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Using silicone slabs as a model analogue for lithospheric plates subducting into a box of glucose syrup, as an analogue of the mantle, we explore the subduction of continental lithosphere in a context of intercontinental collision. The continental indenter pushed by a piston, reproducing the collision, attached to a dense oceanic plate, subducts to two-thirds of the depth of the mantle box. We show that, surprisingly, the continental plate attached to the back wall of the box subducts, even if not attached to a dense oceanic slab. The engine of this subduction is not the weight of the slab, because the slab is lighter than the mantle, but the motion of the piston, which generates horizontal tectonic forces. These are transmitted to the back wall plate through the indenter and the upper plate at the surface, and by the advancing indenter slab through the mantle at shallow depth. We define this process as collisional subduction occurring in a compressional context. The collisional subduction absorbs between 14% and 20% of the convergence, and represents an unexplored component of collisional mass balance. The transmission of tectonic forces far from the collision front favors the formation of a wide plateau. Our experiments reproduce adequately the amount and geometry of the Asian lithosphere subduction episodes inferred during the collision, leading us to conclude that it reproduces adequately the physics of such process. [ABSTRACT FROM AUTHOR]

The tectonic and topographic history of the Himalaya-Tibet orogenic system remains controversial, with several competing models that predict different exhumation histories. Here, we present new low-temperature thermochronological data from the Mount Everest region, which, combined with thermal-kinematic landscape evolution modeling, indicate asymmetric exhumation of Mount Everest consistent with a scenario in which the southern edge of the Tibetan Plateau was located >100 km farther south during the mid-Miocene. Northward plateau retreat was caused by erosional incision during the Pliocene. Our results suggest that the South Tibetan Detachment was a localized structure and that no coupling between precipitation and erosion is required for Miocene exhumation of Greater Himalayan Sequence rocks on Mount Everest. [ABSTRACT FROM AUTHOR]

The tectonic evolution of the Lhasa terrane (southern Tibetan Plateau) played a fundamental role in the formation of the Tibetan Plateau. However, many uncertainties remain with regard to the tectonic and paleogeographic evolution of the Lhasa terrane prior to the India-Asia collision. To determine the early tectonic processes that controlled the topographic evolution of the Lhasa terrane, we analyze the Cretaceous strata exposed in the Coqen Basin (northern Lhasa subterrane), which comprises the Langshan and Daxiong Formations. The Langshan Formation unconformably overlies the volcanic rocks of the Lower Cretaceous Zelong Group and consists of ~80 m of Orbitolina-bearing limestones, which were deposited in a low-energy, shallow marine environment. Micropaleontological analysis indicates that the Langshan Formation in the Coqen Basin was deposited from late Aptian to early Cenomanian times (ca. 113-96 Ma). The overlying Daxiong Formation (~1700 m thick) consists of conglomerate, coarse sandstone, and siltstone with interbedded mud-stone, and represents deposits of alluvial fans and braided rivers. The Daxiong Formation was deposited after the early Cenomanian (ca. 96 Ma) and accumulated until at least ca. 91 Ma, indicating accumulation rates of greater than 0.3 km m.y.-1. By combining paleocurrent data, sandstone petrology, detrital zircon U-Pb ages, and Hf isotope analysis, we demonstrate that the Daxiong Formation was derived from Lower Cretaceous volcanic rocks and pre-Cretaceous strata in the northern Lhasa subterrane. During Late Cretaceous time, two thrust systems with opposite vergence were responsible for transforming the northern Lhasa subterrane into an elevated mountain range. This process resulted in the evolution from a shallow marine environment (Langshan Formation) into a terrestrial depositional environment (Daxiong Formation) on the southern margin of the northern Lhasa subterrane. Given the regional paleogeographic context, we conclude that the Daxiong Formation in the Coqen Basin records local crustal shortening and flexure resulting in foreland basin development on the southern margin of the northern Lhasa subterrane, which implies early topographic growth of the northern Lhasa subterrane in southern Tibet prior to the India-Asia collision. [ABSTRACT FROM AUTHOR]

