali, West Africa." Electronic Thesis or Dissertation, University of Southampton, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362528.
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42
Savage, Derek Allan. "Terminal proterozoic stromatolite reefs with shelly fossils, Salient Platform, British Columbia." Electronic Thesis or Dissertation, McGill University, 2004. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=81434.
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The late Neoproterozoic Salient Platform (Byng Formation, upper Miette Group), located 50 km northwest of Jasper, Alberta, contains one of three known occurrences worldwide of the Cloudina-Namacalathus fossil assemblage.
The Salient Platform initiated in relatively deep water (minimum 30-50 m) on Mount Machray. Lowermost carbonates on Salient Mountain and The Colonel were deposited in quiet environments behind the developing stromatolitic reef. The upper two thirds of the platform formed in shallow water and consists of huge, elongated Platella and Cryptozoon bioherms, within which most shelly fossils are found. Carbonate production is terminated by Gog Group siliciclastic sedimentation. Thin, shell-bearing stromatolitic carbonates discovered within the lowermost Gog Group bring into question the current position of the Precambrian-Cambrian boundary in the southern Rocky Mountains (western Canada).
Petrographic and geochemical data indicate that the Salient Platform has undergone significant diagenetic alteration. delta13C values of microsparitic limestones appear to retain a primary isotopic signature, which correlates well with coeval late Neoproterozoic successions worldwide.
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Anderson, Phillip. "THE PROTEROZOIC TECTONIC EVOLUTION OF ARIZONA (PRECAMBRIAN, PLATE TECTONICS, VOLCANIC, STRATIGRAPHY)." Dissertation-Reproduction (electronic), The University of Arizona, 1986. http://hdl.handle.net/10150/183853.
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Archean tectonics are irreconcilable with modern plate tectonics without clearly understanding Proterozoic tectonic accretionary prosesses. Arizona best displays a convergent margin where Proterozoic accretion to an Archean craton generated a new Proterozoic crust from 1800 to 160 Ma. This 12 year study independently formulated a definitive understanding of Arizona's Proterozoic tectonic evolution with new lithologic, petrologic, geochemical, structural and relative age data, and extensive new mapping. The Northwest Gneiss Belt contains an early Proterozoic arkosic clastic wedge at the Wyoming Archean edge, but only intraoceanic elements--Antler-Valentine and Bagdad volcanic belts--on Proterozoic oceanic crust south of the wedge. The Central Volcanic Belt evolved diachronously on oceanic crust: 1800-1750 Ma formative volcanism (Bradshaw Mountain, Mayer, Ash Creek and Black Canyon Creek Groups) stepped SE to form the Prescott-Jerome island arc above a SE-dipping subduction zone; a 1740 Ma NW subduction flip accreted the arc to the Archean craton, evolved I-type plutons of NW alkali-enrichment opposit to arc tholeiites, and formed calc-alkaline Union Hills Group volcanics at the southeast arc front. Except for hiatal Alder Group deposition in structural troughs, the central magmatic arc emerged as the trench stepped southeastward across SE Arizona with flattening of subduction, growth of the Pinal Schist fore-arc basin, 1700 Ma accretion of the Dos Cabenzas arc to the margin, eruption of felsic ignimbrite fans across the central arc front, and Mazatzal Group shallow marine sedimentation across the emergent arc. Proterozoic plate tectonics were subtly different from modern plate tectonics, producing oceanic crust, island arcs and other features very different in detail from modern and Archean analogs. The Proterozoic Plate Tectonic Style warrants clear distinction from those of other eras. This study establishes for Arizona an extensive, accurate and new Proterozoic data base, for central Arizona a detailed relative chronology surpassing isotopic resolution, and a new formal stratigraphic framework to be the foundation for future studies. This dissertation is superceded by a new book on Arizona's Proterozoic Tectonic Evolution, published by the Precambrian Research Institute, 810 Owens Lane, Payson, Arizona, 85541.
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Roberts, Nicholas Michael William. "From crystal to crust : the Proterozoic crustal evolution of southwest Norway." Electronic Thesis or Dissertation, University of Leicester, 2010. http://hdl.handle.net/2381/8954.
