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Paul Kapp - One of the best experts on this subject based on the ideXlab platform.
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mesozoic and cenozoic tectonic evolution of the shiquanhe area of western tibet
Tectonics, 2003Co-Authors: Lin Ding, Paul Kapp, Michael A Murphy, An Yin, Mark T Harrison, Jinghu GuoAbstract:[1] In the Shiquanhe area of far-western Tibet, mid-Cretaceous strata lie unconformable on ophiolitic Melange and Jurassic flysch associated with the Bangong-Nujiang suture zone. On the basis of our mapping and geochronologic studies, we suggest that these Cretaceous strata were shortened by >57% over a north south distance of 50 km during Late Cretaceous-early Tertiary time. The Late Cretaceous Narangjiapo thrust placed Permian strata >20 km over ophiolitic Melange and Cretaceous strata. North of the Narangjiapo thrust, >40 km of shortening was accommodated by the Late Cretaceous-early Tertiary south directed Jaggang thrust system that involves Jurassic flysch and Cretaceous strata, and roots into a decollement within ophiolitic Melange. The most recent shortening was accommodated to the south of the Narangjiapo thrust, along the north dipping Shiquanhe thrust. The Shiquanhe thrust cuts flat-lying 22.6 ± 0.3 Ma volcanic rocks and underlying folded, Tertiary nonmarine strata in its footwall and was likely active during slip along the Oligocene Gangdese thrust system of southern Tibet. Ophiolitic Melange and structurally overlying Jurassic flysch near Shiquanhe are interpreted to represent remnants of a subduction-accretion complex and forearc basin, respectively, that were obducted southward onto the margin of the Lhasa terrane during Late Jurassic-Early Cretaceous closure of the Bangong-Nujiang Ocean. Subsequent imbrication of the obducted sheet could have produced the two east-west trending belts of ophiolitic Melanges, separated by ∼100 km, in western Tibet. Late Cretaceous-early Tertiary thin-skinned shortening may have been accommodated in the deeper crust by northward underthrusting and duplexing of Lhasa terrane rocks beneath the obducted ophiolitic Melange and the Qiangtang terrane to the north.
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mesozoic and cenozoic tectonic evolution of the shiquanhe area of western tibet
Tectonics, 2003Co-Authors: Michael A Murphy, Paul Kapp, Mark T Harrison, Lin DingAbstract:[1] In the Shiquanhe area of far-western Tibet, mid-Cretaceous strata lie unconformable on ophiolitic Melange and Jurassic flysch associated with the Bangong-Nujiang suture zone. On the basis of our mapping and geochronologic studies, we suggest that these Cretaceous strata were shortened by >57% over a north south distance of 50 km during Late Cretaceous-early Tertiary time. The Late Cretaceous Narangjiapo thrust placed Permian strata >20 km over ophiolitic Melange and Cretaceous strata. North of the Narangjiapo thrust, >40 km of shortening was accommodated by the Late Cretaceous-early Tertiary south directed Jaggang thrust system that involves Jurassic flysch and Cretaceous strata, and roots into a decollement within ophiolitic Melange. The most recent shortening was accommodated to the south of the Narangjiapo thrust, along the north dipping Shiquanhe thrust. The Shiquanhe thrust cuts flat-lying 22.6 ± 0.3 Ma volcanic rocks and underlying folded, Tertiary nonmarine strata in its footwall and was likely active during slip along the Oligocene Gangdese thrust system of southern Tibet. Ophiolitic Melange and structurally overlying Jurassic flysch near Shiquanhe are interpreted to represent remnants of a subduction-accretion complex and forearc basin, respectively, that were obducted southward onto the margin of the Lhasa terrane during Late Jurassic-Early Cretaceous closure of the Bangong-Nujiang Ocean. Subsequent imbrication of the obducted sheet could have produced the two east-west trending belts of ophiolitic Melanges, separated by ∼100 km, in western Tibet. Late Cretaceous-early Tertiary thin-skinned shortening may have been accommodated in the deeper crust by northward underthrusting and duplexing of Lhasa terrane rocks beneath the obducted ophiolitic Melange and the Qiangtang terrane to the north.
