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Johnson, Shannon D. "Structural geology of the Usakos Dome in the Damara Belt, Namibia." Thesis, Stellenbosch : Stellenbosch University, 2005. 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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Glascock, Jacob M. "Exhumation of the Orlica-Snieznik Dome, northeastern Bohemian massif (Poland and Czech Republic)." Ohio : Ohio University, 2004. http://www.ohiolink.edu/etd/view.cgi?ohiou1107879485.
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Crowley, James L. Carleton University Dissertation Earth Sciences. "U-Pb geochronology in Frenchman Cap dome of the Monashee complex, southern Canadian Cordillera; early Tertiary tectonic overprint of a Proterozoic history." Ottawa, 1997.
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Weiland, Richard John. "Emplacement of the Irian ophiolite and unroofing of the Ruffaer metamorphic belt of Irian Jaya, Indonesia /." Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.
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Nejad, K. S. "The geology and tectonic settings of ophiolites and associated rocks in the Neyriz area, south-eastern Iran." Thesis, Bucks New University, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.373604.
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He, Wenjun. "The dalabute ophiolite of the West Junggar Region, Xinjiang, NW China : origin, emplacement and subsequent tectonic evolution /." Hong Kong : University of Hong Kong, 2002. http://sunzi.lib.hku.hk/hkuto/record.jsp?B2472886x.
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Jacobson, Herbert Paul. "Folding of stratigraphic layers in ice domes /." Thesis, Connect to this title online; UW restricted, 2001. http://hdl.handle.net/1773/6837.
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Clements, James Wesley. "Laramide stress conditions and deformations mechanisms during the formation of Hudson and Dallas Domes, Lander Quadrangle, Wind River Mountains, Lander, Wyoming." Diss., Columbia, Mo. : University of Missouri-Columbia, 2008. http://hdl.handle.net/10355/5640.
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Thesis (M.S.)--University of Missouri-Columbia, 2008.The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file and four media files (media file 1.pdf, media file 2.pdf, media file 3.pdf, and media file 4.pdf) Title from title screen of research.pdf file (viewed on August 25, 2008) Vita. Includes bibliographical references.
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Morse, David L. "Glacier geophysics at Taylor Dome, Antarctica /." Thesis, Connect to this title online; UW restricted, 1997. http://hdl.handle.net/1773/6801.
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Brown, Stuart J. A. "Geology and geochemistry of the Whakamaru Group ignimbrites, and associated rhyolite domes, Taupo Volcanic Zone, New Zealand." Thesis, University of Canterbury. Geology, 1994. http://hdl.handle.net/10092/6895.
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The Whakamaru group ignimbrites are a Widespread and voluminous group of welded crystal-rich ignimbrites which outcrop along the eastern and western margins of the Taupo Volcanic Zone (TVZ), New Zealand. They have previously been mapped as Whakamaru (s.s), Manunui, Rangitaiki, Te Whaiti, and Paeroa ignimbrites, and have a combined volume of more than 1000km³ (DRE). The ignimbrites were erupted from a large vent area within central TVZ at 340ka, following a c.350ka hiatus in caldera forming activity in TVZ. This study investigates field and volcanological aspects of the ignimbrites, the geochemistry of pumice clasts and plutonic lithics, and the geochemistry of rhyolite lavas of the Western Dome Belt (WDB).
The postulated vent area for the ignimbrites lies to the north of Lake Taupo and overlaps with the younger Taupo and Maroa volcanoes. Maximum lithic data indicate that the western margin of the vent area was located at or within a few kilometres east of the WDB, and probably overlapped with the northern part of Lake Taupo, providing clear support for a North Taupo/ Maroa caldera source. Isopleths close around an area previously modelled as a deep basement collapse structure, suggesting this area may have been an important focus of eruption and collapse within a broad 'Whakamaru Centre' comprising several nested collapse structures.
On the basis of field evidence, mineral chemistry, and new Ar-Ar dates, Whakamaru, Manunui, Rangitaiki, Te Whaiti, Wairakei, and Paeroa Range Group (PRG) ignimbrites are considered to be correlatives. Manunui ignimbrite represents the stratigraphically lowest unit(s) of Whakamaru that is locally more highly welded and is less crystal rich in distal areas. Manunui ignimbrite therefore correlates with unit A of Briggs (1976) at Maraetai. East of TVZ, Te Whaiti ignimbrite also corresponds to the lowermost part of Lower Rangitaiki ignimbrite, with a gradational boundary between the two. There is no clear evidence for a significant time break between either Manunui and Whakamaru, or Te Whaiti and Rangitaiki ignimbrites. High precision Ar-Ar dating indicates eruptions occurred over a period of less than c.5ka, and lack of field evidence for a significant time break suggests a duration of no more than hundreds of years.
