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Petersen, Nathan T., Paul L. Smith, James K. Mortensen, Robert A. Creaser y Howard W. Tipper. "Provenance of Jurassic sedimentary rocks of south-central Quesnellia, British Columbia: implications for paleogeography". Canadian Journal of Earth Sciences 41, n.º 1 (1 de enero de 2004): 103–25. http://dx.doi.org/10.1139/e03-073.
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Jurassic sedimentary rocks of southern to central Quesnellia record the history of the Quesnellian magmatic arc and reflect increasing continental influence throughout the Jurassic history of the terrane. Standard petrographic point counts, geochemistry, SmNd isotopes and detrital zircon geochronology, were employed to study provenance of rocks obtained from three areas of the terrane. Lower Jurassic sedimentary rocks, classified by inferred proximity to their source areas as proximal or proximal basin are derived from an arc source area. Sandstones of this age are immature. The rocks are geochemically and isotopically primitive. Detrital zircon populations, based on a limited number of analyses, have homogeneous Late Triassic or Early Jurassic ages, reflecting local derivation from Quesnellian arc sources. Middle Jurassic proximal and proximal basin sedimentary rocks show a trend toward more evolved mature sediments and evolved geochemical characteristics. The sandstones show a change to more mature grain components when compared with Lower Jurassic sedimentary rocks. There is a decrease in εNdT values of the sedimentary rocks and Proterozoic detrital zircon grains are present. This change is probably due to a combination of two factors: (1) pre-Middle Jurassic erosion of the Late Triassic Early Jurassic arc of Quesnellia, making it a less dominant source, and (2) the increase in importance of the eastern parts of Quesnellia and the pericratonic terranes, such as Kootenay Terrane, both with characteristically more evolved isotopic values. Basin shale environments throughout the Jurassic show continental influence that is reflected in the evolved geochemistry and SmNd isotopes of the sedimentary rocks. The data suggest southern Quesnellia received material from the North American continent throughout the Jurassic but that this continental influence was diluted by proximal arc sources in the rocks of proximal derivation. The presence of continent-derived material in the distal sedimentary rocks of this study suggests that southern Quesnellia is comparable to known pericratonic terranes.
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Sokolov, S. D., G. Ye Bondarenko, A. K. Khudoley, O. L. Morozov, M. V. Luchitskaya, M. I. Tuchkova y P. W. Layer. "Tectonic reconstruction of Uda-Murgal arc and the Late Jurassic and Early Cretaceous convergent margin of Northeast Asia–Northwest Pacific". Stephan Mueller Special Publication Series 4 (17 de septiembre de 2009): 273–88. http://dx.doi.org/10.5194/smsps-4-273-2009.
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Abstract. A long tectonic zone composed of Upper Jurassic to Lower Cretaceous volcanic and sedimentary rocks is recognized along the Asian continent margin from the Mongol-Okhotsk fold and thrust belt on the south to the Chukotka Peninsula on the north. This belt represents the Uda-Murgal arc, which was developed along the convergent margin between Northeast Asia and Northwest Meso-Pacific. Several segments are identified in this arc based upon the volcanic and sedimentary rock assemblages, their respective compositions and basement structures. The southern and central parts of the Uda-Murgal arc were a continental margin belt with heterogeneous basement represented by metamorphic rocks of the Siberian craton, the Verkhoyansk terrigenous complex of Siberian passive margin and the Koni-Taigonos Late Paleozoic to Early Mesozoic island arc with accreted oceanic terranes. At the present day latitude of the Pekulney and Chukotka segments there was an ensimatic island arc with relicts of the South Anyui oceanic basin in a backarc basin. Accretionary prisms of the Uda-Murgal arc and accreted terranes contain fragments of Permian, Triassic to Jurassic and Jurassic to Cretaceous (Tithonian–Valanginian) oceanic crust and Jurassic ensimatic island arcs. Paleomagnetic and faunal data show significant displacement of these oceanic complexes and the terranes of the Taigonos Peninsula were originally parts of the Izanagi oceanic plate.
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Santos Polo, Alan, Guo Weimin, Fernando Rivera, Colombo Tassinari, Luis Cerpa y 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, n.º 3 (30 de septiembre de 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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Andrew, Anne y Colin I. Godwin. "Lead- and strontium-isotope geochemistry of Paleozoic Sicker Group and Jurassic Bonanza Group volcanic rocks and Island Intrusions, Vancouver Island, British Columbia". Canadian Journal of Earth Sciences 26, n.º 5 (1 de mayo de 1989): 894–907. http://dx.doi.org/10.1139/e89-072.
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Whole-rock and galena lead-isotope analyses have been obtained from the Sicker Group Paleozoic island-arc volcanic package and from a Jurassic island-arc represented by the Bonanza Group volcanics and Island Intrusions. Galena lead-isotope analyses from the volcanogenic ore deposits at the Buttle Lake mining camp in the Sicker Group provide estimates of the initial lead ratios for the Sicker Group. Lead-isotope signatures are uniform within each of the major orebodies, but the Myra orebody is less radiogenic than the older H–W orebody. This has major significance in terms of ore genesis for these important deposits.There are significant differences in isotopic composition between the Sicker Group and Devonian island-arc type rocks in the Shasta district, California, which rules out direct correlations between the rock units of these two areas. Relatively high initial values of 207Pb/204Pb (> 15.56) and 208Pb/204Pb (> 38.00) suggest that large quantities of crustal lead must have been involved in the formation of the Sicker Group volcanic rocks. Thus it is proposed that the trench related to the Paleozoic island arc had a substantial input of continental detritus and may have lain near a continent.The Jurassic island arc is characterized by low 207Pb/204Pb ratios (< 15.59), suggesting a more primitive arc environment than for the Paleozoic arc. Bonanza Group volcanic rocks contain lead that is less radiogenic than lead in the Island Intrusions. Present and initial lead-isotope ratios of both the Bonanza Group volcanics and Island intrusions follow the same trend, supporting the hypothesis that they are comagmatic. Lead isotopes from a galena vein within the Island Copper porphyry deposit plot with the initial ratios for Bonanza Group volcanics and Island Intrusions. This confirms the hypothesis that this mineralization is related to the Jurassic island-arc volcanic event.Initial lead-isotope ratios for the Jurassic rock suite form a linear array on both 207Pb/204Pb versus 206Pb/204Pb and 208Pb/204Pb versus 206Pb/204Pb plots. If interpreted as due to isotopic mixing, the more radiogenic end member has a composition that is lower in 207Pb/204Pb and higher in 206Pb/204Pb than typical upper continental crust. Assimilation of Sicker Group material during the emplacement of the Jurassic arc can explain the mixing trend.
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Chiaradia, Massimo, Lluís Fontboté y Agustín Paladines. "Metal Sources in Mineral Deposits and Crustal Rocks of Ecuador (1° N–4° S): A Lead Isotope Synthesis". Economic Geology 99, n.º 6 (1 de septiembre de 2004): 1085–106. http://dx.doi.org/10.2113/econgeo.99.6.1085.
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Abstract Ecuador consists of terranes having both continental (Chaucha, Tahuin, Loja terranes) and oceanic (Macuchi, Alao, Salado terranes) affinity, which were accreted to the Amazon craton from Late Jurassic to Eocene. Four main magmatic arcs were formed by the subduction of the Farallon/Nazca plate since the Jurassic: a Jurassic continental arc on the western margin of the Amazon craton, a Jurassic island arc (Alao terrane), an early Tertiary island arc (Macuchi terrane), and a middle-late Tertiary continental arc encompassing the terranes of Macuchi, Chaucha, Tahuin, Loja, and Alao after complete assembly of the Ecuadorian crust. Mineral deposits formed during these magmatic arc activities include porphyry-Cu and gold skarn deposits in association with the Jurassic continental arc, polymetallic volcanic-hosted massive sulfide deposits (VHMS) in association with the Jurassic island arc of Alao, Au-Cu-Zn VHMS deposits in association with the early Tertiary island arc of Macuchi, and porphyry-Cu and precious-metal epithermal deposits in association with the middle-late Tertiary continental-arc magmatism on the newly assembled crust of Ecuador (Macuchi, Chaucha, Tahuin, Loja, and Alao terranes). In this study, we have compiled 148 new and 125 previously published lead isotope analyses on Paleozoic to Miocene metamorphic, intrusive, volcanic, and volcanosedimentary rocks, as well as on Jurassic to Miocene magmatic-related ore deposits of Ecuador. Lead isotope compositions of the magmatic rocks of the four main arc events derive from mixing of various sources including mantle, variably enriched by pelagic sediments and/or by a high 238U/204Pb component, and heterogeneous continental crust rocks. Lead isotope compositions of the Ecuadorian ore deposits display a broad range of values (206Pb/204Pb = 18.3–19.3, 207Pb/204Pb = 15.54–15.74, 208Pb/204Pb = 38.2–39.2), which is as large as the range previously reported for all magmatic-related ore deposits of the Central Andean provinces I and II combined. Ore deposits formed before complete assembly of the Ecuadorian crust through complete accretion of the several terranes (i.e., pre-Eocene) have lead isotope compositions overlapping those of the associated magmatic rocks, suggesting a largely magmatic origin for their lead. In contrast, post-assembly ore deposits (i.e., post-Eocene) have lead isotope compositions that only partly overlap those of the coeval magmatic rocks of the continental arc. In fact, several ore deposits have lead isotope compositions shifted toward those of the basement rocks that host them, suggesting that lead derives from a mixture of magmatic lead and basement-rock lead leached by hydrothermal fluids. Most Ecuadorian ores have high 207Pb/204Pb values (>15.55), suggesting a dominant continental crust or pelagic sediment origin of the lead. However, we caution against concluding that chalcophile metals (for example, Cu and Au) also have a continental crust origin. Ore deposits of the different terranes of Ecuador, irrespective of their age, plot in distinct isotopic fields, which are internally homogeneous. This suggests that lithologic factors had an important control on the lead isotope compositions. Ultimately, lead isotope compositions of the ore deposits of Ecuador mirror the isotopic compositions of the rocks of the host terranes and are consistent with the multiterrane nature of the Ecuadorian crust.
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PERRI, FRANCESCO. "Reconstructing chemical weathering during the Lower Mesozoic in the Western-Central Mediterranean area: a review of geochemical proxies". Geological Magazine 155, n.º 4 (9 de enero de 2017): 944–54. http://dx.doi.org/10.1017/s0016756816001205.
