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Devon A. Orme - One of the best experts on this subject based on the ideXlab platform.
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Burial and exhumation history of the Xigaze Forearc Basin, Yarlung suture zone, Tibet
Elsevier, 2019Co-Authors: Devon A. OrmeAbstract:The Cretaceous–Eocene Xigaze Forearc Basin is a crucial data archive for understanding the tectonic history of the Asian continental margin prior to and following collision with India during the early Cenozoic Era. This study reports apatite and zircon (U–Th)/He thermochronologic data from fourteen samples from Albian-Ypresian Xigaze Forearc strata to determine the degree and timing of heating (burial) and subsequent cooling (exhumation) of two localities along the Yarlung suture zone (YSZ) near the towns of Saga and Lazi. Thirty-seven individual zircon He ages range from 31.5 ± 0.8 Ma to 6.06 ± 0.18 Ma, with the majority of grains yielding ages between 30 Ma and 10 Ma. Twenty apatite He ages range from 12.7 ± 0.5 Ma to 3.9 ± 0.3 Ma, with the majority of grains yielding ages between 9 Ma and 4 Ma. These ages suggest that the Xigaze Forearc Basin was heated to 140–200 °C prior to cooling in Oligocene–Miocene time. Thermal modeling supports this interpretation and shows that the samples were buried to maximum temperatures of ∼140–200 °C by 35–21 Ma, immediately followed by the onset of exhumation. The zircon He and apatite He dataset and thermal modeling results indicate rapid exhumation from ∼21 Ma to 15 Ma, and at ∼4 Ma. The 21–15 Ma thermochronometric signal appears to be regionally extensive, affecting all the lithotectonic units of the YSZ, and coincides with movement along the north-vergent Great Counter Thrust system. Thrusting, coupled with enhanced erosion possibly related to the paleo-Yarlung River, likely drove Early Miocene cooling of the Xigaze Forearc Basin. In contrast, the younger phase of rapid exhumation at ∼4 Ma was likely driven by enhanced rock uplift in the footwall of north-striking rifts that cross-cut the YSZ. Keywords: Xigaze, Tibet, Forearc Basin, Thermochronology, Yarlun
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Burial and exhumation history of the Xigaze Forearc Basin, Yarlung suture zone, Tibet
Geoscience Frontiers, 2019Co-Authors: Devon A. OrmeAbstract:Abstract The Cretaceous–Eocene Xigaze Forearc Basin is a crucial data archive for understanding the tectonic history of the Asian continental margin prior to and following collision with India during the early Cenozoic Era. This study reports apatite and zircon (U–Th)/He thermochronologic data from fourteen samples from Albian-Ypresian Xigaze Forearc strata to determine the degree and timing of heating (burial) and subsequent cooling (exhumation) of two localities along the Yarlung suture zone (YSZ) near the towns of Saga and Lazi. Thirty-seven individual zircon He ages range from 31.5 ± 0.8 Ma to 6.06 ± 0.18 Ma, with the majority of grains yielding ages between 30 Ma and 10 Ma. Twenty apatite He ages range from 12.7 ± 0.5 Ma to 3.9 ± 0.3 Ma, with the majority of grains yielding ages between 9 Ma and 4 Ma. These ages suggest that the Xigaze Forearc Basin was heated to 140–200 °C prior to cooling in Oligocene–Miocene time. Thermal modeling supports this interpretation and shows that the samples were buried to maximum temperatures of ∼140–200 °C by 35–21 Ma, immediately followed by the onset of exhumation. The zircon He and apatite He dataset and thermal modeling results indicate rapid exhumation from ∼21 Ma to 15 Ma, and at ∼4 Ma. The 21–15 Ma thermochronometric signal appears to be regionally extensive, affecting all the lithotectonic units of the YSZ, and coincides with movement along the north-vergent Great Counter Thrust system. Thrusting, coupled with enhanced erosion possibly related to the paleo-Yarlung River, likely drove Early Miocene cooling of the Xigaze Forearc Basin. In contrast, the younger phase of rapid exhumation at ∼4 Ma was likely driven by enhanced rock uplift in the footwall of north-striking rifts that cross-cut the YSZ.
