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ZHANG, ZHIYONG, WENBIN ZHU, LIANGSHU SHU, JINBAO SU, and BIHAI ZHENG. "Neoproterozoic ages of the Kuluketage diabase dyke swarm in Tarim, NW China, and its relationship to the breakup of Rodinia." Geological Magazine 146, no. 1 (November 27, 2008): 150–54. http://dx.doi.org/10.1017/s0016756808005839.
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AbstractThe widely exposed Kuluketage diabase dyke swarm, Tarim Block, NW China, has been considered to have been emplaced in Permian times. New precise zircon U–Pb SHRIMP ages for two samples from the dyke swarm yield Neoproterozoic ages of 823.8±8.7 Ma and 776.8±8.9 Ma. Correlated with peaks of magmatism in South China and Australia at c. 825 Ma and c. 780 Ma, these two new ages provide significant information for palaeocontinental reconstructions. The prolonged duration of the magmatic events, combined with regional stratigraphic relationships, imply that the Tarim Block may have been affected by a mantle plume during the breakup of Rodinia.
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Rocha, Brenda C., Joshua H. F. L. Davies, Valdecir A. Janasi, Urs Schaltegger, Antônio J. R. Nardy, Nicolas D. Greber, Ana Carolina F. Lucchetti, and Liza A. Polo. "Rapid eruption of silicic magmas from the Paraná magmatic province (Brazil) did not trigger the Valanginian event." Geology 48, no. 12 (July 31, 2020): 1174–78. http://dx.doi.org/10.1130/g47766.1.
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Abstract The Valanginian Stage is marked by a period of global positive δ13C carbon cycle perturbation and biotic crises, which are collectively referred to as the Valanginian event (VE). Many attempts have been made to link the Paraná-Etendeka large igneous province volcanism with the VE. However, currently there is no conclusive proof to support this hypothesis, since the timing and duration of the volcanic activity are not known with sufficient precision. In this study, we significantly revise the time scales of magmatism and environmental impact of the Paraná magmatic province (PMP) in Brazil with new high-precision zircon U-Pb ages from the low-Ti Palmas and high-Ti Chapecó sequences. Our data demonstrate that significant volumes of low-Ti silicic rocks from the PMP erupted rapidly at ca. 133.6 Ma within 0.12 ± 0.11 k.y. The age of the high-Ti Chapecó sequence from central PMP is constrained at ca. 132.9 Ma and thus extends the duration of magmatic activity by ∼700 k.y. Our new ages are systematically younger than previous ages and postdate the major positive carbon isotope excursion, indicating that PMP silicic magmatism did not trigger the VE but could have contributed to extending its duration. Within the framework of the stratigraphic column of the PMP, the earliest low-Ti basalts could have been responsible for the VE if they are at least 0.5 m.y. older than the low-Ti silicic rocks dated herein.
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CORFU, FERNANDO, STÉPHANE POLTEAU, SVERRE PLANKE, JAN INGE FALEIDE, HENRIK SVENSEN, ANDREW ZAYONCHECK, and NIKOLAY STOLBOV. "U–Pb geochronology of Cretaceous magmatism on Svalbard and Franz Josef Land, Barents Sea Large Igneous Province." Geological Magazine 150, no. 6 (June 11, 2013): 1127–35. http://dx.doi.org/10.1017/s0016756813000162.
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AbstractThe opening of the Arctic oceanic basins in the Mesozoic and Cenozoic proceeded in steps, with episodes of magmatism and sedimentation marking specific stages in this development. In addition to the stratigraphic record provided by sediments and fossils, the intrusive and extrusive rocks yield important information on this evolution. This study has determined the ages of mafic sills and a felsic tuff in Svalbard and Franz Josef Land using the isotope dilution thermal ionization mass spectrometry (ID-TIMS) U–Pb method on zircon, baddeleyite, titanite and rutile. The results indicate crystallization of the Diabasodden sill at 124.5 ± 0.2 Ma and the Linnévatn sill at 124.7 ± 0.3 Ma, the latter also containing slightly younger secondary titanite with an age of 123.9 ± 0.3 Ma. A bentonite in the Helvetiafjellet Formation, also on Svalbard, has an age of 123.3 ± 0.2 Ma. Zircon in mafic sills intersected by drill cores in Franz Josef Land indicate an age of 122.7 Ma for a thick sill on Severnaya Island and a single grain age of ≥122.2 ± 1.1 Ma for a thinner sill on Nagurskaya Island. These data emphasize the importance and relatively short-lived nature of the Cretaceous magmatic event in the region.
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Riggs, N. R., T. B. Sanchez, and S. J. Reynolds. "Evolution of the early Mesozoic Cordilleran arc: The detrital zircon record of back-arc basin deposits, Triassic Buckskin Formation, western Arizona and southeastern California, USA." Geosphere 16, no. 4 (June 30, 2020): 1042–57. http://dx.doi.org/10.1130/ges02193.1.
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Abstract A shift in the depositional systems and tectonic regime along the western margin of Laurentia marked the end of the Paleozoic Era. The record of this transition and the inception and tectonic development of the Permo-Triassic Cordilleran magmatic arc is preserved in plutonic rocks in southwestern North America, in successions in the distal back-arc region on the Colorado Plateau, and in the more proximal back-arc region in the rocks of the Buckskin Formation of southeastern California and west-central Arizona (southwestern North America). The Buckskin Formation is correlated to the Lower–Middle Triassic Moenkopi and Upper Triassic Chinle Formations of the Colorado Plateau based on stratigraphic facies and position and new detrital zircon data. Calcareous, fine- to medium-grained and locally gypsiferous quartzites (quartz siltstone) of the lower and quartzite members of the Buckskin Formation were deposited in a marginal-marine environment between ca. 250 and 245 Ma, based on detrital zircon U-Pb data analysis, matching a detrital-zircon maximum depositional age of 250 Ma from the Holbrook Member of the Moenkopi Formation. An unconformity that separates the quartzite and phyllite members is inferred to be the Tr-3 unconformity that is documented across the Colorado Plateau, and marks a transition in depositional environments. Rocks of the phyllite and upper members were deposited in wholly continental depositional environments beginning at ca. 220 Ma. Lenticular bodies of pebble to cobble (meta) conglomerate and medium- to coarse-grained phyllite (subfeldspathic or quartz wacke) in the phyllite member indicate deposition in fluvial systems, whereas the fine- to medium-grained beds of quartzite (quartz arenite) in the upper member indicate deposition in fluvial and shallow-lacustrine environments. The lower and phyllite members show very strong age and Th/U overlap with grains derived from Cordilleran arc plutons. A normalized-distribution plot of Triassic ages across southwestern North America shows peak magmatism at ca. 260–250 Ma and 230–210 Ma, with relatively less activity at ca. 240 Ma, when a land bridge between the arc and the continent was established. Ages and facies of the Buckskin Formation provide insight into the tectono-magmatic evolution of early Mesozoic southwestern North America. During deposition of the lower and quartzite members, the Cordilleran arc was offshore and likely dominantly marine. Sedimentation patterns were most strongly influenced by the Sonoma orogeny in northern Nevada and Utah (USA). The Tr-3 unconformity corresponds to both a lull in magmatism and the “shoaling” of the arc. The phyllite and upper members were deposited in a sedimentary system that was still influenced by a strong contribution of detritus from headwaters far to the southeast, but more locally by a developing arc that had a far stronger effect on sedimentation than the initial phases of magmatism during deposition of the basal members.
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Mitchell, A. H. G., and J. C. Carlile. "Mineralization, antiforms and crustal extension in andesitic arcs." Geological Magazine 131, no. 2 (March 1994): 231–42. http://dx.doi.org/10.1017/s001675680001075x.
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AbstractThe distribution and stratigraphic position of porphyry copper and epithermal gold deposits in andesitic arcs of the western Pacific and eastern Europe suggest that porphyry copper and epithermal vein deposits of adularia–sericite type develop successively under different stress regimes in an evolving arc, rather than being genetically related as commonly supposed. Absence of coeval high-level stocks in the root zones of many adularia-sericite deposits suggests that circulation of the dominantly meteoric hydrothermal fluids is not driven by shallow intrusions. The location of several world-class deposits on basement geanticlines, and on more localized antiforms of which at least one has been interpreted as a metamorphic core complex, implies that elevation of the arc, emplacement of magmatic sills at depth and adularia–sericite type gold mineralization are genetically related to subduction-induced crustal extension. Ascent of deep hydrothermal fluids, predominantly meteoric but with a metamorphic or magmatic component, may be controlled by regional low-angle structures at depth, analogous to those inferred for some mesothermal gold deposits. Mineralization at shallow (epithermal) depths in high-angle structures largely reflects the high geothermal gradient and mixing of deep fluid with cool meteoric water in or at the base of the permeable volcanic cover. Andesitic magmatism may resume following porphyry copper mineralization, adularia–sericite epithermal gold mineralization, or continued extension to form a ‘back arc’ spreading system, depending on the relative plate motion.
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Sissingh, W. "Palaeozoic and Mesozoic igneous activity in the Netherlands: a tectonomagmatic review." Netherlands Journal of Geosciences - Geologie en Mijnbouw 83, no. 2 (June 2004): 113–34. http://dx.doi.org/10.1017/s0016774600020084.
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AbstractTo date, igneous rocks, either intrusive or extrusive, have been encountered in the Palaeozoic-Mesozoic sedimentary series of the Netherlands in some 65 exploration and production wells. Following 17 new isotopic K/Ar age determinations of the recovered rock material (amounting to a total of 28 isotopic ages from 21 different wells), analysis of the stratigraphic distribution of the penetrated igneous rock bodies showed that the timing of their emplacement was importantly controlled by orogenic phases involving intra-plate wrench and rift tectonics. Magmatism coincided with the Acadian (Late Devonian), Sudetian (early Late Carboniferous), Saalian (Early Permian), Early Kimmerian (late Late Triassic), Mid-Kimmerian (Late Jurassic), Late Kimmerian (earliest Cretaceous) and Austrian (latest Early Cretaceous) tectonic phases. This synchroneity presumably reflects (broadly) coeval structural reorganizations of respectively the Baltica/Fennoscandinavia-Laurentia/Greenland, Laurussia-Gondwana, African-Eurasia and Greenland/Rockall-Eurasia plate assemblies. Through their concomitant changes of the intra-plate tectonic stress regime, inter-plate motions induced intra-plate tectonism and magmatism. These plate-tectonics related events determined the tectonomagmatic history of the Dutch realm by inducing the formation of localized centres, as well as isolated spot occurrences, of igneous activity. Some of these centres were active at (about) the same time. At a number of centres igneous activity re-occurred after a long period of time.
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Cornell, D. H., M. Harris, B. S. Mapani, T. Malobela, D. Frei, M. Kristoffersen, K. Lehman Francko, and R. Hanson. "Dating of Guperas Formation rhyolites changes the stratigraphy of the Mesoproterozoic Sinclair Supergroup of Namibia." South African Journal of Geology 123, no. 4 (November 10, 2020): 633–48. http://dx.doi.org/10.25131/sajg.123.0040.