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AbstractThe Triassic–Jurassic rift-valley stage of Tethyan rifting in the Western-Central Mediterranean area is characterized by a development of a puzzle of plates and microplates with the deposition of continental redbeds (in the internal domains of the Gibraltar Arc and Calabria–Peloritani Arc) that can be considered a regional lithosome. This paper aims to reconstruct the chemical weathering conditions of the Triassic–Jurassic boundary in the Western-Central Mediterranean area using the geochemical and mineralogical composition of continental redbed mudrocks of Mesozoic age. The mudrocks from the Calabria–Peloritani Arc show higher values of weathering (mobility) indices (αMg=(Al/Mg)sed/(Al/Mg)UCC;αK=(Th/K)sed/(Th/K)UCC;αBa=(Th/Ba)sed/(Th/Ba)UCC) than the Gibraltar Arc samples. Furthermore, the CIA (Chemical Index of Alteration) and MIA (Mineralogical Index of Alteration) values and the ‘Rb-type indices’ (e.g. Rb/Sr and Rb/K ratios) are higher for the Calabria–Peloritani Arc mudrocks than the Gibraltar Arc samples. All these geochemical proxies closely resemble each other and show similar variations suggesting climatic changes towards humid conditions through the Uppermost Triassic to Lowermost Jurassic that favoured chemical weathering conditions. This period is probably characterized by seasonal climate alternations corresponding to an increase in palaeoclimatic humidity. The mineralogical compositions of the Mesozoic mudrocks further confirm these indications as shown by a higher abundance of kaolinite, related to warm–humid conditions, in the Calabria–Peloritani Arc mudrocks than in those of the Gibraltar Arc.
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Zhang, Yue Qiao, Wei Hou y Fang Zhang. "The Provenance Tectonic Background Analysis of the Upper Jurassic Mohe Basin in Northeast China". Advanced Materials Research 734-737 (agosto de 2013): 476–79. http://dx.doi.org/10.4028/www.scientific.net/amr.734-737.476.
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The provenance tectonic background of Late Jurassic Mohe Basin was researched through the geochemical composition of sandstone. The Late Jurassic Mohe Basin is characterized by multiple provenances. One provenance is the active continental margin, and another is the island arc. Comparing with the regional lithology, the active continental margin may be from the Mongolia-Okhotsk orogenic belt, and the island arc may be from the northern of the Da Hingan Mountains. The characteristics are concerned with its geotectonic position.
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Xu, Zhongjie, Jintao Kong, Rihui Cheng y Liaoliang Wang. "U–Pb dating of detrital zircons in the eastern Guangdong Basin, South China, and constraints on the tectonic transformation from the Early to Middle Jurassic". Canadian Journal of Earth Sciences 57, n.º 4 (abril de 2020): 477–93. http://dx.doi.org/10.1139/cjes-2019-0050.
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Controversies exist regarding the mechanism of formation of basins located on the continental margin of South China as well as when they formed. It was ascertained based on clastic petrology, geochemical analysis, and zircon U–Pb dating that the sedimentary provenances in the eastern Guangdong Basin are mainly felsic igneous rocks from the late Early Jurassic to the Middle Jurassic. The late Early Jurassic Qiaoyuan Formation mainly shows major age peaks at approximately 238 Ma, 259 Ma, and 1858 Ma, and the Middle Jurassic Tangxia Formation shows major age peaks at approximately 169 Ma and 172 Ma. From the late Early Jurassic to the Middle Jurassic in the eastern Guangdong Basin, the source region changes from southwestern South China and southern South China to the eastern Nanling Range. It was determined by comparing the detrital zircon ages of the Qiaoyuan Formation and the Tangxia Formation with those of the late Paleozoic to early Mesozoic basins, and analyzing both the geochemical data and sedimentation, that the eastern Guangdong Basin changed from the basin-arc foreland basin of the late Early Jurassic to the back-arc extension basin of the Middle Jurassic. The changes in early Mesozoic detrital zircon age peaks indicate that the tectonic regime of the eastern Guangdong Basin ended the transformation from the Tethyan tectonic domain to the paleo-Pacific tectonic domain in the early Middle Jurassic (approximately 172 Ma).
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Friedman, R. M., J. B. Mahoney y Y. Cui. "Magmatic evolution of the southern Coast Belt: constraints from Nd–Sr isotopic systematics and geochronology of the southern Coast Plutonic Complex". Canadian Journal of Earth Sciences 32, n.º 10 (1 de octubre de 1995): 1681–98. http://dx.doi.org/10.1139/e95-133.
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Igneous rocks of the southern Coast Belt (SCB) and adjacent Insular Belt developed within a Jurassic–Quaternary magmatic arc built across accreted juvenile-arc and oceanic terranes. SCB plutons are mostly of intermediate composition, with I-type characteristics and major element, trace element, and rare earth element geochemistry consistent with genesis in a subduction-related magmatic arc. Ubiquitous xenoliths and migmatitic zones at pluton–county rock contacts indicate that assimilation of crustal rock was an important magmatic process. U–Pb zircon crystallization ages for SCB and Insular Belt igneous rocks indicate an overall eastward migration of the magmatic axis from Middle Jurassic through Late Cretaceous time. Although absent in most rocks, traces of old inherited zircon are present in several Middle Jurassic–Upper Cretaceous plutons in the southeastern Coast Belt. The primitive character and restricted range of Nd–Sr isotopic data for Middle Jurassic to Quaternary igneous rocks of the SCB (εNd = +2.4 to +8.0; Sri = 0.7030 − 0.7042) indicate they were generated in an isotopically juvenile magmatic arc. The distribution of isotopic values along the mantle array and the wide range of fSm/Nd values suggest magma was derived from depleted mantle within a mantle wedge, with little or no contribution from old, isotopically evolved continental material. Although field evidence suggests that assimilation of juvenile crust was an important process during magma ascent, isotopic and geochemical data do not permit discrimination between direct mantle derivation of magmas followed by fractionation and crustal assimilation, and wholesale melting of mafic arc-derived lower crust.
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TROUW, R. A. J., C. W. PASSCHIER, L. S. A. SIMÕES, R. R. ANDREIS y C. M. VALERIANO. "Mesozoic tectonic evolution of the South Orkney Microcontinent, Scotia arc, Antarctica". Geological Magazine 134, n.º 3 (mayo de 1997): 383–401. http://dx.doi.org/10.1017/s0016756897007036.
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The South Orkney Islands are the exposed part of a continental fragment on the southern limb of the Scotia arc. The islands are to a large extent composed of metapelites and metagreywackes of probable Triassic sedimentary age. Deformation related to an accretionary wedge setting, with associated metamorphism from anchizone to the greenschist facies, are of Jurassic age (176–200 Ma). On Powell Island, in the centre of the archipelago, five phases of deformation are recognized. The first three, associated with the main metamorphism, are tentatively correlated with early Jurassic subduction along the Pacific margin of Gondwana. D4 is a phase of middle to late Jurassic crustal extension associated with uplift. This extension phase may be related to opening of the Rocas Verdes basin in southern Chile, associated with the breakup of Gondwanaland. Upper Jurassic conglomerates cover the metamorphic rocks unconformably. D5 is a phase of brittle extensional faulting probably associated with Cenozoic opening of the Powell basin west of the archipelago, and with development of the Scotia arc.
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Prokopiev, Andrei V., Victoria B. Ershova y Daniel F. Stockli. "Detrital Zircon U-Pb Data for Jurassic–Cretaceous Strata from the South-Eastern Verkhoyansk-Kolyma Orogen—Correlations to Magmatic Arcs of the North-East Asia Active Margin". Minerals 11, n.º 3 (11 de marzo de 2021): 291. http://dx.doi.org/10.3390/min11030291.
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We performed U-Pb dating of detrital zircons collected from Middle–Upper Jurassic strata of the Sugoi synclinorium and Cretaceous rocks of the Omsukchan (Balygychan-Sugoi) basin, in order to identify their provenance and correlate Jurassic–Cretaceous sedimentation of the south-eastern Verkhoyansk-Kolyma orogenic belt with various magmatic belts of the north-east Asia active margins. In the Middle–Late Jurassic, the Uda-Murgal magmatic arc represented the main source area of clastics, suggesting that the Sugoi basin is a back-arc basin. A major shift in the provenance signature occurred during the Aptian, when granitoids of the Main (Kolyma) batholith belt, along with volcanic rocks of the Uyandina-Yasachnaya and Uda-Murgal arcs, became the main sources of clastics deposited in the Omsukchan basin. In a final Mesozoic provenance shift, granitoids of the Main (Kolyma) batholith belt, along with volcanic and plutonic rocks of the Uyandina-Yasachnaya and Okhotsk-Chukotka arcs, became the dominant sources for clastics in the Omsukchan basin in the latest Cretaceous. A broader comparison of detrital zircon age distributions in Jurassic–Cretaceous deposits across the south-eastern Verkhoyansk-Kolyma orogen illustrates that the Sugoi and Omsukchan basins did not form along the distal eastern portion of the Verkhoyansk passive margin, but in the Late Mesozoic back-arc basins.
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TAKASHIMA, REISHI, HIROSHI NISHI y TAKEYOSHI YOSHIDA. "Late Jurassic–Early Cretaceous intra-arc sedimentation and volcanism linked to plate motion change in northern Japan". Geological Magazine 143, n.º 6 (4 de septiembre de 2006): 753–70. http://dx.doi.org/10.1017/s001675680600255x.
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The Sorachi Group, composed of Upper Jurassic ophiolite and Lower Cretaceous island-arc volcano-sedimentary cover, provides a record of Late Jurassic–Early Cretaceous sedimentation and volcanism in an island-arc setting off the eastern margin of the Asian continent. Stratigraphic changes in the nature and volume of the Sorachi Group volcanic and volcaniclastic rocks reveal four tectonic stages. These stages resulted from changes in the subduction direction of the Pacific oceanic plate. Stage I in the Late Jurassic was characterized by extensive submarine eruptions of tholeiitic basalt from the back-arc basin. Slab roll-back caused rifting and sea-floor spreading in the supra-subduction zone along the active Asian continental margin. Stage II corresponded to the Berriasian and featured localized trachyandesitic volcanism that formed volcanic islands with typical island-arc chemical compositions. At the beginning of this stage, movement of the Pacific oceanic plate shifted from northeastward to northwestward. During Stage III, in the Valanginian, submarine basaltic volcanism was followed by subsidence. The Pacific oceanic plate motion turned clockwise, and the plate boundary between the Asian continent and the Pacific oceanic plate changed from convergent to transform. During Stage IV in the Hauterivian–Barremian, in situ volcanism ceased in the Sorachi–Yezo basin, and the volcanic front migrated west of the Sorachi–Yezo basin.
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Andrew, A., R. L. Armstrong y D. Runkle. "Neodymium–strontium–lead isotopic study of Vancouver Island igneous rocks". Canadian Journal of Earth Sciences 28, n.º 11 (1 de noviembre de 1991): 1744–52. http://dx.doi.org/10.1139/e91-156.