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Sedimentology, provenance and geochronology of the upper Cretaceous-lower Eocene western Xigaze Forearc Basin, southern Tibet
Basin Research, 2014Co-Authors: Devon A. Orme, Barbara Carrapa, Paul KappAbstract:Located on the southern margin of the Lhasa terrane in southern Tibet, the Xigaze Forearc Basin records Cretaceous to lower Eocene sedimentation along the southern margin of Asia, prior to and during the initial stages of continental collision with the Tethyan Himalaya in the Early Eocene. We present new measured stratigraphic sections, totalling 4.5 km stratigraphic thickness, from a 60 km E–Wsegment of the western portion of the Xigaze Forearc Basin, northeast of the Lopu Kangri Range (29.8007° N, 84.91827° E). In addition, we apply U–Pb detrital zircon geochronology to constrain the provenance and maximum depositional ages of investigated strata. Stratigraphic ages range between ca. 88 and ca. 54 Ma and sedimentary facies indicate a shoaling-upward trend from deepmarine turbidites to fluvial deposits. Depositional environments of coeval Cretaceous strata along strike include deep-marine distal turbidites, slope-apron debris-flow deposits and marginal marine carbonates. This along-strike variability in facies suggests an irregular paleogeography of the Asian margin prior to collision. Paleocene–Eocene strata are composed of shallow marine carbonates with abundant foraminifera such as Nummulites-Discocyclina and Miscellanea-Daviesina and transition into fluvial deposits dated at ca. 54 Ma. Sandstone modal analyses, conglomerate clast compositions and detrital zircon U–Pb geochronology indicate that Forearc detritus in this region was derived solely from the Gangdese magmatic arc to the north. In addition, U–Pb detrital zircon age spectra within the upper Xigaze Forearc stratigraphy are similar to those from Eocene foreland Basin strata south of the Indus-Yarlung suture near Sangdanlin, suggesting that the Xigaze Forearc was a possible source of Sangdanlin detritus by ca. 55 Ma. We propose a model in which the Xigaze Forearc prograded south over the accretionary prism and onto the advancing Tethyan Himalayan passive margin between 58 and 54 Ma, during late stage evolution of the Forearc Basin and the beginning of collision with the Tethyan Himalaya. The lack of documented Forearc strata younger than ca. 51 Ma suggests that sedimentation in the Forearc Basin ceased at this time owing to uplift resulting from continued continental collision.
Jiangang Wang - One of the best experts on this subject based on the ideXlab platform.
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The birth of the Xigaze Forearc Basin in southern Tibet
Earth and Planetary Science Letters, 2017Co-Authors: Jiangang Wang, Eduardo Garzanti, Xiao-chi LiuAbstract:Abstract The stratigraphic succession of a Forearc Basin provides crucial information on the history of a convergent plate margin. In particular, it helps to establish the origin of the underlying ophiolites and to unravel the earliest evolutionary stage of arc-trench systems, which remain poorly understood. The Xigaze Forearc Basin in southern Tibet is one of the best examples of a fossil Forearc Basin. This study illustrates detailed stratigraphic and high-precision SIMS U–Pb zircon geochronological and Hf isotopic data from the Chongdui Formation, representing the very base of the Xigaze Forearc-Basin succession, and reconstructs when and how the Basin was formed. The Chongdui Formation includes tuffaceous chert and siliceous mudrocks deposited directly on top of pillow basalts of the Xigaze ophiolite and conformably overlain by volcaniclastic turbidites. Tuff layers are interbedded throughout the unit, and their U–Pb zircon ages range from 119 to 113 Ma in the lower member and from 113 to 110 Ma in the upper member, broadly consistent with the established radiolarian biostratigraphy. U–Pb ages and Hf isotope signatures of zircons contained in both tuff layers and turbiditic sandstones indicate clear affinity with magmatic rocks of the Lhasa terrane. Direct depositional and chronostratigraphic relationship with the underlying oceanic crust, dated between 131 and 124 Ma, proves that the Xigaze ophiolite is the basement of the Xigaze Forearc Basin. After an initial prolonged stage of starved siliceous sedimentation, influx of terrigenous detritus began at 113–110 Ma, reflecting the onset of topographic growth and erosion of the Lhasa terrane in response to intense magmatic activity. Formation of the ophiolitic basement during the early stage of subduction and the subsequent topographic growth of the arc source induced by subduction-related magmatism are thus two critical factors for the birth of the Xigaze Forearc Basin. Similar stratigraphies were identified in the Great Valley and Luzon Central Valley Forearc Basins, suggesting that the initial geodynamic evolution of the Xigaze Forearc Basin may be common to many other Forearc Basins worldwide.