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The geology of the Suldal Sector, southwest Norway, comprises exposures from three orogenic periods; the Telemarkian, Sveconorwegian and Caledonian. Telemarkian (~1500 Ma) basement rocks are interpreted to be the oldest crust in the region; these are intruded by Sveconorwegian granitoid intrusions (~1070-930 Ma). Crystalline nappe units overlie the Mesoproterozoic basement, and from reconnaissance U-Pb dating and zircon hafnium isotopes, are believed to comprise slices of the Mesoproterozoic Norwegian continental margin. The Telemarkian basement comprises meta-plutonic/volcanic lithologies that represent the deformed upper crustal section of a continental arc - the Suldal Arc; U-Pb dating suggests this arc was active from ~1520 to 1475 Ma. Whole-rock geochemistry and hafnium and oxygen isotopes measured in zircon, suggest that arc magmatism recycled older continental crust (20-50% contribution) that had been mixed with mantle-derived material in the lower crust; the older crustal component comprised late-Palaeoproterozoic sedimentary material derived from the Fennoscandian continent. During the arc’s evolution, dehydration of mafic source magma induced by heat from magmatic underplating, and subsequent melting of dehydrated crust enhanced by asthenospheric upwelling, allowed for the intrusion of iron-enriched tholeiitic magmas. The Suldal arc and by extension, the Telemarkia terrane, represent the last stages of continental crust formation within a retreating accretionary orogen that was active since ~1.8 Ga. Based on whole-rock geochemistry, U-Pb, hafnium and oxygen isotopes in zircon, Sveconorwegian granite suites formed between 1.07 and 0.92 Ga, and are largely derived from ~1.5 Ga mafic lower crust with a limited contribution of juvenile mantle-derived material. The geodynamic setting of granitic magmatism evolved from supra-subduction, to overthickened crust, to thinned crust with possible lithospheric delamination. The varying geochemistry of the granite suites (I- to A-type) is controlled not by geodynamic setting, but dominantly by water content in the magma source. Sveconorwegian deformation in the Suldal Sector is bracketed between ~1069 and ~1047 Ma by intrusions of the Storlivatnet plutonic complex.
45
Bjänndal, Erik. "Geophysical investigation of the Arvidsjaur volcanics and the Archean-Proterozoic boundary." Student thesis, Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-72632.
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In this work the magnetic and magnetotelluric (MT) geophysical methods have been used to produce two 3D models for the Laver area in southern Norrbotten. A new discovery of a porphyry copper deposit located at the Lill-Laverberget was reported by Boliden in 2012. The goal with the models is to form a better understanding of the setting for the porphyry deposit and to see if any of the geophysical methods are suited to be used in exploration for it. For starters an edge detector (Beiki, 2010) was used on magnetic data to identify structures and petrological contacts in the area. The magnetic data was modelled using the SimPEG (Cocket, et al., 2015) inversion software to create a 3D model over the area. The Magnetic method quite clearly managed to resolve the volcanic units in the Laver area. MT data was collected during fieldwork in September of 2018 and modelled using the MOD3DEM (Egbert & Kelbert, 2012) inversion software. The MT model did not show any clear anomalies that could be related to the deposit.
I detta arbete så har de magnetiska och magnetotelluriska (MT) geofysiska metoderna används för att skapa två 3D modeller över Laverområdet i södra Norrbotten. I området finns en porfyrkopparfyndighet som Boliden rapporterade in 2012. Målet med båda modellerna är att fördjupa förståelsen för bildningsmiljön för fyndigheten och för att se hur lämpade de geofysiska metoderna är för prospektering. Det första steget var att använda befintliga magnetiska data och processa den med ED funktionen (Beiki, 2010) för att identifiera strukturer och bergartskontakter i området. Den magnetiska data användes för att producera en 3D modell med inversionsprogrammet SimPEG (Cocket, et al., 2015). Denna modell kunde skilja mellan vulkaniska och övriga bergarter i området. Magnetotelluriska data samlades in i september 2018 och modellerades med MOD3DEM (Egbert & Kelbert, 2012), denna modell hade dock problem att finna anomalier i området.
46
Boyce, Alistair. "The Proterozoic building of North America : insights from broadband seismic tomography." Electronic Thesis or Dissertation, Imperial College London, 2018. http://hdl.handle.net/10044/1/62331.
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Cratons, the Archean (≥ 2.5 Ga) cores of the continents are the longest-lived features of Earth’s surface. They are underlain by cold, iron-depleted, thick (>250 km), seismically fast lithospheric mantle roots or keels that have survived thermal and chemical erosion over multiple Wilson cycles. Recently however, numerous studies have shown that cratonic mantle lithosphere can undergo modification andmay be removed entirely. I use passive-source seismology to investigate this further for the Superior Craton of North America and its abutting Proterozoic platform. Initially, I use P- and S-wave relative arrival-time tomography to investigate the regional seismic structure of southeast Canada. Here, three broad zones of decreasing seismic wavespeed span the Archean Superior, Proterozoic Grenville and Phanerozoic Appalachian provinces, respectively. A vertical boundary in wavespeed beneath the Grenville Front is interpreted as evidence for subduction-driven metasomatic enrichment of the Laurentian margin. Due to the loss of the background mean velocity structure, relative arrival-time datasets are not easily combined and are also unsuitable for estimation of the physical properties of the mantle. To address this, I develop the Absolute Arrival-time Recovery Method (AARM) to retrieve absolute arrival-times from temporary seismograph networks, whose data are often noisy. Tests indicate that AARM picks are accurate to ≤0.25 s, akin to uncertainties in ISC bulletins. As a result, small aperture, temporary deployments now represent an exploitable resource with which to fill gaps in global seismic tomographic studies. Finally, I incorporate multiple regional networks from eastern Canada into a continental P-wave absolute arrival-time tomographic inversion to produce the most up-to-date compressional wavespeed image of the North American lithosphere. These results show along-strike variability in upper lithospheric velocity structure within the Proterozoic Grenville Orogen (1.3 − 1.0 Ga). When reconciled with the geological record, these results may provide the first seismological evidence for delamination of subcontinental lithospheric mantle in a Proterozoic large, hot, orogen.
