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Sunlin Chung - One of the best experts on this subject based on the ideXlab platform.
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correlation between magmatism of the ladakh Batholith and plate convergence rates during the india eurasia collision
Gondwana Research, 2014Co-Authors: Gregory J Shellnutt, Michael Brookfield, Sunlin ChungAbstract:Abstract Evidence for episodic magmatism is found within large Batholiths of ancient and modern convergent margin settings and is often attributed to regional geodynamic changes such as an increase in plate convergence rate, lithospheric extension and/or delamination, and intra-crustal/lithospheric shortening. The nature and timing of collision between India and Eurasia remain contentious as many models suggest that the “hard” collision occurred during the Early Paleogene (65 to 45 Ma) whereas other models suggest younger ages (~ 34 Ma) or a diachronous collision. New zircon LA-ICPMS U/Pb ages from rocks of the Ladakh Batholith range from 47.7 ± 0.7 Ma to 57.6 ± 0.7 Ma and correspond to two main episodes of magmatism. The two major episodes of magmatism are correlative to changes in the convergence rate of the Indian and Eurasian plates. The formation of adakitic rocks within the Ladakh Batholith at 49.2 ± 1.2 Ma is facilitated by partial melting of a garnet-bearing thickened lower crust. Therefore we suggest that crustal thickening was initiated by the “hard” collision between India and Eurasia. The convergence slowdown is concurrent with an increase in magmatism within the Ladakh Batholith. Thus the collision is constrained by the decreasing convergence rates at ~ 52 Ma and formation of the adakitic rocks at ~ 49 Ma.
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early eocene crustal thickening in southern tibet new age and geochemical constraints from the gangdese Batholith
Journal of Asian Earth Sciences, 2012Co-Authors: Weiqiang Ji, Fuyuan Wu, Sunlin ChungAbstract:Abstract The Lhasa terrane, southern Tibet is where the thickest part of the Earth’s crust occurs as a result of the India–Asia collision. This paper reports zircon U–Pb age and geochemical data of samples collected from the Gangdese Batholith, southern Lhasa terrane, a subset of which has already been dated at 65–41 Ma using zircon U–Pb geochronology (Ji, W.Q., Wu, F.Y., Chung, S.L., Li, J.X., Liu, C.Z., 2009a. Zircon U–Pb chronology and Hf isotopic constraints on the petrogenesis of Gangdese Batholiths, southern Tibet. Chemical Geology 262, 229–245), to constrain the timing and mechanism(s) responsible for crustal thickening beneath southern Tibet. Our new data indicate that the Gangdese magmatism lasted continuously from ca. 65 to 34 Ma, during which geochemical evidence for crustal thickening is observed. Crustal thickening is best illustrated by the progressive increase in La/Yb and Sr/Y of the Early to latest Eocene magmatic rocks, associated with the decrease in Hf isotopic ratios of Paleocene to Eocene magmatic zircons. We also identify in this study the oldest (ca. 51 Ma), “post-collisional” adakitic granitoids in the Gangdese Batholith, interpreted as products from partial melting of underplated basaltic lower crust. Therefore, a thickened crust likely existed by that time, at least locally, in the southern Lhasa terrane, Tibet.
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india s hidden inputs to tibetan orogeny revealed by hf isotopes of transhimalayan zircons and host rocks
Earth and Planetary Science Letters, 2011Co-Authors: Sunlin Chung, Fuyuan Wu, Suzanne Y Oreilly, Norman J Pearson, Xianhua Li, Jianqing JiAbstract:Abstract To better understand Tibetan orogenesis, which involves complex tectonic processes, here we report the first integrated analysis of Hf isotopes of zircon separates and their host rocks from the Transhimalayan Batholiths. The rocks studied include 19 granitoids from different parts of the Gangdese Batholith, the largest Transhimalayan intrusive complex, and five postcollisional adakites that occurred as plugs or dikes cutting the Gangdese Batholith, in the southern Lhasa terrane, southern Tibet. Published zircon Hf isotope data from other Transhimalayan granitoids and the Linzizong volcanic rocks are also synthesized. The magmatic zircons, crystallizing between ca. 200 and 15 Ma, show depleted mantle-type Hf isotopic characteristics throughout the Mesozoic but shift markedly in the Paleogene. The Hf isotopic shift is interpreted as tracking the evolving progress of Himalayan sediment subduction driven by the approaching Indian continent, and thus signals the initiation of the India–Asia collision that we infer to have occurred by 55 Ma. Our data furthermore indicate that southern Tibet underwent significant crustal thickening during ca. 45 and 30 Ma, before emplacement of the postcollisional adakites that exhibit Hf–Nd isotopic systematics suggesting binary mixing of melts from the juvenile Gangdese mafic crust and incorporated Himalayan sediments in the petrogenesis.