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new insights into the timing of the india asia collision from the paleogene quxia and jialazi formations of the xigaze Forearc Basin south tibet
Gondwana Research, 2016Co-Authors: Xiumian Hu, M K Boudagherfadel, Jiangang Wang, Eduardo Garzanti, Wei AnAbstract:Abstract The Xigaze Forearc Basin provides information on subduction evolution and magmatic growth of the Gangdese arc as well as on the India–Asia continental collision. Recently obtained sedimentological, biostratigraphic, petrographic, geochemical and geochronological data on Cretaceous to Paleogene strata in the Cuojiangding area (Zhongba county, south Tibet) shed new light on the tectonic evolution of the southern margin of the Lhasa Block during closure of Neotethys and initial collision with India. The uppermost Cretaceous Padana and Qubeiya formations, deposited in deltaic to inner shelf environments, and representing the final filling of the Xigaze Forearc Basin, were unconformably overlain by the Quxia and Jialazi formations, deposited in fan-delta environments during the Paleocene/earliest Eocene. Petrographic data and U–Pb ages of detrital zircons document the progressive unroofing of the Gangdese arc, which remained the dominant source of detritus throughout the Late Cretaceous to Paleogene. Detrital Cr-spinels in the Quxia and Jialazi formations are geochemically similar to those in Cretaceous Xigaze Forearc strata but different from those hosted in Yarlung Zangbo ophiolites, suggesting that the latter were not exposed to erosion in the considered time window. Sandstone petrography, Cr-spinel-geochemistry, U–Pb age spectra and Hf isotopic ratios of detrital zircons in the Quxia and Jialazi formations match those in Paleogene sediments deposited on the distal (Sangdanlin and Zheya formations) and proximal Indian margin (Enba and Zhaguo formations), suggesting that the Quxia and Jialazi formations documents syncollisional fan-deltas deposited on top of the nascent Himalayan orogenic belt. In this scenario, the onset of the India–Asia collision predates deposition of the Quxia and Jialazi formations and is thus constrained as younger than 66 Ma and older than 58 Ma.
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Xigaze Forearc Basin revisited (South Tibet): Provenance changes and origin of the Xigaze Ophiolite
Geological Society of America Bulletin, 2014Co-Authors: Eduardo Garzanti, Jiangang Wang, Marcelle K. Boudagher-fadel, Gaoyuan SunAbstract:Our new stratigraphic, sedimentological, and micropaleontological analysis, integrated with basalt geochemistry, sandstone petrography, and detrital-zircon U-Pb and Hf isotope data, suggests the revision of current models for the geological evolution of the Asian active margin during the Cretaceous. The Xigaze Forearc Basin began to form in the late Early Cretaceous, south of the Gangdese arc, during the initial subduction of the Neotethyan oceanic lithosphere under the Lhasa terrane. Well-preserved stratigraphic successions document the classical upwardshallowing pattern of the Forearc-Basin strata and elucidate the origin of the associated oceanic magmatic rocks. The normal midocean-ridge basalt (N-MORB) geochemical signature and stratigraphic contact with the overlying abyssal cherts (Chongdui Formation) indicate that the Xigaze Ophiolite formed by Forearc spreading and represents the basement of the Forearc sedimentary sequence. Volcaniclastic sedimentation began with thick turbiditic sandstones and interbedded shales in the late Albian–Santonian (Ngamring Formation) followed by shelfal, deltaic, and fl uvial strata (Padana Formation), with fi nal fi lling of the Basin by the Campanian age. Forearc sandstones do not show the classical trend from feldspatholithic volcaniclastic to quartzo-feldspathic plutoniclastic compositions, indicating limited unroofi ng of the Gangdese arc prior to collision. U-Pb age spectra of detrital zircons are unimodal with a 107 Ma peak in the lower Ngamring Formation (104–99 Ma), bimodal with a subordinate additional peak at 157 Ma in the middle Ngamring Formation (99– 88 Ma), and multimodal with more abundant pre-Mesozoic ages in the upper Ngamring and Padana Formations (88–76 Ma). These three petrofacies with distinct provenances document the progressive erosional evolution of the Gangdese arc, with uplift of the central Lhasa terrane and expanding river catchments to include the central Lhasa terrane during the Late Cretaceous.