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Abstract The volcanosedimentary Guperas Formation contains the youngest volcanic rocks of the Sinclair Supergroup in the Konkiep Terrane of southern Namibia. Precise U-Pb zircon microbeam dating shows that the Guperas Formation as mapped includes felsic volcanic rocks which belong to both the first (1.37 to 1.33 Ga) and the third (1.11 to 1.07 Ga) magmatic cycle of the Sinclair Supergroup. Volcanic rocks of the ‘true’ Guperas Formation are dated by three samples, with a combined age of 1108 ± 10 Ma. The sedimentary rocks mapped as Guperas Formation are also distinguished by two different detrital age spectra into the ~1 100 Ma true Guperas Formation and the Aruab Member of the ~1 217 Ma Barby Formation. Geochronology now resolves the previous stratigraphic separation of the very similar Nubib and Rooiberg (Sonntag) Granites. The two small outcrops of 1 334 ± 5 Ma Rooiberg Granite are now shown to be part of the regional 1 334 ± 8 Ma Nubib Granite batholith. The Konkiep Terrane was affected by faulting and shear zones, but was only gently folded and not involved in regional metamorphism, despite its proximity to the Namaqua-Natal Province to the southwest. This is due to the Konkiep Terrane having a thick and strong continental basement which may have formed as part of the mainly Palaeoproterozoic Rehoboth Province. However no Palaeoproterozoic rocks are exposed in the Konkiep Terrane, which is now interpreted as an unaffiliated terrane. The three cycles of extrusive and plutonic magmatism in the Sinclair Supergroup formed in chronologically distinct periods and different tectonic settings, which requires revision of the stratigraphic nomenclature. The Konkiep Group is replaced by three new groups which are separated by >100 million-year unconformities. The Betta Group, represented by the mainly volcanic Kumbis, Nagatis and Welverdiend formations in the first magmatic cycle, probably formed in a passive continental rift setting due to breakup of the Rehoboth Province between 1 374 and 1 334 Ma. The Vergenoeg Group, represented by the sedimentary Kunjas and volcanic Barby and Haiber Flats formations, formed in a subduction setting at the margin of the Konkiep Terrane. This ~1 217 to 1204 Ma magmatic cycle ended with the accretion of Namaqua-Natal terranes to the Kalahari Craton. The ~1 100 Ma Ganaams Group, represented by the volcanic Guperas Formation and sedimentary Aubures Formation, was the result of interplay between the continental-scale Umkondo mantle heating event and movements between crustal blocks following the Namaqua-Natal collisional orogeny.
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Zhong, Yuting, Roland Mundil, Jun Chen, Dongxun Yuan, Steven W. Denyszyn, Adam B. Jost, Jonathan L. Payne, Bin He, Shuzhong Shen, and Yigang Xu. "Geochemical, biostratigraphic, and high-resolution geochronological constraints on the waning stage of Emeishan Large Igneous Province." GSA Bulletin 132, no. 9-10 (February 3, 2020): 1969–86. http://dx.doi.org/10.1130/b35464.1.
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Abstract The initiation and peak magmatic periods of the Emeishan Large Igneous Province (LIP) are well constrained by both biostratigraphic and radioisotopic dating methods; however, the age of cessation of volcanism is poorly constrained and continues to be debated. Marine carbonates interbedded with volcanic ashes across the Guadalupian–Lopingian boundary (GLB) are widespread in south China, and these ashes provide an opportunity to study its timing, origin, and potential relationship with the Emeishan LIP. Here we present biostratigraphic constraints, mineralogical and geochemical characteristics, and high-resolution geochronology of ash layers from the Maoershan and Chaotian sections. Stratigraphic correlation, especially conodont biostratigraphy, confines these ashes to the early Wuchiapingian. Those altered ashes are geochemically akin to alkali tonsteins from the coal seams of the lower Xuanwei/Lungtan Formation in southwest China. The ashes postdating the GLB yield a coherent cluster of zircon U-Pb ages with weighted mean 206Pb/238U ages of 258.82 ± 0.61 Ma to 257.39 ± 0.68 Ma, in agreement with the ages of intrusive rocks (259.6 ± 0.5 Ma to 257.6 ± 0.5 Ma) in the central Emeishan LIP. Moreover, the ɛHf(t) values of zircons from the ashes vary from +2.5 to +10.6, a range consistent with that of the Emeishan LIP. The results collectively suggest that the early Wuchiapingian volcanic ashes are a product of extrusive alkaline magmatism and most likely mark the waning stage of the Emeishan volcanism, which may have continued until ca. 257.4 Ma in the early Wuchiapingian.
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Zhang, Feng-Qi, Hong-Xiang Wu, Yildirim Dilek, Wei Zhang, Kong-Yang Zhu, and Han-Lin Chen. "Guadalupian (Permian) onset of subduction zone volcanism and geodynamic turnover from passive- to active-margin tectonics in southeast China." GSA Bulletin 132, no. 1-2 (May 14, 2019): 130–48. http://dx.doi.org/10.1130/b32014.1.
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Abstract New stratigraphic, geochemical, and geochronological data from the late Paleozoic depositional record in Anhui Province, China, signal the onset of active-margin magmatism in East Asia. Chert-shale sequences of the Gufeng Formation are part of a Carboniferous–Permian carbonate platform that developed along the passive margin of the South China block. Thin tuffaceous interlayers in these sequences represent distal ash deposits, marking discrete volcanic events. Sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon dating of the stratigraphically bottom and near-top tuffaceous interlayers has revealed crystallization ages of 270 Ma and 264 Ma, respectively, constraining the time span of subaerial eruptions to ∼6 m.y. during the Guadalupian Epoch. High SiO2 and Al2O3 contents, enrichments in large ion lithophile and light rare earth elements, and depletion patterns of high field strength and heavy rare earth elements indicate a calc-alkaline magma source in an arc setting for the origin of these volcanic tuff deposits. Detrital zircon geochronology of sandstones in the overlying Longtan Formation shows two prominent age populations of 290–250 Ma and 1910–1800 Ma. The former age cluster overlaps with the tightly constrained zircon ages obtained from the Gufeng Formation. The latter age group is compatible with the known magmatic-metamorphic ages from Cathaysia in the South China block, and it points to the existence of a NE-SW–trending topographic high as a major sediment source. We interpret this topographic high and silicic volcanism to represent an Andean-type active margin, developed above a north-dipping paleo-Pacific slab. Our tightly constrained Guadalupian eruption ages indicate the inception of magmatic arc construction and mark a major switch from passive- to active-margin tectonics along SE Asia.
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Van Kranendonk, M. J. "Gliding and overthrust nappe tectonics of the Barberton Greenstone Belt revisited: A review of deformation styles and processes." South African Journal of Geology 124, no. 1 (March 1, 2021): 181–210. http://dx.doi.org/10.25131/sajg.124.0017.
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Abstract Interpretations of the structural/tectonic evolution of the Barberton Greenstone Belt (BGB) and its surrounding granitoid rocks remain controversial, with proponents for both horizontal thrust-accretion (plate tectonic) and partial convective overturn (vertical tectonic) models. Here, an area of complex folds that was used to support the operation of plate tectonic-derived gliding and overthrust nappe tectonics is re-investigated in detail and placed within the broader structural development of the BGB and surrounding granitoid domains via a re-analysis of structures, and geochronological, stratigraphic and metamorphic data across the whole of this important geological terrain. The results of detailed field mapping show that the complex folds, which occur on the northern limb of the 20 km wavelength, vertically plunging, Onverwacht Anticline, do not represent a re-folded, originally recumbent, isoclinal fold, as previously interpreted. Instead, the folds represent a moderately shallow east-plunging fold train that formed from a single episode of deformation. Fold asymmetry is consistent with formation during originally north-side-up reverse shear on bounding faults, consistent with the offset direction required to explain the fault-repeated slices of Mendon Formation + Fig Tree Group rocks that uniquely occur across the northern limb of the Onverwacht Anticline. More broadly, a review of the BGB and surrounding granitoid rocks show that formation was likely through two discrete, ~120 Ma long, episodes of mantle upwelling, or plume, magmatism, each of which led to crustal melting and partial convective overturn (PCO), a tectonic mechanism that arises from the gravity-driven interaction between dense, upper crustal greenstones and partially melted, more buoyant, granitoid-dominated middle crust. The first mantle upwelling episode, at 3 530 to 3 410 Ma, commenced with long-lived eruption of ultramafic-mafic lavas of the Sandspruit, Theespruit, Komati, and lower Hooggenoeg formations (3 530 to 3 470 Ma). Heat from this magmatic event gave rise to partial melting of the crust that, combined with fractionation of mafic magma chambers produced widespread felsic magmatism at 3 470 to 3 410 Ma (upper Hooggenoeg Formation and Buck Reef Chert), the latter parts of which were accompanied by the formation of D1 dome-and-keel structures via PCO in deeper-levels of the crust represented by the Stolzburg Domain in the far southwest part of the belt. The second mantle upwelling, or plume, episode commenced at 3 334 to 3 215 Ma with the eruption of ultramafic-mafic lavas of the Kromberg, Mendon and Weltevreden formations. Heat from this magmatic event gave rise to renewed partial melting of the crust that, combined with fractionation of mafic magma chambers, produced widespread felsic magmatism at 3 290 to 3 215 Ma. A second, longer-lived and more complex, multi-stage episode of PCO (D2-D4) accompanied deposition of the Fig Tree and Moodies groups from 3 250 to 3 215 Ma. Late D5 deformation accompanied emplacement of the Mpulizi and Piggs Peak batholiths at ca. 3.01 Ga, as previously identified. The Inyoka and Kromberg faults, which separate domains with distinct structural styles, represent neither terrane boundaries nor suture zones, but rather axial faults that separate deformed but generally inward-facing greenstone panels that sank inwards off rising granitoid domains that surround the BGB.
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Hongn, Fernando D., José M. Tubía, Aitor Aranguren, Néstor Vegas, Ricardo Mon, and Gregory R. Dunning. "Magmatism coeval with lower Paleozoic shelf basins in NW-Argentina (Tastil batholith): Constraints on current stratigraphic and tectonic interpretations." Journal of South American Earth Sciences 29, no. 2 (March 2010): 289–305. http://dx.doi.org/10.1016/j.jsames.2009.07.008.
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Masson, Henri, François Bussy, Marc Eichenberger, Niels Giroud, Caroline Meilhac, and Sergei Presniakov. "Early Carboniferous age of the Versoyen ophiolites and consequences: non-existence of a “Valais ocean” (Lower Penninic, western Alps)." Bulletin de la Société Géologique de France 179, no. 4 (July 1, 2008): 337–55. http://dx.doi.org/10.2113/gssgfbull.179.4.337.
