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A central issue when studying landscape evolution is to quantify the effect of surface processes on tectonic deformation. To address this question, we systematically examine the relationship between the late Cenozoic pattern of sedimentary dispersal system in the endorheic Qaidam Basin in the northern Tibetan Plateau and its spatiotemporal variation in hydrological conditions. At present, the depocenter of the Qaidam Basin is located in the southern Qaidam Basin, which correlates with the largest stream runoff, whereas smaller depressions are located in the northern Qaidam Basin owing to lower stream runoffs. The northwestern boundary without obvious runoff corresponds to large-scale modern erosion regions in the northwestern Qaidam Basin. Based on these findings, good spatiotemporal couplings between sedimentary depressions and hydrological conditions have been proved in the Qaidam Basin, indicating that the changing hydrological pattern in the basin-bounding ranges has played as a first-order role in controlling the Quaternary landscape evolution of the Qaidam Basin.

The Denan Depression is a unique depression in the northeastern Qaidam basin, with a maximum Cenozoic sedimentary thickness of ~ 5 km. Detailed field work, interpretation of seismic profiles and analyzation of well data were conducted to define the Cenozoic tectonic evolution of the northeastern Qaidam basin. All geological evidences indicate that the Denan Depression is controlled by the northeast-directed Olongbulak Thrust at its southern boundary. The Denan Depression grew in concert with the development of the northeast-directed Olongbulak Thrust at least since it began to accept the Xiaganchaigou Formation, supporting the early Cenozoic growth of the northern Tibetan Plateau. Surface and subsurface data both point to enhanced tectonic activity since the Quaternary in the northeastern Qaidam basin, leading to a more individual Denan Depression relative to the main Qaidam basin. The northern boundary of the Denan Depression is a passive boundary, and no foreland developed at the northern slope of the Denan Depression.

Deye 1 Well (DY 1 Well) completed in 2013 is the first drilling well that reached the early Paleoproterozoic crystalline basement in the northeastern Qaidam basin. This paper analyzes the drilling core samples from DY 1 Well. Petrology and geochemistry indicate that the drilling core samples belong to high-Na trondhjemite. LA-ICP-MS zircon dating for the drilling core samples yields a weighted mean 207 Pb/ 206 Pb age of 2383.1 ± 6.3 Ma, which is consistent with its upper interception age. Meanwhile, the geochemical characteristics and the deformation degree of high-Na trondhjemite are significantly different from its adjacent gneisses and the Mohe quartz-dioritic rocks in the Quanji Massif. It implies that the basement of the Qaidam basin under thick Cenozoic sediments may be different from its surrounding outcrops, and differential crustal attributes lead to intensely differential Cenozoic vertical motions between basins and mountains. Meanwhile, the widespread familiarity between the Qaidam and Tarim basins implies that the basement of the Qaidam basin may be a part of the Tarim Block during the Precambrian.

The southern Junggar Basin has enormous hydrocarbon mainly from the Jurassic and Permian source rocks, which indicated the importance of exploration of the deeply buried Jurassic reservoirs, therefore, the study of the deeply buried Upper Jurassic Qigu Formation (J3q) reservoirs in Well DS-1 in the Dushanzi anticline was carried out through microscopic observation and measurement, nuclear magnetic resonance (NMR), scanning electron microscopy (SEM) and high pressure mercury injection. Results showed that the main reservoir storage spaces in the deeply buried Upper Jurassic Qigu Formation reservoirs were fractures and dissolved pores. The J3q reservoirs with low porosity and permeability values of 0–12% and (0–5) × 10−3μm2 respectively, were generally tight. According to the mercury injection data, heterogeneity existed in the deeply buried Qigu Formation reservoirs with inhomogeneous pores and changeable sizes of pores throats. Pores and pore throats in the silt-fine sandstones of the lower Qigu Formation (J3q1) were more big and wide respectively than that in the argillaceous siltstones of the upper Qigu Formation (J3q3). Reservoirs in J3q1 had more mobile fluid and better conductivities than reservoirs in J3q3. The strong compaction and multistage diagenesis resulted in the tight J3q reservoirs. Anhydrite and quartz cementation, and various authigenetic minerals (e.g. hematite, kaolinite, illite/smectite formation, illite, chlorite and zeolite) filled in the pores. The homogenization temperature of brine inclusions (63.1–161.7 °C) in quartz overgrowth indicated the quartz had grown since the late Eocene. Due to the Tian Shan reactivity in the Late Cenozoic, the structure fractures were developed and promoted dissolution by oil and formation water in the reservoirs of J3q1. Keywords: Tight reservoirs evolution, Heterogeneity, Fluid inclusion, Structure fractures, Qigu Formation, The Dushanzi anticline, Southern Junggar Basin