Electron microprobe analysis of whole-rock samples throughout the ignimbrite sequence identify multiple populations of hornblende and biotite, whereas orthopyroxene has a relatively narrow compositional range. There is apparently no systematic variation in the chemistry of ferromagnesian silicate minerals with stratigraphic height. In contrast, Fe-Ti oxide minerals show considerable variability with stratigraphic height, becoming more Mg-rich toward the base of the ignimbrite. There is a corresponding trend in calculated Fe-Ti oxide temperatures, with generally high equilibrium temperatures (800-820°C) at the base, and generally lower, but widely variable (730-900+°C) temperatures in middle and upper parts.
Study of juvenile pumices has identified five distinct magma types (rhyolites A-D, and high alumina basalt) and significant gradients in temperature, water content, and Sr isotopic composition in the preeruptive magma system. Rhyolite pumice clasts range from 70 to 77 wt% SiO₂, and mixed basalt/rhyolite clasts range from 51.7 to 68.0% SiO₂. There is a marked variation in mineral assemblage with composition. The low silica type A rhyolite pumices contain plagioclase, quartz, orthopyroxene, hornblende, biotite, and magnetite with distinctive large rounded quartz phenocrysts. High silica type B and C pumices contain quartz (smaller, subhedral phenocrysts), plagioclase, sanidine, biotite, and magnetite/ilmenite. Biotite therefore becomes the dominant mafic phase at high silica compositions as orthopyroxene and hornblende disappear in response to increasing P(H20) and decreasing temperature conditions. Calculated Fe-Ti oxide equilibrium temperatures range from 730°C in high silica pumices to 820°C in low silica type A pumices. Rare earth elements show a general enrichment in the more evolved pumices, and progressively increasing Eu* from type A to C. More evolved rhyolite types B and C are related to type A magma by a two-stage crystal fractionation process, probably by side wall crystallisation and convective fractionation within a large, zoned magma chamber. The first step involved 30-40% fractionation of a plagioclase-dominated (but sanidine-free) assemblage to produce a type B magma, which in turn underwent fractionation of a plagioclase/quartzlsanidine assemblage to produce the highly evolved, but relatively Ba-depleted type C magmas. Petrographic and temperature trends in ignimbrite wholerock suggest that eruptions commenced with the hottest, least evolved magmas, and more evolved magmas became important at a later stage in the eruption. This sequence precludes simple sequential tapping of a large zoned magma chamber, and indicates a complex magma chamber configuration and/or withdrawal dynamics during eruption.
Two types of plutonic lithics have been recovered from Whakamaru group ignimbrite; leucocratic biotite monzogranite, and medium- to fine-grained dolerites. Whakamaru granites are chemicallymore evolved, and are strongly depleted in HREE compared to granitoid lithics from Atiamuri and Tarawera. They are chemically unlike pumices from Whakamaru group ignimbrite, and are not comagmatic.
Rhyolite lavas of the WDB were extruded along a N-S trending curvilinear structure that marks the western boundary of the TVZ, and also coincides with the western margin of the Whakamaru caldera. Analyses fall into two compositional groups; the Western Dome Complex, south of the Waikato River are chemically variable (73.4-76.4% SiO₂), whereas the Northwestern Dome Complex are predominantly high-silica rhyolites (>77% SiO₂). The lavas have similar trace element and REE characteristics to Whakamaru pumices, but have lower ⁸⁷Sr/⁸⁶Sr ratios, indicating they are not simply degassed remnants of the Whakamaru magma system, but represent new crustal melts.
The Whakamaru magma system provides clear evidence that (less evolved) low silica rhyolites undergo significant fractionation at shallow crustal levels in TVZ, to produce the generally more evolved rhyolites most commonly erupted at the surface. Type A magma with its relatively high Sr, low Rb and SiO₂, and lack of a significant Eu anomaly may be close to a 'primary' crustal melt composition. Trace element and REE characteristics for selected rhyolite domes and ignimbrites suggest the crustal source for TVZ rhyolites is not homogenous, but may be variable, at least with respect to mineral composition and melting behaviour in space and time.
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Chinyuku, Donald Tichaona. "The Kansanshi Cu-Au deposit, Domes region, Zambia : geology, mineralisation and alteration characteristics in the main pit." Thesis, Rhodes University, 2014. http://hdl.handle.net/10962/d1011758.
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The Kansanshi Cu-Au deposit located in the Domes region of the North West province of Zambia is characterised by structurally controlled high angle veins and associated alteration halos. The northwest trending Kansanshi antiform flanks the Solwezi syncline to the north and hosts the Kansanshi deposit and consists of tillites and metasedimentary rocks. Mineralisation is associated with Neoproterozoic Pan African deformation events experienced during the formation of the Lufilian fold belt; however recent findings confirm that structures in the form of reverse and normal faults and drag folds are critical controls on mineralisation within the deposit, Main pit in particular. Low angle faults occurring below the current pit are believed to have served as major fluid pathways during mineralisation. Age dating data from the Kansanshi deposit suggest that mineralisation took place between 512 and 503 Ma indicating that the event was associated with metamorphism. Two types of alteration are dominant within the Main pit (Kansanshi deposit) with the type and intensity of alteration being largely controlled by lithological units. Albite alteration occurs dominantly in phyllites and schists whereas dolomitisation is prevalent in calcareous units. Alteration is associated with mineralisation, and therefore is used as a condition for predicting vein or disseminated mineralisation. The high Au tenor at Kansanshi can be attributed to gold grains occurring in association with melonite (NiTe₂) and microfractured pyrite intergrown with chalcopyrite in sulphide and quartz dominated veins and veinlets. Analysis of gold grade distribution within the Main pit shows a clear concentration of the element along the major north-south trending structures like the 4800 and 5400 zones, possibly through supergene enrichment in the oxide-transition-sulphide zones. It is imperative that exploration for Kansanshi-type deposits will require geochemical and geophysical studies, understanding of the geology of an area to identify the three lithostratigraphic units (red beds, evaporites and reducing strata).
