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The Tertiary lacustrine Niubao Formation is well exposed in the middle-western part of the Lunpola Basin, central Tibetan Plateau, where crude oil was once discovered during drilling campaigns. Sedimentological, organic petrographic and geochemical work was performed on the upper and middle members of this formation in order to investigate its hydrocarbon source rock potential. Sedimentological analyses indicate that both members were deposited in relatively deep lake conditions away from the influence of big stream system, with the upper Niubao Formation (UNF) having higher sand content. The two members contain abundant high-quality Type I kerogen derived mainly from plankton, algae, and bacteria. Compared with samples of the middle Niubao Formation (MNF), UNF samples also contain more Type II and Type III kerogens of terrestrial origin. Biomarkers of source rock extracts suggest that a long-standing anoxic, stratified, and saline ancient lake occupid the basin during deposition of the two members, which was conducive to the preservation of organic matter. However, higher gammacerane content and the presence of β-carotane in MNF samples imply a more saline lake condition. Rock-Eval T max and biomarker parameters reveal marginal maturity and immaturity for samples from MNF and UNF, respectively. Therefore, MNF has better source rocks of higher maturity might be the main hydrocarbon generating member of the basin; similar diagnostic biomarkers and biomarker parameters reported in the crude oil also imply its affiliation with the source rocks of MNF. [ABSTRACT FROM AUTHOR]

Long-standing problems in the geological evolution of the Tibetan–Himalayan orogen include where the India–Asia convergence was accommodated and how the plateau grew. To clarify these problems, we review the deformations and their role in the plateau's growth. Our results show that ~ 1630 km of shortening occurred across the Tibetan–Himalayan orogen since ~ 55 Ma, with more than ~ 1400 km accommodated by large-scale thrust belts. These thrust belts display an outward expansion from central Tibet and couple with the surficial uplift. The development of the Tibetan plateau involved three significant steps: Primitive plateau (~ 90–55 Ma), Proto-plateau (~ 55–40 Ma), and Neoteric plateau (~ 40–0 Ma). Several processes have collaborated to produce the Proto-plateau, including the pre-existing Primitive plateau, the India–Asia collision, and subductions of Greater India and Songpan–Ganzi beneath the Lhasa–Qiangtang terrane. Since ~ 40 Ma, the Proto-plateau, which was dominated by a topographic gradient, lower crustal flow and continuous India–Asia convergence, experienced three periods of rapid outward growth (~ 40–23, ~ 23–10, and ~ 10–0 Ma) in general. The N–S trending rifts were caused by the eastward growth of the plateau dominated by thrusting and crust flow in central Tibet, while they were the results of intense N–S shortening in Himalaya. [ABSTRACT FROM AUTHOR]

Abstract: The surface uplift history of the Tibetan Plateau (TP) offers a key testing ground for evaluating models of collisional tectonics and holds important implications for processes ranging from global cooling to the onset of the Asian monsoon. Various models have been proposed to reveal the surface uplift history of the TP, but controversies remain. We evaluate these models using data from sedimentology and stratigraphy, structural geology, magmatism, exhumation, and paleoaltimetry studies. Structural analyses indicate that thrust belts, which spread from the central TP outward toward its surrounding margins, accommodated most of the India–Asia convergence, and facilitated crustal shortening and thickening in the central TP. Eocene adakitic rocks located in the Qiangtang and the Lhasa blocks likely were generated by partial melting of an eclogitic source. Paleogene (50–30Ma) potassic rocks only occur in the Qiangtang block, whereas Late Oligocene–Late Miocene (26–8Ma) potassic rocks occur both in the Qiangtang and Lhasa blocks. Low-temperature thermochronologic ages in the central TP are older than 40–35Ma, whereas those in the margins are younger than 20Ma (mostly Late Miocene, and Pliocene/Pleistocene in age). Independent paleoaltimetry estimates suggest that the Lhasa and Qiangtang terranes attained their current elevations during the Eocene, most likely due to the initial collision between India and Lhasa, whereas the Hoh Xil basin area to the north and Himalayas to the south were still low, even below sea level in the latter case. We argue for an inside-out growth pattern for the Tibetan Plateau. The TP grew southward and northward from a nucleus of high topography and is likely to continue expanding along the Mazar Tagh fault to the northwest, the Kuantai Shan-Hei Shan-Longshou Shan to the northeast, the Longquan Shan to the east and the Shillong plateau to the south if the northward force of India would not diminished. [Copyright &y& Elsevier]