Lin Ding - One of the best experts on this subject based on the ideXlab platform.
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tectonostratigraphy and provenance of an accretionary complex within the yarlung zangpo suture zone southern tibet insights into subduction accretion processes in the neo tethys
Tectonophysics, 2012Co-Authors: Fulong Cai, Lin Ding, Ryan J Leary, Houqi Wang, Liyun Zhang, Yahui YueAbstract:Abstract Accretionary complexes record critical information about the history of subduction and accretion along the southern margin of Asia prior to the India–Asia collision. This paper presents detailed field mapping, petrographic and detrital zircon U–Pb data from an accretionary complex within the Yalung–Zangpo suture zone, southern Tibet. From structurally higher to lower levels, the accretionary complex consists of a serpentinite Melange, the chert-matrix Tangga Melange, the mud-matrix Pomunong Melange, and the coherent Rongmawa Formation. The Tangga Melange consists of Late Triassic–Early Cretaceous abyssal chert and siliceous shale with blocks of chert and mafic to ultra-mafic rocks. The Tangga Melange was accreted beneath ophiolitic rocks during the Aptian. The Pomunong Melange consists of a Late Jurassic–Early Cretaceous hemipelagic siliceous shale and chert matrix with blocks from Early Permian seamounts and from Late Cretaceous trench-fill sandstones; it was accreted beneath the Tangga Melange after the Aptian but prior to 71 Ma. Structurally beneath these Melanges to the south, the uppermost Cretaceous Rongmawa Formation consists of turbiditic sandstone, pelagic chert, and siliceous shale and records a transition in depositional setting from lower abyssal plain to upper trench. Detrital zircons from sandstone blocks of the Pomunong Melange and the coherent Rongmawa Formation display similar U–Pb age spectra and are dominated by peaks at 71–231 Ma, 481–693 Ma, and 701–1372 Ma. These age peaks overlap with igneous crystallization ages and detrital zircon ages from sedimentary strata in the Lhasa terrane. Our data indicate that the serpentinite Melange, Tangga Melange, Pomunong Melange and Rongmawa Formation comprise a southward-younging accretionary complex that developed during the northward subduction of Neo-Tethyan oceanic lithosphere beneath the south margin of the Lhasa terrane and that all exposed ophiolitic and accretionary complex assemblages were accreted to the Asian margin prior to the India–Asia continental collision.
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mesozoic and cenozoic tectonic evolution of the shiquanhe area of western tibet
Tectonics, 2003Co-Authors: Lin Ding, Paul Kapp, Michael A Murphy, An Yin, Mark T Harrison, Jinghu GuoAbstract:[1] In the Shiquanhe area of far-western Tibet, mid-Cretaceous strata lie unconformable on ophiolitic Melange and Jurassic flysch associated with the Bangong-Nujiang suture zone. On the basis of our mapping and geochronologic studies, we suggest that these Cretaceous strata were shortened by >57% over a north south distance of 50 km during Late Cretaceous-early Tertiary time. The Late Cretaceous Narangjiapo thrust placed Permian strata >20 km over ophiolitic Melange and Cretaceous strata. North of the Narangjiapo thrust, >40 km of shortening was accommodated by the Late Cretaceous-early Tertiary south directed Jaggang thrust system that involves Jurassic flysch and Cretaceous strata, and roots into a decollement within ophiolitic Melange. The most recent shortening was accommodated to the south of the Narangjiapo thrust, along the north dipping Shiquanhe thrust. The Shiquanhe thrust cuts flat-lying 22.6 ± 0.3 Ma volcanic rocks and underlying folded, Tertiary nonmarine strata in its footwall and was likely active during slip along the Oligocene Gangdese thrust system of southern Tibet. Ophiolitic Melange and structurally overlying Jurassic flysch near Shiquanhe are interpreted to represent remnants of a subduction-accretion complex and forearc basin, respectively, that were obducted southward onto the margin of the Lhasa terrane during Late Jurassic-Early Cretaceous closure of the Bangong-Nujiang Ocean. Subsequent imbrication of the obducted sheet could have produced the two east-west trending belts of ophiolitic Melanges, separated by ∼100 km, in western Tibet. Late Cretaceous-early Tertiary thin-skinned shortening may have been accommodated in the deeper crust by northward underthrusting and duplexing of Lhasa terrane rocks beneath the obducted ophiolitic Melange and the Qiangtang terrane to the north.