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Garlick, Sarah R. "Granulite- to amphibolite-facies metamorphism and penetrative deformation in a disrupted ophiolite, Kangaroo Mountain area, Klamath Mountains, California a deep view into the basement of an accreted, oceanic island arc /." Laramie, Wyo. : University of Wyoming, 2007. http://proquest.umi.com/pqdweb?did=1317326781&sid=1&Fmt=2&clientId=18949&RQT=309&VName=PQD.
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Hawley, Robert L. "Borehole investigations of firn processes /." Thesis, Connect to this title online; UW restricted, 2005. http://hdl.handle.net/1773/6796.
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Armstrong, Thomas Robert. "Structural and Petrologic Evolution of Acadian Dome Structures in Southern Vermont." Diss., Virginia Tech, 1995. http://hdl.handle.net/10919/37857.
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Petrologic and thermobarometric studies, coupled with geologic mapping and structural analysis, provide critical evaluation of several different models for Acadian (Late Silurian to Middle Devonian) dome evolution in southern Vermont. Previous models considered diapiric uprise and composite nappe-stage crustal thickening and subsequent diapirism as likely causes of dome formation. Both of these previous models result in symmetrical distribution of P-T values about the dome structures with corresponding coreward increases in temperature, and typically, coreward decrease in associated pressures. Thermobarometric calculations made during this study demonstrate that both P and T increase eastward across the entire region and are not symmetrically distributed about dome axes. The P-T data coupled with petrographically derived relative age relationships and available geochronology also suggest that attainment of peak metamorphic conditions and concurrent dome-stage deformation are diachronous and young from west to east. These relationships are consistent with new geologic mapping and structural analysis which show that all of the domes in southern Vermont are low-amplitude fold interference structures. A current tectonic model indicates that Acadian Barrovian metamorphism in this region was a consequence of west-directed crustal thickening of an eastward dipping tectonic wedge, presumably from the Bronson Hill Terrane; an Ordovician arc sequence. The basal surface of this allochthonous mass projects above the present land surface within this area. Accretion of lower-plate rocks (of this study) into the thrust complex and continued west-directed thrusting of the accreted package over a seismically recognizable east dipping ramp structure provided the necessary geometry and mechanism for dome-stage fabric development, calculated uplift rates (1.2 to 1.7 km/m.y. and west to east younging of Acadian structural and metamorphic evolution.
Thermobarometric and geochronologic estimates of metamorphic pressure - temperature (P-T) conditions and metamorphic cooling ages were used to constrain the required thermal and tectonic input parameters for use in one-dimensional thermal modeling of an Acadian (Silurian-Devonian} tectonotherma! regime within the pre-Silurian Taconide zone of southern Vermont. This regime includes: 1) garnet-grade rocks from the eastern flank of an Acadian composite dome structure (Sadawga Dome; the western domain); 2) staurolite/kyanite-grade rocks from the western flank of a second composite structure, the Athens dome (eastern domain). Results from thermal modeling include development of P-T paths, temperature-time (T-t) and pressure-time (P-t) curves, related values of maximum temperature and pressure, pressure conditions at maximum temperature, predicted closure ages for radiogenic phases, and integrated uplift and cooling rates.
Thermal modeling results are remarkably similar to independently obtained data for Acadian regional metamorphism in western New England, and provide some important constraints on regional thermal evolution: 1) pressure values contemporaneous with peak temperature on P-T paths may be substantially lower than actual maximum pressure (> 2.5 kbars); 2) differences in peak temperature for rocks initially loaded to similar crustal depths (garnetgrade vs. staurolite-grade), differences in calculated uplift rates, and differences in Ar closure ages, are consequences of variations in durations of isobaric heating events (or "residence periods"), and differences in actual tectonic uplift rates. These modeling results are internally consistent with structural model that suggests west to east younging of specific Acadian deformations and resultant diachroneity of peak metamorphic and Ar closure ages. Regional variations in timing and conditions of metamorphism may be controlled by diachronous deformational events coupled with variations in crustal levels to which rocks were initially loaded during the ca. 400 Ma onset of Acadian orogenesis in western New England.Ph. D.
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Rose, Shellie. "Timing constraints and significance of Paleoproterozoic metamorphism within the Penokean orogen, northern Wisconsin and Michigan (USA)." Ohio University / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1090940526.
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Lai, Chun-kit, and 黎俊傑. "Genetic relations between gabbros and sheeted dykes in the Troodos ophiolite, Cyprus." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2011. http://hub.hku.hk/bib/B46089147.