Neil Lundberg - One of the best experts on this subject based on the ideXlab platform.
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destruction of luzon Forearc Basin from subduction to taiwan arc continent collision
Tectonophysics, 2009Co-Authors: Justin Hirtzel, Wu-cheng Chi, Donald L. Reed, Liwen Chen, Char-shine Liu, Neil LundbergAbstract:Abstract Along offshore to the east of southern Taiwan, different stages of subduction and collision occur simultaneously along strike of the convergent boundary. As a result, the evolution of the Luzon arc and its Forearc Basin can be studied from the younger subduction zone to the south to the collision zone to the north. Examining more than 8000 km of seismic lines, we analyzed the seismic stratigraphy of strata in a Forearc Basin and its successive Basins in the collision zone, to study the processes related to arc collapse and Forearc Basin closure. The study area presents three evolutional stages: intra-oceanic subduction, initial arc–continent collision, and arc–continent collision. We divided 9 seismic sequences in the Forearc Basin and found older, sub-parallel Basin-fill sequences (4–9) and younger, divergent sequences (1–3). Isochron maps of the sequences were used to interpret different deformation modes and their areal extends. On the arc side of the Basin of the subduction and initial collision zones, we found relatively undisturbed strata, showing little arc deformation. On the trench side, the growth strata in sequences 1 through 3 are the result of recent tectonic wedging along the rear of the accretionary prism. Tectonic wedging and back-thrusts incorporate the Forearc strata into the rear of the accretionary prism until they close the Forearc Basin at a region with a 2200 m basement relief. This relief is not caused by active deformation, as young flat Forearc strata lap onto it and mark the transition from initial collision to collision where many growth strata to the north suggest abrupt increase in active arc basement deformation. The (1) deforming basement, (2) back-thrusts, and (3) other sedimentary processes affect the architecture of the successive Basins in the collision zone until the arc is juxtaposed to the rear of the fold and thrust belt on land.
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Destruction of Luzon Forearc Basin from subduction to Taiwan arc–continent collision
Tectonophysics, 2009Co-Authors: Justin Hirtzel, Wu-cheng Chi, Donald L. Reed, Liwen Chen, Char-shine Liu, Neil LundbergAbstract:Abstract Along offshore to the east of southern Taiwan, different stages of subduction and collision occur simultaneously along strike of the convergent boundary. As a result, the evolution of the Luzon arc and its Forearc Basin can be studied from the younger subduction zone to the south to the collision zone to the north. Examining more than 8000 km of seismic lines, we analyzed the seismic stratigraphy of strata in a Forearc Basin and its successive Basins in the collision zone, to study the processes related to arc collapse and Forearc Basin closure. The study area presents three evolutional stages: intra-oceanic subduction, initial arc–continent collision, and arc–continent collision. We divided 9 seismic sequences in the Forearc Basin and found older, sub-parallel Basin-fill sequences (4–9) and younger, divergent sequences (1–3). Isochron maps of the sequences were used to interpret different deformation modes and their areal extends. On the arc side of the Basin of the subduction and initial collision zones, we found relatively undisturbed strata, showing little arc deformation. On the trench side, the growth strata in sequences 1 through 3 are the result of recent tectonic wedging along the rear of the accretionary prism. Tectonic wedging and back-thrusts incorporate the Forearc strata into the rear of the accretionary prism until they close the Forearc Basin at a region with a 2200 m basement relief. This relief is not caused by active deformation, as young flat Forearc strata lap onto it and mark the transition from initial collision to collision where many growth strata to the north suggest abrupt increase in active arc basement deformation. The (1) deforming basement, (2) back-thrusts, and (3) other sedimentary processes affect the architecture of the successive Basins in the collision zone until the arc is juxtaposed to the rear of the fold and thrust belt on land.
Sean P.s. Gulick - One of the best experts on this subject based on the ideXlab platform.