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zircon u pb and hf isotopic constraints from eastern transhimalayan Batholiths on the precollisional magmatic and tectonic evolution in southern tibet
Tectonophysics, 2009Co-Authors: Hanyi Chiu, Sunlin Chung, Dunyi Liu, Yuhsuan Liang, Ijhen Lin, Yoshiyuki Iizuka, Liewen Xie, Yanbin Wang, Mei Fei ChuAbstract:Abstract Before the Indian collision with Asia, northward subduction of the Neo-Tethyan oceanic lithosphere produced an Andean-type convergent margin in South Asia characterized by arc magmatism starting from the early Jurassic and lasting until the Eocene. The magmatic arc is now represented by widespread intrusive bodies or the so-called Transhimalayan Batholiths in the Lhasa terrane of southern Tibet that have been divided into two main magmatic suites, i.e., the northern plutonic belt and the southern Gangdese Batholith. Their temporal distribution, concerning how exactly the magmatic suites correlate eastwards and then southeastwards around the eastern Himalayan syntaxis, however, remains poorly constrained. Here we report the first combined zircon U–Pb and Hf isotopic study of the Transhimalayan Batholiths from the eastern part of the Lhasa terrane (∼ 95–97.5°E and ∼ 28.5–30°N), SE Tibet. Zircon U–Pb dating results of 24 granitoids indicate that the rocks were emplaced principally in the Early Cretaceous (∼ 133–110 Ma) and subordinately in the Paleocene (∼ 66–57 Ma), long after an older granite intrusion in the earliest Jurassic (∼ 198 Ma). The zircon eHf(T) values range from + 5 to − 20, yielding Hf crustal model ages (TDMC) between 0.8 and 2.4 Ga that peak at ∼ 1.7 Ga, suggesting a major episode of crustal growth in the Proterozoic and a predominantly, or even exclusively, crustal source for the granitoid petrogenesis. These zircon U–Pb and Hf isotopic constraints, together with whole-rock geochemical characteristics, allow us to correlate them to S-type granitoids in the northern plutonic belt, rather than to the I-type Gangdese Batholith from the central part of the southern Lhasa terrane. In contrast to the Gangdese magmatism that formed with a significant juvenile mantle input related to the Neo-Tethyan subduction, these S-type granitoids show geochemical similarities to the North American Cordilleran Interior Batholiths that did not form directly from a subduction setting. Thus, we attribute the petrogenesis of the widespread Early Cretaceous granitoids in the northern belt and eastern Himalayan Batholiths to a postcollisional regime due to the Late Jurassic–Early Cretaceous continental collision between the Lhasa and Qiangtang terranes. Under this framework, the S-type magmatism was generated in response to collision-induced crustal thickening, which may have capabilities of causing crustal anatexis by itself in the region. However, continued interplay with the Neo-Tethyan subduction zone processes such as back-arc extension could also have played a crucial, and long-lasting, role in the magma generation.