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Abstract Ophiolites occur at several places in the Lower Penninic of the W and Central Alps. They are generally ascribed to oceanic crust of a so-called “Valais ocean” of Cretaceous age which plays a fundamental role in many models of Alpine paleogeography and geodynamics. The type locality and only observational base for the definition of a “Valais ocean” in the W Alps is the Versoyen ophiolitic complex, on the French-Italian boundary W of the Petit St-Bernard col. The idea of a “Valais ocean” is based on two propositions that are since 40 years the basis for most reconstructions of the Lower Penninic: (1) The Versoyen forms the (overturned) stratigraphic base of the Cretaceous-Tertiary Valais-Tarentaise series; and (2) it has a Cretaceous age. We present new field and isotopic data that severely challenge both propositions. (1) The base of the Versoyen ophiolite is a thrust. It overlies a wildflysch with blocks of Versoyen rocks, named the Méchandeur Formation. This “supra-Tarentaise” wildflysch has been confused with an (overturned) stratigraphic transition from the Versoyen to the Valais-Tarentaise series. Thus the contact Versoyen/Tarentaise is not stratigraphic but tectonic, and the Versoyen ophiolite has no link with the Valais basin. This thrust corresponds to an inverse metamorphic discontinuity and to an abrupt change in tectonic style. (2) The contact of the Versoyen complex with the overlying Triassic-Jurassic Petit St-Bernard (PSB) series is stratigraphic (and not tectonic as admitted by all authors since 50 years). Several types of sedimentary structures polarize it and show that the PSB series is younger than the Versoyen. Consequently the Versoyen ophiolitic complex is Paleozoic and forms the basement of the PSB Mesozoic sediments. They both belong to a single tectonic unit, named the Versoyen-Petit St-Bernard nappe. (3) Ion microprobe U-Pb isotopic data on zircons from the main gabbroic intrusion in the Versoyen complex give a crystallization age of 337.0 ± 4.1 Ma (Visean, Early Carboniferous). These zircons show typical oscillatory zoning and no overgrowth or corrosion, and are interpreted to date the Versoyen magmatism. These U-Pb data are in excellent agreement with our field observations and confirm the Paleozoic age of the Versoyen ophiolite. The existence of a “Valais ocean” of Cretaceous age in the W Alps becomes very improbable. The eclogite facies metamorphism of the Versoyen-Petit St-Bernard nappe results from an Alpine intra-continental subduction, guided by a Paleozoic oceanic suture. This is an example of the long term influence of inherited deep-seated structures on a much younger orogeny. This might well be a major cause of the inherent complexity of the Alps.
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Chang, Jih-Hsin, Eason Yi-Cheng Yang, Ho-Han Hsu, Tzu-Ting Chen, Char-Shine Liu, and Shye-Donq Chiu. "Igneous Activity and Structural Development of the Mianhua Terrace, Offshore North Taiwan." Minerals 11, no. 3 (March 16, 2021): 303. http://dx.doi.org/10.3390/min11030303.
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Using bathymetric and multichannel seismic (MCS) data, we explored the volcanic influence on the bathymetric and stratigraphic features of the Mianhua Terrace. The Mianhua Terrace occupies the marine counterpart of the Northern Taiwan Volcanic Zone (NTVZ) along the collapsed Taiwan orogenic wedge and is dominated by post-collisional magmatism and extensional structures. The bathymetric data showed several semicircular-shaped features near the shelf break. The MCS profiles showed that the Pleistocene unconformity buried beneath the Mianhua Terrace is partly difficult to observe due to seafloor multiples, suggesting that the seafloor is dominated by physically hard lithology, probably volcanic lavas. We interpreted the high-amplitude reflectors and their projected seafloor relief as intrusive sills and associated extrusive edifice. Similarly, we interpreted high-amplitude reflectors in the vicinity of normal faults as intrusive sills emplaced and facilitated by fault structures. A volcanic or hydrothermal mound was also recognized. We propose that the Mianhua Terrace is a breached ramp in a transfer zone between the tips of two successive normal faults along the shelf break. Once the fault tips reactivate and extend toward each other, the Mianhua Terrace may continue to collapse, leading to catastrophic volcanic or associated hydrothermal events.
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Harland, W. Brian, and Nicholas J. Butterfield. "Chapter 12 Pre-Vendian history." Geological Society, London, Memoirs 17, no. 1 (1997): 227–43. http://dx.doi.org/10.1144/gsl.mem.1997.017.01.12.
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It so happens that rocks of Vendian age are extensive and are well exposed in Svalbard. This applies especially to early Vendian, i.e. Varanger, with two distinctive glacial horizons as are treated in the Chapter 13. The Early Varanger (Smalfjord) episode can be correlated in most sections and so provides a reference horizon which serves approximately to identify pre-Varanger rocks. The pre-Vendian rocks have yet to show such good correlation characters. Therefore in Svalbard it is convenient to consider pre-Vendian successions together. Their distribution is shown in the map (Fig. 12.1).Some pre-Vendian sequences are punctuated by unconformities. Moreover, the sequences contain both high-grade metamorphosed and highly deformed rocks as well as undeformed fossiliferous strata. Therefore it is of interest to determine any Preeambrian diastroph-ism and even tectonothermal events. The term proto-basement was introduced (Harland 1997) to distinguish a Preeambrian basement, that formed in (say) Proterozoic time, from the ubiquitous basement formed by Early to mid Paleozoic tectogenesis, but made largely of Preeambrian rocks. It is to distinguish proto-basement within the basement underlying Devonian and Carboniferous strata. Proto-basement from such a study (structural, stratigraphic, isotopic) is shown in darker ornament in Fig. 12.1 and discussed in Section 12.3.Were the spatial relationships between these localities originally as now, intense tectonism, metamorphism and magmatism would suggest a division of Preeambrian history in Svalbard by such events. But Svalbard, small though it is on a global scale, comprises three or more distinct provinces which in Preeambrian and early Paleozoic times may have
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Hao, Wenxing, Rixiang Zhu, and Guang Zhu. "Jurassic tectonics of the eastern North China Craton: Response to initial subduction of the Paleo-Pacific Plate." GSA Bulletin 133, no. 1-2 (April 27, 2020): 19–36. http://dx.doi.org/10.1130/b35585.1.
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Abstract The Yanshan fold-and-thrust belt (YFTB) on the northern margin of the eastern North China Craton (NCC) contains a succession of Jurassic volcano-sedimentary rocks that record the response of the NCC to the initial stages of subduction of the Paleo-Pacific Plate. We present stratigraphic profiles and new zircon U-Pb data from four basins in the YFTB to constrain the ages of the Jurassic lithological units and tectonic events related to the initial subduction. Following uplift at 200–190 Ma, protracted eruption of basalt at 188–167 Ma reflects the earliest tectonic activity in the YFTB. The eruption occurred in a backarc extensional setting, and migrated toward the west, consistent with WNW-directed subduction of the Paleo-Pacific Plate. The measured profiles and geochronological data demonstrate that the earliest phase of shortening in the YFTB during the Jurassic (event A of the Yanshan Movement in the Chinese literature) took place at 167 Ma. This compression terminated the magmatism and extension of the Early–Middle Jurassic, and resulted in the development of local thrusts, regional uplift, and a disconformity, without involvement of intense folding or the development of an angular unconformity. These observations are consistent with a weak to moderate intensity of deformation. The Jurassic rocks in the YFTB record the response of a backarc to the initial stages of subduction of the Paleo-Pacific Plate. Jurassic tectonics in the YFTB and the entire eastern China continent suggests that initial subduction of the Paleo-Pacific Plate began at ca. 190 Ma, and is consistent with the passive margin collapse model.
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Eccles, D. Roy, Robert A. Creaser, Larry M. Heaman, and Jeff Ward. "Rb–Sr and U–Pb geochronology and setting of the Buffalo Head Hills kimberlite field, northern AlbertaThis article is one of a selection of papers published in this Special Issue on the theme Geology of northeastern British Columbia and northwestern Alberta: diamonds, shallow gas, gravel, and glaciers." Canadian Journal of Earth Sciences 45, no. 5 (May 2008): 513–29. http://dx.doi.org/10.1139/e07-050.
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New Rb–Sr phlogopite and U–Pb perovskite age determinations for 12 of 38 known ultramafic bodies in the Buffalo Head Hills area of north-central Alberta show that kimberlitic magmatism occurred in at least two separate episodes during Late Cretaceous and Paleocene time. Nine kimberlites yield Coniacian to Campanian ages of between 88 ± 5 Ma (U–Pb perovskite, K5A) and 81.2 ± 2.3 Ma (Rb–Sr phlogopite, K252). A Danian U–Pb perovskite isochron age of 63.5 ± 0.7 Ma was obtained for the BM2 kimberlite, and Selandian Rb–Sr ages of 59.6 ± 2.8 and 60.3 ± 0.8 Ma were determined for the K1A and K19 bodies, respectively. These specific periods of magmatism correspond to characteristic intra-field features such as kimberlite spatial distribution, diamond content, rock classification, and mechanisms of emplacement. The ∼88–81 Ma group generally occurs in the northwestern part of the field and defines the diamond window for the Buffalo Head Hills kimberlite field. This volcanism is contemporaneous with sedimentary host rock deposition, which has important implications for the size and morphological complexity of the kimberlite bodies. The ∼64 Ma BM2 body represents the only known occurrence of hypabyssal-facies kimberlite in this field and is similar in terms of source composition to the ∼88–81 Ma kimberlites, but is not diamond bearing. The ∼60 Ma group occurs in the southwestern part of the field, is derived from a weakly diamondiferous – barren hybrid ultramafic source and features bodies that are eroded to present-day stratigraphic levels.
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Vladimir Aleksandrovich, DUSHIN. "Metallogeny of the Lyapinsky megablock (Subpolar Urals)." NEWS of the Ural State Mining University, no. 2 (June 15, 2021): 88–105. http://dx.doi.org/10.21440/2307-2091-2021-2-88-105.
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Purpose of the work: elucidation of the geological structure, manifestations of magmatism, geodynamics and metallogeny of one of the largest segments of the paleocontinental sector of the Lyapin megablock in the Urals. The peculiarity of the metallogenic specialization of the latter for uranium, thorium, rare metals, gold, optical quartz caused both increased interest and contradictory ideas about its geology, composition of rock complexes, their age and genesis. Methodology of the work: generalization, analysis and synthesis of materials from long-term studies of the geology and metallogeny of the region, including experimental, methodological, thematic and geological survey work (GDP-200/2 sheets P-40-VI, P-40-XII) with the involvement of extensive literary sources. Results. For the first time, on the basis of the created formation map and the developed author’s legend of the territory, the geological structure is shown, the geological structure, geodynamic conditions of formation, metallogenic features of uneven-aged rock associations are shown. The Lyapinsky megablock, which corresponds to the Lyapinsky mineragenic zone, is a component of the West Ural megazone of the Ural Mineragenic Province, including the Mankhambovsky, Malopatoksky, Nyartinsky and Sаledsky ore nodes. In their history of development, four metallogenic epochs are distinguished: the Pre-Riphean, Riphean-Cambrian, Paleozoic and MesozoicCenozoic, specialized in noble, rare, radioactive, and non-ferrous metals, the largest objects of which include the Yasnoye, Narodnoye, Turman, Chudnoye, Sosnovoye, Telaizskoye, Torgovskoye, Turupinskoye, Kholodnoye, Kozhimskoye, and others. Conclusions. The results obtained indicate that along with a certain ore specialization of metallogenic epochs, an important factor affecting the ore content of the territory is the activated suture zones established in the course of research, in the areas where the largest ore objects, including stratiform and porphyry deposits, are localized, as well as unconventional objects of the “structural-stratigraphic disagreement” type.
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Schaubs, Peter M., and Sharon D. Carr. "Geology of metasedimentary rocks and Late Cretaceous deformation history in the northern Valhalla complex, British Columbia." Canadian Journal of Earth Sciences 35, no. 9 (September 1, 1998): 1018–36. http://dx.doi.org/10.1139/e98-048.