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Early sedimentation and deformation in the Kumano Forearc Basin linked with Nankai accretionary prism evolution, southwest Japan
Geochemistry Geophysics Geosystems, 2015Co-Authors: S. G. Ramirez, Sean P.s. Gulick, Nicholas W. HaymanAbstract:Early Forearc Basin sedimentation and subsidence appear to be linked with convergent margin evolution, yet they do not follow predictable spatiotemporal patterns. In the Kumano Basin of southwest Japan, 3-D seismic mapping of major unconformities, combined with biostratigraphic age constraints from two Integrated Ocean Drilling Program (IODP) drill sites illustrates the development of several tectonostratigraphic packages during early evolution and initial creation of accommodation space in the Forearc Basin. Between ∼3.8 Ma and ∼2.06 Ma, a series of slope Basins developed between thrust-anticlines oriented along a plate convergence-perpendicular axis. A thin and sheet-like interval, likely slope-cover, unconformably overlies the slope Basin sediments. Deposition of this interval at IODP Site C0009 lasted from ∼2.06 Ma until between ∼1.24 Ma and ∼1.34 Ma and was partly coeval with the early upper Kumano Basin sedimentary packages. Landward, postdating the slope-cover sediments, a third sedimentary package was deposited before ∼0.9 Ma. This section correlates with an interval rich in terrigenous material (e.g., woody debris), indicating a possible distinct source or sediment routing system. Our work supports the idea that early Forearc Basin sediments may be deposited in an actively deforming outer wedge environment and that the outer-to-inner wedge transition of the lower Forearc Basin is likely a multistage process. The unsteady spatiotemporal nature of inner-outer wedge coupling may lead to erratic stratigraphic patterns, such as have been observed in Forearc Basins worldwide.
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Rapid Forearc Basin uplift and megasplay fault development from 3D seismic images of Nankai Margin off Kii Peninsula, Japan
Earth and Planetary Science Letters, 2010Co-Authors: Sean P.s. Gulick, Gregory F. Moore, Juichiro Ashi, Harold Tobin, Nathan L. Bangs, K. M. Martin, Dale S. Sawyer, Shin'ichi Kuramoto, Asahiko TairaAbstract:Abstract Offshore Kii Peninsula, Japan, a large thrust within the overriding Forearc, the megasplay fault, appears to move coseismically during great earthquakes. 3D seismic images of the Kumano Forearc Basin that overlies the megasplay, correlated with IODP drilling data, are a potential record of the history of large-scale motion along this structure. In the early Quaternary, uplift occurred in the southwest portion of the Basin that may be a preliminary phase of motion along the megasplay. More extensive landward tilting of the outer Basin sediments across the seismic volume occurred over ~ 300 kyr in the middle to late Quaternary (1.3–1 Ma); this tilting event may represent the major period of motion along the megasplay that formed the modern fault geometry. Extensive normal faulting that cuts the Forearc Basin sediments clearly formed subsequent to the late Quaternary tilting and in many cases offset the modern seafloor; these faults may form either due to gravitational response to the uplift or as a by-product of sediment underthusting. These results suggest that the megasplay is a recently formed and transient structure and support the idea that out-of-sequence thrusts serving as the dominant structure for convergence-driven shortening in a subduction zone may be short-lived geologically but dominate a margin during these intervals.
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Effect of the northward-migrating Mendocino triple junction on the Eel River Forearc Basin, California: Structural evolution
Geological Society of America Bulletin, 2002Co-Authors: Sean P.s. Gulick, Anne S. MeltzerAbstract:Offshore northern California, the Gorda plate is subducting obliquely beneath North America; the resulting complicated tectonic setting forms the southern end of the Cascadia subduction zone. The southern Cascadia subduction zone and overlying Eel River Forearc Basin lie just north of the unstable Mendocino triple junction. The Neogene strata of the Eel River Basin record structural deformation caused by the underthrusting of the Gorda plate as well as deformation generated by northward migration and encroachment of the Mendocino triple junction. Three distinct deformation regimes are present in the Eel River Forearc Basin. (1) Along the western margin of the Forearc Basin and within the foreslope of the accretionary prism, thrust faults and anticlines record Pliocene– Pleistocene shortening caused by subduction of the Gorda plate. (2) The southern part of the Basin rotated counterclockwise in the late Pleistocene, resulting in modern transpressional deformation offshore Humboldt Bay. The rotation and deformation are caused by north-south convergence across the boundary between the Pacific plate and the southernmost part of the Forearc Basin at the triple junction. (3) The northeastern margin of the Eel River Basin is deformed by high-angle faults with a component of strike-slip motion that may represent the incipient northward propagation of the Pacific–North American transform system north of the triple junction.