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zircon u pb and hf isotopic constraints from eastern transhimalayan Batholiths on the precollisional magmatic and tectonic evolution in southern tibet
Tectonophysics, 2009Co-Authors: Hanyi Chiu, Fuyuan Wu, Sunlin Chung, Yuhsuan Liang, Yoshiyuki Iizuka, Yanbin WangAbstract:Abstract Before the Indian collision with Asia, northward subduction of the Neo-Tethyan oceanic lithosphere produced an Andean-type convergent margin in South Asia characterized by arc magmatism starting from the early Jurassic and lasting until the Eocene. The magmatic arc is now represented by widespread intrusive bodies or the so-called Transhimalayan Batholiths in the Lhasa terrane of southern Tibet that have been divided into two main magmatic suites, i.e., the northern plutonic belt and the southern Gangdese Batholith. Their temporal distribution, concerning how exactly the magmatic suites correlate eastwards and then southeastwards around the eastern Himalayan syntaxis, however, remains poorly constrained. Here we report the first combined zircon U–Pb and Hf isotopic study of the Transhimalayan Batholiths from the eastern part of the Lhasa terrane (∼ 95–97.5°E and ∼ 28.5–30°N), SE Tibet. Zircon U–Pb dating results of 24 granitoids indicate that the rocks were emplaced principally in the Early Cretaceous (∼ 133–110 Ma) and subordinately in the Paleocene (∼ 66–57 Ma), long after an older granite intrusion in the earliest Jurassic (∼ 198 Ma). The zircon eHf(T) values range from + 5 to − 20, yielding Hf crustal model ages (TDMC) between 0.8 and 2.4 Ga that peak at ∼ 1.7 Ga, suggesting a major episode of crustal growth in the Proterozoic and a predominantly, or even exclusively, crustal source for the granitoid petrogenesis. These zircon U–Pb and Hf isotopic constraints, together with whole-rock geochemical characteristics, allow us to correlate them to S-type granitoids in the northern plutonic belt, rather than to the I-type Gangdese Batholith from the central part of the southern Lhasa terrane. In contrast to the Gangdese magmatism that formed with a significant juvenile mantle input related to the Neo-Tethyan subduction, these S-type granitoids show geochemical similarities to the North American Cordilleran Interior Batholiths that did not form directly from a subduction setting. Thus, we attribute the petrogenesis of the widespread Early Cretaceous granitoids in the northern belt and eastern Himalayan Batholiths to a postcollisional regime due to the Late Jurassic–Early Cretaceous continental collision between the Lhasa and Qiangtang terranes. Under this framework, the S-type magmatism was generated in response to collision-induced crustal thickening, which may have capabilities of causing crustal anatexis by itself in the region. However, continued interplay with the Neo-Tethyan subduction zone processes such as back-arc extension could also have played a crucial, and long-lasting, role in the magma generation.
Michel Faure - One of the best experts on this subject based on the ideXlab platform.
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multiple emplacement and exhumation history of the late mesozoic dayunshan mufushan Batholith in southeast china and its tectonic significance 2 magnetic fabrics and gravity survey
Journal of Geophysical Research, 2018Co-Authors: Ya Che, Ke Che, Wei Wei, Michel FaureAbstract:The Late Mesozoic magmatic province is a prominent feature of the South China block (SCB). However, the tectonic regimes associated with the magmatism are still elusive. A combined anisotropy of magnetic susceptibility (AMS) and gravity study has been carried out to determine the fabric patterns and shape at depth of the Dayunshan–Mufushan composite Batholith in the north-central SCB. This is a companion paper to Part 1 that presented the structural and geochronological data of this Batholith. The magnetic fabrics in the Batholith interior predominantly reflect magma flow structures. Two distinct patterns of the magnetic lineations are defined, around NNE–SSW and WNW–ESE trends for the early-stage and late-stage intrusions of the Batholith, respectively. The gravity survey reveals that the early-stage intrusion has a main feeder zone located below its northern part while several linear feeder zones trending NNE–SSW are inferred for the late-stage intrusion. Integrating all results, a two-stage construction of the Batholith with distinct tectonic regimes has been established. It is concluded that the early-stage intrusion experienced a southward magma transport during its emplacement, partially assisted by far-field compression from the north at ca. 150 Ma. Conversely, the emplacement and exhumation of the late-stage intrusion was accommodated by a NW–SE crustal stretching involving a lateral magma expansion above the multiple feeder zones (likely corresponding to extensional fractures) and ductile shearing during 132–95 Ma localized mainly along the Dayunshan detachment fault. Finally, we discuss the geodynamic linkage between the Paleo-Pacific subduction and the Late Mesozoic tectono-magmatism in the SCB.