In their comment on our publications on pervasive remagnetization of Jurassic-Paleogene carbonate rocks of the Tibetan Himalaya [Huang et al., 2017, Journal of Geophysical Research: Solid Earth, 122, doi: 810.1002/2016JB013662 and 122, doi: 10.1002/2017JB013987], Yi et al. [this volume] questioned our fold tests applied to their published paleomagenetic results from the Paleogene Zongpu and latest Cretaceous Zongshan carbonate rocks [Patzelt et al., 1996, Tectonophysics, 259(4), 259-284; Yi et al., 2011, Earth and Planetary Science Letters, 309(1), 153-165]. They argued that authigenic magnetite pseudomorphic after pyrite, which is the dominant magnetic carrier within these carbonate rocks as indicated by our thorough rock magnetic and petrographic investigations, was formed during early diagenesis and that the primary natural remanent magnetization (NRM) is retained by these carbonate rocks. However, their statement for the invalidity of our fold tests is based on unrealistic assumptions that these carbonate rocks carry primary NRM and that the upper Zongpu Formation was deposited on a 10° primary dip. Their argument for immediate oxidization of pyrite to authigenic magnetite after carbonate deposition onto the continental passive margin ignores that sulphate-reducing conditions were prevailing during early diagenesis, it is also inconsistent with the timing of the secondary remanence acquisition in remagnetized carbonate rocks elsewhere. As previously demonstrated, and agreed upon by Yi et al. [this volume], the Zongpu and Zongshan carbonate rocks in Gamba are remagnetized; here we argue that the timing of remagnetization cannot be demonstrated to shortly post-date sedimentation. These data should therefore not be used for tectonic reconstructions.

Netherlands Organization for Scientific Research (NWO) with a Rubicon grant [825.15.016]; Institute for Rock Magnetism (IRM) at the University of Minnesota; Instruments and Facilities program of NSF; ERC Starting Grant [306810]; NWO VIDI [864.11.004]

We have identified a new crustally derived granite pluton that is related to the Emeishan Large Igneous Province (ELIP). This pluton (the Wase pluton, near Dali) shows two distinct SHRIMP zircon U–Pb age groups (~768 and ~253 Ma). As it has an intrusive relationship with Devonian limestone, the younger age is interpreted as its formation, which is related to the ELIP event, whereas the ~768 Ma Neoproterozoic-aged zircons were inherited from Precambrian crustal component of the Yangtze Block, implying the pluton has a crustally derived origin. This is consistent with its peraluminous nature, negative Nb–Ta anomaly, enrichment in light rare earth elements, high 87Sr/86Sr(i) ratio (0.7159–0.7183) and extremely negative e(Nd)(i) values (−12.15 to −13.70), indicative of melts derived from upper crust materials. The Wase pluton-intruded Devonian strata lie stratigraphically below the Shangcang ELIP sequence, which is the thickest volcanic sequence (~5400 m) in the whole ELIP. The uppermost level of the Shangcang sequence contains laterally restricted rhyolite. Although the rhyolite has the same age as the Wase pluton, its geochemical features demonstrate a different magma origin. The rhyolite displays moderate 87Sr/86Sr(i) (0.7053), slightly negative e(Nd)(i) (−0.18) and depletions in Ba, Cs, Eu and Sr, implying derivation from differentiation of a mantle-derived mafic magma source. The coexistence of crustally and mantle-derived felsic systems, along with the robust development of dike swarms, vent proximal volcanics and thickest flood basalts piles in Dali, shows that the Dali area was probably where the most active Emeishan magmatism had once existed.