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Effect of the northward-migrating Mendocino triple junction on the Eel River Forearc Basin, California: Stratigraphic development
Geological Society of America Bulletin, 2002Co-Authors: Sean P.s. Gulick, Anne S. Meltzer, Samuel H. ClarkeAbstract:The Eel River Forearc Basin, northern California, lies at the southern end of the Cascadia subduction zone and at the leading edge of the migrating Mendocino triple junction. Stratigraphic relationships within the Eel River Forearc Basin suggest that the current outer-arc high formed between ca. 3 and 2 Ma when the margin switched from a nonaccretionary to an accretionary phase and then uplifted to attain critical taper. Between ca. 2 and 1 Ma, an influx of sedimentation from the ancestral Klamath and Eel River systems increased the width of the northern California margin and caused continued uplift followed by widespread erosion of the western margin of the Basin at ca. 1 Ma. In the northeastern part of the Forearc Basin, localized erosion of the shelf occurred at ca. 500 ka. The arrival of the northward-migrating Mendocino triple junction at ca. 500 ka is documented by uplift, northward tilting, erosion of the margin as much as 20 km north of Cape Mendocino, and reduced deposition within the Forearc Basin as much as 80 km north of the current position of the triple junction. Terrestrial sediments delivered to the continental margin and eroded sediments near the triple junction largely bypassed the southern part of the Basin and were likely deposited in northern areas of the Basin or flowed down the Eel Canyon to be deposited within the Gorda Fan.
Eduardo Garzanti - One of the best experts on this subject based on the ideXlab platform.
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The birth of the Xigaze Forearc Basin in southern Tibet
Earth and Planetary Science Letters, 2017Co-Authors: Jiangang Wang, Eduardo Garzanti, Xiao-chi LiuAbstract:Abstract The stratigraphic succession of a Forearc Basin provides crucial information on the history of a convergent plate margin. In particular, it helps to establish the origin of the underlying ophiolites and to unravel the earliest evolutionary stage of arc-trench systems, which remain poorly understood. The Xigaze Forearc Basin in southern Tibet is one of the best examples of a fossil Forearc Basin. This study illustrates detailed stratigraphic and high-precision SIMS U–Pb zircon geochronological and Hf isotopic data from the Chongdui Formation, representing the very base of the Xigaze Forearc-Basin succession, and reconstructs when and how the Basin was formed. The Chongdui Formation includes tuffaceous chert and siliceous mudrocks deposited directly on top of pillow basalts of the Xigaze ophiolite and conformably overlain by volcaniclastic turbidites. Tuff layers are interbedded throughout the unit, and their U–Pb zircon ages range from 119 to 113 Ma in the lower member and from 113 to 110 Ma in the upper member, broadly consistent with the established radiolarian biostratigraphy. U–Pb ages and Hf isotope signatures of zircons contained in both tuff layers and turbiditic sandstones indicate clear affinity with magmatic rocks of the Lhasa terrane. Direct depositional and chronostratigraphic relationship with the underlying oceanic crust, dated between 131 and 124 Ma, proves that the Xigaze ophiolite is the basement of the Xigaze Forearc Basin. After an initial prolonged stage of starved siliceous sedimentation, influx of terrigenous detritus began at 113–110 Ma, reflecting the onset of topographic growth and erosion of the Lhasa terrane in response to intense magmatic activity. Formation of the ophiolitic basement during the early stage of subduction and the subsequent topographic growth of the arc source induced by subduction-related magmatism are thus two critical factors for the birth of the Xigaze Forearc Basin. Similar stratigraphies were identified in the Great Valley and Luzon Central Valley Forearc Basins, suggesting that the initial geodynamic evolution of the Xigaze Forearc Basin may be common to many other Forearc Basins worldwide.