A curved belt consisting of terranes or blocks and associated late Paleozoic to early Mesozoic sutures are features of the southeastern part of the Tibetan Plateau. The southeastern Tibetan Plateau Paleotethyan belt is divided into a northwestern segment (central Tibetan Plateau) and a southern segment (the Sanjiang orogenic belt). The Paleotethyan tectonic history of this belt remains a subject of considerable debate. A major controversy concerns whether or not it evolved as a single genetic element. This paper provides new geochronological, geochemical, and structural data to constrain the Paleotethyan tectonics of this belt. A detailed field study across three sections of the Sanjiang orogenic belt has identified two volcaniclastic successions separated by a regional angular unconformity in the northwestern segment, and one continuous volcaniclastic succession in the southern segment. New zircon U-Pb ages reveal that: (1) the lower succession of the northwestern segment was produced by three volcanic phases at ca. 272 Ma, 253-247 Ma, and 240-235 Ma; (2) the upper succession of the northwestern segment formed during a shorter period along the Yushu-Yidun arc from ca. 227 to 211 Ma; and (3) the single volcaniclastic succession of the southern segment was produced continuously from ca. 260 to 210 Ma. Whole-rock geochemical data including trace elements show that the late Paleozoic to early Mesozoic magmatic activity has a continental arc-like affinity. The spatial distribution and field relationships of the magmatic rocks define two continuous vol canic arcs in the southeastern Tibetan Plateau, which correspond to two phases of arclike magmatism. The Late Triassic Yushu-Yidun arc belt is exposed along the northern half of the northwestern segment to the south of the western Jinsha-Garzê-Litang suture. Southward subduction along the western Jinsha-Garzê-Litang suture is likely to have generated the Yushu-Yidun arc. The second arc (Jomda-Weixi-Yunxian) was diachronous and is continuous through the southeastern Tibetan Plateau. The northwestern part of the Jomda-Weixi-Yunxian arc belt is overlain by the Yushu-Yidun arc from the north. From northwest to southeast, the cessation of magmatism in the Jomda-Weixi-Yunxian arc varies from the Middle Triassic (ca. 235 Ma) to the Late Triassic (ca. 210 Ma), whereas the onset of magmatism appears to have been in the Early Permian throughout the arc. Zircon Lu-Hf isotopic data suggest that large degrees of melting of a depleted mantle source produced the earliest magmas in each segment of the Jomda-Weixi-Yunxian arc. The similarity in zircon ages of the ophiolitic units and their distribution imply that the Longmu Co-Shuanghu suture is a continuation of the Changning-Menglian suture. The spatial relationship between the Jomda-Weixi-Yunxian arc and the Longmu Co-Shuanghu-Changning-Menglian suture suggests that diachronous eastward subduction of part of the Paleotethys along the suture produced the Jomda-Weixi-Yunxian arc belt. Widespread folds of the continental arc-volcaniclastics with orogen-parallel hinges reflect compression perpendicular to the orogen, subsequent to arc magmatism. As such, the Paleotethyan tectonics of the southeastern Tibetan Plateau are characterized by two-phase subduction and subsequent two-phase continent-continent collision. [ABSTRACT FROM AUTHOR]

Ungulate and carnivore diversity patterns since 30 Ma in different regions of the western United States suggest abrupt increased diversification at 17-17.5 Ma, followed by decreases ca. 11 Ma, and stasis thereafter. Although global climate change presumably affects evolution, we hypothesize that widespread extensional tectonism in the western U.S. also helped drive diversity increases ca. 17.5 Ma through a topographically induced increase in floral and habitat diversity. The decreases in diversities ca. 11 Ma, as well as the rapid increase in C4 ecosystems (RICE) worldwide at 7-8 Ma may have responded to climate teleconnections and increased seasonality linked to global cooling and growth of orogenic plateaus, particularly the Tibetan Plateau between 13 and 8 Ma. Thus, biodiversity complexly responds both to climate and to tectonics. [ABSTRACT FROM AUTHOR]