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The Valhalla complex, a Cordilleran metamorphic core complex, is a domal culmination made up of gently dipping interlayered sheets of igneous and supracrustal rocks that were deformed and metamorphosed in the Middle Jurassic and Late Cretaceous, and exhumed by extensional faults in the Eocene. Mapping, fabric, and metamorphic studies of predominantly metasedimentary rocks in Valhalla and Passmore domes in the northern part of the complex, together with published geochronological data, reveal a significant Late Cretaceous tectonic history. This includes extensive magmatism, the culmination of upper amphibolite facies metamorphism (approx. 800°C and 8 GPa), migmatization, development of a dominant penetrative transposition foliation, and localization of strain on ductile thrust faults termed the Gwillim Creek shear zones. The Valhalla assemblage, a package of metasedimentary rocks in Valhalla and Passmore domes, comprises a heterogeneous sequence of pelitic schist, marble, calc-silicate gneiss, psammitic gneiss, metaconglomerate, quartzite, amphibolite gneiss, and ultramafic rocks. Based on the presence of distinct laterally continuous marker units and similar lithologic ordering, we propose that the Valhalla assemblage is correlative with part of the Palaeozoic North American stratigraphic succession. If this is correct, then the Valhalla assemblage represents an inverted sequence of strata that has been thinned by as much as 60%; thinning may have occurred during Late Cretaceous transposition foliation development. The Gwillim Creek shear zones, originally mapped in a restricted locality in Gwillim Creek, were found to merge into one broad, ductile shear zone beneath Valhalla dome and extend throughout the entire Valhalla complex. The general style and timing of Late Cretaceous deformation in the Valhalla complex is characteristic of that found throughout the Shuswap complex in a belt of rocks that were at mid-crustal levels during the Cretaceous. This zone is thought to have accommodated Cretaceous - Early Tertiary shortening in the eastern Cordillera, and is the ductile equivalent of the higher level Rocky Mountain thrust belt to the east.
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Zhang, Shao-Hua, Wei-Qiang Ji, Hao Zhang, Guo-Hui Chen, Jian-Gang Wang, Zhong-Yu Meng, and Fu-Yuan Wu. "Identification of Forearc Sediments in the Milin-Zedong Region and Their Constraints on Tectonomagmatic Evolution of the Gangdese Arc, Southern Tibet." Lithosphere 2020, no. 1 (November 2, 2020): 1–20. http://dx.doi.org/10.2113/2020/8835259.
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Abstract The Xigaze forearc sediments revealed the part of the tectonomagmatic history of the Gangdese arc that the bedrocks did not record. However, the sediments’ development is restricted to the region around and west of Xigaze City. Whether the eastern segment of the arc had a corresponding forearc basin is yet to be resolved. In this study, a field-based stratigraphic study, detrital zircon U-Pb geochronology (15 samples), and Hf isotopic analyses (11 of the 15 samples) were carried out on four sections in the Milin-Zedong area, southeast Tibet. The analytical results revealed the existence of three distinct provenances. The lower sequence is characterized by fine-grained sandstone, interbedded mudstone, and some metamorphic rocks (e.g., gneiss and schist). The detrital zircon U-Pb age distribution of this sequence is analogous to those of the Carboniferous-Permian strata and metasediments of the Nyingtri group in the Lhasa terrane. The middle and upper sequences are predominantly composed of medium- to coarse-grained volcaniclastic/quartzose sandstones, which are generally interbedded with mudstone. The detrital zircon U-Pb ages and Hf isotope signatures indicate that the middle sequences are Jurassic to Early Cretaceous in age (~200–100 Ma) and show clear affinity with the Gangdese arc rocks, that is, positive εHft values. In contrast, the upper sequences are characterized by Mesozoic detrital zircons (150–100 Ma) and negative εHft values, indicative of derivation from the central Lhasa terrane. The overall compositions of the detrital zircon U-Pb ages and Hf isotopes of the middle to upper sequences resemble those of the Xigaze forearc sediments, implying that related forearc sediments may have been developed in the eastern part of the Gangdese arc. It is possible that the forearc equivalents were eroded or destroyed during the later orogenesis. Additionally, the detrital zircons from these forearc sediments indicate that this segment of the Gangdese arc experienced more active and continuous magmatism from the Early Jurassic to Early Cretaceous than its bedrock records indicate.
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Fasulo, Cooper R., and Kenneth D. Ridgway. "Detrital zircon geochronology of modern river sediment in south-central Alaska: Provenance, magmatic, and tectonic insights into the Mesozoic and Cenozoic development of the southern Alaska convergent margin." Geosphere 17, no. 4 (June 10, 2021): 1248–67. http://dx.doi.org/10.1130/ges02270.1.
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Abstract New and previously published detrital zircon U-Pb ages from sediment in major rivers of south-central Alaska archive several major episodes of magmatism associated with the tectonic growth of this convergent margin. Analysis of detrital zircons from major trunk rivers of the Tanana, Matanuska-Susitna, and Copper River watersheds (N = 40, n = 4870) documents major <250 Ma age populations that are characteristic of the main phases of Mesozoic and Paleogene magmatism in the region as documented from limited U-Pb ages of igneous rocks. Key points from our detrital record include: (1) Major magmatic episodes occurred at 170, 150, 118, 95, 72, 58, and 36 Ma. The overall pattern of these ages suggests that felsic magmatism was episodic with periodicity ranging between ~14 and 32 m.y. with an average of ~22 m.y. (2) Magmatism in south-central Alaska shows similar age trends with both the Coast Mountains batholith and the along-strike Alaska Peninsula forearc basin strata, demonstrating a spatial and temporal relationship of felsic magmatism along the entire northern Cordilleran margin. (3) Topography and zircon fertility appear to influence the presence and/or absence of detrital zircon populations in individual watersheds. Results from this study indicate that regionally integrated detrital zircon populations from modern trunk rivers are faithful recorders of Mesozoic and Paleogene magmatic events along a convergent margin, but there appears to be a lag time for major rivers to record Neogene and ongoing magmatic events.
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Lindsay, Mark D., Sandra Occhipinti, Crystal Laflamme, Alan Aitken, and Lara Ramos. "Mapping undercover: integrated geoscientific interpretation and 3D modelling of a Proterozoic basin." Solid Earth 11, no. 3 (June 24, 2020): 1053–77. http://dx.doi.org/10.5194/se-11-1053-2020.
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Abstract. Gravity and 3D modelling combined with geochemical analysis examine the subsurface within and below the poorly exposed Palaeoproterozoic Yerrida Basin in central Western Australia. Understanding the structure of a region is important as key features indicating past geodynamic processes and tectonic activity can be revealed. However, in stable, post-depositional tectonic settings only the younger sedimentary units tend to be widely exposed, rendering direct observation of basement and intrusive rocks impossible. Geophysical imaging and modelling can reveal the structure of a region undercover. High-magnitude density anomalies around the basin cannot be reconciled with current geological knowledge in the case presented here. The gravity anomalies infer an abundance of buried and high-density material not indicated by the surface geology. A hypothetical causative source for the high-magnitude gravity anomalies is mafic rocks that were intruded and extruded during basin rifting. The simplest and plausible stratigraphic attribution of these interpreted mafic rocks is to the Killara Formation within the Mooloogool Group. However, geochemistry reveals that the Killara Formation is not the only host to mafic rocks within the region. The mafic rocks present in the Juderina Formation are largely ignored in descriptions of Yerrida Basin magmatism, and results indicate that they may be far more substantial than once thought. Sulfur isotopic data indicate no Archean signature to these mafic rocks, a somewhat surprising result given the basement to the basin is the Archean Yilgarn Craton. We propose the source of mafic rocks is vents located to the north along the Goodin Fault or under the Bryah sub-basin and Padbury Basin. The conclusion is that the formation of the Yerrida Basin involves a geodynamic history more complex than previously thought. This result highlights the value in geophysics and geochemistry in revealing the complexity of the earlier geodynamic evolution of the basin that may be indiscernible from surface geology but may have high importance for the tectonic development of the region and its mineral resources.
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Capaldi, T. N., N. R. McKenzie, B. K. Horton, C. Mackaman-Lofland, C. L. Colleps, and D. F. Stockli. "Detrital zircon record of Phanerozoic magmatism in the southern Central Andes." Geosphere 17, no. 3 (May 6, 2021): 876–97. http://dx.doi.org/10.1130/ges02346.1.
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Abstract The spatial and temporal distribution of arc magmatism and associated isotopic variations provide insights into the Phanerozoic history of the western margin of South America during major shifts in Andean and pre-Andean plate interactions. We integrated detrital zircon U-Th-Pb and Hf isotopic results across continental magmatic arc systems of Chile and western Argentina (28°S–33°S) with igneous bedrock geochronologic and zircon Hf isotope results to define isotopic signatures linked to changes in continental margin processes. Key tectonic phases included: Paleozoic terrane accretion and Carboniferous subduction initiation during Gondwanide orogenesis, Permian–Triassic extensional collapse, Jurassic–Paleogene continental arc magmatism, and Neogene flat slab subduction during Andean shortening. The ~550 m.y. record of magmatic activity records spatial trends in magma composition associated with terrane boundaries. East of 69°W, radiogenic isotopic signatures indicate reworked continental lithosphere with enriched (evolved) εHf values and low (<0.65) zircon Th/U ratios during phases of early Paleozoic and Miocene shortening and lithospheric thickening. In contrast, the magmatic record west of 69°W displays depleted (juvenile) εHf values and high (>0.7) zircon Th/U values consistent with increased asthenospheric contributions during lithospheric thinning. Spatial constraints on Mesozoic to Cenozoic arc width provide a rough approximation of relative subduction angle, such that an increase in arc width reflects shallower slab dip. Comparisons among slab dip calculations with time-averaged εHf and Th/U zircon results exhibit a clear trend of decreasing (enriched) magma compositions with increasing arc width and decreasing slab dip. Collectively, these data sets demonstrate the influence of subduction angle on the position of upper-plate magmatism (including inboard arc advance and outboard arc retreat), changes in isotopic signatures, and overall composition of crustal and mantle material along the western edge of South America.
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Barnes, Calvin G., and Melanie A. Barnes. "The western Hayfork terrane: Remnants of the Middle Jurassic arc in the Klamath Mountain province, California and Oregon." Geosphere 16, no. 4 (June 30, 2020): 1058–81. http://dx.doi.org/10.1130/ges02229.1.