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Combined neodymium, strontium, and lead isotope measurements show that Vancouver Island is made up of Phanerozoic crustal material accreted to North America in the Mesozoic and early Cenozoic, but that there are differences in the relative proportions of depleted mantle and aged, enriched crustal components in the Phanerozoic magmatic episodes that contribute to this new crust.The Devonian Sicker Group volcanic arc has an isotopic signature that can be explained by mixing mantle material with subducted continentally derived sediments. The Early to Middle Jurassic Bonanza Volcanics and Island Intrusions magmatic arc isotopic signature indicates mixing of magma from a depleted mantle source with crustal material of Sicker arc-type, rather than of continental origin. This is consistent with large-scale assimilation of Sicker Group and Karmutsen rocks by Jurassic mantle-derived magmas, or introduction of arc-derived sediments into the Jurassic mantle by subduction. Eocene calc-alkaline Flores Volcanics – Catface Intrusions may be derived from reworked Vancouver Island crust with little addition of mantle material.Late Triassic Karmutsen Formation flood basalts are similar to the lower parts of the Columbia River Basalt in all three isotope systems and in petrochemistry. Radiogenic isotopic data are consistent with the interpretation that the Karmutsen basalts were extruded in a post-arc or back-arc setting, with mantle lithosphere and depleted mantle components, and perhaps some plume source input and crustal contamination, but the latter are not provable from the radiogenic isotopic data alone.Early Eocene Metchosin basalts show a depleted mantle source, consistent with their origin as ocean islands, before Middle to Late Eocene accretion to the rest of Vancouver Island.
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Lee, Seung Hwan, Chang Whan Oh y Soolim Jung. "Jurassic Igneous Activity in the Yuseong Area on the Southern Margin of the Gyeonggi Massif, Korean Peninsula, and Its Implications for the Tectonic Evolution of Northeast Asia during the Jurassic". Minerals 11, n.º 5 (28 de abril de 2021): 466. http://dx.doi.org/10.3390/min11050466.
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Jurassic dioritic to granitic igneous rocks extensively intrude into the southern Korean Peninsula, including the Yuseong area located at the boundary between the southern margin of the Gyeonggi Massif and the northern margin of the Okcheon Belt. In this study, the petrogenesis and sources of Jurassic igneous rocks in the Yuseong area were investigated. The U–Pb zircon age data from the Jurassic plutonic rocks in the Yuseong area give two igneous ages, ca. 178–177 Ma and 169–168 Ma, indicating that two stages of igneous activity occurred in the Yuseong area during the Jurassic. The geochemical characteristics of Jurassic diorites indicate that they originated from enriched mid-ocean ridge basalt (E-MORB; Nb/Yb = 5.63–7.27; Zr/Yb = 118–156). The enriched Th/Yb ratios (5.5–8.0) in the diorites imply that they experienced crustal contamination during magma ascent. The Jurassic granitoids in the Yuseong area are divided into I- and S-type granites. The Jurassic I-type granitoids may have formed via the partial melting of mafic rocks with mixtures of 10–40% pelite-derived melt, while the S-type granites originated from felsic pelite. The Jurassic diorites have low Nb/Th ratios with depletion of the Nb and Ta components, indicating that they formed in a volcanic arc tectonic environment. On the other hand, the Jurassic granitoids show two different tectonic environments: a volcanic arc, and a syncollisional environment. The granites with syncollisional character are S-type granites, and may give incorrect information about tectonic setting because of the changes in the trace elements of the S-type granite due to fractional crystallization. Early Jurassic (200–190 Ma) igneous rocks are distributed only in the southeastern Korean Peninsula, including the Yeongnam Massif; Jurassic igneous rocks formed at ca. 190–180 Ma occur mainly in the Okcheon Belt and southern Gyeonggi Massif, which includes the Yuseong area. Middle Jurassic igneous rocks widely intruded from the Okcheon Belt, through the Gyeonggi and Nangrim massifs in the Korean Peninsula, to the Liaoning area in the North China Craton at 180–160 Ma. This distribution pattern of the Jurassic granitoids suggests that flat subduction started after 180 Ma in Northeast Asia.
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Kowallis, Bart, Douglas Sprinkel, Eric Christiansen, Skylor Steed y David Wheatley. "Rhyolite ignimbrite boulders and cobbles in the Middle Jurassic Carmel Formation of Utah and Arizona—age, composition, transport, and stratigraphic setting". Geology of the Intermountain West 7 (21 de abril de 2020): 69–96. http://dx.doi.org/10.31711/giw.v7.pp69-96.
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A stratigraphic layer containing rhyolite cobbles and boulders in the Middle Jurassic Carmel Formation of southern Utah represents a singular, unusual event in the otherwise low-energy sedimentation of this formation. A laser-fusion, single-crystal 40Ar/39Ar age of 171.73 ± 0.19 Ma obtained from sanidine in one of the clasts is about 8 m.y. older than a zircon U-Pb age obtained on a fallout tuff from the sediments surrounding the clasts (163.9 ± ~3.3 Ma). The volcanic clasts are poorly-welded rhyolite ignimbrites that may have been deposited as much as 200 km from the eruptive center, perhaps along pre-existing valleys. The tuff deposits then remained in place for several million years during which time they were subjected to weathering, alteration, and perhaps topographic inversion, creating mesas capped with tuff underlain by soft Middle Jurassic silt and mud. Triggered by unusual rainfall or earthquakes, debris flows carried the clasts a few 10s of kilometers from their outcrops to the depositional site. Earlier work proposed that the Middle Jurassic arc was a low-standing, arc-graben. If this was the case, then the tectonic setting was likely similar to the modern Central American arc in the vicinity of Nicaragua where tuffs erupted from a low-standing arc deposited onto an adjacent highland and were then eroded by streams flowing to the east onto a fluvial plain that is near the sea.
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Uruski, C. y P. Baillie. "MESOZOIC EVOLUTION OF THE GREATER TARANAKI BASIN AND IMPLICATIONS FOR PETROLEUM PROSPECTIVITY". APPEA Journal 44, n.º 1 (2004): 385. http://dx.doi.org/10.1071/aj03014.
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A paradigm of New Zealand petroleum geology was that the oldest source rocks known in the region were of Cretaceous age, so any older sedimentary rocks were considered to be economic basement. Two major projects have revealed that this is not universally the case and that a Jurassic petroleum system should now be considered.Firstly, the Astrolabe 2D speculative survey, acquired by TGS-NOPEC in 2001, has revealed that a significant section underlies the traditional Cretaceous petroleum systems. Secondly, the Wakanui–1 well, drilled by Conoco, Inpex and Todd in 1999, which has recently become open-file, penetrated a Mid-Jurassic coal measure sequence.Jurassic rocks, including coal measure units, are known onshore in New Zealand, They are part of the Murihiku Supergroup, one of the basement terranes comprising the Permian to Cretaceous volcanic arc that forms the basement rocks of the present New Zealand landmass. Wherever they have been seen in outcrop, these rocks generally record low grade metamorphism and have been discounted as petroleum source rocks. Where rocks of the same age were deposited distal to the volcanic arc (and the effects of heat and pressure), however, they may form components of an effective petroleum system.The New Caledonia Basin, extending more than 2,000 km from Taranaki to New Caledonia, may have been the site of a Mesozoic back-arc basin. Jurassic coal measure successions and their equivalent marine units may be locally, or regionally important as source rocks. Implications of a Jurassic petroleum system for prospectivity of the region are investigated.
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Mihalynuk, Mitchell G., Moira T. Smith, Janet E. Gabites, Dita Runkle y David Lefebure. "Age of emplacement and basement character of the Cache Creek terrane as constrained by new isotopic and geochemical data". Canadian Journal of Earth Sciences 29, n.º 11 (1 de noviembre de 1992): 2463–77. http://dx.doi.org/10.1139/e92-193.
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New U–Pb and Rb–Sr isotopic and major and trace element geochemical data are reported for Late Triassic to Eocene granite bodies that intrude the Cache Creek and Stikine terranes in the Atlin–Bennett area of northwestern British Columbia. The U–Pb isotopic age data help constrain closure of the Cache Creek ocean and obduction of the Cache Creek terrane to before 172 Ma (Middle Jurassic). Low 87Sr/86Sr initial ratios (0.7037–0.7046) and lack of evidence for inheritance in zircons suggest that rocks underlying the Cache Creek terrane are largely primitive in nature, with derivation of intrusive rocks predominantly from unevolved sources.A genetic link between Late Triassic granitic plutons and Stuhini arc volcanics of Stikinia is supported by trace and rare-earth element data which indicate generation of magma in a volcanic-arc setting. Geochemical patterns for postaccretion Middle Jurassic and Late Cretaceous to early Tertiary age plutons are similar to those of the Late Triassic, indicating that Middle Jurassic and younger plutons could be derived from the same source area as the Late Triassic plutons.These data do not support recent theories proposing that the Cache Creek and Stikine terranes are klippe overlying a thick section of deformed, Proterozoic and lower Paleozoic continental-margin strata and attenuated cratonal basement. Rather, they are consistent with models in which remnants of Cache Creek ocean basin are placed over the Stikine arc in the Early to Middle Jurassic. Both terranes in turn overlie mainly late Paleozoic to early Mesozoic juvenile crustal material or the upper mantle.
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Naranjo, J. A., A. Puig y M. Suárez. "A note on Lower Jurassic magmatism in the Coastal Cordillera of Atacama, Chile". Geological Magazine 123, n.º 6 (noviembre de 1986): 699–702. http://dx.doi.org/10.1017/s0016756800024213.
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AbstractRadiometric dates on specimens of plutons of the Coastal Cordillera of Atacama span the period 300–110 Ma. A group of dates cluster around 190 Ma and evidence is presented which strongly suggests that they represent near crystallization ages. The geographic distribution of these plutons, adjacent to Liassic tuffs and lavas (Pan de Azúcar and Posada de los Hidalgo formations), suggests a genetic relationship between them, and that the plutons were the roots of the Lower Jurassic volcanic chain. The location of these granitoids to the west of the Liassic volcanic rocks, favours a previous idea that the Liassic basin extended eastwards as a back-arc or intra-arc basin. The host rocks to the Lower Jurassic plutons include Palaeozoic granitoids and metasedimentary rocks, indicating that the volcanic chain was founded on continental crust. The distance from the Liassic plutons to the present-day trench is less than 100 km, which indicates the possibility that part of the arc-trench system of that time is missing.
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MERCIER, J. L. y P. VERGELY. "The Paikon massif revisited, comments on the late Cretaceous - Paleogene geodynamics of the Axios-Vardar zone. How many Jurassic ophiolitic basins? (Hellenides, Macedonia, Greece)". Bulletin of the Geological Society of Greece 34, n.º 6 (1 de enero de 2002): 2099. http://dx.doi.org/10.12681/bgsg.16852.