The Qaidam basin is the largest topographic depression inside the Tibetan plateau. Because of its central position, understanding the tectonic origin of the Qaidam basin has important implications for unraveling the formation mechanism and growth history of the Tibetan plateau. In order to achieve this goal, we analyzed regional seismic-reflection profiles across the basin and a series of thickness-distribution patterns of Cenozoic strata at different time slices. The first-order structure of the basin is a broad Cenozoic synclinorium, which has an amplitude ranging from >16 km in the west to <4 km in the east. The synclinorium has expanded progressively eastward across the Qaidam region: from the western basin against the Altyn Tagh fault at 65-50 Ma to the eastern basin at 24 Ma. The half-wavelength of the regional fold complex changes from ~170 km in the west to ~50 km in the east. The formation of the synclinorium was induced by an older thrust system initiated ca. 65-50 Ma in the northern margin and a younger thrust system initiated ca. 29-24 Ma in the southern basin margin. Cenozoic upper-crustal shortening decreases eastward across basin from >48% in the west to <1% in the east; the associated strain rates vary from 3.2 x 10-15 s-1 to 1.3 x 10-17 s-1. The eastward decrease in upper-crustal shortening requires a progressive shift in crustal-thickening mechanisms across Qaidam basin, from dominantly upper-crustal shortening in the west to dominantly lower-crustal shortening in the east. Although sedimentation began synchronously at 65-50 Ma across the entire basin, the initiation ages of the southern and northern basin-bounding structures are significantly different; deformation started at 65-50 Ma in the north and at 29-24 Ma in the south. This information and the existing inference that the uplift of the Eastern Kunlun Range south of Qaidam basin began after 30-20 Ma imply that the Paleogene (65-24 Ma) Qaidam and Hoh Xil basins on both sides of the Eastern Kunlun Range may have been parts of a single topographic depression, >500 km wide in the north-south direction between the Qilian Shan and Fenghuo Shan thrust belts in the north and south. The development of this large Paleogene basin in central Tibet and its subsequent destruction and partitioning by the Neogene uplift of the Eastern Kunlun Range requires a highly irregular sequence of deformation, possibly controlled by preexisting weakness in the Tibetan lithosphere. [ABSTRACT FROM AUTHOR]

Cenozoic Qaidam basin, the largest active intermountain basin inside Tibet, figures importantly in the debates on the history and mechanism of Tibetan plateau formation during the Cenozoic Indo-Asian collision. To determine when and how the basin was developed, we conducted detailed geologic mapping and analyses of a dense network of seismic reflection profiles from the southern Qilian Shan-Nan Shan thrust belt and northern Qaidam basin. Our geologic observations provide new constraints on the timing and magnitude of Cenozoic crustal thickening in northern Tibet. Specifically, our work shows that the southernmost part of the Qilian Shan-Nan Shan thrust belt and contractional structures along the northern margin of Qaidam basin were initiated in the Paleocene-early Eocene (65-50 Ma), during or immediately after the onset of the Indo-Asian collision. This finding implies that stress was transferred rapidly through Tibetan lithosphere to northern Tibet from the Indo-Asian convergent front located >1000 km to the south. The development of the thrust system in northern Qaidam basin was driven by motion on the Altyn Tagh fault, as indicated by its eastward propagation away from the Altyn Tagh fault. The eastward lengthening of the thrust system was spatially and temporally associated with eastward expansion of Qaidam basin, suggesting thrust loading was the main control on the basin formation and evolution. The dominant structure in northern Qaidam basin is a southwest-tapering triangle zone, which started to develop since the Paleocene and early Eocene (65-50 Ma) and was associated with deposition of an overlying southwest-thickening, growth-strata sequence. Recognition of the triangle zone and its longevity in northern Qaidam basin explains a long puzzling observation that Cenozoic depocenters have been located consistently along the central axis of the basin. This basin configuration is opposite to the prediction of classic foreland-basin models that require the thickest part of foreland sediments deposited along basin edges against basin-bounding thrusts. Restoration of balanced cross sections across the southern Qilian Shan-Nan Shan thrust belt and northern Qaidam basin suggests that Cenozoic shortening strain is highly inhomogeneous, varying from ~20% to >60%, both vertically in a single section and from section to section across the thrust belt. The spatially variable strain helps explain the conflicting paleomagnetic results indicating different amounts of Cenozoic rotations in different parts of Qaidam basin. The observed crustal shortening strain also implies that no lower-crustal injection or thermal events in the mantle are needed to explain the current elevation (~3000-3500 m) and crustal thickness (45-50 km) of northern Qaidam basin and the southern Qilian Shan-Nan Shan thrust belt. Instead, thrusting involving continental crystalline basement has been the main mechanism of plateau construction across northern Qaidam basin and the southern Qilian Shan-Nan Shan region. [ABSTRACT FROM AUTHOR]