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mesozoic and cenozoic tectonic evolution of the shiquanhe area of western tibet
Tectonics, 2003Co-Authors: Michael A Murphy, Paul Kapp, Mark T Harrison, Lin DingAbstract:[1] In the Shiquanhe area of far-western Tibet, mid-Cretaceous strata lie unconformable on ophiolitic Melange and Jurassic flysch associated with the Bangong-Nujiang suture zone. On the basis of our mapping and geochronologic studies, we suggest that these Cretaceous strata were shortened by >57% over a north south distance of 50 km during Late Cretaceous-early Tertiary time. The Late Cretaceous Narangjiapo thrust placed Permian strata >20 km over ophiolitic Melange and Cretaceous strata. North of the Narangjiapo thrust, >40 km of shortening was accommodated by the Late Cretaceous-early Tertiary south directed Jaggang thrust system that involves Jurassic flysch and Cretaceous strata, and roots into a decollement within ophiolitic Melange. The most recent shortening was accommodated to the south of the Narangjiapo thrust, along the north dipping Shiquanhe thrust. The Shiquanhe thrust cuts flat-lying 22.6 ± 0.3 Ma volcanic rocks and underlying folded, Tertiary nonmarine strata in its footwall and was likely active during slip along the Oligocene Gangdese thrust system of southern Tibet. Ophiolitic Melange and structurally overlying Jurassic flysch near Shiquanhe are interpreted to represent remnants of a subduction-accretion complex and forearc basin, respectively, that were obducted southward onto the margin of the Lhasa terrane during Late Jurassic-Early Cretaceous closure of the Bangong-Nujiang Ocean. Subsequent imbrication of the obducted sheet could have produced the two east-west trending belts of ophiolitic Melanges, separated by ∼100 km, in western Tibet. Late Cretaceous-early Tertiary thin-skinned shortening may have been accommodated in the deeper crust by northward underthrusting and duplexing of Lhasa terrane rocks beneath the obducted ophiolitic Melange and the Qiangtang terrane to the north.
Loren A. Raymond - One of the best experts on this subject based on the ideXlab platform.
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Perspectives on the roles of Melanges in subduction accretionary complexes: A review
Gondwana Research, 2019Co-Authors: Loren A. RaymondAbstract:Abstract Melanges play three principal, overlapping roles in the architecture of subduction accretionary complexes (SACs) during and after SAC formation. First, tectonic Melanges serve as zones of concentrated deformation within and below the accreted rocks that are assembled during the subduction-accretion process. These Melanges facilitate preservation of inter-Melange, less deformed, accretionary units (AUs). Beneath the trench side of the SAC, the initial deformation zone along the decollement at the top of the down-going plate is marked by non-Melange, tectonically dismembered formations or thinner units of scaly rock and breccia that separate accreted rocks above from the subducting rocks below. Olistostromal rocks may be incorporated into the decollement here. In the mid-arc to inner-arc areas of the SAC, exotic block-bearing Melanges develop in zones of tectonic fragmentation and mixing of accreting ocean plate stratigraphy, in mud diapirs, and along out-of-sequence faults, some of which facilitate uplift of high-pressure rocks and serpentinite-matrix Melanges. Second, after accretion, the sedimentary, tectonic, diapiric, and polygenetic Melange units serve as single block or sheet architectural AUs (or subunits within larger accreted AUs) of the SAC. Diapiric Melanges and sedimentary olistostromal Melanges formed in and above SAC fault blocks, respectively, may become incorporated into the SAC during ongoing deformation and become architectural units, as well. Third, Melanges serve as post-subduction stress guides that focus shear strain during continuing and post-accretion deformation of SACs, allowing ongoing modification of the SAC during progressive deformation of the orogen. Examples of each type of role reveal the importance of all three processes in the current architecture of outer orogenic belts.