International audience; The timing and mechanism of formation of the Tibet Plateau remain elusive, and even the present-day structure of the Tibetan lithosphere is hardly resolved, due to conflicting interpretations of the geophysical data. We show here that significant advances in our understanding of this orogeny could be achieved through a better assessment of the composition and rheological properties of the deepest parts of the Tibetan lithosphere, leading in particular to a reinterpretation of the global tomographic cross sections. We report mantle phlogopite xenocrysts and carbonate-bearing ultramafic cumulates preserved in Eocene potassic rocks from the Eastern Qiangtang terrane, which provide evidence that the lithospheric mantle in Central Tibet was enriched in H 2 O and CO 2 prior to the India-Asia collision. Rheological calculations and numerical modeling suggest that (1) such metasomatized mantle would have been significantly weaker than a normal mantle but buoyant enough to prevent its sinking into the deep mantle; (2) the slow seismic anomalies beneath Central Tibet may image a weakened lithosphere of normal thickness rather than a lithosphere thinned and heated by the convective removal of its lower part; and (3) melting of such soft and fusible metasomatized mantle would have been possible during intracontinental subduction, supporting a subduction origin for the studied Eocene potassic magmatism. These results demonstrate that the inheritance a soft and buoyant precollisional Tibetan lithosphere may have conditioned the growth and the present-day structure of the Tibet Plateau. Plain Language Summary The Tibetan Plateau is the largest relief on the Earth's surface, but also one of the least understood geodynamic phenomena, due to the lack of constrain on its growth evolution and mechanism. Here we have discovered, enclosed in Eocene (35-Ma-old) lavas from Central Tibet, hydrous and carbonated minerals derived from the underlying upper mantle, which reveal an unsuspected abundance of water and CO 2 in this upper mantle. We show that, consequently, the upper mantle beneath Central Tibet has been anomalously weak since before the collision of India with Asia. It was previously thought to have disappeared, foundered in a process called "delamination," but we demonstrate here that this was an artifact: Most of the tibetan mantle is still there, but it is very weak and therefore does not appear on the seismic images. This implies that models expecting the Tibet Plateau to be a result of a delam-ination process are probably wrong; instead, we propose a model in which the weak upper mantle beneath our study area was easily indented by the strong adjacent continental block; this model manages to explain both Eocene magmatism and uplift in our study area.

International audience; The timing and mechanisms of the Cretaceous sea incursions into Central Asia are still poorly constrained. We provide a new chronostratigraphic framework based on biostratigraphy and magnetostratigraphy together with detailed paleoenvironmental analyses of Cretaceous records of the proto-Paratethys Sea fluctuations in the Tajik and Tarim basins. The Early Cretaceous marine incursion in the western Tajik Basin was followed by major marine incursions during the Cenomanian (ca. 100 Ma) and Santonian (ca. 86 Ma) that reached far into the eastern Tajik and Tarim basins. These marine incursions were separated by a Turonian-Coniacian (ca. 92-86 Ma) regression. Basin-wide tectonic subsidence analyses imply that the Early Cretaceous sea incursion into the Tajik Basin was related to increased Pamir tectonism. We find that thrusting along the northern edge of the Pamir at ca. 130-90 Ma resulted in increased subsidence in a retro-arc basin setting. This tectonic event and coeval eustatic highstand resulted in the maximum observed geographic extent of the sea during the Cenomanian (ca. 100 Ma). The following Turonian-Coniacian (ca. 92-86 Ma) major regression, driven by eustasy, coincides with a sharp slowdown in tectonic subsidence during the late orogenic unloading period with limited thrusting. The Santonian (ca. 86 Ma) major sea incursion was likely controlled by eustasy as evidenced by the coeval fluctuations in the west Siberian Basin. An early Maastrichtian cooling (ca. 71-70 Ma), potentially connected to global Late Cretaceous trends, is inferred from the replacement of mollusk-rich limestones by bryozoan-and echinoderm-rich limestones.

The Cenozoic retreat of the Paratethys Sea, as well as uplift of the Tibet plateau and global cooling, have been considered as the main mechanisms for the onset of the Asian monsoon. However, due to the weak constraints on the time and path of the Paratethys Sea, the relative contribution of each of the three factors to the onset of the Asian monsoon remains debatable. Previous studies on the retreat process of the Paratethys suggested that its east coastline had already withdrawn from the Chinese Tianshan area to the west by the Oligocene. Here, we provide a new perspective on this discussion through the study of the Oligocene Anjihaihe dolomite from the northern Chinese Tianshan. Through the comparisons of carbon, oxygen, magnesium, and strontium isotope compositions between the dolomite beds and their interlayered precursor lacustrine limestone beds, we show that the Anjihaihe dolomites were formed at the end of the Oligocene from dolomitization by a fluid characterized by high δ18O, low δ26Mg, low temperature, relatively poor in carbon and Sr. This fluid was likely derived from seawater from the close-by Paratethys Sea at the time. This discovery suggests a larger Paratethys Sea during the Oligocene than previously thought and may have important implications to understand the evolution of the palaeogeography in the Chinese Tianshan region and the onset of the Asian monsoon.