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Abstract Arc magmatism was widespread in the Cordillera of North America during Middle Jurassic time. The predominant representative of this arc magmatism in the Klamath Mountain province is the western Hayfork terrane (WHT). This terrane is primarily metasedimentary, consisting mainly of crystal-lithic arenite, argillitic sediments and lahar deposits, rare lavas, and sparse quartz-rich arenite. Because lavas are rare, petrologic study using bulk-rock compositions is restricted to analysis of cobbles in lahar deposits. Moreover, the WHT underwent greenschist-facies regional metamorphism with consequent modification of bulk-rock compositions. However, many of the sandstones preserve igneous clinopyroxene and calcic amphibole, which were phenocrysts in the original volcanic rocks. Major- and trace-element compositions of the magmatic pyroxene and amphibole permit reconstruction of the range of rock types eroded from the arc, specifically scant basalt, volumetrically dominant basaltic andesite and andesite, and smaller but significant amounts of dacite and rhyodacite. Eruptive temperatures reached ∼1180 °C and may have been as low as ∼800 °C on the basis of pyroxene and amphibole thermometry, with most eruptive temperatures >1000 °C. On the basis of augite compositions, WHT magmatism is divided into two suites. One features high-Mg augite with high abundances of Cr and Sr, high Sr/Y and Nd/Yb values, and low Y and heavy rare-earth elements (REE). These compositions are typical of high-Mg andesite and dacite suites in which garnet is a residual mineral, most probably in a metasomatized upper mantle setting. The other suite contains augite with lower Sr, Sr/Y, and Nd/Yb; these features are typical of normal calc-alkaline magmas. Augite from a coeval pluton emplaced inboard of the western Hayfork outcrop belt is similar to augite from the low-Sr group of WHT samples. In contrast, augite from the Ironside Mountain pluton, previously considered the plutonic equivalent of WHT sediments, is Fe-rich, with low Cr and Sr and relatively high Zr and REE. Previous suggestions that the Ironside Mountain pluton is correlative with the WHT are not supported by these data. The magmatic diversity of the WHT is typical of the modern Aleutian and Cascade arcs, among others, and could reflect subduction of relatively young oceanic lithosphere or fragmentation of the subduction slab. Although we favor the former setting, present data cannot rule out the latter. The presence of scant quartz-rich sedimentary rocks within the predominantly volcanogenic WHT is consistent with deposition as a sedimentary apron associated with a west-facing magmatic arc with late-stage input from cratonal sources. The results of this study indicate that detailed petrographic study of arc-derived sedimentary rocks, including major- and trace-element analysis of preserved magmatic phases, yields information about magmatic affinities, processes, and temperatures.
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Berkelhammer, Samuel E., Matthew E. Brueseke, Jeffrey A. Benowitz, Jeffrey M. Trop, Kailyn Davis, Paul W. Layer, and Maridee Weber. "Geochemical and geochronological records of tectonic changes along a flat-slab arc-transform junction: Circa 30 Ma to ca. 19 Ma Sonya Creek volcanic field, Wrangell Arc, Alaska." Geosphere 15, no. 5 (September 10, 2019): 1508–38. http://dx.doi.org/10.1130/ges02114.1.
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Abstract The Sonya Creek volcanic field (SCVF) contains the oldest in situ volcanic products in the ca. 30 Ma–modern Wrangell Arc (WA) in south-central Alaska, which commenced due to Yakutat microplate subduction initiation. The WA occurs within a transition zone between Aleutian subduction to the west and dextral strike-slip tectonics along the Queen Charlotte–Fairweather and Denali–Duke River fault systems to the east. New 40Ar/39Ar geochronology of bedrock shows that SCVF magmatism occurred from ca. 30–19 Ma. New field mapping, physical volcanology, and major- and trace-element geochemistry, coupled with the 40Ar/39Ar ages and prior reconnaissance work, allows for the reconstruction of SCVF magmatic evolution. Initial SCVF magmatism that commenced at ca. 30 Ma records hydrous, subduction-related, calc-alkaline magmatism and also an adakite-like component that we interpret to represent slab-edge melting of the Yakutat slab. A minor westward shift of volcanism within the SCVF at ca. 25 Ma was accompanied by continued subduction-related magmatism without the adakite-like component (i.e., mantle-wedge melting), represented by ca. 25–20 Ma basaltic-andesite to dacite domes and associated diorites. These eruptions were coeval with another westward shift to anhydrous, transitional-tholeiitic, basaltic-andesite to rhyolite lavas and tuffs of the ca. 23–19 Ma Sonya Creek shield volcano; we attribute these eruptions to intra-arc extension. SCVF activity was also marked by a small southward shift in volcanism at ca. 21 Ma, characterized by hydrous calc-alkaline lavas. SCVF geochemical compositions closely overlap those from the <13 Ma WA, and no alkaline lavas that characterize the ca. 18–10 Ma eastern Wrangell volcanic belt exposed in Yukon Territory are observed. Calc-alkaline, transitional-tholeiitic, and adakite-like SCVF volcanism from ca. 30–19 Ma reflects subduction of oceanic lithosphere of the Yakutat microplate beneath North America. We suggest that the increase in magmatic flux and adakitic eruptions at ca. 25 Ma, align with a recently documented change in Pacific plate direction and velocity at this time and regional deformation events in southern Alaska. By ca. 18 Ma, SCVF activity ceased, and the locus of WA magmatism shifted to the south and east. The change in relative plate motions would be expected to transfer stress to strike-slip faults above the inboard margin of the subducting Yakutat slab, a scenario consistent with increased transtensional-related melting recorded by the ca. 23–19 Ma transitional-tholeiitic Sonya Creek shield volcano between the Denali and Totschunda faults. Moreover, we infer the Totschunda fault accommodated more than ∼85 km of horizontal offset since ca. 18 Ma, based on reconstructing the initial alignment of the early WA (i.e., 30–18 Ma SCVF) and temporally and chemically similar intrusions that crop out to the west on the opposite side of the Totschunda fault. Our results from the SCVF quantify spatial-temporal changes in deformation and magmatism that may typify arc-transform junctions over similar time scales (>10 m.y.).
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Kos'ko, M., and E. Korago. "Review of geology of the New Siberian Islands between the Laptev and the East Siberian Seas, North East Russia." Stephan Mueller Special Publication Series 4 (September 17, 2009): 45–64. http://dx.doi.org/10.5194/smsps-4-45-2009.
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Abstract. The New Siberian Islands comprise De Long Islands, Anjou Islands, and Lyakhov Islands. Early Paleozoic, Mesozoic and Cenozoic sediments and igneous rocks are known on the De Long Islands. Cambrian slate, siltstone, mudstone and silicified limestone occur on Bennett Island. Ordovician volcanogenic turbidites, lavas, and small intrusions of andesite-basalt, basalt, dolerite, and porphyritic diorite were mapped on Henrietta Island. The igneous rocks are of calc-alkaline island arc series. The Ordovician age of the sequence was defined radiometrically. Early Paleozoic strata were faulted and folded presumably in the Caledonian time. Early Cretaceous sandstone and mudstone are known on Bennett Island. They are overlain by a 106–124 Ma basalt unit. Cenozoic volcanics are widespread on the De Long Islands. Zhokhov Island is an eroded stratovolcano. The volcanics are mostly of picrite-olivine type and limburgite. Radiometric dating indicates Miocene to Recent ages for Cenozoic volcanism. On the Anjou islands Lower-Middle Paleozoic strata consist of carbonates, siliciclastics, and clay. A Northwest-southeast syn-sedimentary facies zonation has been reconstructed. Upper Paleozoic strata are marine carbonate, clay and siliciclastic facies. Mudstone and clay predominate in the Triassic to Upper Jurassic section. Aptian-Albian coal bearing deposits uconformably overlap lower strata indicating Early Cretaceous tectonism. Upper Cretaceous units are mostly clay and siltstone with brown coal strata resting on Early Cretaceous weathered rhyolite. Cenozoic marine and nonmarine silisiclastics and clay rest upon the older units with a transgressive unconformity including a weathering profile in the older rocks. Manifestations of Paleozoic and Triassic mafic and Cretaceous acidic magmatism are also found on these islands. The pre-Cretaceous structure of the Anjou islands is of a block and fold type Late Cimmerian in age followed by faulting in Cenozoic time. The Lyakhov islands are located at the western end of the Late Cimmerian South Anyui suture. Sequences of variable age, composition, and structural styles are known on the Lyakhov Islands. These include an ancient metamorphic sequence, Late Paleozoic ophiolitic sequence, Late Mesozoic turbidite sequence, Cretaceous granites, and Cenozoic sediments. Fold and thrust imbricate structures have been mapped on southern Bol'shoi Lyakhov Island. North-northwestern vergent thrusts transect the Island and project offshore. Open folds of Jurassic–Early Cretaceous strata are characteristic of Stolbovoi and Malyi Lyakhov islands. Geology of the New Siberian Islands supports the concept of a circum Arctic Phanerozoic fold belt. The belt is comprised of Caledonian, Ellesmerian, Early Cimmerian and Late Cimmerian fold systems, manifested in many places on the mainland and on islands around the Arctic Ocean. Knowledge of the geology of the New Siberian Islands has been used to interpret anomalous gravity and magnetic field maps and Multi Channel Seismic (MCS) lines. Two distinguishing structural stages are universally recognized within the offshore sedimentary cover which correlate with the onshore geology of the New Siberian Islands. Dating of the upper structural stage and constituent seismic units is based on structural and stratigraphic relationships between Late Mesozoic and Cenozoic units in the archipelago. The Laptev Sea–western East Siberian Sea seismostratigraphic model for the upper structural stage has much in common with the seismostratigraphic model in the American Chukchi Sea.
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Santos Polo, Alan, Guo Weimin, Fernando Rivera, Colombo Tassinari, Luis Cerpa, and Shoji Kojima. "Early Jurassic arc related magmatism associated with porphyry copper mineralization at Zafranal, Southern Peru unraveled by zircon U-Pb ages." Andean Geology 46, no. 3 (September 30, 2019): 445. http://dx.doi.org/10.5027/andgeov46n3-3041.
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Early Jurassic arc-related igneous rocks host porphyry copper prospects and gold-bearing quartz vein deposits in southern Peru. Ten new zircon U-Pb ages for wall rocks of gold-bearing quartz veins, Jurassic rocks and copper-mineralized porphyry bodies in Zafranal porphyry copper, together with published ages for Jurassic rocks, reveal a continuous magmatic evolution of the early Jurassic arc. The Jurassic rocks and gold-bearing quartz vein systems in the western flank of the Western Cordillera are hosted by Paleo- and Meso-proterozoic orthogneisses of the Arequipa Massif (1.75-1.44 Ga) that underwent Grenville-age metamorphism ~1 Ga. The early mafic magmatism is recorded between 199.6-193.2 Ma, and was followed by dominantly felsic magmatism from 184.1-174.9 Ma. Both magmatic events have formed the thinnest intrusive belt (
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Riddell, Janet. "Lithostratigraphic and tectonic framework of Jurassic and Cretaceous Intermontane sedimentary basins of south-central British Columbia1This article is one of a series of papers published in this Special Issue on the theme of New insights in Cordilleran Intermontane geoscience: reducing exploration risk in the mountain pine beetle-affected area, British Columbia." Canadian Journal of Earth Sciences 48, no. 6 (June 2011): 870–96. http://dx.doi.org/10.1139/e11-034.
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The south-central Intermontane belt of British Columbia has a complex architecture comprising late Paleozoic to Mesozoic volcanic and plutonic arc magmatic suites, marine and nonmarine clastic basins, high-grade metamorphic complexes, and accretionary rocks. Jurassic and Cretaceous clastic basins within this framework contain stratigraphy with hydrocarbon potential. The geology is complicated by Cretaceous to Eocene deformation, dismemberment, and dislocation. The Eocene to Neogene history of the southern Intermontane belt is dominated by non-arc volcanism, followed by Pleistocene to Recent glaciation. The volcanic and glacial cover makes this a difficult region to explore for resources. Much recent work has involved re-evaluating the challenges that the overlying volcanic cover has historically presented to geophysical imaging of the sedimentary rocks in this region in light of technological advances in geophysical data collection and analysis. This paper summarizes the lithological and stratigraphic framework of the region, with emphasis on description of the sedimentary units that have been the targets of hydrocarbon exploration.