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sandstone matrix Melanges architectural subdivision and geologic history of accretionary complexes a sedimentological and structural perspective from the franciscan complex of sonoma and marin counties california usa
Geosphere, 2015Co-Authors: Loren A. Raymond, David A BeroAbstract:Understanding details of accretionary complex architecture is essential to understanding construction of oceanic “outer” sides of orogens. The architecture of the Franciscan Complex (California), considered by many to be the “type” accretionary complex, is widely viewed in the context of terranes or belts delimited by reconnaissance mapping that reveals neither regional variations within terranes nor critical details of stratigraphy and structure. The architectural importance of Franciscan Melanges is recognized, but the importance of sandstone-matrix Melanges and olistostromal sandstones is not. Large-scale mapping in Sonoma and Marin counties, California, shows that Franciscan rocks are deformed, submarine-fan units of Facies A–E, plus Facies F olistolith-bearing submarine channel sandstones and olistostromal sandstone- and shale-matrix Melanges. Some Melanges are polygenetic with a sedimentary origin and a tectonic overprint. Glaucophane schists were recycled into conglomerates and olistostromes. Mappable units constitute members, broken and dismembered formations, and Melanges. Considering the stratigraphy and structure evident at the 1:24,000 scale, accretion via a subduction channel mechanism is impossible. The Sonoma-Marin Central belt or Central terrane (Melange) is not a monolithic shale-matrix Melange and lacks this characteristic of rocks assigned the same name to the north. Franciscan rocks here structurally underlie thrust-faulted fragments of a regional ultramafic sheet and, locally, an underlying exotic block-bearing serpentinite-matrix Melange. The detailed mapping shows that regional relations among and within Franciscan terranes and belts are poorly understood and suggests that such mapping is needed to clarify accretionary complex architecture and history. The implication for accretionary complex studies, in general, is that, while terrane or belt designations provide a general picture of the collage nature of accretionary complexes and clarification of regional relationships, only large-scale structural and stratigraphic studies can elucidate the architectural details of these orogenic complexes.
Gaku Kimura - One of the best experts on this subject based on the ideXlab platform.
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Tectonic mélange as fault rock of subduction plate boundary
Tectonophysics, 2011Co-Authors: Gaku Kimura, Asuka Yamaguchi, Megumi Hojo, Yujin Kitamura, Jun Kameda, Kohtaro Ujiie, Yohei Hamada, Mari Hamahashi, Shoko HinaAbstract:Abstract An assemblage of quantitative data sets is examined to evaluate tectonic Melange as a plate boundary fault rocks in subduction zone. The research object is the latest Cretaceous Mugi Melange in the Shimanto Belt, southwest Japan. Systematic age younging from pelagic to terrigenous through hemipelagic sediments is well-documented even though original stratigraphy is disrupted. Systematic shear fabric consistent with ancient plate convergence is reconstructed. The Melange was formed at temperatures of ~ 130–200 °C by cataclastic comminution of sandstone layers accompanied by tensile cracking, and plastic deformation and the dehydration of clayey shale matrix, with subsequent peeling off and underplating of the oceanic basement. The temperature setting for the Mugi Melange indicates around the up-dip limit of the seismogenic zone, therefore includes various fault rocks suggestive of earthquake fault; pseudotachylyte, fluidized ultracataclasite with heating evidence, amorphous silica and so on. These suggest that fluid induced lubrication was dominated. Localized cataclastic shear, which is a candidate of small earthquake or very low frequency earthquake, is also recognized especially in sandstone blocks dominated portion in Melange. These observations are consistent with the Melange being a fault rock along the plate boundary that records various types of earthquakes in a subduction zone. The quantitative examination of the Mugi Melange suggests several criteria to define the tectonic Melange of the plate boundary fault in subduction zone from other Melanges in orogenic belt.