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In the Axios-Vardar zone, the Paikon massif has been revisited. To the west, it is composed of a pile-up of SW dipping slices. These have been thrust toward the NNE while the Almopias zone was folding with a SSW vergence. Subsequently thrusting with a SW vergence occurred on the eastern flank of the Paikon massif and in the Almopias zone. These tectonic events took place during the Paleocene - early Eocene and during the upper Eocene - lower Oligocene respectively. During the late Cretaceous, the Almopias zone was a trough whose floor was a late Jurassic ophiolitic sheet. It was located between the Paikon carbonate platform and the Pelagonian platform. This analysis leads to the conclusion that the ophiolites were already located in the Almopias zone before the late Cretaceous and even before the upper Jurassic-lower Cretaceous. It is concluded that during the Jurassic the Almopias zone was an oceanic crust basin, the Paikon zone an island arc and the Peonias zone a back-arc basin. This analysis is a first step which is necessary to precise the geodynamic significance of the Axios- Vardar zone as a whole during the Triassic - Jurassic taking into account the stratigraphie, paleogeographic and structural data and the location in space and time of the magmatic and metamorphic belts
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LANG, XINGHAI, DONG LIU, YULIN DENG, JUXING TANG, XUHUI WANG, ZONGYAO YANG, ZHIWEI CUI et al. "Detrital zircon geochronology and geochemistry of Jurassic sandstones in the Xiongcun district, southern Lhasa subterrane, Tibet, China: implications for provenance and tectonic setting". Geological Magazine 156, n.º 4 (18 de abril de 2018): 683–701. http://dx.doi.org/10.1017/s0016756818000122.
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AbstractJurassic sandstones in the Xiongcun porphyry copper–gold district, southern Lhasa subterrane, Tibet, China were analysed for petrography, major oxides and trace elements, as well as detrital zircon U–Pb and Hf isotopes, to infer their depositional age, provenance, intensity of source-rock palaeo-weathering and depositional tectonic setting. This new information provides important evidence to constrain the tectonic evolution of the southern Lhasa subterrane during the Late Triassic – Jurassic period. The sandstones are exposed in the lower and upper sections of the Xiongcun Formation. Their average modal abundance (Q21F11L68) classifies them as lithic arenite, which is also supported by geochemical studies. The high chemical index of alteration values (77.19–85.36, mean 79.96) and chemical index of weathering values (86.19–95.59, mean 89.98) of the sandstones imply moderate to intensive weathering of the source rock. Discrimination diagrams based on modal abundance, geochemistry and certain elemental ratios indicate that felsic and intermediate igneous rocks constitute the source rocks, probably with a magmatic arc provenance. The detrital zircon ages (161–243 Ma) and εHf(t) values (+10.5 to +16.2) further constrain the sandstone provenance as subduction-related Triassic–Jurassic felsic and intermediate igneous rocks from the southern Lhasa subterrane. A tectonic discrimination method based on geochemical data of the sandstones, as well as detrital zircon ages from sandstones, reveals that the sandstones were most likely deposited in an oceanic island-arc setting. These results support the hypothesis that the tectonic background of the southern Lhasa subterrane was an oceanic island-arc setting, rather than a continental island-arc setting, during the Late Triassic – Jurassic period.
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Rees, P. M. "Revised interpretations of Mesozoic palaeogeography and volcanic arc evolution in the northern Antarctic Peninsula region". Antarctic Science 5, n.º 1 (marzo de 1993): 77–85. http://dx.doi.org/10.1017/s0954102093000100.
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Terrestrial sedimentary rocks at Hope Bay, northern Graham Land are well known for their diverse but poorly-preserved fossil flora, previously assigned ages ranging from Early Jurassic-Early Cretaceous. The beds form part of the Botany Bay Group, which comprises several outcrops of terrestrial sediments in northern Graham Land and the South Orkney Islands. A latest Jurassic or earliest Cretaceous age for the Hope Bay plant bearing sequence (and by extension for the rest of the Botany Bay Group) has been adopted in most recent publications dealing with Mesozoic volcanic arc evolution and palaeogeography of the northern Antarctic Peninsula region. New evidence, based upon the study of extensive collections of previously undescribed fossil plants from Hope Bay and nearby Botany Bay, indicates that they should be assigned an Early Jurassic age. The new palaeobotanical findings, combined with recently-published radiometric data from overlying volcanic sequences, show that a Cretaceous age is no longer tenable for these floras nor, therefore, for the Botany Bay Group in Graham Land. Interpretations of Mesozoic volcanic arc evolution and palaeogeography in this region are revised accordingly.
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Hunter, Morag A., David J. Cantrill y Michael J. Flowerdew. "Latest Jurassic–earliest Cretaceous age for a fossil flora from the Latady Basin, Antarctic Peninsula". Antarctic Science 18, n.º 2 (junio de 2006): 261–64. http://dx.doi.org/10.1017/s0954102006000290.
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Dating Jurassic terrestrial floras in the Antarctic Peninsula has proved problematic and controversial. Here U–Pb series dating on detrital zircons from a conglomerate interbedded with fossil plant material provide a maximal depositional age of 144 ± 3 Ma for a presumed Jurassic flora. This is the first confirmed latest Jurassic-earliest Cretaceous flora from the Latady Basin, and represents some of the youngest sedimentation in this basin. The presence of terrestrial sedimentation at Cantrill Nunataks suggests emergence of the arc closer to the Latady Basin margin in the south compared to Larsen Basin in the north, probably as a result of the failure of the southern Weddell Sea to undergo rifting.
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Smellie, John L. "Chapter 1.2 Antarctic volcanism: volcanology and palaeoenvironmental overview". Geological Society, London, Memoirs 55, n.º 1 (2021): 19–42. http://dx.doi.org/10.1144/m55-2020-1.
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AbstractSince Jurassic time (c.200 Ma), Antarctica has had a greater diversity of volcanism than other southern continents. It includes: (1) voluminous mafic and felsic volcanism associated with the break-up of Gondwana; (2) a long-lived continental margin volcanic arc, including back-arc alkaline volcanism linked to slab rollback; (3) small-volume mafic alkaline volcanism associated with slab-window formation; and (4) one of Earth's major continental rift zones, the West Antarctic Rift System (WARS), with its numerous large alkaline central volcanoes. Several of Antarctica's volcanoes are still active. This chapter is a review of the major volcanic episodes and their principal characteristics, in their tectonic, volcanological and palaeoenvironmental contexts. Jurassic Gondwana break-up was associated with large-scale volcanism that caused global environmental changes and associated mass extinctions. The volcanic arc was a major extensional arc characterized by alternating volcanic flare-ups and lulls. The Neogene rift-related alkaline volcanism is dominated by effusive glaciovolcanic eruptions, overwhelmingly as both pāhoehoe- and ‘a‘ā-sourced lava-fed deltas. The rift is conspicuously poor in pyroclastic rocks due to the advection and removal of tephra erupted during glacial intervals. Volcanological investigations of the Neogene volcanism have also significantly increased our knowledge of the critical parameters and development of the Antarctic Ice Sheet.
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DeBari, Susan M., Robert G. Anderson y James K. Mortensen. "Correlation among lower to upper crustal components in an island arc: the Jurassic Bonanza arc, Vancouver Island, Canada". Canadian Journal of Earth Sciences 36, n.º 8 (21 de agosto de 1999): 1371–413. http://dx.doi.org/10.1139/e99-029.
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The Westcoast Crystalline Complex (WCC), Island Intrusions, and Bonanza Group of Vancouver Island, Canada, form three different crustal levels of the Early to Middle Jurassic Bonanza island arc. Differential uplift has exposed the plutonic roots and the volcanic carapace of the arc for a strike length of ~500 km, and for another 250 km on the Queen Charlotte Islands. At deeper crustal levels within the arc, influx of mantle-derived magmas was accompanied by metamorphism and melting of Wrangellian basement rocks, yielding the heterogeneous WCC. Upward mobilization and hybridization of magmas to shallower levels in the crust resulted in the batholiths of the Island Intrusions and the lavas and pyroclastic rocks of the Bonanza Group. New U-Pb crystallization ages for plutonic rocks of the arc span an age range of 190.3 ± 1.0 to 168.6 ± 5.3 Ma. Ages of the WCC and western Island Intrusions are indistinguishable and overlap with published fossil and isotopic ages for the Bonanza Group. Younger Middle Jurassic ages for the eastern Island Intrusions overlap with those for plutonic rocks in the southern Coast Belt and Queen Charlotte Islands. All plutonic and volcanic rocks within the arc have overlapping geochemical signatures, supporting their comagmatic origin. All are light rare earth element-enriched with abundances 10-50× chondrites. The most mafic noncumulate gabbroic rocks have compositions typical of island arc basalts, with intermediate values of Al2O3 (16-17 wt.%) and high MgO (7-9 wt.%). More differentiated rocks follow a calc-alkaline trend with concomitant increase in Al2O3 (18-20 wt.%). Their geochemistry indicates varying degrees of mixing with melts of mafic Wrangellian basement.
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Liu, De-Liang, Min Shi y Shao-Yong Jiang. "Dating Oceanic Subduction in the Jurassic Bangong–Nujiang Oceanic Arc: A Zircon U–Pb Age and Lu–Hf Isotopes and Al-in-Hornblende Barometry Study of the Lameila Pluton in Western Tibet, China". Minerals 9, n.º 12 (4 de diciembre de 2019): 754. http://dx.doi.org/10.3390/min9120754.
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The subduction and close of the Mesozoic Bangong–Nujiang Ocean (BNO) led to a collision of the Lhasa and Qiangtang blocks, which formed the backbone of the Tibetan Plateau (the largest and highest plateau on Earth). However, the detailed subduction processes (in particular, the oceanic subduction processes) within the BNO are still not clear. Here, we focus on the plutonic complex of the oceanic arc in the Bangong–Nujiang suture (BNS) and report field observations on zircon U–Pb ages, Lu–Hf isotopes, and the Al-in-hornblende barometry of quartz diorites from the Lameila pluton in western Tibet. Zircon from the quartz diorites yielded a LA-ICP-MS U–Pb age of 164 Ma. The zircon showed very positive εHf(t) values from 10.5 to 13.9, suggesting the Lameila pluton was likely sourced from the depleted-mantle wedge, which is in contrast with contemporary (164–161 Ma) volcanic rocks in the region that had negative εHf(t) values of −7.4 to −16.2 and a magma source from partial melting of subducted sediments. The Lameila pluton showed a temperature-corrected Al-in-hornblende pressure of 3.9 ± 0.8 kbar, corresponding to an emplacement depth of 13 ± 3 km. Therefore, the thickness of the Jurassic oceanic arc crust must have doubled since the initial growth of the oceanic arc on the BNO crust, with a crustal thickness of 6.5 km during the Middle Jurassic. In combination with previous works on volcanic rocks, this study further supports a two-subduction zone model in association with the BNO during the Middle Jurassic, namely, a north-dipping BNO–Qiangtang subduction zone and an oceanic subduction zone within the BNO. The latter oceanic subduction zone produced the depleted-mantle-derived Lameila pluton and the subducted sediment-derived volcanic rocks in the fore arc.
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Lynch, Gregory. "Deformation of Early Cretaceous volcanic-arc assemblages, southern Coast Belt, British Columbia". Canadian Journal of Earth Sciences 29, n.º 12 (1 de diciembre de 1992): 2706–21. http://dx.doi.org/10.1139/e92-214.