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multiple emplacement and exhumation history of the late mesozoic dayunshan mufushan Batholith in southeast china and its tectonic significance 1 structural analysis and geochronological constraints
Journal of Geophysical Research, 2018Co-Authors: Michel Faure, Wenbin Ji, Yan ChenAbstract:The South China block (SCB) experienced a polyphase reworking by the Phanerozoic tectono-thermal events. To better understand its Late Mesozoic tectonics, an integrated multidisciplinary investigation has been conducted on the Dayunshan–Mufushan composite Batholith in the north-central SCB. This Batholith consists of two major intrusions that recorded distinct emplacement features. According to our structural analysis, two deformation events in relation to Batholith emplacement and subsequent exhumation are identified. The early one (D1) was observed mostly at the southern border of the Batholith, characterized by a top-to-the-SW ductile shearing in the early-stage intrusion and along its contact zone. This deformation, chiefly associated with the pluton emplacement at ca. 150 Ma, was probably assisted by far-field compression from the Yangtze foreland belt. The second but main event (D2) involved two phases: (1) ductile shearing (D2a) prominently expressed along the Dayunshan detachment fault at the western border of the Batholith where the syntectonic late-stage intrusion and minor metasedimentary basement in the footwall suffered mylonitization with top-to-the-NW kinematics; (2) subsequent brittle faulting (D2b) further exhumed the entire Batholith that behaved as rift shoulder with half-graben basins developed on its both sides. Geochronological constraints show that the crustal ductile extension occurred during 132–95 Ma. Such a Cretaceous NW–SE extensional tectonic regime, as indicated by the D2 event, has been recognized in a vast area of East Asia. This tectonism was responsible not only for the destruction of the North China craton but also for the formation of the so-called "Southeast China basin and range tectonics".
Wenbin Ji - One of the best experts on this subject based on the ideXlab platform.
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multiple emplacement and exhumation history of the late mesozoic dayunshan mufushan Batholith in southeast china and its tectonic significance 1 structural analysis and geochronological constraints
Journal of Geophysical Research, 2018Co-Authors: Michel Faure, Wenbin Ji, Yan ChenAbstract:The South China block (SCB) experienced a polyphase reworking by the Phanerozoic tectono-thermal events. To better understand its Late Mesozoic tectonics, an integrated multidisciplinary investigation has been conducted on the Dayunshan–Mufushan composite Batholith in the north-central SCB. This Batholith consists of two major intrusions that recorded distinct emplacement features. According to our structural analysis, two deformation events in relation to Batholith emplacement and subsequent exhumation are identified. The early one (D1) was observed mostly at the southern border of the Batholith, characterized by a top-to-the-SW ductile shearing in the early-stage intrusion and along its contact zone. This deformation, chiefly associated with the pluton emplacement at ca. 150 Ma, was probably assisted by far-field compression from the Yangtze foreland belt. The second but main event (D2) involved two phases: (1) ductile shearing (D2a) prominently expressed along the Dayunshan detachment fault at the western border of the Batholith where the syntectonic late-stage intrusion and minor metasedimentary basement in the footwall suffered mylonitization with top-to-the-NW kinematics; (2) subsequent brittle faulting (D2b) further exhumed the entire Batholith that behaved as rift shoulder with half-graben basins developed on its both sides. Geochronological constraints show that the crustal ductile extension occurred during 132–95 Ma. Such a Cretaceous NW–SE extensional tectonic regime, as indicated by the D2 event, has been recognized in a vast area of East Asia. This tectonism was responsible not only for the destruction of the North China craton but also for the formation of the so-called "Southeast China basin and range tectonics".
Fuyuan Wu - One of the best experts on this subject based on the ideXlab platform.