Abstract: Understanding why continental deformation departs from the theory of plate tectonics requires a detailed knowledge of three-dimensional structures at a lithospheric scale. In Tibet, the end-member models of continental deformation make distinctively different predictions on strain distribution and contrasting structural geometry as a function of depth. Specifically, the thin-viscous-sheet model predicts vertically coherent deformation while channel-flow and continental-subduction models predict the presence of sub-horizontal detachment zones within or at the base of the Tibetan crust during the Cenozoic deformation. To differentiate the above models, we conducted a high-resolution seismic-reflection survey across the active left-slip Kunlun fault and its nearby contractional structures. The results of this work show that the actively deforming middle Tibetan crust is dominated by discrete sub-horizontal simple-shear zones that terminate the sub-vertical, left-slip Kunlun fault above and mantle-cutting thrusts below. The flat shear zones appear to act as roof and floor thrusts of large duplex structures that transfer shortening strain from locally deformed and coupled lower crust and mantle lithosphere below to the high-strain domains of the upper crust above. The middle-crustal strain-transfer model proposed here implies that the weak Tibetan middle crust may not be active everywhere during the Indo-Asian collision. It also predicts that the kinematics of the activated portions of the middle crust, whether being deformed by simple shear or channel-flow deformation, may vary from place to place, depending strongly on the lateral variation of mechanical strength at different depths of the lithosphere. Our approach of establishing the kinematics of middle-crust deformation departs significantly from the early work that emphasizes exclusively the role of vertically varying rheology in controlling the mode of continental deformation. [Copyright &y& Elsevier]

Abstract: The Zhuonai Lake and Lunpori oil shale, located in the central Tibetan Plateau, were deposited in a Tertiary lacustrine environment in the Hoh Xil and Lunpola Basins, respectively. A combined investigation of sedimentary, organic geochemistry, and organic carbon isotope was performed to define source rock potential, the palaeoenvironment, and source of the organic matter. Three types of facies sequences are developed in the Zhuonai Lake section and oil shale mainly occurs in the oil shale-marl sequence. The oil shale-silty claystone and oil shale-marl facies sequences are developed in the Lunpori section. Both oil shales are finely stratified especially for the Lunpori oil shale with thickness of the laminae about 10μm which contains abundant pyrite crystals and fossilized fish bones. Both the Zhuonai Lake and Lunpori oil shale contain high values of total organic matter (TOC), S2, and hydrogen index (HI), indicating the oil shales have good oil source rock potential. Tmax values show an immature stage of organic matter for the Zhuonai Lake oil shale and thermally marginally mature for the Lunpori oil shale because of difference in their burial history. Lunpori oil shale shows the characteristics of amorphous organic matter (AOM) dominance, odd-over-even predominance, maximum n-alkanes peak at nC25 or nC23, higher proportion of C29 sterane, light δ13Corg values (−30.0‰ to −27.4‰), high concentrations of phytane (Pr/Ph ratio ranging from 0.02 to 0.18), high values of gammacerane index (up to 25.26), and presence of β-carotane, which are consistent with a reducing, stratified, and hypersaline palaeo-lake with main contribution of algae and bacteria to the organic matter (OM). Oil shale samples from the lower and upper part of the Zhuonai Lake section are characterized by low H/C ratios and high O/C ratios, amorphous humic OM and vitrinite dominance, odd-over-even predominance with long-chain n-alkanes dominance, heavy organic carbon isotope, and C29 >C27 sterane distribution, in agreement with a main contribution of land plant. The heavy organic carbon isotope suggests the expanding of C4 land plant during the early Miocene. While the most samples show characteristics of AOM dominance, maximum peak at nC29 or nC31, and high C27 sterane concentration, consistent with a main contribution from algae to the OM. The Pr/Ph ratio cannot be applied as a measure for redox conditions in the section because of maturity effects. Biomarker analysis indicates that the salinity during the deposition of the Zhuonai Lake oil shale was not enhanced. The Oligocene Lunpori oil shale and the Early Miocene Zhuonai Lake oil shale recorded the variation of palaeolimnological water chemistry. The development history of the palaeo-lakes from the Oligocene saline to the Early Miocene fresh water reflects the variation of palaeoclimate from dry to humid in the central Tibetan Plateau. [Copyright &y& Elsevier]

Abstract: The northeast of the Qinghai-Tibet Plateau, from the Hoh Xil Basin to the Hexi Corridor Basin, demonstrates a basin-ridge geomorphy that is the result of the long-term uplift of the Qinghai-Tibet Plateau. The geological evolution of the Qinghai-Tibet Plateau is recorded in its associated basins. From the Cenozoic sedimentary filling pattern in the Hoh Xil, Qaidam and Jiuquan Basins, we find that the evolution of these basins is similar: they began as strike-slip basins, evolved into foreland basins, and then to intermontane basins. Foreland basins are the direct result of orogenic activity in the northeast of Qinghai-Tibet Plateau, and can be documented to have formed over the following time periods: 49–23 Ma for the Hoh Xil foreland basin, 46–2.45 Ma for the Qaidam foreland basin, and 29.5–0 Ma for the Jiuquan foreland basin. This northward migration in the timing of foreland basin development suggests that the northeastern part of Tibet grew at least in part by accretion of Cenozoic sedimentary basins to its northern margin. [Copyright &y& Elsevier]