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depth of oceanic crust underplating in a subduction zone inferences from fluid inclusion analyses of crack seal veins
Geology, 2003Co-Authors: M Matsumura, Gaku Kimura, Yoshitaka Hashimoto, K Ohmoriikehara, M Enjohji, Eisei IkesawaAbstract:Fluid inclusions in crack-seal veins are analyzed in accreted Melange now on land. The vein I inclusions are observed in the necked parts of sandstone blocks in Melange, and the vein II inclusions developed in shale below the thrust fault, which cuts the Melanges. The pressure and temperature estimations from the inclusions within vein I show that the cracks were sealed at ;125-195 8C under ;92-144 MPa of fluid pressure. Vein II formed in cracks that might have opened in a damage zone caused by the thrust fault as it broke through oceanic crust and into the Melange; these veins contain fluid inclusions trapped at ;135-245 8C under ;107-149 MPa of fluid pressure. The depth ( ;4-6 km below the seafloor) and temperature estimates are consistent with the conditions where an aseismic decollement within sedimentary rocks steps down into the oceanic basement, so that a thin section of oceanic crust underplates in the hanging wall. Such a step-down site is the updip limit of the seismogenic zone in the modern Nankai Trough.
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Underplated units in an accretionary complex: Melange of the Shimanto Belt of eastern Shikoku, southwest Japan
Tectonics, 1991Co-Authors: Gaku Kimura, Atsuhiko MukaiAbstract:Imbricated thrust stacks composed of Melange and oceanic slabs occur in the Shimanto Belt, eastern Shikoku, SW Japan. The Melanges are divided into two types: Melange I consists of lenticular sandstone blocks surrounded by scaly shale matrix, and Melange II is composed of blocks of oceanic material, such as basalts, cherts and red shale, in a scaly matrix of shale. Melange II is observed only near the boundaries between Melange I and oceanic slabs. The fabric of Melange I indicates progressive deformation during underthrusting of originally coherent trench-fill turbidites. Layer-parallel extension characterizes early deformation and is divided into two stages: an early stage formed during normal faulting, and a subseguent stage formed perpendicular to the early extension. The early extension is interpreted in terms of Riedel shear associated with layer-parallel shearing and tectonically induced loading normal to the layering. The second extension is due to sticking-thrust movement. Late deformation of Melange I is represented by folding in association with layer-parallel shearing. This appears to be related to compression just before or during underplating of Melange I beneath the accretionary prism. Layer-parallel shear extends downward due to strain hardening of sheared sediments and then reaches to the base of the sediments. Subsequently, the shear zone penetrates pelagic sediments and, finally, oceanic basement. At this time, Melange II is formed by the shearing. An imbricated stack of Melanges I, II and oceanic slabs forms duplexes during the underplating process. The weak metamorphism of the Melange complex in the study area suggests that underplating occurs at shallow depths where trench fill is thin.
John C. Schumacher - One of the best experts on this subject based on the ideXlab platform.
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Arc magmas sourced from Melange diapirs in subduction zones
Nature Geoscience, 2012Co-Authors: Horst R Marschall, John C. SchumacherAbstract:At subduction zones, crustal material enters the mantle. Some of this material, however, is returned to the overriding plate through volcanic and plutonic activity. Magmas erupted above subduction zones show a characteristic range of compositions that reflect mixing in the magma source region between three components: hydrous fluids derived from the subducted oceanic crust, components of the thin veneer of subducted sediments and peridotite mantle rocks. The mechanism for mixing and transport of these components has been enigmatic. A combination of results from the fields of petrology, numerical modelling, geophysics and geochemistry suggests a two-step process. First, intensely mixed metamorphic rock formations—Melanges—form along the interface between the subducted slab and the mantle. As the Melange contains the characteristic three-component geochemical pattern of subduction-zone magmas, we suggest that Melange formation provides the physical mixing process. Then, blobs of low-density Melange material—diapirs—rise buoyantly from the surface of the subducting slab and transport the well-mixed Melange material into the mantle beneath the volcanoes. Magma erupted at subduction-zone volcanoes contains mantle rocks and a mixture of fluids and sediments derived from the subducted slab. A synthesis of work over past years provides an integrated physico-chemical framework for subduction zones with mixing at the slab–mantle interface and transport towards the surface volcanoes by buoyant diapirs.