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new insights into the timing of the india asia collision from the paleogene quxia and jialazi formations of the xigaze Forearc Basin south tibet
Gondwana Research, 2016Co-Authors: Xiumian Hu, M K Boudagherfadel, Jiangang Wang, Eduardo Garzanti, Wei AnAbstract:Abstract The Xigaze Forearc Basin provides information on subduction evolution and magmatic growth of the Gangdese arc as well as on the India–Asia continental collision. Recently obtained sedimentological, biostratigraphic, petrographic, geochemical and geochronological data on Cretaceous to Paleogene strata in the Cuojiangding area (Zhongba county, south Tibet) shed new light on the tectonic evolution of the southern margin of the Lhasa Block during closure of Neotethys and initial collision with India. The uppermost Cretaceous Padana and Qubeiya formations, deposited in deltaic to inner shelf environments, and representing the final filling of the Xigaze Forearc Basin, were unconformably overlain by the Quxia and Jialazi formations, deposited in fan-delta environments during the Paleocene/earliest Eocene. Petrographic data and U–Pb ages of detrital zircons document the progressive unroofing of the Gangdese arc, which remained the dominant source of detritus throughout the Late Cretaceous to Paleogene. Detrital Cr-spinels in the Quxia and Jialazi formations are geochemically similar to those in Cretaceous Xigaze Forearc strata but different from those hosted in Yarlung Zangbo ophiolites, suggesting that the latter were not exposed to erosion in the considered time window. Sandstone petrography, Cr-spinel-geochemistry, U–Pb age spectra and Hf isotopic ratios of detrital zircons in the Quxia and Jialazi formations match those in Paleogene sediments deposited on the distal (Sangdanlin and Zheya formations) and proximal Indian margin (Enba and Zhaguo formations), suggesting that the Quxia and Jialazi formations documents syncollisional fan-deltas deposited on top of the nascent Himalayan orogenic belt. In this scenario, the onset of the India–Asia collision predates deposition of the Quxia and Jialazi formations and is thus constrained as younger than 66 Ma and older than 58 Ma.
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Xigaze Forearc Basin revisited (South Tibet): Provenance changes and origin of the Xigaze Ophiolite
Geological Society of America Bulletin, 2014Co-Authors: Eduardo Garzanti, Jiangang Wang, Marcelle K. Boudagher-fadel, Gaoyuan SunAbstract:Our new stratigraphic, sedimentological, and micropaleontological analysis, integrated with basalt geochemistry, sandstone petrography, and detrital-zircon U-Pb and Hf isotope data, suggests the revision of current models for the geological evolution of the Asian active margin during the Cretaceous. The Xigaze Forearc Basin began to form in the late Early Cretaceous, south of the Gangdese arc, during the initial subduction of the Neotethyan oceanic lithosphere under the Lhasa terrane. Well-preserved stratigraphic successions document the classical upwardshallowing pattern of the Forearc-Basin strata and elucidate the origin of the associated oceanic magmatic rocks. The normal midocean-ridge basalt (N-MORB) geochemical signature and stratigraphic contact with the overlying abyssal cherts (Chongdui Formation) indicate that the Xigaze Ophiolite formed by Forearc spreading and represents the basement of the Forearc sedimentary sequence. Volcaniclastic sedimentation began with thick turbiditic sandstones and interbedded shales in the late Albian–Santonian (Ngamring Formation) followed by shelfal, deltaic, and fl uvial strata (Padana Formation), with fi nal fi lling of the Basin by the Campanian age. Forearc sandstones do not show the classical trend from feldspatholithic volcaniclastic to quartzo-feldspathic plutoniclastic compositions, indicating limited unroofi ng of the Gangdese arc prior to collision. U-Pb age spectra of detrital zircons are unimodal with a 107 Ma peak in the lower Ngamring Formation (104–99 Ma), bimodal with a subordinate additional peak at 157 Ma in the middle Ngamring Formation (99– 88 Ma), and multimodal with more abundant pre-Mesozoic ages in the upper Ngamring and Padana Formations (88–76 Ma). These three petrofacies with distinct provenances document the progressive erosional evolution of the Gangdese arc, with uplift of the central Lhasa terrane and expanding river catchments to include the central Lhasa terrane during the Late Cretaceous.