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Early Cretaceous clastic volcanic-arc rocks of the Gambier Group in the southern Coast Belt were deposited in estuarine and marine environments on a deeply incised unconformity exposing Jurassic plutonic and arc assemblages. The Cretaceous arc was deformed in response to Late Cretaceous oblique subduction, producing orogen-parallel and orogen-normal shortening. Supracrustal Early Cretaceous rocks are preserved, in part, within the footwalls of overthrust sheets.Basal conglomerate and transgressive clastic successions underlie the volcanic edifices, with clasts reflecting volcanic – plutonic provenance. Volcanic rocks are calc-alkalic and span the complete basalt–andesite–dacite–rhyolite association typical of composite volcanoes. Extensive coarse pyroclastic deposits record an explosive volcanic environment.The Gambier Group occurs within the foreland of the major structural and metamorphic culmination of the southeastern Coast Belt. Early thin-skinned thrusting occurred to the east, repeating the Cretaceous stratigraphy. Overturned detached folds are associated with southerly directed thrusting developed during orogen-parallel shortening, likely in relation to large strike-slip fault systems. Later southwest-directed thrusting and associated large-amplitude folding occurred during Late Cretaceous arc-normal shortening, folding the earlier thrusts. To the southwest, tectonic wedging developed, with much of the Gambier Group preserved in the footwall of opposite southwest- and northeast-facing thrust systems; here southwest-directed thrusts emplaced Late Jurassic plutonic rocks, an unconformity, and lower Gambier strata over younger members, whereas concomitant or younger northeast-directed back thrusts emplaced the mid-Cretaceous plutonic roots of the arc above its volcanic derivative.
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Johannson, Gary G., Paul L. Smith y Steven P. Gordey. "Early Jurassic evolution of the northern Stikinian arc: evidence from the Laberge Group, northwestern British Columbia". Canadian Journal of Earth Sciences 34, n.º 7 (1 de julio de 1997): 1030–57. http://dx.doi.org/10.1139/e17-085.
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This study resolves fundamental questions concerning the age, provenance, and depositional history of Laberge Group strata in the Whitehorse Trough. The Jurassic Inklin Formation straddles the Stikine and Cache Creek terranes along much of the length of the Whitehorse Trough. Ammonite biochronology indicates an age range of early Sinemurian to late Pliensbachian and provides the temporal framework for interpreting basin history. Strong temporal trends in both paleocurrent patterns and sandstone–conglomerate petrofacies allow definition of three discrete phases in basin-fill history. Stable tectonics characterized by relative volcanic quiescence and low sedimentation rates prevailed during the Sinemurian. Sinemurian sandstone–conglomerate petrofacies record a transitional-arc provenance derived from erosion of the Upper Triassic volcanic pile, flanking coastal sediments, and arc roots of Stikinia to the southwest. During the early Pliensbachian, arc dissection was interrupted by a major magmatic episode with widespread rejuvenated volcanism that caused a strong provenance shift to volcanigenic sources, indicating derivation from a largely undissected Stikinian arc. Southwest-derived, northerly longitudinal paleoflow during the Sinemurian changed to opposed bidirectional radial or transverse paleoflow systems in the early Pliensbachian. Cannibalism of broadly coeval basinal strata and (or) reflected sediment gravity flows were the result of episodic growth of a mobile outer forearc rise, initiating southwest-directed paleoflow systems during the early Pliensbachian and the possible development of a ridged forearc phase. U–Pb dates of [Formula: see text] and 186 ± 1 Ma from a granite clast and tuff unit, respectively, of the Kunae Zone (early late Pliensbachian) and sandstone–conglomerate petrofacies indicate a late Pliensbachian depositional regime dominated by tectonic controls. The influx of granitic detritus indicates a rapid transition to a fully dissected arc provenance, where accelerated uplift of segments of the arc massif, accompanied by intra-arc strike-slip faulting, resulted in rapid arc dissection and unroofing of comagmatic Pliensbachian plutons.
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Leat, Philip T. y Teal R. Riley. "Chapter 3.1a Antarctic Peninsula and South Shetland Islands: volcanology". Geological Society, London, Memoirs 55, n.º 1 (2021): 185–212. http://dx.doi.org/10.1144/m55-2018-52.
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AbstractThe voluminous continental margin volcanic arc of the Antarctic Peninsula is one of the major tectonic features of West Antarctica. It extends from the Trinity Peninsula and the South Shetland Islands in the north to Alexander Island and Palmer Land in the south, a distance ofc.1300 km, and was related to east-directed subduction beneath the continental margin. Thicknesses of exposed volcanic rocks are up toc.1.5 km, and the terrain is highly dissected by erosion and heavily glacierized. The arc was active from Late Jurassic or Early Cretaceous times until the Early Miocene, a period of climate cooling from subtropical to glacial. The migration of the volcanic axis was towards the trench over time along most of the length of the arc. Early volcanism was commonly submarine but most of the volcanism was subaerial. Basaltic–andesitic stratocones and large silicic composite volcanoes with calderas can be identified. Other rock associations include volcaniclastic fans, distal tuff accumulations, coastal wetlands and glacio-marine eruptions.Other groups of volcanic rocks of Jurassic age in Alexander Island comprise accreted oceanic basalts within an accretionary complex and volcanic rocks erupted within a rift basin along the continental margin that apparently predate subduction.
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Affinati, Suzanne Craddock, Thomas D. Hoisch, Michael L. Wells y Jeffrey D. Vervoort. "Pressure-temperature-time paths from the Funeral Mountains, California, reveal Jurassic retroarc underthrusting during early Sevier orogenesis". GSA Bulletin 132, n.º 5-6 (17 de septiembre de 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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Danelian, Taniel, Alastair H. F. Robertson y Sarantis Dimitriadis. "Age and significance of radiolarian sediments within basic extrusives of the marginal basin Guevgueli Ophiolite (northern Greece)". Geological Magazine 133, n.º 2 (marzo de 1996): 127–36. http://dx.doi.org/10.1017/s0016756800008645.
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AbstractWell-preserved Radiolaria have been discovered in calcareous silt turbidites and mudstones intercalated with basic extrusives of the Guevgueli Ophiolite, northern Greece. The mudstones contain terrigenous silt, probably derived from adjacent continental basement of the Serbo-Macedonian and/or Paikon units. Volcanic quartz and rare volcanic glass were probably derived from an active continental margin arc (Paikon volcanic arc) to the west. The radiolarian sediments were deposited within fault-controlled hollows in the ophiolitic extrusives, and then covered by massive and pillowed extrusives. The radiolarian assemblage is indicative of an early Late Jurassic (Oxfordian) age, which therefore dates the genesis of the Guevgueli Ophiolite. Our data are consistent with the age of the intrusive Late Jurassic Fanos Granite, believed to be contemporaneous with the Guevgueli Ophiolite. In general, the Guevgueli and related ophiolites of northern Greece are thought to have formed within a transtensional intra-continental marginal basin, generated in response to oblique eastward subduction of older Tethyan oceanic crust (Almopias ocean).
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Baumgartner, Renaud. "Vers une gestion intégrée des pâturages boisés – carte de visite du paysage jurassien | Towards an integrated management of the wooded pastures – typical of the Jura landscape". Schweizerische Zeitschrift fur Forstwesen 162, n.º 3 (1 de marzo de 2011): 81–86. http://dx.doi.org/10.3188/szf.2011.0081.
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The wooded pastures arose from the colonisation of the valleys and high plateaux of the Jurassic Arc. They are the product of a mixed exploitation combining agricultural and silvicultural elements, and are dependent for their conservation on a form of management where a balance between cattle grazing and wood cutting is maintained. The abandon of farmland and fewer cattle at pasture in summer, the small returns from logging and the introduction of grants based on surface area of agriculturally used land (SAU) have together completely disturbed this balance. The necessity of an integrated management system which takes into account the interests of agriculture, silviculture, nature, landscape and leisure activities has led to the creation of interdisciplinary commissions on wooded pastures of the Bernese Jura and the Jurassic Arc. An Interreg IIIA project France-Switzerland has enabled the creation of a model integrated management plan. Due to the lack of funds from the Federal Office of Agriculture, the cantonal services promote the development of integrated management plans.
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Demant*, Alain, Stéphanie Touron, Henriette Lapierre y Delphine Bosch. "Cretaceous arc volcanism of Byers Peninsula, Livingston Island, Antarctica : new petrological, geochemical and isotope data". Bulletin de la Société Géologique de France 175, n.º 2 (1 de marzo de 2004): 131–45. http://dx.doi.org/10.2113/175.2.131.
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Abstract On Byers Peninsula, the largest summer ice-free area in the South Shetland Islands, a thick Upper Jurassic-Lower Cretaceous sedimentary sequence and penecontemporaneous igneous activity records the progressive emersion of a volcanic arc. The oldest rocks are represented by voluminous basaltic flows intercalated within late Jurassic shallow marine sediments. Following the emersion, Lower Cretaceous strata were deposited. Welded and nonwelded dacitic to rhyolitic ignimbrites are exposed locally at the base of the continental succession. However, the majority of the outcrops consists of Lower Cretaceous basaltic to basaltic andesite plugs and dykes, representing the roots of a volcanic arc, which form most of the topographic highs of the peninsula. Byers Peninsula lavas are porphyritic with mineralogical associations typical of orogenic series. Major, trace and rare-earth element data show that all the rocks are relatively poor in K2O, enriched in large ion lithophile elements and that they have a clear subduction imprint (Nb-Ta anomaly). Furthermore, a tholeiitic tendency is shown by the REE patterns of some basaltic lavas. Sr- Nd- and Pb isotopic data support an origin from the sub-arc asthenosphere. Byers lavas have isotope signatures similar to that of the South Sandwich intra-oceanic arc. The enriched nature of most of the samples, revealed by Pb isotope ratios and Th/Yb enrichment, indicates that the MORB-like mantle source has been modified by fluids and sediments derived from the subducting slab. No clear temporal chemical change is observed during the evolution of this near-trench volcanic arc.
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Sarifakioglu, E., Y. Dilek y M. Sevin. "Jurassic–Paleogene intraoceanic magmatic evolution of the Ankara Mélange, north-central Anatolia, Turkey". Solid Earth 5, n.º 1 (19 de febrero de 2014): 77–108. http://dx.doi.org/10.5194/se-5-77-2014.