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early eocene crustal thickening in southern tibet new age and geochemical constraints from the gangdese Batholith
Journal of Asian Earth Sciences, 2012Co-Authors: Weiqiang Ji, Fuyuan Wu, Sunlin ChungAbstract:Abstract The Lhasa terrane, southern Tibet is where the thickest part of the Earth’s crust occurs as a result of the India–Asia collision. This paper reports zircon U–Pb age and geochemical data of samples collected from the Gangdese Batholith, southern Lhasa terrane, a subset of which has already been dated at 65–41 Ma using zircon U–Pb geochronology (Ji, W.Q., Wu, F.Y., Chung, S.L., Li, J.X., Liu, C.Z., 2009a. Zircon U–Pb chronology and Hf isotopic constraints on the petrogenesis of Gangdese Batholiths, southern Tibet. Chemical Geology 262, 229–245), to constrain the timing and mechanism(s) responsible for crustal thickening beneath southern Tibet. Our new data indicate that the Gangdese magmatism lasted continuously from ca. 65 to 34 Ma, during which geochemical evidence for crustal thickening is observed. Crustal thickening is best illustrated by the progressive increase in La/Yb and Sr/Y of the Early to latest Eocene magmatic rocks, associated with the decrease in Hf isotopic ratios of Paleocene to Eocene magmatic zircons. We also identify in this study the oldest (ca. 51 Ma), “post-collisional” adakitic granitoids in the Gangdese Batholith, interpreted as products from partial melting of underplated basaltic lower crust. Therefore, a thickened crust likely existed by that time, at least locally, in the southern Lhasa terrane, Tibet.
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india s hidden inputs to tibetan orogeny revealed by hf isotopes of transhimalayan zircons and host rocks
Earth and Planetary Science Letters, 2011Co-Authors: Sunlin Chung, Fuyuan Wu, Suzanne Y Oreilly, Norman J Pearson, Xianhua Li, Jianqing JiAbstract:Abstract To better understand Tibetan orogenesis, which involves complex tectonic processes, here we report the first integrated analysis of Hf isotopes of zircon separates and their host rocks from the Transhimalayan Batholiths. The rocks studied include 19 granitoids from different parts of the Gangdese Batholith, the largest Transhimalayan intrusive complex, and five postcollisional adakites that occurred as plugs or dikes cutting the Gangdese Batholith, in the southern Lhasa terrane, southern Tibet. Published zircon Hf isotope data from other Transhimalayan granitoids and the Linzizong volcanic rocks are also synthesized. The magmatic zircons, crystallizing between ca. 200 and 15 Ma, show depleted mantle-type Hf isotopic characteristics throughout the Mesozoic but shift markedly in the Paleogene. The Hf isotopic shift is interpreted as tracking the evolving progress of Himalayan sediment subduction driven by the approaching Indian continent, and thus signals the initiation of the India–Asia collision that we infer to have occurred by 55 Ma. Our data furthermore indicate that southern Tibet underwent significant crustal thickening during ca. 45 and 30 Ma, before emplacement of the postcollisional adakites that exhibit Hf–Nd isotopic systematics suggesting binary mixing of melts from the juvenile Gangdese mafic crust and incorporated Himalayan sediments in the petrogenesis.