The Hoh Xil Basin is the largest Cenozoic sedimentary basin in the hinterland of the Tibetan Plateau. Tertiary sedimentary strata 5.8 km thick, comprising the Fenghuoshan, Yaxicuo and Wudaoliang groups, provide compelling evidence concerning the crustal shortening, erosion and peneplanation of the northern Tibetan Plateau. The basal Fenghuoshan and overlying Yaxicuo groups span the Eocene-Early Oligocene stratigraphically, and have been dated by magnetostratigraphy as 56–30 Ma old. Both groups are composed of terrigenous rocks. Provenance analysis of sandstones and conglomerates demonstrates that Permian and Triassic strata in the Tanggula Orogenic Zone in the south were the source for the Fenghuoshan Group. In contrast, the Carboniferous–Triassic strata in the Tanggula, Bairizhajia, and Heishishan-Gaoshan orogenic zones in the north, were the source for the Yaxicuo Group.During the Late Oligocene, northern Tibet underwent strong north–south crustal shortening (∼43%) and thickening. Extensive erosion, which occurred over the entire plateau surface near the end of the Oligocene, resulted in development of a peneplain surface. The latter is overlain by the Early Miocene Wudaoliang Group, composed of fresh water limestones. These are exposed both on summit surfaces, as well as on the valley floors, showing that a phase of differential uplift occurred after the deposition of the Wudaoliang Group. This post-Miocene differential uplift was due to regional extension, in a region of overall shortening. Even though we have not succeeded in obtaining conclusive data about the exact timing of phases of rapid uplift of the Tibetan Plateau, it is most likely that the major phase of uplift occurred during the Late Oligocene. [Copyright &y& Elsevier]

[Display omitted] • The parent rocks of detrital spinels in the Upper Triassic sandstones of the Songpan-Ganzi Terrane are ophiolites and stratiform intrusions. • These detrital spinels were mainly recycled from the Lower-Middle Triassic strata of the West Qinling Terrane. • The eastern Paleo-Tethys ocean basin was closed before the Carnian stage. The Late Triassic evolution of the Songpan-Ganzi Terrane in the eastern Tibetan Plateau is crucial for understanding the closure of the eastern Paleo-Tethys Ocean. However, the strong thickening and deformation of sedimentary cover make the Songpan-Ganzi geological records complicated and even obscured, impeding the reconstruction of regional tectonic evolution. In this study, we provide new geochemical data of detrital spinels from the Upper Triassic strata in the eastern Songpan-Ganzi Terrane to reveal the provenance and the regional tectonic events involved in the eastern Paleo-Tethyan closure. Results show that detrital spinels from the Upper Triassic Xinduqiao, Zhuwo, and Zagunao formations have variable concentrations of Cr 2 O 3 (24.36–68.56 wt%), Al 2 O 3 (0.13–39.17 wt%), MgO (0.20–21.25 wt%), FeOT (11.15–48.49 wt%), and TiO 2 (0.00–4.66 wt%). They are geochemically similar to spinels from both ophiolites and stratiform intrusions, and affinitive to the counterparts from island-arc, supra-subduction zone, or mid-ocean ridge settings. Based on comparison with the spinel compositions from adjacent tectonic zones and in combination with previously published evidence from paleogeography, paleocurrent orientation, and geochronology, we propose the detrital spinels from the Upper Triassic sequence in the eastern Songpan-Ganzi Terrane were mainly recycled from the Lower–Middle Triassic strata in the West Qinling Terrane, with minor concentrations derived from the A'nyemaqen ophiolites. This provenance inference presents a new insight into the closure time of the eastern Paleo-Tethys Ocean. [ABSTRACT FROM AUTHOR]