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Abstract. Oceanic rocks in the Ankara Mélange along the Izmir–Ankara–Erzincan suture zone (IAESZ) in north-central Anatolia include locally coherent ophiolite complexes (~ 179 Ma and ~ 80 Ma), seamount or oceanic plateau volcanic units with pelagic and reefal limestones (96.6 ± 1.8 Ma), metamorphic rocks with ages of 256.9 ± 8.0 Ma, 187.4 ± 3.7 Ma, 158.4 ± 4.2 Ma, and 83.5 ± 1.2 Ma indicating northern Tethys during the late Paleozoic through Cretaceous, and subalkaline to alkaline volcanic and plutonic rocks of an island arc origin (~ 67–63 Ma). All but the arc rocks occur in a shale–graywacke and/or serpentinite matrix, and are deformed by south-vergent thrust faults and folds that developed in the middle to late Eocene due to continental collisions in the region. Ophiolitic volcanic rocks have mid-ocean ridge (MORB) and island arc tholeiite (IAT) affinities showing moderate to significant large ion lithophile elements (LILE) enrichment and depletion in Nb, Hf, Ti, Y and Yb, which indicate the influence of subduction-derived fluids in their melt evolution. Seamount/oceanic plateau basalts show ocean island basalt (OIB) affinities. The arc-related volcanic rocks, lamprophyric dikes and syenodioritic plutons exhibit high-K shoshonitic to medium- to high-K calc-alkaline compositions with strong enrichment in LILE, rare earth elements (REE) and Pb, and initial εNd values between +1.3 and +1.7. Subalkaline arc volcanic units occur in the northern part of the mélange, whereas the younger alkaline volcanic rocks and intrusions (lamprophyre dikes and syenodioritic plutons) in the southern part. The late Permian, Early to Late Jurassic, and Late Cretaceous amphibole-epidote schist, epidote-actinolite, epidote-chlorite and epidote-glaucophane schists represent the metamorphic units formed in a subduction channel in the northern Neotethys. The Middle to Upper Triassic neritic limestones spatially associated with the seamount volcanic rocks indicate that the northern Neotethys was an open ocean with its MORB-type oceanic lithosphere by the early Triassic (or earlier). The latest Cretaceous–early Paleocene island arc volcanic, dike and plutonic rocks with subalkaline to alkaline geochemical affinities represent intraoceanic magmatism that developed on and across the subduction–accretion complex above a N-dipping, southward-rolling subducted lithospheric slab within the northern Neotethys. The Ankara Mélange thus exhibits the record of ~ 120–130 million years of oceanic magmatism in geological history of the northern Neotethys.
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Sarifakioglu, E., Y. Dilek y M. Sevin. "Jurassic–Paleogene intra-oceanic magmatic evolution of the Ankara Mélange, North-Central Anatolia, Turkey". Solid Earth Discussions 5, n.º 2 (13 de noviembre de 2013): 1941–2004. http://dx.doi.org/10.5194/sed-5-1941-2013.
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Abstract. Oceanic rocks in the Ankara Mélange along the Izmir–Ankara–Erzincan suture zone (IAESZ) in North-Central Anatolia include locally coherent ophiolite complexes (~179 Ma and ~80 Ma), seamount or oceanic plateau volcanic units with pelagic and reefal limestones (96.6 ± 1.8 Ma), metamorphic rocks with ages of 187.4 ± 3.7 Ma, 158.4 ± 4.2 Ma, and 83.5 ± 1.2 Ma, and subalkaline to alkaline volcanic and plutonic rocks of an island arc origin (~67–63 Ma). All but the arc rocks occur in a shaly-graywacke and/or serpentinite matrix, and are deformed by south-vergent thrust faults and folds that developed in the Middle to Late Eocene due to continental collisions in the region. Ophiolitic volcanic rocks have mid-ocean ridge (MORB) and island arc tholeiite (IAT) affinities showing moderate to significant LILE enrichment and depletion in Nb, Hf, Ti, Y and Yb, which indicate the influence of subduction-derived fluids in their melt evolution. Seamount/oceanic plateau basalts show ocean island basalt (OIB) affinities. The arc-related volcanic rocks, lamprophyric dikes and syeno-dioritic plutons exhibit high-K shoshonitic to medium-to high-K calc-alkaline compositions with strong enrichment in LILE, REE and Pb, and initial &varepsilon;Nd values between +1.3 and +1.7. Subalkaline arc volcanic units occur in the northern part of the mélange, whereas the younger alkaline volcanic rocks and intrusions (lamprophyre dikes and syeno-dioritic plutons) in the southern part. The Early to Late Jurassic and Late Cretaceous epidote-actinolite, epidote-chlorite and epidote-glaucophane schists represent the metamorphic units formed in a subduction channel in the Northern Neotethys. The Middle to Upper Triassic neritic limestones spatially associated with the seamount volcanic rocks indicate that the Northern Neotethys was an open ocean with its MORB-type oceanic lithosphere by the Early Triassic. The Latest Cretaceous–Early Paleocene island arc volcanic, dike and plutonic rocks with subalkaline to alkaline geochemical affinities represent intraoceanic magmatism that developed on and across the subduction-accretion complex above a N-dipping, southward-rolling subducted lithospheric slab within the Northern Neotethys. The Ankara Mélange thus exhibits the record of ~120–130 million years of oceanic magmatism in geological history of the Northern Neotethys.
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Kee, Weon‐Seo, Sung Won Kim, Youn‐Joong Jeong y Sanghoon Kwon. "Characteristics of Jurassic Continental Arc Magmatism in South Korea: Tectonic Implications". Journal of Geology 118, n.º 3 (mayo de 2010): 305–23. http://dx.doi.org/10.1086/651503.
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BEIERSDORFER, R. E. "Metamorphism of a Late Jurassic volcano-plutonic arc, northern California, USA". Journal of Metamorphic Geology 11, n.º 3 (mayo de 1993): 415–28. http://dx.doi.org/10.1111/j.1525-1314.1993.tb00158.x.
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Mortimer, N., P. van der Heyden, R. L. Armstrong y J. Harakal. "U–Pb and K–Ar dates related to the timing of magmatism and deformation in the Cache Creek terrane and Quesnellia, southern British Columbia". Canadian Journal of Earth Sciences 27, n.º 1 (1 de enero de 1990): 117–23. http://dx.doi.org/10.1139/e90-009.
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U–Pb dating of zircon from the Guichon Creek batholith indicates an emplacement age of 210 ± 3 Ma. Comparison with previously published K–Ar (211–188 Ma) and Rb–Sr (205 and 196 Ma) dates reveals that intrusion, mineralization, cooling, and uplift of the batholith took some 20 Ma, spanning the Triassic–Jurassic boundary on the Decade of North American Geology (DNAG) time scale.The Mount Martley pluton and Tiffin Creek stock yield Late Jurassic dates of 155 ± 2 Ma (U–Pb, zircon) and 152 ± 5 Ma (K–Ar, hornblende), respectively, and provide a reliable minimum age (Kimmeridgian) for penetrative deformation in the Cache Creek terrane. K–Ar whole-rock dates from Cache Creek terrane and Ashcroft Formation argillites range from Early Permian (266 ± 8 Ma) and Early Jurassic (194 ± 6 Ma) to Late Jurassic, Kimmeridgian (154 ± 5 Ma). We interpret the younger dates as recording Middle–Late Jurassic tectonism and the older ones as possible relics from earlier deformation episodes.An Early Cretaceous K–Ar date (129 ± 5 Ma) for a lamprophyre dike that cuts the Nicola Group suggests that the Early Cretaceous magmatic arc of the Coast Plutonic Complex had an eastern alkalic fringe in the Intermontane Belt.
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Leat, P. T., M. J. Flowerdew, T. R. Riley, M. J. Whitehouse, J. H. Scarrow y I. L. Millar. "Zircon U-Pb dating of Mesozoic volcanic and tectonic events in north-west Palmer Land and south-west Graham Land, Antarctica". Antarctic Science 21, n.º 6 (3 de agosto de 2009): 633–41. http://dx.doi.org/10.1017/s0954102009990320.
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AbstractNew whole rock Rb-Sr and zircon U-Pb geochronological data and Sm-Nd isotopic data are presented from the central magmatic arc domain of the Antarctic Peninsula in the area of north-west Palmer Land and south-west Graham Land, Rb-Sr isochrons indicate an age of 169 ± 6 Ma for basement orthogneisses and 132 ± 9 to 71 ± 9 Ma for plutons. A U-Pb age of 183 ± 2.1 Ma, with no detectable inheritance, on zircons from an orthogneiss from Cape Berteaux provides the first reliable age for the orthogneisses, which are interpreted as metamorphosed silicic volcanic rocks, and Sm-Nd data indicate derivation in a mature volcanic arc. The age indicates they may be correlatives of the Jurassic ‘Chon Aike’ volcanism of the eastern Antarctic Peninsula. A U-Pb zircon age of 107 ± 1.7 Ma on a terrestrial volcanic sequence overlying an uncomformity strongly suggests a mid-Cretaceous age for the extensive volcanic cover of north-west Palmer Land that was previously thought to be Jurassic. The unconformity is interpreted to have been a result of compressional uplift related to the Palmer Land event. This is the first date for the event in the western part of the central magmatic arc terrane of the Antarctic Peninsula.
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ORTEGA-FLORES, BERLAINE, LUIGI A. SOLARI y FELIPE DE JESÚS ESCALONA-ALCÁZAR. "The Mesozoic successions of western Sierra de Zacatecas, Central Mexico: provenance and tectonic implications". Geological Magazine 153, n.º 4 (17 de diciembre de 2015): 696–717. http://dx.doi.org/10.1017/s0016756815000977.
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AbstractCentral Mexico was subject to active tectonics related to subduction processes while it occupied a position in western equatorial Pangea during early Mesozoic time. The subduction of the palaeo-Pacific plate along the western North American and South American active continental margins produced volcanic arc successions which were subsequently rifted and re-incorporated to the continental margin. In this context, the fringing arcs are important in unravelling the continental accretionary record. Using petrographic analysis, detrital zircon geochronology and structural geology, this paper demonstrates that the Guerrero Arc (Guerrero Terrane) formed on top of a felsic volcaniclastic unit (Middle Jurassic La Pimienta Formation) and siliciclastic strata (Upper Triassic Zacatecas Formation and Arteaga Complex) of continental Mexican provenance, deposited across the continental margin and oceanic substrate. This assemblage was rifted away from continental Mexico to form an intervening oceanic assemblage (Upper Jurassic – Lower Cretaceous Las Pilas Volcanosedimentary Complex of the Arperos Basin), then accreted back more or less at the same place, all above the same east-dipping subduction zone. The accretion of the Guerrero Arc to the Mexican continental mainland (Sierra Madre Terrane) caused the deposition of a siliciclastic unit (La Escondida Phyllite), which recycled detritus from the volcaniclastic and siliciclastic underlying strata.
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Leat, Philip T. y Teal R. Riley. "Chapter 3.1b Antarctic Peninsula and South Shetland Islands: petrology". Geological Society, London, Memoirs 55, n.º 1 (2021): 213–26. http://dx.doi.org/10.1144/m55-2018-68.