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Adamson, Thomas Keeley. "Structural development of the Dun Mountain Ophiolite Belt in the Permian, Bryneira Range, western Otago, New Zealand : a thesis submitted in partial fulfilment of the requirements for the degree of Master of Science in Geological Science at the University of Canterbury /." Thesis, University of Canterbury. Geological Sciences, 2008. http://hdl.handle.net/10092/1587.
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The deformed Permian Dun Mountain Ophiolite Belt (DMOB) forms the basement of the Dun Mountain-Maitai terrane and is traceable through the entire length of New Zealand. The DMOB contains a variably serpentinised mantle portion and a crustal portion containing gabbros, dolerites, cross cutting dikes and extrusives, together they are similar to oceanic crust. The initial crustal portion, however, is atypical when compared to other ophiolites, being thin and lacking a sheeted dike complex, but has well spaced inclined intrusive sheets and sills. At least four post-Permian deformation periods affect the DMOB; collision and rotation during emplacement of the DMOB on the Gondwana margin, compression during Mesozoic orogenies, extensional deformation during the Gondwana break-up and transpressive deformation related to the modern plate boundary through New Zealand. Structural work in the Northern Bryneira Range focused on well preserved outcrops to investigate crustal growth and contemporaneous deformation during the Permian. Structural evidence of Permian deformation was determined by examination of pseudostratigraphy, structures constrainable to the Permian, and the geometric relationships with the overlying Maitai sedimentary sequence. Crosscutting by intrusive phases was used to determine a chronological order of crustal growth and deformation episodes. It was concluded that all deformation was extensional and that two major phases of magmatism were separated by a period of deformation and were followed by ongoing syn-sedimentary deformation during the deposition of the Maitai Group. After removal of Mesozoic rotation, the resulting orientations of paleo-horizontal markers and diverse orientations of intrusive sheets were analysed. Two hypothesises were tested to assess the origin of inclined intrusive sheets: a) that the diverse orientations were the result of tectonic rotation coeval with the intrusion of dikes. b) that primary orientations of the sheets had been diverse. Results show that the sheets were intruded with diverse orientations, probably related to variation in the principle horizontal stress over time. Further rotation of the assemblage of sheets occurred during the last stages of magmatism and during the subsequent period of sedimentation. The last stage probably relates to large scale normal faulting during the development of the sedimentary basin. iii
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Dangerfield, Anne. "Geochemistry, structure, and tectonic evolution of the Eldivan ophiolite, Ankara Melange, central Turkey." Diss., CLICK HERE for online access, 2008. http://contentdm.lib.byu.edu/ETD/image/etd2423.pdf.
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Chum, Chun-yip, and 覃進業. "Cumulate pyroxenite and pyroxenite dykes in the Troodos ophiolite, Cyprus." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/197511.
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The Troodos ophiolite is a type example of ophiolite and has been studied for more than 50 years. Albeit numerous findings have been derived from previous investigations, some questions about the details of its formation processes are still outstanding. One of them concerns the origin of the pyroxenites in the mantle and the lower crustal section, and this is the main theme of this thesis. Integrated field, petrographical and geochemical work was conducted in this study. On the basis of distribution, the pyroxenites can be divided into two categories, crustal pyroxenites and mantle pyroxenite dykes.
The results show that the layered or massive crustal pyroxenites can be distinguished by their magmatic features, and their formations have been controlled by a series of factors, including the melt composition, change of pressure, magma replenishment and magma mixing. The crystallization sequences of the crustal ultramafic unit samples are classified into two trends. Trend (i) olivine, orthopyroxene, clinopyroxene, plagioclase has been derived from tholeiitic-boninitic transitional melts, whereas trend (ii) olivine, clinopyroxene, plagioclase, orthopyroxene from depleted boninitic melts.
Regarding the mantle section, the pyroxenite dykes have been formed by focused flow of melt during migration towards the crust. Data show that they are products of several processes, including melt-rock reactions and fractional crystallization. On the basis of modal composition, the pyroxenite dykes are divided into clinopyroxenites and orthopyroxenites. Geochemical compositions suggest that the clinopyroxenites have been derived from island arc tholeiitic melts, whereas the orthopyroxenites from boninitic melts.
The important overlap of the tholeiitic and the boninitic series throughout the sections of the ophiolite, as well as the presence of lithologies with compositions transitional between the two series, suggests that the two magmatic suites existed together. A tectonic model of subduction initiation, during which the subducting slab rolled-back rapidly, triggering asthenospheric mantle flow into the mantle wedge, inducing partial melting at a shallow level of the mantle to generate a series of island arc tholeiitic magmas and at deeper level, a series of depleted boninitic magmas. The two magmatic series have possibly been mixed during migration in the mantle, producing transitional units of the two series.published_or_final_version
Earth Sciences
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Master of Philosophy
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Whattam, Scott A. "Evolution of the Northland ophiolite, New Zealand: geochemical, geochronological and palaeomagneticconstraints." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2003. http://hub.hku.hk/bib/B31244890.