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Sharkov, E. V., and M. M. Bogina. "Evolution of paleoproterozoic magmatism: Geology, geochemistry, and isotopic constraints." Stratigraphy and Geological Correlation 14, no. 4 (July 2006): 345–67. http://dx.doi.org/10.1134/s0869593806040010.
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Bischoff, Alan Patrick, Andrew Nicol, and Mac Beggs. "Stratigraphy of architectural elements in a buried volcanic system and implications for hydrocarbon exploration." Interpretation 5, no. 3 (August 31, 2017): SK141—SK159. http://dx.doi.org/10.1190/int-2016-0201.1.
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The interaction between magmatism and sedimentation creates a range of petroleum plays at different stratigraphic levels due to the emplacement and burial of volcanoes. This study characterizes the spatio-temporal distribution of the fundamental building blocks (i.e., architectural elements) of a buried volcano and enclosing sedimentary strata to provide insights for hydrocarbon exploration in volcanic systems. We use a large data set of wells and seismic reflection surveys from the offshore Taranaki Basin, New Zealand, compared with outcropping volcanic systems worldwide to demonstrate the local impacts of magmatism on the evolution of the host sedimentary basin and petroleum system. We discover the architecture of Kora volcano, a Miocene andesitic polygenetic stratovolcano that is currently buried by more than 1000 m of sedimentary strata and hosts a subcommercial discovery within volcanogenic deposits. The 22 individual architectural elements have been characterized within three main stratigraphic sequences of the Kora volcanic system. These sequences are referred to as premagmatic (predate magmatism), synmagmatic (defined by the occurrence of intrusive, eruptive, and sedimentary architectural elements), and postmagmatic (degradation and burial of the volcanic structures after magmatism ceased). Potential petroleum plays were identified based on the distribution of the architectural elements and on the geologic circumstances resulting from the interaction between magmatism and sedimentation. At the endogenous level, emplacement of magma forms structural traps, such as drag folds and strata jacked up above intrusions. At the exogenous level, syneruptive, intereruptive, and postmagmatic processes mainly form stratigraphic and paleogeomorphic traps, such as interbedded volcano-sedimentary deposits, and upturned pinchout of volcanogenic and nonvolcanogenic coarse-grained deposits onto the volcanic edifice. Potential reservoirs are located at systematic vertical and lateral distances from eruptive centers. We have determined that identifying the architectural elements of buried volcanoes is necessary for building predictive models and for derisking hydrocarbon exploration in sedimentary basins affected by magmatism.
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Campbell, Roderick W., Luke P. Beranek, Stephen J. Piercey, and Richard Friedman. "Early Paleozoic post-breakup magmatism along the Cordilleran margin of western North America: New zircon U-Pb age and whole-rock Nd- and Hf-isotope and lithogeochemical results from the Kechika group, Yukon, Canada." Geosphere 15, no. 4 (May 8, 2019): 1262–90. http://dx.doi.org/10.1130/ges02044.1.
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AbstractPost-breakup magmatic rocks are recognized features of modern and ancient passive margin successions around the globe, but their timing and significance to non-plume-related rift evolution is generally uncertain. Along the Cordilleran margin of western North America, several competing rift models have been proposed to explain the origins of post-breakup igneous rocks that crop out from Yukon to Nevada. New zircon U-Pb age and whole-rock geochemical studies were conducted on the lower Paleozoic Kechika group, south-central Yukon, to test these rift models and constrain the timing, mantle source, and tectonic setting of post-breakup magmatism in the Canadian Cordillera. The Kechika group contains vent-proximal facies and sediment-sill complexes within the Cassiar platform, a linear paleogeographic high that developed outboard of continental shelf and trough basins. Chemical abrasion (CA-TIMS) U-Pb dates indicate that Kechika group mafic rocks were generated during the late Cambrian (488–483 Ma) and Early Ordovician (473 Ma). Whole-rock trace-element and Nd- and Hf-isotope results are consistent with the low-degree partial melting of an enriched lithospheric mantle source during margin-scale extension. Equivalent continental shelf and trough rocks along western North America are spatially associated with transfer-transform zones and faults that were episodically reactivated during Cordilleran rift evolution. Post-breakup rocks emplaced along the magma-poor North Atlantic margins, including those near the Orphan Knoll and Galicia Bank continental ribbons, are proposed modern analogues for the Kechika group. This scenario calls for the release of in-plane tensile stresses and off-axis, post-breakup magmatism along the nascent plate boundary prior to the onset of seafloor spreading.
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Lipman, Peter W., and Matthew J. Zimmerer. "Magmato-tectonic links: Ignimbrite calderas, regional dike swarms, and the transition from arc to rift in the Southern Rocky Mountains." Geosphere 15, no. 6 (September 30, 2019): 1893–926. http://dx.doi.org/10.1130/ges02068.1.
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Abstract Radial and linear dike swarms in the eroded roots of volcanoes and along rift zones are sensitive structural indicators of conduit and eruption geometry that can record regional paleostress orientations. Compositionally diverse dikes and larger intrusions that radiate westward from the polycyclic Platoro caldera complex in the Southern Rocky Mountain volcanic field (southwestern United States) merge in structural trend, composition, and age with the enormous but little-studied Dulce swarm of trachybasaltic dikes that continue southwest and south for ∼125 km along the eastern margin of the Colorado Plateau from southern Colorado into northern New Mexico. Some Dulce dikes, though only 1–2 m thick, are traceable for 20 km. More than 200 dikes of the Platoro-Dulce swarm are depicted on regional maps, but only a few compositions and ages have been published previously, and relations to Platoro caldera have not been evaluated. Despite complications from deuteric alteration, bulk compositions of Platoro-Dulce dikes (105 new X-ray fluorescence and inductively coupled plasma mass spectrometry analyses) become more mafic and alkalic with distance from the caldera. Fifty-eight (58) new 40Ar/39Ar ages provide insight into the timing of dike emplacement in relation to evolution of Platoro caldera (source of six regional ignimbrites between 30.3 and 28.8 Ma). The majority of Dulce dikes were emplaced during a brief period (26.5–25.0 Ma) of postcaldera magmatism. Some northeast-trending dikes yield ages as old as 27.5 Ma, and the northernmost north-trending dikes have younger ages (20.1–18.6 Ma). In contrast to high-K lamprophyres farther west on the Colorado Plateau, the Dulce dikes are trachybasalts that contain only anhydrous phenocrysts (clinopyroxene, olivine). Dikes radial to Platoro caldera range from pyroxene- and hornblende-bearing andesite to sanidine dacite, mostly more silicic than trachybasalts of the Dulce swarm. Some distal andesite dikes have ages (31.2–30.4 Ma) similar to those of late precaldera lavas; ages of other proximal dikes (29.2–27.5 Ma) are akin to those of caldera-filling lavas and the oldest Dulce dikes. The largest radial dikes are dacites that have yet younger sanidine 40Ar/39Ar ages (26.5–26.4 Ma), similar to those of the main Dulce swarm. The older andesitic dikes and precaldera lavas record the inception of a long-lived upper-crustal magmatic locus at Platoro. This system peaked in magmatic output during ignimbrite eruptions but remained intermittently active for at least an additional 9 m.y. Platoro magmatism began to decline at ca. 26 Ma, concurrent with initial basaltic volcanism and regional extension along the Rio Grande rift, but no basalt is known to have erupted proximal to Platoro caldera prior to ca. 20 Ma, just as silicic activity terminated at this magmatic locus. The large numbers and lengths of the radial andesitic-dacitic dikes, in comparison to the absence of similar features at other calderas of the San Juan volcanic locus, may reflect location of the Platoro system peripheral to the main upper-crustal San Juan batholith recorded by gravity data, as well as its proximity to the axis of early rifting. Spatial, temporal, and genetic links between Platoro radial dikes and the linear Dulce swarm suggest that they represent an interconnected regional-scale magmatic suite related to prolonged assembly and solidification of an arc-related subcaldera batholith concurrently with a transition to regional extension. Emplacement of such widespread dikes during the late evolution of a subcaldera batholith could generate earthquakes and trigger dispersed small eruptions. Such events would constitute little-appreciated magmato-tectonic hazards near dormant calderas such as Valles, Long Valley, or Yellowstone (western USA).
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DRAUT, AMY E., PETER D. CLIFT, DAVID M. CHEW, MATTHEW J. COOPER, REX N. TAYLOR, and ROBYN E. HANNIGAN. "Laurentian crustal recycling in the Ordovician Grampian Orogeny: Nd isotopic evidence from western Ireland." Geological Magazine 141, no. 2 (March 2004): 195–207. http://dx.doi.org/10.1017/s001675680400891x.
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Because magmatism associated with subduction is thought to be the principal source for continental crust generation, assessing the relative contribution of pre-existing (subducted and assimilated) continental material to arc magmatism in accreted arcs is important to understanding the origin of continental crust. We present a detailed Nd isotopic stratigraphy for volcanic and volcaniclastic formations from the South Mayo Trough, an accreted oceanic arc exposed in the western Irish Caledonides. These units span an arc–continent collision event, the Grampian (Taconic) Orogeny, in which an intra-oceanic island arc was accreted onto the passive continental margin of Laurentia starting at ∼ 475 Ma (Arenig). The stratigraphy corresponding to pre-, syn- and post-collisional volcanism reveals a progression of εNd(t) from strongly positive values, consistent with melt derivation almost exclusively from oceanic mantle beneath the arc, to strongly negative values, indicating incorporation of continental material into the melt. Using εNd(t) values of meta-sediments that represent the Laurentian passive margin and accretionary prism, we are able to quantify the relative proportions of continent-derived melt at various stages of arc formation and accretion. Mass balance calculations show that mantle-derived magmatism contributes substantially to melt production during all stages of arc–continent collision, never accounting for less than 21% of the total. This implies that a significant addition of new, rather than recycled, continental crust can accompany arc–continent collision and continental arc magmatism.
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Vence, Eleine, and Paul Mann. "Subsurface basement, structure, stratigraphy, and timing of regional tectonic events affecting the Guajira margin of northern Colombia." Interpretation 8, no. 4 (November 1, 2020): ST69—ST105. http://dx.doi.org/10.1190/int-2020-0016.1.
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We have combined previous data from Mesozoic-Cenozoic outcrops in the Guajira Peninsula of northern Colombia with regional gravity, bathymetric, and seismic interpretations to demonstrate the existence of a 280 km long western extension of the Great Arc of the Caribbean (GAC) along the continental margin of Colombia. Seismic data reveal an 80–100 km wide domal-shaped basement high that exhibits internal chaotic seismic facies. This elongate and domal-shaped structure extends 1800 km from the Aves Ridge in the Caribbean Sea to the study area in offshore Colombia. The western extension of the GAC in Colombia and western Venezuela is buried by 700–3000 m of continental margin sedimentary rocks as a result of the GAC colliding earlier with the Colombian margin (Cretaceous-early Paleogene collision) than its subaerially exposed eastern extension along the Leeward Antilles ridge (late Paleogene-Neogene). Our compilation of geologic information from the entire GAC reveals that GAC magmatism occurred from 128 to 74 Ma with magmatism ages progressively younger toward the east. Six upper Eocene to recent marine seismic sequences overlying the domal basement high of the GAC have been mapped by our analysis of 2400 km of seismic lines and 12 well logs. Based on subsurface mapping correlated with well-log information and onland geology in the Guajira Peninsula, these six sequences record four major deformational events: (1) late Eocene rifting in an east–west direction produced half-grabens in the northern part of the area, (2) Oligocene transtension in the southern part of the area expressed by right-lateral Oligocene strike-slip faulting and extensional basin formation, (3) early-middle Miocene transtension, and (4) late Miocene-early Pliocene Andean uplift accompanied by rapid erosion and clastic infilling of offshore basins by the Magdalena delta and deep-sea fan. The significance of this basin framework is discussed for known and inferred hydrocarbon systems.