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AbstractThe Antarctic Peninsula contains a record of continental-margin volcanism extending from Jurassic to Recent times. Subduction of the Pacific oceanic lithosphere beneath the continental margin developed after Late Jurassic volcanism in Alexander Island that was related to extension of the continental margin. Mesozoic ocean-floor basalts emplaced within the Alexander Island accretionary complex have compositions derived from Pacific mantle. The Antarctic Peninsula volcanic arc was active from about Early Cretaceous times until the Early Miocene. It was affected by hydrothermal alteration, and by regional and contact metamorphism generally of zeolite to prehnite–pumpellyite facies. Distinct geochemical groups recognized within the volcanic rocks suggest varied magma generation processes related to changes in subduction dynamics. The four groups are: calc-alkaline, high-Mg andesitic, adakitic and high-Zr, the last two being described in this arc for the first time. The dominant calc-alkaline group ranges from primitive mafic magmas to rhyolite, and from low- to high-K in composition, and was generated from a mantle wedge with variable depletion. The high-Mg and adakitic rocks indicate periods of melting of the subducting slab and variable equilibration of the melts with mantle. The high-Zr group is interpreted as peralkaline and may have been related to extension of the arc.
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Ding, Xiang-Li, Lin Ding, Li-Yun Zhang, Chao Wang y Ya-Hui Yue. "Identification and Origin of Jurassic (~182 Ma) Zircon Grains from Chromitite within the Peridotite of the Jijal Complex, Kohistan Arc in North Pakistan". Minerals 10, n.º 12 (3 de diciembre de 2020): 1085. http://dx.doi.org/10.3390/min10121085.
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The Jijal ultramafic–mafic complex in Pakistan probably preserves the most complete fragments of the petrological Moho. However, a few studies argue for multiple origins (including petrogenetic speculations and tectonic reconstructions) for different lithologies. One of the main reasons for this dispute is the lack of direct age information of the ultramafic rocks. Zircon grains, despite generally being exotic in ultramafic rocks, can provide significant insights into the petrogenetic process of the host ultramafic rocks. This study reports the first zircon U–Pb age and Lu–Hf and trace element data for zircon grains separated from chromitite lenses within the peridotite, which is commonly considered the lowermost part of the Jijal complex. These zircon grains yield concordant 206Pb/238U ages of ~182 ± 3 Ma, which is much older than the late Early Cretaceous age (<120 Ma) of the Jijal complex, and lying above it, the other complexes of the Kohistan paleo-arc. Furthermore, these Jurassic zircon grains present radiogenic εHf(t) values (+9.7 to +6.0) which are obviously lower than the values for the Cretaceous zircon grains of the Kohistan arc. From integrated analysis of the zircon trace element signatures (e.g., high Th, U, Th/U, and U/Yb ratios) and regional geology, we speculate that these zircon grains came from a ‘missing’ Early Jurassic arc akin to the Gangdese belt to the east, and entered the mantle by oceanic subduction processes. Although these Jurassic zircon grains cannot actually constrain the formation age of the chromitite as well as the peridotite, it reminds us that some cryptic pre-Cretaceous complexes and geodynamic processes were incorporated in building the oceanic crust of the Jijal intra-oceanic arc, or the mantle section (at least part of it) should probably belong to the Indus ophiolite mélange. Further research, particularly chronological studies on mantle (or ultramafic) rocks, as well as detailed geological mapping, should be carried out in the future for solving this issue.
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Box, Stephen E., Susan M. Karl, James V. Jones, Dwight C. Bradley, Peter J. Haeussler y Paul B. O’Sullivan. "Detrital zircon geochronology along a structural transect across the Kahiltna assemblage in the western Alaska Range: Implications for emplacement of the Alexander-Wrangellia-Peninsular terrane against North America". Geosphere 15, n.º 6 (16 de octubre de 2019): 1774–808. http://dx.doi.org/10.1130/ges02060.1.
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Abstract The Kahiltna assemblage in the western Alaska Range consists of deformed Upper Jurassic and Cretaceous clastic strata that lie between the Alexander-Wrangellia-Peninsular terrane to the south and the Farewell and other pericratonic terranes to the north. Differences in detrital zircon populations and sandstone petrography allow geographic separation of the strata into two different successions, each consisting of multiple units, or petrofacies, with distinct provenance and lithologic characteristics. The northwestern succession was largely derived from older, inboard pericratonic terranes and correlates along strike to the southwest with the Kuskokwim Group. The southeastern succession is characterized by volcanic and plutonic rock detritus derived from Late Jurassic igneous rocks of the Alexander-Wrangellia-Peninsular terrane and mid- to Late Cretaceous arc-related igneous rocks and is part of a longer belt to the southwest and northeast, here named the Koksetna-Clearwater belt. The two successions remained separate depositional systems until the Late Cretaceous, when the northwestern succession overlapped the southeastern succession at ca. 81 Ma. They were deformed together ca. 80 Ma by southeast-verging fold-and-thrust–style deformation interpreted to represent final accretion of the Alexander-Wrangellia-Peninsular terrane along the southern Alaska margin. We interpret the tectonic evolution of the Kahiltna successions as a progression from forearc sedimentation and accretion in a south-facing continental magmatic arc to arrival and partial underthrusting of the back-arc flank of an active, south-facing island-arc system (Alexander-Wrangellia-Peninsular terrane). A modern analogue is the ongoing collision and partial underthrusting of the Izu-Bonin-Marianas island arc beneath the Japan Trench–Nankai Trough on the east side of central Japan.
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Fainstein, Roberto, Juvêncio De Deus Correia do Rosário, Helio Casimiro Guterres, Rui Pena dos Reis y Luis Teófilo da Costa. "Coastal and offshore provinces of Timor-Leste — Geophysics exploration and drilling". Leading Edge 39, n.º 8 (agosto de 2020): 543–50. http://dx.doi.org/10.1190/tle39080543.1.
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Regional geophysics research provides for prospect assessment of Timor-Leste, part of the Southeast Asia Archipelago in a region embracing the Banda Arc, Timor Island, and the northwest Australia Gondwana continental margin edge. Timor Island is a microcontinent with several distinct tectonic provinces that developed initially by rifting and drifting away from the Australian Plate. A compressive convergence began in the Miocene whereby the continental edge of the large craton collided with the microcontinent, forming a subduction zone under the island. The bulk of Timor Island consists of a complex mélange of Tertiary, Cretaceous, Jurassic, Triassic, Permian, and volcanic features over a basal Gondwana craton. Toward the north, the offshore consists of a Tertiary minibasin facing the Banda Arc Archipelago, with volcanics interspersed onshore with the basal Gondwana pre-Permian. A prominent central overthrust nappe of Jurassic and younger layers makes up the mountains of Timor-Leste, terminating south against an accretionary wedge formed by this ongoing collision of Timor and Australia. The northern coast of the island is part of the Indonesian back arc, whereas the southern littoral onshore plus shallow waters are part of the accretionary prism. Deepwater provinces embrace the Timor Trough and the slope of the Australian continental margin being the most prospective region of Timor-Leste. Overall crust and mantle tectonic structuring of Timor-Leste is interpreted from seismic and potential field data, focusing mostly on its southern offshore geology where hydrocarbon prospectivity has been established with interpretation of regional seismic data and analyses of gravity, magnetic, and earthquake data. Well data tied to seismic provides focal points for stratigraphic correlation. Although all the known producing hydrocarbon reservoirs of the offshore are Jurassic sands, interpretation of Permian and Triassic stratigraphy provides knowledge for future prospect drilling risk assessment, both onshore and offshore.
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Lawton, Timothy F., Jeffrey M. Amato, Sarah E. K. Machin, John C. Gilbert y Spencer G. Lucas. "Transition from Late Jurassic rifting to middle Cretaceous dynamic foreland, southwestern U.S. and northwestern Mexico". GSA Bulletin 132, n.º 11-12 (8 de abril de 2020): 2489–516. http://dx.doi.org/10.1130/b35433.1.
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Abstract Subsidence history and sandstone provenance of the Bisbee basin of southwestern New Mexico, southern Arizona, and northern Sonora, Mexico, demonstrate basin evolution from an array of Late Jurassic–Early Cretaceous rift basins to a partitioned middle Cretaceous retroarc foreland basin. The foreland basin contained persistent depocenters that were inherited from the rift basin array and determined patterns of Albian–early Cenomanian sediment routing. Upper Jurassic and Valanginian–Aptian strata were deposited in three narrow extensional basins, termed the Altar-Cucurpe, Huachuca, and Bootheel basins. Initially rapid Late Jurassic subsidence in the basins slowed in the Early Cretaceous, then increased again from mid-Albian through middle Cenomanian time, marking an episode of foreland subsidence. Sandstone composition and detrital zircon provenance indicate different sediment sources in the three basins and demonstrate their continued persistence as depocenters during Albian foreland basin development. Late Jurassic basins received sediment from a nearby magmatic arc that migrated westward with time. Following a 10–15 m.y. depositional hiatus, an Early Cretaceous continental margin arc supplied sediment to the Altar-Cucurpe basin in Sonora as early as ca. 136 Ma, but local sedimentary and basement sources dominated the Huachuca basin of southern Arizona until catchment extension tapped the arc source at ca. 123 Ma. The Bootheel basin of southwestern New Mexico received sediment only from local basement and recycled sedimentary sources with no contemporary arc source evident. During renewed Albian–Cenomanian subsidence, the arc continued to supply volcanic-lithic sand to the Altar-Cucurpe basin, which by then was the foredeep of the foreland basin. Sandstone of the Bootheel basin is more quartzose than the Altar-Cucurpe basin, but uncommon sandstone beds contain neovolcanic lithic fragments and young zircon grains that were transported to the basin as airborne ash. Latest Albian–early Cenomanian U-Pb tuff ages, detrital zircon maximum depositional ages ranging from ca. 102 Ma to 98 Ma, and ammonite fossils all demonstrate equivalence of middle Cretaceous proximal foreland strata of the U.S.-Mexico border region with distal back-bulge strata of the Cordilleran foreland basin. Marine strata buried a former rift shoulder in southwestern New Mexico during late Albian to earliest Cenomanian time (ca. 105–100 Ma), prior to widespread transgression in central New Mexico (ca. 98 Ma). Lateral stratigraphic continuity across the former rift shoulder likely resulted from regional dynamic subsidence following late Albian collision of the Guerrero composite volcanic terrane with Mexico and emplacement of the Farallon slab beneath the U.S.–Mexico border region. Inferred dynamic subsidence in the foreland of southern Arizona and southwestern New Mexico was likely augmented in Sonora by flexural subsidence adjacent to an incipient thrust load driven by collision of the Guerrero superterrane.
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Leat, P. T., J. H. Scarrow y I. L. Millar. "On the Antarctic Peninsula batholith". Geological Magazine 132, n.º 4 (julio de 1995): 399–412. http://dx.doi.org/10.1017/s0016756800021464.