International audience; The pre-Cenozoic structural pattern of Asia has had a strong impact on the localization and propagation of the Cenozoic deformation that gave birth to the Tibetan Plateau. Northern Tibet represents a key area to decipher the structural and kinematic links between the Mesozoic and Cenozoic evolution of Tibet. Nonetheless, the Mesozoic tectonic setting of the North Tibet and the role that the Paleozoic inherited Altyn Tagh Fault (ATF) shearing zone played in controlling the regional tectonic pattern during the deposition of the Mesozoic strata remain controversial. This study is based on seismic reflections, isopach maps of the Mesozoic strata in the Qaidam Basin, and provenance analysis using detrital zircon geochronological and heavy mineral contents. Seismic reflections and isopach maps demonstrate that sustained strike-slip motion along the ATF during the Early to Late Jurassic induced transtensional basin formation. Further away from the main ATF (eastern parts of the Qilian Shan and the northern Qaidam Basin), transtension also occurred along major faults, although local transpression developed in relay zones. Rotation in the regional stress field induced compression and basin inversion during the Late Jurassic to Early Cretaceous. The Cenozoic sedimentary rocks in these regions display widespread growth strata and angular unconformities characteristic of compression. This is consistent with topographic changes marked by sediment source variation evidenced by detrital zircon geochronology and heavy mineral analysis. We propose that the mechanism driving the Jurassic extension/transtension in North Tibet could be related to far-field effects of subduction processes along the southern margins of the continent.

International audience; Paleogeographic reconstructions of terranes can greatly benefit from the provenance analysis of sediments. A series of Cenozoic basins provide key sedimentary archives for investigating the growth of the Tibetan Plateau, yet the provenance of the sediments in these basins has never been constrained robustly. Here we report sedimentary petrological and detrital zircon geochronological data from the Paleocene-Eocene Nangqian-Xialaxiu and Gongjue basins. Sandstone detrital modes and zircon morphology suggest that the samples collected in these two basins were sourced from recycled orogen. Detrital zircon geochronology indicates that sediments in the Nangqian-Xialaxiu Basin are characterized by two distinct age populations at 220–280 Ma and 405–445 Ma. In contrast, three predominant age populations of 207–256 Ma, 423–445 Ma, and 1851–1868 Ma, and two subordinate age populations of ~50 Ma and ~2500 Ma, are recognized in the Gongjue Basin. Comparison with detrital zircon ages from the surrounding terranes suggests that sediments in the Nangqian-Xialaxiu Basin come from the neighboring thrust belts, whereas sediments from the Gongjue Basin are predominantly derived from the distant Songpan-Ganzi Terrane with minor contribution from the surrounding areas. A three-stage Cenozoic evolution of the eastern Tibetan Plateau is proposed. During the Paleocene, the Nangqian-Xialaxiu Basin appeared as a set of small intermontane sub-basins and received plentiful sediments from the neighboring mountain belts; during the Eocene, the Gongjue Basin kept a relatively low altitude and was a depression at the edge of a proto-Plateau; since the Oligocene, the Tibetan Plateau further uplifted and the marginal Gongjue Basin was involved in the Tibetan interior orogeny, indicating the eastward propagation of the Tibetan Plateau.

This file is the supporting information for "Nanogoethite as a potential indicator of remagnetization in red beds" published in Geophysical Research Letters. It contains one text, six figures and six tables further detailing the Nangqian red beds samples and their tests results described in the paper.

Carbonate rocks, widely used for paleomagnetically quantifying the drift history of the Gondwana derived continental blocks of the Tibetan Plateau and evolution of the Paleo/Meso/Neo-Tethys Oceans, are prone to pervasive remagnetization. Identifying remagnetization is difficult because it is commonly undetectable through the classic paleomagnetic field tests. Here we apply comprehensive paleomagnetic, rock magnetic, and petrographic studies to upper Triassic limestones in the eastern Qiangtang block. Our results reveal that detrital/biogenic magnetite, which may carry the primary natural remanent magnetization (NRM), is rarely preserved in these rocks. In contrast, authigenic magnetite and hematite pseudomorphs after pyrite, and monoclinic pyrrhotite record three episodes of remagnetization. The earliest remagnetization was induced by oxidation of early diagenetic pyrite to magnetite, probably related to the collision between the northeastern Tibetan Plateau and the Qiangtang block after closure of the Paleo-Tethys Ocean in the Late Triassic. The second remagnetization, residing in hematite and minor goethite, which is the further subsurface oxidation product of pyrite/magnetite, is possibly related to the development of the localized Cenozoic basins soon after India-Asia collision in the Paleocene. The youngest remagnetization is a combination of thermoviscous and chemical remanent magnetization carried by authigenic magnetite and pyrrhotite, respectively. Our analyses suggest that a high supply of organic carbon during carbonate deposition, prevailing sulfate reducing conditions during early diagenesis, and widespread orogenic fluid migration related to crustal shortening during later diagenesis, have altered the primary remanence of the shallow-water Tethyan carbonate rocks of the Tibetan Plateau. We emphasize that all paleomagnetic results from these rocks must be carefully examined for remagnetization before being used for paleogeographic reconstructions. Future paleomagnetic investigations of the carbonate rocks in orogenic belts should be accompanied by thorough rock magnetic and petrographic studies to determine the origin of the NRM. (C) 2019 Elsevier B.V. All rights reserved.