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Alsop, G. I., and D. H. W. Hutton. "Major southeast-directed Caledonian thrusting and folding in the Dalradian rocks of mid-Ulster: implications for Caledonian tectonics and mid-crustal shear zones." Geological Magazine 130, no. 2 (March 1993): 233–44. http://dx.doi.org/10.1017/s0016756800009882.
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AbstractThe dominant structure controlling the disposition of Dalradian stratigraphy in mid-Ulster has hitherto been regarded as a southeast-facing gently inclined F1 anticline, a gross geometry modelled on, and thought to be a possible correlative of, the Tay Nappe in Scotland. Remapping of the supposedly inverted southern limb of this major fold reveals that much of it is in fact the correct way up. However, a stratigraphie repetition coupled with a reversal in younging does occur in the Sperrin Mountains, much further south than previously realized. This hitherto unrecognized upward southeast-facing isoclinal Sperrin Nappe is, however, a D2 structure, traceable for at least 40 km along strike and responsible for a regional stratigraphie inversion over an area of 300 km2. Following D2, a major 10 km thick D3 ductile shear zone resulted in translation towards the east-southeast. In the south, this deformation carried the Dalradian over Ordovician volcanics of the Tyrone Igneous Complex along the Omagh Thrust. Penecontemporaneity of magmatism with deformation clearly demonstrates that D3 is Caledonian (Arenig-Llanvirn). This deformation correlates with similar southeast-directed Caledonian thrusting in southern Donegal and Connemara. The apparent absence of Dalradian deformation of this age in southwestern Scotland may imply that Caledonian collision of outboard terranes with the miogeoclinal margin was initiated in Ireland and/or subsequent strike-slip has removed the evidence for deformation of this age from southwestern Scotland. The D3 shear zone in the Sperrin Mountains affects a very large volume of psammitic rocks. Within this shear zone the strain is not markedly higher than surrounding areas; however, its existence is demonstrated by the reorientation of mineral lineations over a large area. Such broad zones of only moderate strain may, we believe, be typical of translatory tectonics in areas of the mid-crust where there is little lithological diversity.
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Wilson, Marjorie. "Magmatism and the geodynamics of basin formation." Sedimentary Geology 86, no. 1-2 (July 1993): 5–29. http://dx.doi.org/10.1016/0037-0738(93)90131-n.
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Boyce, Jeremy W., and Richard L. Hervig. "Magmatic degassing histories from apatite volatile stratigraphy." Geology 36, no. 1 (2008): 63. http://dx.doi.org/10.1130/g24184a.1.
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Vladimirov, A. G., L. A. Phan, A. V. Travin, E. I. Mikheev, N. G. Murzintsev, and I. Yu Annikova. "The Geology and Thermochronology of Cretaceous Magmatism of Southeastern Vietnam." Russian Journal of Pacific Geology 14, no. 4 (July 2020): 305–25. http://dx.doi.org/10.1134/s1819714020040065.
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McKibbin, Seann J., Bill Landenberger, and C. Mark Fanning. "First magmatism in the New England Batholith, Australia: forearc and arc–back-arc components in the Bakers Creek Suite gabbros." Solid Earth 8, no. 2 (April 5, 2017): 421–34. http://dx.doi.org/10.5194/se-8-421-2017.
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Abstract. The New England Orogen, eastern Australia, was established as an outboard extension of the Lachlan Orogen through the migration of magmatism into forearc basin and accretionary prism sediments. Widespread S-type granitic rocks of the Hillgrove and Bundarra supersuites represent the first pulse of magmatism, followed by I- and A-types typical of circum-Pacific extensional accretionary orogens. Associated with the former are a number of small tholeiite–gabbroic to intermediate bodies of the Bakers Creek Suite, which sample the heat source for production of granitic magmas and are potential tectonic markers indicating why magmatism moved into the forearc and accretionary complexes rather than rifting the old Lachlan Orogen arc. The Bakers Creek Suite gabbros capture an early ( ∼ 305 Ma) forearc basalt-like component with low Th ∕ Nb and with high Y ∕ Zr and Ba ∕ La, recording melting in the mantle wedge with little involvement of a slab flux and indicating forearc rifting. Subsequently, arc–back-arc like gabbroic magmas (305–304 Ma) were emplaced, followed by compositionally diverse magmatism leading up to the main S-type granitic intrusion ( ∼ 290 Ma). This trend in magmatic evolution implicates forearc and other mantle wedge melts in the heating and melting of fertile accretion complex sediments and relatively long ( ∼ 10 Myr) timescales for such melting.
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Blatchford, Hannah J., Keith A. Klepeis, Joshua J. Schwartz, Richard Jongens, Rose E. Turnbull, Elena A. Miranda, Matthew A. Coble, and Andrew R. C. Kylander-Clark. "Interplay of Cretaceous transpressional deformation and continental arc magmatism in a long-lived crustal boundary, central Fiordland, New Zealand." Geosphere 16, no. 5 (August 31, 2020): 1225–48. http://dx.doi.org/10.1130/ges02251.1.
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Abstract Recovering the time-evolving relationship between arc magmatism and deformation, and the influence of anisotropies (inherited foliations, crustal-scale features, and thermal gradients), is critical for interpreting the location, timing, and geometry of transpressional structures in continental arcs. We investigated these themes of magma-deformation interactions and preexisting anisotropies within a middle- and lower-crustal section of Cretaceous arc crust coinciding with a Paleozoic boundary in central Fiordland, New Zealand. We present new structural mapping and results of Zr-in-titanite thermometry and U-Pb zircon and titanite geochronology from an Early Cretaceous batholith and its host rock. The data reveal how the expression of transpression in the middle and lower crust of a continental magmatic arc evolved during emplacement and crystallization of the ∼2300 km2 lower-crustal Western Fiordland Orthogneiss (WFO) batholith. Two structures within Fiordland’s architecture of transpressional shear zones are identified. The gently dipping Misty shear zone records syn-magmatic oblique-sinistral thrust motion between ca. 123 and ca. 118 Ma, along the lower-crustal WFO Misty Pluton margin. The subhorizontal South Adams Burn thrust records mid-crustal arc-normal shortening between ca. 114 and ca. 111 Ma. Both structures are localized within and reactivate a recently described >10 km-wide Paleozoic crustal boundary, and show that deformation migrated upwards between ca. 118 and ca. 114 Ma. WFO emplacement and crystallization (mainly 118–115 Ma) coincided with elevated (>750 °C) middle- and lower-crustal Zr-in-titanite temperatures and the onset of mid-crustal cooling at 5.9 ± 2.0 °C Ma−1 between ca. 118 and ca. 95 Ma. We suggest that reduced strength contrasts across lower-crustal pluton margins during crystallization caused deformation to migrate upwards into thermally weakened rocks of the mid-crust. The migration was accompanied by partitioning of deformation into domains of arc-normal shortening in Paleozoic metasedimentary rocks and domains that combined shortening and strike-slip deformation in crustal-scale subvertical, transpressional shear zones previously documented in Fiordland. U-Pb titanite dates indicate Carboniferous–Cretaceous (re)crystallization, consistent with reactivation of the inherited boundary. Our results show that spatio-temporal patterns of transpression are influenced by magma emplacement and crystallization and by the thermal structure of a reactivated boundary.
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Busby, Cathy, Alison Graettinger, Margarita López Martínez, Sarah Medynski, Tina Niemi, Claire Andrews, Emilie Bowman, et al. "Volcanic record of the arc-to-rift transition onshore of the Guaymas basin in the Santa Rosalía area, Gulf of California, Baja California." Geosphere 16, no. 4 (May 26, 2020): 1012–41. http://dx.doi.org/10.1130/ges02094.1.
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Abstract The Gulf of California is an archetype of continental rupture through transtensional rifting, and exploitation of a thermally weakened arc to produce a rift. Volcanic rocks of central Baja California record the transition from calcalkaline arc magmatism, due to subduction of the Farallon plate (ca. 24–12 Ma), to rift magmatism, related to the opening of the Gulf of California (<12 Ma). In addition, a suite of postsubduction rocks (<12 Ma), referred to as “bajaites,” are enriched in light rare-earth and other incompatible elements (e.g., Ba and Sr). These are further subdivided into high-magnesian andesite (with 50%–58% SiO2 and MgO >4%) and adakite (>56% SiO2 and MgO <3%). The bajaites correlate spatially with a fossil slab imaged under central Baja and are inferred to record postsubduction melting of the slab and subduction-modified mantle by asthenospheric upwelling associated with rifting or slab breakoff. We report on volcanic rocks of all three suites, which surround and underlie the Santa Rosalía sedimentary rift basin. This area represents the western margin of the Guaymas basin, the most magmatically robust segment of the Gulf of California rift, where seafloor spreading occurred in isolation for 3–4 m.y. (starting at 6 Ma) before transtensional pull-apart basins to the north and south ruptured the continental crust. Outcrops of the Santa Rosalía area thus offer the opportunity to understand the magmatic evolution of the Guaymas rift, which has been the focus of numerous oceanographic expeditions. We describe 21 distinct volcanic and hypabyssal map units in the Santa Rosalía area, using field characteristics, petrographic data, and major- and trace-element geochemical data, as well as zircon isotopic data and ten new 40Ar-39Ar ages. Lithofacies include lavas and lava domes, block-and-ash-flow tuffs, ignimbrites, and hypabyssal intrusions (plugs, dikes, and peperites). Calcalkaline volcanic rocks (13.81–10.11 Ma) pass conformably upsection, with no time gap, into volcanic rocks with rift transitional chemistry (9.69–8.84 Ma). The onset of rifting was marked by explosive eruption of silicic ignimbrite (tuff of El Morro), possibly from a caldera, similar to the onset of rifting or accelerated rifting in other parts of the Gulf of California. Epsilon Hf zircon data are consistent with a rift transitional setting for the tuff of El Morro. Arc and rift volcanic rocks were then juxtaposed by normal faults and tilted eastward toward a north-south fault that lay offshore, likely related to the north-south normal faults documented for the early history of the Guaymas basin, prior to the onset of northwest-southeast transtenional faulting. Magmatism in the Santa Rosalía area resumed with emplacement of high-magnesian andesite lavas and intrusions, at 6.06 Ma ± 0.27 Ma, coeval with the onset of seafloor spreading in the Guaymas basin at ca. 6 Ma. The 9.69–8.84 Ma rift transitional volcanic rocks underlying the Santa Rosalía sedimentary basin provide a maximum age on its basal fill. Evaporites in the Santa Rosalía sedimentary basin formed on the margin of the Guaymas basin, where thicker evaporites formed. Overlying coarse-grained clastic sedimentary fill of the Santa Rosalía basin and its stratiform Cu-Co-Zn-Mn sulfides may have accumulated rapidly, coeval with emplacement of 6.06 Ma high-magnesian andesite intrusions and the ca. 6 Ma onset of seafloor spreading in the Guaymas basin.