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Jackson, Matthew G. (Matthew Gerald). "Dismantling the deep earth : geochemical constraints from hotspot lavas for the origin and lengthscales of mantle heterogeneity." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/43157.
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Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2008.Includes bibliographical references (p. 135-140).
Chapter 1 presents the first published measurements of Sr-isotope variability in olivine-hosted melt inclusions. Melt inclusions in just two Samoan basalt hand samples exhibit most of the total Sr-isotope variability observed in Samoan lavas. Chapter 3 deals with the largest possible scales of mantle heterogeneity, and presents the highest magmatic 3He/4He (33.8 times atmospheric) discovered in Samoa and the southern hemisphere. Along with Samoa, the highest 3He/4He sample from each southern hemisphere high 3He/4He hotspot exhibits lower 143Nd/144Nd ratios than their counterparts in the northern hemisphere. Chapter 2 presents geochemical data for a suite of unusually enriched Samoan lavas. These highly enriched Samoan lavas have the highest 87Sr/86Sr values (0.72163) measured in oceanic hotspot lavas to date, and along with trace element ratios (low Ce/Pb and Nb/U ratios), provide a strong case for ancient recycled sediment in the Samoan mantle. Chapter 4 explores whether the eclogitic and peridotitic portions of ancient subducted oceanic plates can explain the anomalous titanium, tantalum and niobium (TITAN) enrichment in high 3He/4He ocean island basalts (OIBs). The peridotitic portion of ancient subducted plates can contribute high 3He/4He and, after processing in subduction zones, a refractory, rutile-bearing eclogite may contribute the positive TITAN anomalies.
by Matthew G. Jackson.
Ph.D.
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何文軍 and Wenjun He. "The dalabute ophiolite of the West Junggar Region, Xinjiang, NW China: origin, emplacement and subsequent tectonicevolution." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2002. http://hub.hku.hk/bib/B31226012.
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Johnson, Christopher M., and Daalen Christopher M. Van. "Mineralogy and geochemistry of Late Archean and Paleoproterozoic granites and pegmatites in the Northern Penokean terrane of Marquette and Dickinson Counties, Michigan." ScholarWorks@UNO, 2015. http://scholarworks.uno.edu/td/2088.
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This thesis focuses on mineralogy, geochemistry, and origin of eight pegmatites and two spatially associated granites of Late Archean and Paleoproterozoic ages located in Marquette and Dickinson Counties, Michigan. Biotite geochemistry reveals that both granites and all pegmatites are peraluminous and have an orogenic signature. However, bulk composition reveals the Humboldt granite is a peraluminous A-type granite and the Bell Creek granite is a peraluminous mix between I-, S-, and A-type granites. The Republic Mine pegmatite appears to be geochemically similar to the Bell Creek granite and Grizzly pegmatite. The Crockley pegmatite is genetically related to the Humboldt granite. The Groveland Mine, Sturgeon River, and Hwy69 pegmatites appear to be a product of the Peavy Pond Complex being contaminated with the Marquette Range Super Group. Contamination and anatexis have made classification of the granites and pegmatites problematic. The Grizzly should be classified as a primitive LCT-type even though this pegmatite lacks characteristic enrichment associated with LCT pegmatites. Mineralogical geochemistry reveals that the Republic Mine is relatively more primitive than other pegmatites and should be classified as a primitive Mixed-type pegmatite. Groveland Mine has mineralogy and geochemistry not normally associated with NYF-type pegmatites and should be classified as Mixed. The Crockley pegmatite should be classified as NYF-type with a primitive LCT overprint. Dolfin, Hwy69, Sturgeon River, and Black River pegmatites should be classified as Rare Element, REE, NYF-type, although the Black River has slight tantalum enrichment expressed in columbite group minerals.
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Phillips, Charity M. "Seafloor Spreading Processes in Protoarc-Forearc Settings: Eastern Albanian Ophiolite as a Case Study." Oxford, Ohio : Miami University, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=miami1083687853.
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Abily, Bénédicte. "Caractéristiques pétrographique, géochimique et structurale de la section crustale profonde de l'ophiolite d'Oman : Implications pour la genèse des magmas et le fonctionnement des chambres magmatiques à l'aplomb d'un centre d'expansion océanique." Phd thesis, Université Paul Sabatier - Toulouse III, 2011. http://tel.archives-ouvertes.fr/tel-00627553.