47
Green, Damian Alan. "Stratigraphic visualisation for archaeological investigation." Electronic Thesis or Dissertation, Brunel University, 2003. http://bura.brunel.ac.uk/handle/2438/2168.
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The principal objective of archaeology is to reconstruct in all possible ways the life of a community at a specific physical location throughout a specific time period. Distinctly separate layers of soil provide evidence for a specific time period. Discovered artefacts are most frequently used to date the layer. An artefact taken out of context is virtually worthless; hence the correct registration of the layer in which they were uncovered is of great importance. The most popular way to record temporal relationships between stratigraphic layers is through the use of the 2D Harris Matrix method. Without accurate 3D spatial recording of the layers, it is difficult if not impossible, to form new stratigraphic correspondences or correlations. New techniques for archaeological recording, reconstruction, visualisation and interpretation in 3D space are described in these works and as a result software has been developed. Within the developed software system, legacy stratigraphy data, reconstructed from archaeological notebooks can be integrated with contemporary photogrammetric models and theodolite point data representations to provide as comprehensive a reconstruction as possible. The new methods developed from this research have the capability to illustrate the progression of the excavation over time. This is made possible after the entry of only two or more strata. Sophisticated, yet easy-to-use tools allow the navigation of the entire site in 3D. Through the use of an animation-bar it is possible to replay through time both the excavation period and the occupation period, that is to say the various time periods in antiquity when human beings occupied these locations. The lack of complete and consistent recording of the soil layers was an issue that proved to be an obstacle for complete reconstruction during the development of these methods. A lack of worldwide archaeological consensus on the methods of stratigraphic recording inhibited development of a universal scientific tool. As a result, new recording methods are suggested to allow more scientific stratigraphic reconstruction.
48
Brewer, T. S. "Geochemistry, geochronology and tectonic setting of the proterozoic Telemark supracrustals, Southern Norway." Electronic Thesis or Dissertation, University of Nottingham, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303806.
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49
Callow, Richard H. T. "The co-evolution of biology anf taphonomy across the proterozoic-cambrian transition." Electronic Thesis or Dissertation, University of Oxford, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.504316.
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50
Ciborowski, Thomas. "The geochemistry and petrogenesis of the early Proterozoic Matachewan Large Igneous Province." Electronic Thesis or Dissertation, Cardiff University, 2013. http://orca.cf.ac.uk/51146/.
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The Matachewan Large Igneous Province (LIP) is interpreted to have formed during mantle plume-induced continental break-up during the early Proterozoic. When the Matachewan LIP is reconstructed to its original configuration, the dyke swarms,layered intrusions and flood basalt provinces emplaced over the lifetime of the province comprise one of the largest magmatic provinces recognised in the geological record. New geochemical data allow, for the first time, the Matachewan LIP to be treated as a single, coherent entity. The major and trace element data presented here show that Matachewan LIP suites share a common tholeiitic composition and trace element geochemistry characterised by enrichment in the most incompatible elements and depletion in the less incompatible elements. This signature, ubiquitous in early Proterozoic continental magmatic rocks, may indicate that the Matachewan LIP formed through contamination or mixing of its primary magmas with crustal material or that the early Proterozoic mantle had a fundamentally different composition to the modern mantle. Aside from the radiating geometry of the dyke swarms, a plume origin for the Matachewan LIP is implied by the geochemistry of some of the suites, used here to constrain the potential temperature of the magmatism. Comparison of these potential temperatures with the temperature of the early Proterozoic upper mantle, shows that the province is the product of anomalously hot magmatism as predicted by mantle plume theory. Geochemical data from coeval intrusions suggest that the plume head was compositionally heterogeneous and sampled material from both depleted and enriched mantle. Sr-Nd-Pb isotopic data show that this source heterogeneity dictates the Ni-Cu-PGE potential of the related intrusions. The enormity of the Matachewan LIP cannot be overstated and its potential impact on the early Proterozoic global environment was likely immense – it may even have been the trigger to the irreversible oxygenation of our planet.

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