The recent dramatic increase in seismic anisotropy and surface global positioning system (GPS) data for central Asia permits a comprehensive examination of the mantle's role in mountain building. A joint analysis of 178 shear-wave-splitting and 2000 GPS observations using a new technique reveals that the crust and lithospheric mantle deform coherently, arguing for crust-mantle mechanical coupling during deformation. The observed spatial variations in anisotropy reflect the large-scale pattern of lithospheric deformation, as well as a change in deformational style from simple shear on the Tibetan Plateau transitioning to pure shear in surrounding regions. [ABSTRACT FROM AUTHOR]

The Xianshuihe fault system is a highly active, left-lateral slip fault that has played an important role in accommodating late Cenozoic crustal deformation of the Eastern Tibetan Plateau. The left-lateral displacement on the western portion of the fault system, the Ganzi fault, is ~80 km, based on geologic and geomorphic markers. Left-lateral movement along the fault may have initiated in middle Miocene time (12 Ma), followed by the intensive, brittle, left-lateral movement in late Cenozoic time (2-4 Ma). Lying within the headwater regions of the Jinsha (Yangtze) River in the Yushu region, the northwestern end of the Xianshuihe fault system consists of four branches. These are, from north to south--the Dangjiang fault, the Yushu fault, the Batang fault, and the Xialaxiu fault. Both the Yushu and Dangjiang faults display clear geologic and geomorphic evidence for active, left-lateral slip movement. Several offset markers of Triassic age along the Dangjiang fault suggest ~39 km of left-lateral slip, but the geomorphic evidence along the Dangjiang and Yushu faults suggests only ~16 km and ~25 km of left-lateral slip, respectively. Both the Batang and Xialaxiu faults demonstrate clear evidence for normal dip slip, by an associated series of E-W--trending grabens and horsts that absorb ~9 km of left-lateral movement in early to middle Pleistocene time. About 32 km of left-lateral movement on the fault system was estimated to be absorbed by NE-SW shortening along the rugged North Yushu block in late Neogene time. This is interpreted to have formed as a rhomb-shaped restraining bend, along which the left-lateral movement along the northwestern end of the fault system was partially transferred into crustal shortening. The westward continuation of the Dangjiang fault is marked by an E-W--trending fault, which can be traced westward for 150 km to central Tibet, where it joins the Fenghuo Shan thrust belt. This thrust belt is interpreted to represent the northwestern continuation of the Xianshuihe fault system, along which 39 km of the left-lateral movement was entirely transferred into the N-S shortening. It indicates that the left-lateral movement within the southeastern part of the Tibetan Plateau along the fault system, either caused by lateral extrusion or by clockwise rotation, is largely restricted to the northwestern end of the fault system. Quaternary extension occurred along the northwestern continuation of the Xianshuihe-Xiaojiang fault was coeval with extension along its southern end, indicating that the southeastern margin of the plateau underwent clockwise rotation. [ABSTRACT FROM AUTHOR]