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Ce travail repose sur (1) une étude de terrain des cumulats lités de l'ophiolite d'Oman, notamment dans plusieurs massifs où cette unité restait largement inexplorée, (2) une étude pétrographique et géochimique (microsonde électronique et LA-ICP-MS) d'environ 700 échantillons et (3) une simulation en laboratoire de la cristallisation de magmas boninitiques en présence d'eau. La cinquantaine de faciès pétrographiques définie, gabbroïques et ultrabasiques, est indispensable pour décrire rigoureusement la croûte profonde omanaise. Cette variété lithologique est révélatrice de la très grande variabilité des paramètres intensifs (P, T°, PH2O ...) et extensifs (composition) lors de la cristallisation des magmas au sein des chambres magmatiques à l'aplomb d'un centre d'expansion océanique. L'orthopyroxène précoce dans les cumulats primitifs (XMg > 80 %) est beaucoup plus commun que ce qui était proposé jusqu'à présent, ce qui remet en cause certaines idées reçues concernant l'origine de l'ophiolite. Je démontre que cette variété lithologique, l'abondance d'orthopyroxène, et d'autres caractéristiques pétrographiques et géochimiques des cumulats d'Oman s'expliquent par le mélange, dans des proportions variables, de deux principaux magmas : un d'affinité tholéiitique issu de la fusion d'une source asthénosphérique " N-MORB ", et un d'affinité andésitique à boninitique issu de la fusion hydratée d'une source lithosphérique déprimée. Ces deux magmas ont circulé dans des chenaux mantelliques (" filons ") avant d'alimenter les chambres. Le rôle de " mélangeur " des chambres magmatiques est ainsi confirmé. La contribution relative de ces deux magmas évolue au cours de l'ascension de diapirs asthénosphériques dans la lithosphère. Des variations abruptes de la pression partielle d'eau sont également indispensables pour rendre compte de l'ensemble de mes observations. Je montre aussi que les failles syn-accrétions, dont l'importance en Oman restait largement sousévaluée, sont un vecteur principal de la pénétration de fluides hydrothermaux jusque dans la croûte profonde en cours de cristallisation. Mon étude me permet également de mieux contraindre l'origine, encore très discutée, des intrusions " wehrlitiques " et de la zone de transition dunitique.
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France, Lydéric. "Interactions entre processus magmatiques et hydrothermaux aux dorsales océaniques à expansion rapide : implications pour la dynamique de la lentille magmatique axiale." Phd thesis, Université Montpellier II - Sciences et Techniques du Languedoc, 2009. http://tel.archives-ouvertes.fr/tel-00448699.
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Ce travail de thèse est basé sur des observations de terrain, sur une étude pétrographique et géochimique des roches formées à la base du complexe filonien dans l'ophiolite d'Oman et au niveau du Site IODP 1256, ainsi que sur une étude expérimentale. De nouvelles contraintes sont apportées sur les processus se produisant à la transition magma / système hydrothermal dans la croute océanique formée au niveau des dorsales à expansion rapide. L'intrusion de gabbros isotropes dans la base du complexe filonien a provoqué son réchauffement et sa recrystallization en « dikes granoblastiques » jusqu'à des températures de 1030°C. Des xénolites de microgabbro à orthopyroxene dérivées des dikes granoblastiques sont souvent observées dans le niveau de gabbros isotropes épais de 100 mètres environ qui est présent à la base du complexe filonien. Ces différentes caractéristiques sont à relier à des migrations verticales vers le haut du sommet de la lentille magmatique supérieure qui est observée aux dorsales rapides. Les nombreuses évidences d'assimilation (xénolites et patchs granoblastiques) dans le niveau des gabbros isotropes appuient l'hypothèse que ce niveau représente la fossilisation de la lentille magmatique supérieure. L'étude expérimentale a consisté à tester l'effet de la fusion partielle du complexe filonien préalablement hydrothermalisé. Les résultats montrent que la fusion commence à 850°C, confirment l'origine résiduelle des dikes granoblastiques et des xénolites associées, et attestent de l'origine anatectique des plagiogranites océaniques qui sont couramment observés à proximité de la base du complexe filonien. La composition en éléments majeurs et traces du liquide anatectique a été déterminée. Ce liquide représente le principal contaminant pour les MORBs primitifs émis au niveau des dorsales rapides. La lentille magmatique supérieure présente au niveau des dorsales médio-océaniques à expansion rapide est ici décrite comme un système dynamique qui peut migrer verticalement, et qui est fossilisée lorsqu'elle se déplace hors axe.
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Lemennicier, Yves. "Le complexe métamorphique du sud Karakorum dans le secteur du Chogo Lungma (Baltistan-Nord Pakistan) : étude structurale, métamorphique, géochimique et radiochronologique." Université Joseph Fourier (Grenoble), 1996. http://www.theses.fr/1996GRE10117.