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Safonova, I., G. Biske, R. L. Romer, R. Seltmann, V. Simonov, and S. Maruyama. "Middle Paleozoic mafic magmatism and ocean plate stratigraphy of the South Tianshan, Kyrgyzstan." Gondwana Research 30 (February 2016): 236–56. http://dx.doi.org/10.1016/j.gr.2015.03.006.
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Affinati, Suzanne Craddock, Thomas D. Hoisch, Michael L. Wells, and Jeffrey D. Vervoort. "Pressure-temperature-time paths from the Funeral Mountains, California, reveal Jurassic retroarc underthrusting during early Sevier orogenesis." GSA Bulletin 132, no. 5-6 (September 17, 2019): 1047–65. http://dx.doi.org/10.1130/b35095.1.
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Abstract New metamorphic pressure-temperature (P-T) paths and Lu-Hf garnet ages reveal a temporal correlation between Middle to Late Jurassic retroarc underthrusting and arc magmatism in southwestern North America. P-T paths were determined for 12 garnet porphyroblasts from six samples from the Chloride Cliff area of the Funeral Mountains in southeastern California. The composite path shows a pressure increase from 4.2 to 6.5 kbar as temperature increased from 550 to 575 °C, followed by a pressure decrease to 5.1 kbar during a further increase in temperature to 590 °C. Lu-Hf garnet ages from a pelitic schist (167.3 ± 0.7 Ma) and a garnet amphibolite (165.1 ± 9.2 Ma) place these P-T paths in the Middle Jurassic. We interpret the near-isothermal pressure increase portion of the P-T path to have developed during thrust-related burial, similar to lower grade rocks at Indian Pass, 8 km to the southeast, where garnet P-T paths show a pressure increase dated by the Lu-Hf method at 158.2 ± 2.6 Ma. We interpret the pressure decrease portion of the composite P-T path from the Chloride Cliff area to reflect exhumation contemporaneous with cooling in the Indian Pass area documented from muscovite 40Ar/39Ar step-heating ages of 152.6 ± 1.4 and 146 ± 1.1 Ma. The conditions and timing of metamorphism determined for the Indian Pass and Chloride Cliff areas, and isogradic surfaces that cut across stratigraphy, support the interpretation that the strata were dipping moderately NW during metamorphism, parallel to the thrust ramp that buried the rocks. Burial likely resulted from top-SE motion along the Funeral thrust, which was later reactivated as a low-angle normal fault with opposite motion to become the currently exposed Boundary Canyon detachment that was responsible for Miocene and possibly older exhumation. The part of the burial history captured by garnet growth occurred ∼6 m.y. before the 161 Ma peak of high-flux magmatism in the arc. Burial was contemporaneous with metamorphic ages from the western Sierra Nevada metamorphic belt, with the possible timing of accretion of arc terranes in northern California, and with the initiation of Franciscan subduction. Burial ages are also similar in timing with generally E-W crustal shortening in the retroarc that produced the East Sierra thrust system, the Luning-Fencemaker fold and thrust belt, the possible early history of the Central Nevada thrust belt, and the western thrusts of the southern Sevier belt. The timing of tectonic burial documented in this study and of high-flux magmatism in the arc supports the interpretation that the development of a coherent arc-trench system in the Early Jurassic resulted in the underthrusting of melt-fertile material beneath the arc along west- to northwest-dipping faults such as the Funeral thrust in the Jurassic, which penetrated the basement to the west as well as the roots of the magmatic arc, leading to increased magmatism.
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Umhoefer, Paul J., Margaret E. Rusmore, and G. J. Woodsworth. "Contrasting tectono-stratigraphy and structure in the Coast Belt near Chilko Lake, British Columbia: unrelated terranes or an arc – back-arc transect?" Canadian Journal of Earth Sciences 31, no. 11 (November 1, 1994): 1700–1713. http://dx.doi.org/10.1139/e94-152.
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Stratigraphy and structural styles vary greatly in two areas of the Coast Belt near Chilko Lake (Chilcotin Ranges in the east and Coast Mountains in the west). No definite continuity between the two belts has been established in the pre-mid-Cretaceous geology, but this area may be a long-lived, episodic magmatic arc and nearby arc-related basin. The stratigraphic contrasts may reflect inherent differences between an arc and related basinal sequence. Triassic volcanic-arc sequences are part of the Stikine (western belt) and Cadwallader (eastern belt) terranes, which may be part of the same arc. The Jurassic is represented by one dated pluton in the west compared with almost continuous deposition of volcanogenic clastic rocks in the east. Lower Cretaceous sequences in the west and east may represent a volcanic arc and back-arc basin. The Taylor Creek Group (Albian) is the first definitive link between the two belts and represents an arc and intra-arc or back-arc basin. The structural evolution of the two belts also differs significantly. The early Late Cretaceous Eastern Waddington thrust belt comprises all major structures in the west, but only has minor expression in the east. Most of the structures in the east are part of the latest Cretaceous(?) to early Tertiary dextral-strike-slip, Yalakom fault system. These differences were most likely caused by the Late Cretaceous change from nearly orthogonal subduction to a dextral-oblique convergent margin.
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Stanton, Natasha, Andres Gordon, Cassia Cardozo, and Nick Kusznir. "Morphostructure, emplacement and duration of the Abrolhos Magmatic Province: A geophysical analysis of the largest post-breakup magmatism of the South-Eastern Brazilian margin." Marine and Petroleum Geology 133 (November 2021): 105230. http://dx.doi.org/10.1016/j.marpetgeo.2021.105230.
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Samsonov, A. V., and Yu O. Larionova. "Geochemical evolution of magmatism in Archean granite-greenstone terrains." Stratigraphy and Geological Correlation 14, no. 3 (May 2006): 225–39. http://dx.doi.org/10.1134/s0869593806030014.
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Farmer, G. Lang, Allen F. Glazner, Winifred T. Kortemeier, Michael A. Cosca, Craig H. Jones, Jessica E. Moore, and Richard A. Schweickert. "Mantle lithosphere as a source of postsubduction magmatism, northern Sierra Nevada, California." Geosphere 9, no. 5 (October 2013): 1102–24. http://dx.doi.org/10.1130/ges00885.1.
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Díaz-Bravo, Beatriz A., Arturo Gómez-Tuena, Carlos Ortega-Obregón, and Ofelia Pérez-Arvizu. "The origin of intraplate magmatism in the western Trans-Mexican Volcanic Belt." Geosphere 10, no. 2 (April 2014): 340–73. http://dx.doi.org/10.1130/ges00976.1.
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Jackson, Lily J., Brian K. Horton, and Cristian Vallejo. "Detrital zircon U-Pb geochronology of modern Andean rivers in Ecuador: Fingerprinting tectonic provinces and assessing downstream propagation of provenance signals." Geosphere 15, no. 6 (November 8, 2019): 1943–57. http://dx.doi.org/10.1130/ges02126.1.
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Abstract Recognizing detrital contributions from sediment source regions is fundamental to provenance studies of active and ancient orogenic settings. Detrital zircon U-Pb geochronology of unconsolidated sands from modern rivers that have source catchments with contrasting bedrock signatures provides insight into the fidelity of U-Pb age signatures in discriminating tectonic provenance and downstream propagation of environmental signals. We present 1705 new detrital zircon U-Pb ages for 15 samples of unconsolidated river sands from 12 modern rivers over a large spatial extent of Ecuador (∼1°N–5°S and ∼79°–77°W). Results show distinctive U-Pb age distributions with characteristic zircon age populations for various tectonic provinces along the Andean convergent margin, including the forearc, magmatic arc, and internal (hinterland) and external (foreland) segments of the fold-thrust belt. (1) Forearc and magmatic arc (Western Cordillera) river sands are characterized by Neogene–Quaternary age populations from magmatic sources. (2) Rivers in the hinterland (Eastern Cordillera) segment of the Andean fold-thrust belt have substantial populations of Proterozoic and Paleozoic ages, representing upper Paleozoic–Mesozoic sedimentary and metasedimentary rocks of ultimate cratonic origin. (3) River sands in the frontal fold-thrust belt (Subandean Zone to Oriente Basin) show distinctive bimodal Jurassic age populations, a secondary Triassic population, and subordinate Early Cretaceous ages representative of Mesozoic plutonic and metamorphic bedrock. Detrital zircon U-Pb results from a single regional watershed (Rio Pastaza) spanning the magmatic arc to foreland basin show drastic downstream variations, including the downstream loss of magmatic arc and hinterland signatures and abrupt introduction and dominance of selected sources within the fold-thrust belt. Disproportionate contributions from Mesozoic crystalline metamorphic rocks, which form high-elevation, high-relief areas subject to focused precipitation and active tectonic deformation, are likely the product of focused erosion and high volumes of local sediment input from the frontal fold-thrust belt, leading to dilution of upstream signatures from the hinterland and magmatic arc.
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Ramacciotti, Carlos Dino, César Casquet, Edgardo Gaspar Baldo, Sebastián Osvaldo Verdecchia, Matías Martín Morales, and Priscila Soledad Zandomeni. "Metamorfismo de alto gradiente P/T en la Sierra de Pie de Palo (Sierras Pampeanas, Argentina): modelado de equilibrio de fases minerales e implicancias geodinámicas en el antearco famatiniano." Andean Geology 46, no. 3 (September 30, 2019): 526. http://dx.doi.org/10.5027/andgeov46n3-3198.
Full textAbstract:
The Sierra de Pie de Palo (SPP, Western Sierras Pampeanas) shows evidence of two regional metamorphisms: one Mesoproterozoic attributed to the Grenvillian orogeny and other of Ordovician age related to the Famatinian orogeny. The Neoproterozoic-to-Cambrian sedimentary successions that cover the Grenvillian basement only record the Ordovician event. One staurolite-schist from the Ediacaran Difunta Correa Metasedimentary Sequence collected in the southeastern side of the SPP allows to constrain, by means of pseudosections, a prograde evolution from ca. 3 kbar and 515 ºC up to ca. 9 kbar and 640 ºC corresponding to a high P/T gradient. The SPP and the immediately east Loma de Las Chacras outcrop were part of the famatinian forearc which shows a progressive decrease of P (from ca. 13 kbar to 6 kbar), T (from ca. 900 ºC to 450 ºC), and P/T gradient (from ca. 85 ºC/kbar to 35 ºC/kbar) towards the active continental margin on the west. The Caucete Group, in the western side of the SPP, represents the westernmost part of the forearc, near to the active continental margin. Metamorphism was apparently coeval with the Famatinian magmatism and with ductile underthrusting at ca. 470-465 Ma, which led to burial of the forearc beneath the magmatic arc.
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Cocco, Fabrizio, Giacomo Oggiano, Antonio Funedda, Alfredo Loi, and Leonardo Casini. "Stratigraphic, magmatic and structural features of Ordovician tectonics in Sardinia (Italy): a review." Journal of Iberian Geology 44, no. 4 (July 13, 2018): 619–39. http://dx.doi.org/10.1007/s41513-018-0075-1.
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