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AbstractThe plutonic rocks of the Antarctic Peninsula magmatic arc form one of the major batholiths of the circum-Pacific rim. The Antarctic Peninsula batholith is a 1350 km long by < 210 km wide structure which was emplaced over the period ˜240 to 10 Ma, with a Cretaceous peak of activity that started at 142 Ma and waned during the Late Cretaceous. Early Jurassic and Late Jurassic–Early Cretaceous gaps in intrusive activity probably correspond to episodes of arc compression. In a northern zone of the Antarctic Peninsula, the batholith intrudes Palaeozoic–Mesozoic low-grade meta-sedimentary rocks, and in a central zone it intrudes schists and ortho- and paragneisses which have Late Proterozoic Nd model ages and were deformed during Triassic to Early Jurassic compression. In a southern zone the oldest exposed rocks are Permian sedimentary rocks and deformed Jurassic volcanic and sedimentary rocks. All these pre-batholith rocks formed a belt of relatively immature crust along the Gondwana margin. With few exceptions, Jurassic plutons crop out only within the central zone: many are peraluminous, having ‘S-like’ mineralogies and relatively high 87sr/86sri. They are considered to consist largely of partial melts of upper crust schists and gneisses and components of mafic magmas that caused the partial fusion. By contrast, Early Cretaceous plutons crop out along the length of the batholith. Few magma compositions appear to have been affected by upper crust, the bulk being compositionally independent of the type of country rock they intrude. They are dominated by metaluminous, calcic, Si-oversaturated, 1-type granitoid rocks with relatively low 87sr/86sri intermediate-silicic compositions (< 5% MgO). We interpret these to represent partial melts of basic to intermediate, igneous, locally garnet-bearing, lower crust. Contemporaneous mafic magmas (e.g. syn-plutonic dykes) form a more alkaline, Si-saturated series having higher 143Nd/144Nd at the same87sr/86sr than the intermediate-silicic series, to which they are not petrogenetically related. The change from limited partial fusion of upper crust in Jurassic times to widespread partial fusion of lower crust in Early Cretaceous times is considered to be a result of an increasing volume of basaltic intrusion into the crust with time.
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Chao, Hui, Mingcai Hou, Wenjian Jiang, Haiyang Cao, Xiaolin Chang, Wen Luo y James G. Ogg. "Paleoclimatic and Redox Condition Changes during Early-Middle Jurassic in the Yili Basin, Northwest China". Minerals 11, n.º 7 (24 de junio de 2021): 675. http://dx.doi.org/10.3390/min11070675.
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The Jurassic was mainly a “greenhouse” period characterized by global warming and by significant peat accumulations in some continental basins. However, studies of Jurassic climate and environments have mainly focused on marine records and only a few on terrestrial sediments. Yili Basin, a mid-latitude terrestrial basin in present Northwest China, included accumulation of the important recoverable coal seams. In this study, geological data, clay mineral analysis, and palynological assemblages were employed on fine-grained samples from the Su’asugou section in southern Yili Basin. The factors (paleoclimate, depositional conditions, and paleo-vegetation) impacting peat accumulation were investigated. The results suggest that the siliciclastics may have been derived from exposed Carboniferous rocks in a continental arc environment. A warm and humid paleoclimate in the Yili basin dominated during the early-Early Jurassic deposition of the Badaowan Formation and the Middle Jurassic deposition of the Xishanyao Formation. This climate contributed to high sedimentary rates and to a high productivity of peat-forming paleo-vegetation that was preserved under dysoxic conditions. In contrast, during the late-Early Jurassic between these two formations, the Sangonghe Formation was an interval of relatively aridity that included red beds preserved under more hypoxic sedimentary conditions, and with an interruption in peat formation and preservation.
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Umhoefer, Paul J. "Stratigraphy and tectonic setting of the upper part of the Cadwallader terrane, southwestern British Columbia". Canadian Journal of Earth Sciences 27, n.º 5 (1 de mayo de 1990): 702–11. http://dx.doi.org/10.1139/e90-069.
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The Upper Triassic to Middle Jurassic Cadwallader terrane lies on the northeastern edge of the Coast Plutonic Complex in southwestern British Columbia. Previous work on the Cadwallader Group, the basal unit of the terrane, suggested it was an Upper Triassic (Carnian to middle Norian) volcanic arc and related clastic rocks. Volcanism ceased in early Norian time. A detailed study of the upper part of the Cadwallader terrane (Tyaughton Group and overlying Last Creek formation) shows that it is a sedimentary sequence deposited on the fringe of the inactive Cadwallader magmatic arc. The Upper Triassic (middle to upper Norian) Tyaughton Group consists of nonmarine to shallow-marine clastic rocks and limestones that show sudden changes in depositional setting. The Lower to Middle Jurassic Last Creek formation, a transgressive sequence of clastic rocks, disconformably overlies the Tyaughton Group. The clastic rocks in the two units were derived from a mixed volcanic and plutonic source region that also included a minor metamorphic component and local lower Norian limestones. The stratigraphy of the upper part of the Cadwallader terrane records long-term thermal subsidence of the basin caused by cooling of the magmatic arc after volcanism ceased in the early Norian. The detailed stratigraphy of the upper Cadwallader terrane supports correlation of the Cadwallader with the Stikine terrane, along which it is currently structurally juxtaposed.
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Mortimer, N. "The Nicola Group: Late Triassic and Early Jurassic subduction-related volcanism in British Columbia". Canadian Journal of Earth Sciences 24, n.º 12 (1 de diciembre de 1987): 2521–36. http://dx.doi.org/10.1139/e87-236.
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Mafic lavas of the Nicola Group are divided into three distinct petrographic and geochemical types: type 1 lavas are strongly augite-porphyritic picrites, basalts, and andesites that belong to a high-potassium to shoshonitic rock series; type 2 lavas are augite- and plagioclase-porphyritic basalts and andesites that belong to a low-potassium calc-alkaline series; and type 3 lavas are petrographically variable tholeiitic to transitional basalts and andesites.Low concentrations of Ti, Zr, Y, and Nb and moderate to high concentrations of K, Rb, Ba, and Sr in type 1 and 2 lavas clearly indicate a subduction-related tectonic setting of eruption. Type 3 lavas show chemical affinities intermediate between modern-day island-arc and intraplate volcanics. Type 1 (shoshonitic) lavas generally lie east of and are younger than type 2 (calc-alkaline) lavas, a relationship that implies an east-dipping early Mesozoic subduction zone beneath the Nicola arc. These interpretations resolve previous uncertainties regarding the tectonic setting of eruption of the Nicola Group.Several major 205–220 Ma plutons that intrude the Nicola Group crystallized from type 1 and 2 magmas and represent the final stages of Late Triassic to Early Jurassic arc-related igneous activity in southern Quesnellia.
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Mahoney, J. Brian, Richard M. Friedman y Sean D. McKinley. "Evolution of a Middle Jurassic volcanic arc: stratigraphic, isotopic, and geochemical characteristics of the Harrison Lake Formation, southwestern British Columbia". Canadian Journal of Earth Sciences 32, n.º 10 (1 de octubre de 1995): 1759–76. http://dx.doi.org/10.1139/e95-137.
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The Harrison Lake Formation is an Early to Middle Jurassic volcanic-arc assemblage unconformably overlying Triassic oceanic basement in the eastern Coast Belt of southwestern British Columbia. The formation is subdivided into four members including, in ascending order, the Celia Cove Member (conglomerate), the Francis Lake Member (fine-grained strata), the Weaver Lake Member (flows and breccias), and the Echo Island Member (pyroclastic and epiclastic strata). New biostratigraphic constraints pinpoint the initiation of volcanism to late early Toarcian. U–Pb geochronology demonstrates the arc was active until at least late Bajocian–early Bathonian time (166.0 ± 0.4 Ma), and that the timing of arc volcanism strongly overlaps emplacement of both hypabyssal intrusions (Hemlock Valley stock) and deep-seated plutons (Mount Jasper pluton) within and adjacent to the arc. Geochemical data indicate the arc is of medium- to high-K calc-alkaline affinity, and is strongly light rare earth element enriched (LaN/YbN = 1.5 – 2.5). Nd and Sr isotopic data from primary volcanic rocks demonstrate the juvenile nature of the magmatic system, but isotopic data from associated fine-grained sedimentary rocks suggest temporally controlled variations in isotopic composition interpreted to represent two-component mixing between juvenile volcanic detritus and a more evolved detrital component. The succession of facies in the Harrison Lake Formation records initial basin subsidence in the Early Jurassic, initiation of explosive volcanism in the late early Toarcian, a change to effusive volcanism in the early Aalenian, and late-stage explosive volcanism in the late Bajocian. The Harrison Lake Formation contains mesoscopic folds and overturned bedding that are absent in the overlying Callovian Mysterious Creek Formation, strongly suggesting the existence of a regional Bathonian deformational event in the southern Coast Belt.
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Rusmore, Margaret E. "Geology of the Cadwallader Group and the Intermontane–Insular superterrane boundary, southwestern British Columbia". Canadian Journal of Earth Sciences 24, n.º 11 (1 de noviembre de 1987): 2279–91. http://dx.doi.org/10.1139/e87-213.
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Several lower Mesozoic, fault-bounded units separate the Intermontane and Insular superterranes in southwestern British Columbia. Detailed study of one of these Mesozoic units, the Cadwallader Group, helps clarify the boundary between the superterranes and establish the tectonic evolution of southwestern British Columbia. The Cadwallader Group is the oldest unit in an Upper Triassic through Middle Jurassic volcanic and sedimentary tectono-stratigraphic terrane. Two formations, the Pioneer and the Hurley, compose the Cadwallader Group; the previously recognized Noel Formation is no longer considered valid. The Pioneer Formation contains pillow basalt, flows, and basalt breccia. Siltstone, sandstone, conglomerate, and minor amounts of limestone megabreccia and basalt belonging to the Hurley Formation conformably overlie the Pioneer. The Hurley spans latest Carnian or earliest Norian to middle Norian time. Two episodes of deformation affected the Cadwallader, and a thrust fault separates the group from slightly younger clastic rocks of the Tyaughton Group. Similarities in clastic rocks indicate the Tyaughton was deposited on the Cadwallader; together the units form the Cadwallader terrane. Basalts and clastic rocks in the terrane record deposition in or near a Carnian to earliest Norian volcanic arc. Volcanism waned later in the Norian, but presence of the arc is preserved in the clastic rocks.Oceanic rocks of the Middle Triassic to Middle Jurassic Bridge River terrane became juxtaposed with the Cadwallader terrane in Middle Jurassic time, after which the terranes functioned as a single tectonic block. Contrasting volcanic histories suggest that the Cadwallader terrane was not accreted to the Intermontane superterrane until Middle Jurassic or Early Cretaceous time, although the similar tectonic settings of Stikinia and the Cadwallader terrane allow a common earlier history. The Cadwallader terrane is not part of either the Alexander terrane or Wrangellia, and so the inboard margin of the Insular superterrane must lie west of the Cadwallader terrane.