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Les aspects tectonometamorphiques et plutoniques du complexe metamorphique du karakorum (kmc) on ete etudies dans le secteur du chogo lungma (n. Pakistan). Quatre ensembles d'orthogneiss, repris dans l'evolution tectonometamorphique, ont ete identifies, certains presentant des similitudes avec des granitoides deja connus plus au nord : l'ensemble bukpun est un equivalent des plutons de subduction cretaces de type hunza ou ghamu bar ; l'ensemble basha d'origine crustale probable presente quelques similitudes avec le granite oligo-miocene du baltoro ; l'ensemble bolocho a des caracteres intermediaires entre des complexes subalcalins et alcalins (d'ages cretaces a paleogenes). Les caracteristiques du quatrieme (aralter) sont originales dans le karakorum. L'histoire tectonometamorphique du kmc inclut : (i) des plis isoclinaux n100e a vergence sud associes a une schistosite s1 plan axial et formes dans un regime en aplatissement dominant. Ils correspondent au pic de metamorphisme (620 - 730c pour 7,5 - 11 kbar) ; (ii) des domes allonges n100e a n140e qui reprennent et deforment s1. Ils sont associes a une evolution metamorphique principalement en decompression (7,5 a 4 kbar). Ces domes seraient issus d'une deformation heterogene avec extrusion - a composantes verticale et decrochante - le long du mkt. Ils sont contemporains de la mise en place du pluton syenitique d'hemasil, magma potassique probablement issu d'une source mantellique enrichie et ayant certainement subi une contamination crustale. Les donnees #4#0ar/#3#9ar permettent d'estimer un age de mise en place a 9 ma. Il apparait donc qu'une partie de l'evolution tectonometamorphique et magmatique du kmc est tres recente et probablement en relation avec l'activation des grands decrochements regionaux. Elle est a rapprocher de celle du haut himalaya du nanga parbat situe au sud-ouest.
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Bridges, Nathan Thomas. "The origin of Venusian steep-sided domes." 1997. https://scholarworks.umass.edu/dissertations/AAI9737508.
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Steep-sided domes are interesting and enigmatic landforms on Venus. Despite superficially resembling silicic lava domes on Earth, they are much larger. Their compositions and eruptive styles have important implications for Venusian geology. Geologic mapping shows that the domes formed shortly after global resurfacing. The oldest domes on Venus are more tectonized and embayed than younger domes. Accurate heights derived from raw Magellan altimetry and stereo measurements show that many previous investigations have underestimated dome heights and that the oldest domes are also the shortest. An investigation of 390 seamounts off the coast of Hawaii finds that 55% possess steep-sides and flat-tops, similar to the Venusian domes. The seamounts and domes also have comparable ancillary attributes, such as summit pits and mounds, truncated edges, merged boundaries with adjacent seamounts/domes, landslides, and superposed graben. Of all the possible terrestrial analogs, seamounts are most like the domes. Models of lava flow properties predict that basalts on Venus and the seafloor have similar rheologies and gross shapes. Taken together, these results support the hypothesis that Venusian steep-sided domes are made of basalt and formed shortly after global resurfacing atop a relatively thin lithosphere.
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Dunsworth, Sherry Mary. "Multiple intrusion and deformation within the northwestern quadrant of the plutonic complex, Troodos Ophiolite, Cyprus /." 1989. http://collections.mun.ca/u?/theses,74438.
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Moore, Paul J. "Geology and geochemistry of mafic rocks from ophiolites of East Nelson, New Zealand /." 1991. http://collections.mun.ca/u?/theses,73302.
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Ash, Christopher Henry. "Development and subsequent demise of an oceanic spreading center : the Troodos ophiolite, Cyprus /." 1990. http://collections.mun.ca/u?/theses,84264.
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Van, Everdingen David Allard. "Geological development of and nature of fractures in the sheeted dyke complex of the Spilia-Politiko area, Troodos Ophiolite, Cyprus : implications for permeability in oceanic crust /." 1993. http://collections.mun.ca/u?/theses,44249.
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Sandeman, Hamish A. I. "A field, petrographical and geochemical investigation of the Kennack Gneiss, Lizard Peninsula, southwest England /." 1988. http://collections.mun.ca/u?/theses,114030.
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Scott, James L. "Mineralization in the Karmoy Ophiolite, southwest Norway /." 1992. http://collections.mun.ca/u?/theses,98135.
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Saunders, Cynthia Margaret. "Controls of mineralization in the Betts Cove ophiolite /." 1985. http://collections.mun.ca/u?/theses,113375.
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"Transitions in Eruption Style at Silicic Volcanoes: From Stable Domes to Pyroclastic Flows and Explosive Plumes." Doctoral diss., 2016. http://hdl.handle.net/2286/R.I.40333.
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abstract: Silicic volcanoes produce many styles of activity over a range of timescales. Eruptions vary from slow effusion of viscous lava over many years to violent explosions lasting several hours. Hazards from these eruptions can be far-reaching and persistent, and are compounded by the dense populations often surrounding active volcanoes. I apply and develop satellite and ground-based remote sensing techniques to document eruptions at Merapi and Sinabung Volcanoes in Indonesia. I use numerical models of volcanic activity in combination with my observational data to describe the processes driving different eruption styles, including lava dome growth and collapse, lava flow emplacement, and transitions between effusive and explosive activity.
Both effusive and explosive eruptions have occurred recently at Merapi volcano. I use satellite thermal images to identify variations during the 2006 effusive eruption and a numerical model of magma ascent to explain the mechanisms that controlled those variations. I show that a nearby tectonic earthquake may have triggered the peak phase of the eruption by increasing the overpressure and bubble content of the magma and that the frequency of pyroclastic flows is correlated with eruption rate. In 2010, Merapi erupted explosively but also shifted between rapid dome-building and explosive phases. I explain these variations by the heterogeneous addition of CO2 to the melt from bedrock under conditions favorable to transitions between effusive and explosive styles.