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zircon u pb and hf isotopic constraints from eastern transhimalayan Batholiths on the precollisional magmatic and tectonic evolution in southern tibet
Tectonophysics, 2009Co-Authors: Hanyi Chiu, Fuyuan Wu, Sunlin Chung, Yuhsuan Liang, Yoshiyuki Iizuka, Yanbin WangAbstract:Abstract Before the Indian collision with Asia, northward subduction of the Neo-Tethyan oceanic lithosphere produced an Andean-type convergent margin in South Asia characterized by arc magmatism starting from the early Jurassic and lasting until the Eocene. The magmatic arc is now represented by widespread intrusive bodies or the so-called Transhimalayan Batholiths in the Lhasa terrane of southern Tibet that have been divided into two main magmatic suites, i.e., the northern plutonic belt and the southern Gangdese Batholith. Their temporal distribution, concerning how exactly the magmatic suites correlate eastwards and then southeastwards around the eastern Himalayan syntaxis, however, remains poorly constrained. Here we report the first combined zircon U–Pb and Hf isotopic study of the Transhimalayan Batholiths from the eastern part of the Lhasa terrane (∼ 95–97.5°E and ∼ 28.5–30°N), SE Tibet. Zircon U–Pb dating results of 24 granitoids indicate that the rocks were emplaced principally in the Early Cretaceous (∼ 133–110 Ma) and subordinately in the Paleocene (∼ 66–57 Ma), long after an older granite intrusion in the earliest Jurassic (∼ 198 Ma). The zircon eHf(T) values range from + 5 to − 20, yielding Hf crustal model ages (TDMC) between 0.8 and 2.4 Ga that peak at ∼ 1.7 Ga, suggesting a major episode of crustal growth in the Proterozoic and a predominantly, or even exclusively, crustal source for the granitoid petrogenesis. These zircon U–Pb and Hf isotopic constraints, together with whole-rock geochemical characteristics, allow us to correlate them to S-type granitoids in the northern plutonic belt, rather than to the I-type Gangdese Batholith from the central part of the southern Lhasa terrane. In contrast to the Gangdese magmatism that formed with a significant juvenile mantle input related to the Neo-Tethyan subduction, these S-type granitoids show geochemical similarities to the North American Cordilleran Interior Batholiths that did not form directly from a subduction setting. Thus, we attribute the petrogenesis of the widespread Early Cretaceous granitoids in the northern belt and eastern Himalayan Batholiths to a postcollisional regime due to the Late Jurassic–Early Cretaceous continental collision between the Lhasa and Qiangtang terranes. Under this framework, the S-type magmatism was generated in response to collision-induced crustal thickening, which may have capabilities of causing crustal anatexis by itself in the region. However, continued interplay with the Neo-Tethyan subduction zone processes such as back-arc extension could also have played a crucial, and long-lasting, role in the magma generation.
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zircon u pb geochronology and hf isotopic constraints on petrogenesis of the gangdese Batholith southern tibet
Chemical Geology, 2009Co-Authors: Weiqiang Ji, Fuyuan Wu, Sunlin Chung, Jinxiang LiAbstract:Abstract During the Mesozoic–Cenozoic, northward Neotethyan subduction and subsequent India–Asia collision gave rise to the extensive Transhimalayan magmatism that stretches from Burma and western Yunnan through southern Tibet to the Ladakh and Kohistan complexes. To understand the age distribution and petrogenesis of the Gangdese Batholith, the largest intrusive exposure along the Transhimalayan magmatic belt, fifty granitic samples were selected for in situ zircon U–Pb and Hf isotopic analyses. The U–Pb data suggest four discrete stages of magmatic activity, i.e., ~ 205–152, ~ 109–80, ~ 65–41 and ~ 33–13 Ma, respectively, with the 65–41 Ma stage being the most prominent. The Hf isotopic data indicate that the Gangdese Batholith is overwhelmed by positive e Hf ( t ) values, which are comparable to those of the Kohistan–Ladakh Batholiths in the west but differ markedly from those of the Chayu–Burma Batholiths in the east. Most of the Gangdese granites show similar and young Hf model ages (1000–300 Ma), indicating their derivation from juvenile crust. However, those formed in the 65–41 Ma stage exhibit more heterogeneous Hf isotopic ratios, with negative e Hf ( t ) values being observed in some granites younger than 50 Ma, suggesting the involvement of old Indian continental crust in their petrogenesis. This age may thus mark the onset of the India–Asia collision. The newly established zircon U–Pb age and Hf isotope database of the Gangdese Batholith can be used as a powerful tracer or “fingerprint” when studying the source-to-sink relation of the sediments eroded from the southern Tibetan Plateau.
Scott R Paterson - One of the best experts on this subject based on the ideXlab platform.