Ongoing plate convergence between India and Eurasia provides a natural laboratory for studying the dynamics of continental collision, a first-order precess in the evolution of continents, regional climate, and natural hazards. In southeastern Tibet, the fast directions of seismic anisotropy determined using shear-wave splitting analysis correlate with the surficial geology including major sutures and shear zones and with the surface strain derived from the global positioning system velocity field. These observations are consistent with a clockwise rotation of material around the eastern Himalayan syntaxis and suggest coherent distributed lithospheric deformation beneath much of southeastern Tibet. At the southeastern edge of the Tibetan Plateau we observe a sharp transition in mantle anisotropy with a change in fast directions to a consistent E-W direction and a clockwise rotation of the surface velocity, surface strain field, and fault network toward Burma. Around the eastern Himalayan syntaxis, the coincidence between structural crustal features, surface strain, and mantle anisotropy suggests that the deformation in the lithosphere is mechanically coupled across the crust-mantle interface and that the lower crust is sufficiently strong to transmit stress. At the southeastern margin of the plateau in Vunnan province, a change in orientation between mantle anisotropy and surface strain suggests a change in the relationship between crustal and mantle deformation. Lateral variations in boundary conditions and rheological properties of the lithosphere play an important role in the geodynamic evolution of the Himalayan orogen and Tibetan Plateau and require the development of three-dimensional models that incorporate lateral heterogeneity. [ABSTRACT FROM AUTHOR]

The collision of the Indian subcontinent with Asia drives the growth and evolution of the greater Tibetan Plateau region. Fault slip rates resulting from the relative motion between crustal blocks can provide a kinematic description of the distribution of present-day deformation. I construct a three-dimensional, regional-scale elastic block model of the India-Asia collision zone that is consistent with geodetic observations of interseismic deformation, mapped fault system geometry, historical seismicity, and the mechanics of the earthquake cycle. This mechanical model of the elastic upper crust yields a set of kinematically consistent fault slip rates and block motions that may serve to constrain dynamic models of continental crustal dynamics. [ABSTRACT FROM AUTHOR]

The age of surface uplift in southeastern Tibet is currently unknown, but the initiation of major river incision can be used as a proxy for the timing of initial uplift. The topographically high eastern plateau and gently dipping southeastern plateau margin are mantled by an elevated, low-relief relict landscape that formed at a time of slow erosion at low elevation and low tectonic uplift rates prior to uplift of the eastern Tibetan Plateau. Thermochronology from deep river gorges that are cut into the relict landscape shows slow cooling between ca. 100 and ca. 10–20 Ma and a change to rapid cooling after ca. 13 Ma with initiation of rapid river incision at 0.25–0.5 mm/yr between 9 and 13 Ma. A rapid increase in mean elevation of eastern Tibet beginning at this time supports tectonic-climate models that correlate the lateral (eastern) expansion of high topography in Tibet with the late Miocene intensification of the Indian and east Asian monsoons. [ABSTRACT FROM AUTHOR]

The stable isotope composition of pedogenic and early diagenetic carbonates from the Oiyug Basin of southern Tibet allows model estimates of the paleoaltimetry of the Tibetan Plateau for the middle Miocene. Pedogenic calcium carbonate nodules have average 81soot values of -19.6‰, whereas nodular lacustrine dolomites range in composition from -7.6‰ to -5.5‰. The most negative of the carbonate isotope values can be used to constrain the oxygen isotope composition of paleoprecipitation, from which model estimates of paleoaltimetry can be made. Model results indicate that the southern Tibetan Plateau achieved elevations of ∼5200 +1370/-605 m by at least 15 Ma. Our results are identical within uncertainty to previous workers' paleoelevation estimates based on Oiyug Basin fossil floral physiognomy. This is the first time that two paleoaltimeters have been directly compared and are in accord. Collectively, these data strongly support tectonic models in which thickening of mantle lithosphere beneath the domain of crustal thickening and subsequent detachment of the mantle lithosphere plays an indiscernible role in the elevation history of this part of the Himalaya-Tibet orogenic system. [ABSTRACT FROM AUTHOR]