At Sinabung, I use photogrammetry and satellite images to describe the emplacement of a viscous lava flow. I calculate the flow volume (0.1 km3) and average effusion rate (4.4 m3 s-1) and identify active regions of collapse and advance. Advance rate was controlled by the effusion rate and the flow’s yield strength. Pyroclastic flow activity was initially correlated to the decreasing flow advance rate, but was later affected by the underlying topography as the flow inflated and collapsed near the vent, leading to renewed pyroclastic flow activity.
This work describes previously poorly understood mechanisms of silicic lava emplacement, including multiple causes of pyroclastic flows, and improves the understanding, monitoring capability, and hazard assessment of silicic volcanic eruptions.Dissertation/Thesis
Doctoral Dissertation Geological Sciences 2016
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Timpa, Sean. "The geological history of the Metchosin igneous complex." 2004. http://hdl.handle.net/1828/526.
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The Metchosin Igneous Complex, a partial ophiolite exposed on southern Vancouver Island, is the most northerly exposure of the Eocene Crescent Terrane. The role of the Crescent Terrane in crustal genesis and Cordilleran tectonics would be affected by its tectonic setting, however that setting is in debate. Analysis of trace element compositions of basalt from the Metchosin Igneous Complex by ICP-MS was used to determine the tectonic setting in which the complex formed. REE and HFSE compositions are transitional between N-MORB and E-MORB and do not suggest a unique tectonic setting. Strong enrichments of Nb and Ta relative to N-MORB are contrary to formation in a subduction zone. In conjunction with existing plate motion data, this makes a rifted-margin origin unlikely. Interaction at a distance between the Yellowstone hot spot and the Kula-Farallon ridge is proposed to satisfy all the geological and geochemical data. Many studies of ophiolites have interpreted high-temperature phases as hydrothermal in origin despite high permeability and low temperatures in sea floor volcanics. Metamorphic assemblages and compositions of metamorphic minerals were used to determine if alteration in the Metchosin Igneous Complex was related to sea floor alteration or obduction. Chlorite geothermometry and amphibole compositions show that peak metamorphic temperatures increase from east to west across the complex. The metamorphic facies increase from prehnite-actinolite and greenschist in the east to amphibolite in the west, corresponding with the temperatures inferred from mineral compositions. The temperature gradient is perpendicular to stratigraphy, whereas hydrothermal patterns are expected to be parallel to stratigraphy. Therefore the pattern of alteration in the Metchosin Igneous Complex is unrelated to sea floor alteration. Metamorphism during obduction has overprinted any hydrothermal alteration patterns. The east-west thermal gradient is attributed to tilting of the complex, either by tectonic forces or by unequal exhumation due to orographic effects.
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Edwards, Stephen John. "Magmatic and fluid processes in the upper mantle : a study of the Bay of Islands ophiolite complex, Newfoundland /." 1991. http://collections.mun.ca/u?/theses,111984.
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Saby, Patrick. "La lithosphère océanique de la Téthys ligure : etude du magmatisme et des minéralisations associées dans les ophiolites du Queyras ( zone piémontaise des Alpes occidentales)." Phd thesis, 1986. http://tel.archives-ouvertes.fr/tel-00523836.
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Les unités ophiolitiques du Queyras (zone Alpes occidentales) représentent des petits massifs de roche vertes dispersées dans les Schistes lustrés piémontais à l'Ouest du Mont Viso. Leur étude permet de reconstruire la structure du substratum d'une partie du segment ligure de la Téthys. Bien que de nombreuses observations de terrain conduisent à envisager une coupure majeure entre la mise en place des ultramafites et gabbros associés et l'épanchement des basaltes, l' analyse pétrographique et géochimique permet de conclure à un assemblage cohérent et comparable avec d'autres massifs ophiolitiques de l' Apennin et de la Corse. Les résultats obtenus soulignent le caractère tholéïtique de la lignée magmatique à l'origine des matériaux basiques, intermédiaires et acides des différentes unités. La typologie des zircons conforte cette hypothèse au niveau des roches acides. La répartition des éléments inertes, Y, Ti, Zr, Nb, montre les liens cogénétiques entre les matériaux basiques et les différenciats acides. La nature du fractionnement ainsi que l'estimation du degré de fusion partielle suggèrent une mise en place dans un environnement géotectonique à caractère transitionnel avec océanisation à proximité de marges continentales passives, ainsi qu'un magmatisme analogues à ceux à l'origine des ophiolites de la Méditerranée occidentale (magmatisme de type I). Les éléments de granitoïdes d'une brèche sédimentaire localisée à l' interface ultramafites-laves, se caractérisent par un cachet calcoalcalin et permettent d'envisager la proximité d'une croûte continentale dont le démantèlement a vraisemblablement été contemporain des stades précoces de l'ouverture de l'océan ligure. Les circulations hydrothermales liées à ce contexte océanique sont responsables des processus de spilitisation et des minéralisations localisées à l'interface substratum océanique / sédiments: le gîte Fe/Cu de Viafiorcia (Val Germanasca, Italie) en est un exemple.