The Cenozoic lacustrine Lunpola oil shale, located in the central Tibetan Plateau, has received little research interest in its depositional history although it is estimated to be a huge resource reserve. This study investigates the palaeoclimate, provenance, and regional drainage system of the ancient lakes using a combined analysis of element geochemistry and stratigraphy to elucidate the depositional history of the Lunpola oil shale. Most of the samples in the lower part of the section have chemical index of alteration (CIA) values between 65 and 75, reflecting a moderate weathered source, while samples in the upper part the section have CIA values between 60 and 65, which indicate relatively weak chemical weathering in the source area. This stratigraphic grouping suggests a paleoclimate transition from a relatively warm or humid period to a cold or dry period. The Zr/Sc and Th/Sc ratios of the samples reveal that sorting and recycling were minor during deposition of the oil shale. The geochemical results (Al 2 O 3 –(CaO ⁎ + Na 2 O)–K 2 O (A–CN–K) diagrams, high contents of Th, plots of Co/Th–La/Sc and Cr/Th–Sc/Th) demonstrate that the sedimentary sources were felsic rocks. Plots of La–Th–Sc, Th–Sc–Zr/10, Th–Co–Zr/10, and Ti/Zr versus La/Sc illustrate that the source rocks were from continental arc and active continental margin. The Baingoin batholiths to the south of the Lunpola Basin consisting mainly of Cretaceous granodiorite and adamellite are likely responsible for supplying materials to the Lunpola oil shale. Similar special REE patterns further suggest the affiliation of the oil shale with the batholiths. Provenance analyses indicate a main river from the south; moreover, stratigraphic study confirms an upstream ancient Baingoin Lake between the source area and the ancient Lunpola Lake. In this drainage system, paleoclimate clearly restricted the development of rivers around the lakes. Although terrestrial organic matter (higher plants) dominated the drainage area, the main river originating from the south could only bring a certain amount of them to the lakes. Moreover, considering the filtration of the upstream ancient Baingoin Lake, minor terrestrial organic matter could be carried and deposited in the ancient Lunpola Lake. Therefore, lacustrine algae could proliferate as the main organic source and preserve in the stratified hypersaline lake to form the largest oil shale resource in Tibet. [ABSTRACT FROM AUTHOR]

The subduction of the Bangong–Nujiang Ocean is a long-standing problem in the study of the geological evolution of the Tibetan Plateau. Based on recent data acquired from the Abushan volcanic rocks in the Qiangtang Terrane, we will discuss the relationship between the Cretaceous volcanism and the evolution of the Bangong–Nujiang Ocean. The Abushan volcanic rocks are mainly composed of trachy-andesites, dacites, and rhyolites. Zircon U–Pb dating constrains the time of emplacement as the Middle Cretaceous (102.6 ± 1.6–96.1 ± 2.4 Ma). Major element geochemistry shows that the volcanic rocks belong to the high-K calc-alkaline and calc-alkaline series. All of the volcanic rocks are enriched in light rare earth elements (LREE) and some large ion lithophile elements (LILE, Rb, Th, and U) and are depleted in heavy rare earth elements (HREE) and some high field strength elements (HFSE, Nb, Ta, and Ti). The geochemical characteristics of the Abushan volcanic rocks are correlated with those of the volcanic arc rocks in the subduction zone. The petrogenesis of the Abushan volcanic rocks suggests that they were derived from the partial melting of the relict subducted oceanic crust combined with the input of oceanic sediments. Oceanic crust will melt upon reaching its hydrous solidus in the amphibolite facies after plate collision; this induces the formation of the Abushan volcanic rocks. Our data, compared with the previous studies on volcanism in the Lhasa Terrane, leads us to propose that the Bangong–Nujiang Ocean crust was subducted beneath the Qiangtang Terrane and underwent bidirectional subduction during the Cretaceous. [ABSTRACT FROM AUTHOR]

Sedimentary records indicate that subtropical and mid-latitude East Asia exhibited considerable drying and wetting, respectively, during the mid-Cretaceous, which is considered to be relevant to much higher atmospheric carbon dioxide (p CO 2) concentrations and/or proto-Tibetan Plateau (proto-TP) uplift. In order to explore and compare their roles on the East Asian climate evolution, we conducted simulations of the mid-Cretaceous climate system with different atmospheric p CO 2 levels and varying topographies. The results show that both factors had significant influences on the East Asian climate. As the increase in atmospheric p CO 2 levels from ∼560–1120 ppmv to ∼1120–2240 ppmv, the precipitation increases considerably over mid-latitude East Asia, but only small changes in the subtropical portion of East Asia occur. Simultaneously, the effects of the proto-TP uplift are opposite to those of global warming trend during that period. Generally, it leads to a precipitation decrease over subtropical East Asia, but rather minor changes over mid-latitude East Asia. These changes are qualitatively consistent with the deduction based on the geological records, but the magnitudes of the modeled precipitation changes are relatively smaller. Therefore, we can conclude that the subtropical East Asian drying during the mid-Cretaceous can be partly explained by the proto-TP uplift, while the mid-latitude East Asian wetting was partly due to global warming. However, additional factor(s) also played a significant role in the East Asian climate evolution during the mid-Cretaceous. • East Asian climate evolution was dependent on the latitude of the proto-Tibetan Plateau in the deep past; • Global warming induced wetting at mid-latitude East Asian in the mid-Cretaceous; • The proto-Tibetan Plateau uplift led to drying in the subtropical East Asian in the mid-Cretaceous. [ABSTRACT FROM AUTHOR]