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post emplacement fluids and pluton thermobarometry mount stuart Batholith washington cascades
International Geology Review, 2012Co-Authors: Lawford J Anderson, Jean Morrison, Scott R PatersonAbstract:The effects of post-emplacement infiltration of externally derived, high-temperature fluids into arc-related Batholiths are often not well characterized. Such infiltration can have far-reaching effects on the elemental and light isotopic chemistry of a Batholith and on its mineral phases. At high temperature, fluid infiltration can be less easily detected, especially if widespread. The Mount Stuart Batholith of the Washington Cascades is offered as an example of high-temperature infiltration of high δ18O fluids derived from its contact aureole. Some of the fluid infiltration coincided with and may have been partly derived from a kyanite-grade, post-emplacement metamorphic event that affected northern portions of the Batholith. However, the effects of the fluid infiltration were far reaching and affected the entire margin of the Batholith, including southerly portions that did not experience post-emplacement metamorphism. The result led to an oxygen isotopic zonation of the Batholith, which is viewed as se...
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magmatic lobes as snapshots of magma chamber growth and evolution in large composite Batholiths an example from the tuolumne intrusion sierra nevada california
Geological Society of America Bulletin, 2010Co-Authors: Valbone Memeti, Scott R Paterson, J E P Matzel, Roland Mundil, D A OkayaAbstract:Precise chemical abrasion–thermal ionization mass spectrometry (CA-TIMS) U-Pb zircon ages in combination with detailed field mapping, 40 Ar/ 39 Ar thermochronology, and finite difference thermal modeling in the magmatic lobes of the Tuolumne Batholith characterize these 10–60 km 2 bodies as shorter-lived, simpler magmatic systems that represent increments of Batholith growth. Lobes provide shorter-term records of internal and external processes that are potentially obliterated in the main body of long-lived, composite Batholiths. Zircon ages complemented by thermal modeling indicate that lobe-sized magma chambers were present between ∼0.2 and 1 m.y., representing only a small fraction of the total duration of melt presence in the main body. During these shorter intervals, a concentric pattern of normal compositional zoning formed during inward crystallization and widespread zircon recycling in the lobes. Lobes largely evolved as individual magma bodies that did not interact significantly with the main, more complex magma chamber(s). Antecrystic zircons and the range of autocrysts, used to track the extent of interconnected melt, record only a limited range of ages and have contrasting zircon populations to those found in the same units in the main Batholith. We consider lobes to either be single batches formed during continuous magma flow or multiple, quickly coalescing pulses that in either case formed separate magma chambers that failed to amalgamate with other compositionally distinct pulses such as those occurring in the central Batholith. Zircon age comparisons between all four lobes and the main body imply that growth of the Tuolumne intrusion was not stationary, but that the locus of magmatism shifted both inward and northwestward.
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Magmatic erosion of the solidification front during reintrusion: the eastern margin of the Tuolumne Batholith, Sierra Nevada, California
International Journal of Earth Sciences, 2010Co-Authors: Scott R PatersonAbstract:The Tuolumne Batholith, Sierra Nevada, California, consists of several nested granitoid units and is an example of upper-crustal normally zoned intrusions. The two outermost units of the Batholith are separated by a wide gradational contact in what is interpreted to represent a large magma chamber. In the Potter Point area near the eastern margin of the Batholith, the gradational contact is cross-cut by a network of interconnected mafic–felsic sheets, which grade into zones of magmatic erosion by stoping where the host granodiorite between the sheets was entirely removed and replaced by younger enclave-rich quartz diorite. We interpret these features to record disruption of a steep solidification front, which migrated inwards from the eastern Batholith margin and separated the mushy to solidified margin from the remaining active magma chamber. When intersecting the gradational contact, the solidification front started to break up via a network of tectonically driven fractures accompanied by simultaneous injection of localized magma pulses. The solidification front break-up is interpreted here as an initial stage of a “recycling” process, whereby older magma mush is disrupted and incorporated into younger magma batches, a process we propose to have been widespread along internal contacts in the Tuolumne magma chamber.