To better understand the mechanics of restraining double bends and the strike-slip faults in which they occur, we investigated the relationship between topography and bedrock structure within the Akato Tagh, the largest restraining double bend along the active, left-slip Altyn Tagh fault. The bend comprises a ∼90-km long, east-west striking central fault segment flanked by two N70°E-striking sections that parallel the regional strike of the Altyn Tagh system. The three segments form two inside corners in the southwest and northeast sectors of the uplift where they link. We find that both the topography and bedrock structure of the Akato Tagh restraining bend are strongly asymmetric. The highest and widest parts of the uplift are focused into two topographic nodes, one in each inside corner of the bend. Structural mapping of the western half of the bend suggests the southwest node coincides with a region of anomalously high, bend-perpendicular shortening. We also find that partitioned, transpressional deformation within the Akato Tagh borderlands is absorbed by bend-parallel strike-slip faulting and bend-perpendicular folding, unlike the thrusting reported from many other double bends. Synthesis of these results leads to three implications of general significance. First, we show that focusing of bend-perpendicular shortening into the two inside corners of a restraining double bend may cause both the bend and the fault to undergo vertical-axis rotation, thereby reducing the bend angle and smoothing the trace during progressive deformation. Such vertical-axis rotation may help explain why fault trace complexity is inversely related to total displacement along strike-slip faults. Second, we calculate four independent age estimates for the Akato Tagh bend, all of which are much younger than the Altyn Tagh system. We use these estimates in a companion study to postulate that the Altyn Tagh and similarly multi-stranded strike-slip systems may evolve by net strain hardening. Third, comparison of the Akato Tagh with other restraining double bends highlights systematic differences in the style of borderland faulting and we speculate that these variations result from different states of stress adjacent to the bends. Strike-slip dominated bends such as the Akato Tagh may form where σH = σ1, σv = σ2, and σh = σ3 whereas thrust-dominated bends like the Santa Cruz bend along the San Andreas fault form when σH = σ1, σh = σ2, σv = σ3. This hypothesis predicts that the style of faulting along a restraining double bend can evolve during progressive deformation, and we show that either weakening of borderland faults or growth of restraining bend topography can convert thrust-dominated bends into strike-slip dominated uplifts such as the Akato Tagh. [ABSTRACT FROM AUTHOR]

Global positioning system velocities from 553 control points within the Tibetan Plateau and on its margins show that the present-day tectonics in the plateau is best described as deformation of a continuous medium, at least when averaged over distances of >∼100 km. Deformation occurs throughout the plateau interior by ESE-WNW extension and slightly slower NNE-SSW shortening. Relative to Eurasia, material within the plateau interior moves roughly eastward with speeds that increase toward the east, and then flows southward around the eastern end of the Himalaya. Crustal thickening on the northeastern and eastern margins of the plateau occurs over a zone ∼400 km wide and cannot be the result of elastic strain on a single major thrust fault. Shortening there accommodates much of India's penetration into Eurasia. A description in terms of movements of rigid blocks with elastic strain associated with slip on faults between them cannot match the velocity field. [ABSTRACT FROM AUTHOR]

Examines the tectonic evolution of the northern edge of the Tibetan Plateau in China. Preservation of the Mesozoic and early Cenozoic history of the area; Conduction of petrographic analysis; Derivation of the area from lithologically diverse source terranes.

Investigates the lower crustal flow along the margins of the Tibetan Plateau in China. Account on the two end-member morphologies of the margins; Implication of the upper crustal shortening across the eastern plateau for thickening and composition of the deep crust; Formulation of a model for flux of a Newtonian fluid through a lower crustal channel of uniform thickness.

Studies the late Cenozoic to Holocene deformation found in southwestern Sichuan and Yunnan, both in China, and their role in forming the southeastern portion of the Tibetan Plateau. Indication of a common evolution based on the similarity of structural development between the sites; Evidence for a complex, homogenous and diachronous plateau formation.

The article discusses the lithospheric deformation of oceanic plates at the equatorial Indian Ocean. The diffuse oceanic plate boundary between the Indian and Capricorn plates was investigated. Research revealed that plate reconstructions and deformations were largely settled due to seismic reflection profiles at the area. The surface uplift at the Tibetan Plateau was also explored wherein the uplift reached a maximum elevation. An estimated pole of rotation of the Indian plate with respect to the Capricorn plate was estimated through compact confidence limits.