The surface uplift history of the Tibetan Plateau remains one of the most important unresolved issues in geosciences. Numerous models have been proposed to account for the growth of the Tibetan Plateau. This paper tries to analyze the surface uplift of the Tibetan Plateau from isostatic effects of the Cenozoic sedimentary accumulation. Based on isostatically-compensated basin infilling model, we show that the surface uplift magnitudes caused by the Cenozoic sedimentary accumulation constitute the main part of the modern elevations of the Qaidam and Tarim basins around the Tibetan Plateau, but only a small part of the modern elevations of the Hoh Xil and Lunpola basins inside the Tibetan Plateau. Paleogene sediments account for the uplift magnitudes of >900 m in both the Hoh Xil and Lunpola basins, while the uplift magnitudes caused by Neogene sediments are

This paper focuses on the strain modelling of extensional fault-propagation folds to reveal the effects of key factors on the strain accumulation and the relationship between the geometry and strain distribution of fault-related folds. A velocity-geometry-strain method is proposed for the analysis of the total strain and its accumulation process within the trishear zone of an extensional fault-propagation fold. This paper improves the non-linear trishear model proposed by Jin and Groshong (2006). Based on the improved model, the distribution of the strain rate within the trishear zone and the total strain are obtained. The numerical simulations of different parameters performed in this study indicate that the shape factor R, the total apical angle, and the P/S ratio control the final geometry and strain distribution of extensional fault-propagation folds. A small P/S ratio, a small apical angle, and an R value far greater or far smaller than 1 produce an asymmetric, narrow, and strongly deformed trishear zone. The velocity-geometry-strain analysis method is applied to two natural examples from Big Brushy Canyon in Texas and the northwestern Red Sea in Egypt. The strain distribution within the trishear zone is closely related to the geometry of the folds.

Netherlands Organization for Scientific Research (NWO) [825.15.016]; Institute for Rock Magnetism (IRM) at the University of Minnesota - Instruments and Facilities Program of NSF

The Huangshi structure, as one of the NWW-trending S-shaped structures in the southwestern Qaidam Basin, holds important implications for unraveling the regional structural pattern. There are four dominant sets of surface strike-slip fractures at the core of the Huangshi structure. The fractures with orientations of N28°E, N47°E and N65°E correlate well with conjugate Riedel shears (R′), tension fractures (T) and Riedel shears (R) in the Riedel shear model, respectively. Two conjugate strike-slip fracture sets occur at the surface of the Hongpan structure (secondary to the Huangshi structure) and the southwestern part of the Huangshi structure. In seismic sections, the Huangshi structure is present as a positive flower or Y-shaped structure governed by steeply dipping faults, whereas Hongpan and Xiaoshaping structures, located symmetrically to the Huangshi structure, are thrust-controlled anticlines. The Riedel shear pattern of surface strike-slip fractures, the positive flower or Y-shaped structure in seismic sections and the NW-trending secondary compressional anticlines consistently demonstrate that the Huangshi structure is dominated by left-lateral strike-slip faults which comprise a strike-slip fault network. Considering the similar S-shaped configuration and NWW trend of structures across the southwestern Qaidam Basin, it can be further speculated that these structures are also predominantly of left-lateral strike-slip types.

The Junggar Basin, located in northwestern China, provides important records for investigating Mesozoic tectonic and climate evolution in Central Asia. The Upper Jurassic-lowermost Cretaceous strata in the basin include the Qigu, Kalazha, and Qingshuihe Formations in ascending order. By synthesizing outcrop and well data and previous research, we conducted a detailed sedimentologic and stratigraphic correlation analysis for the three formations. Our study shows that a sharp lithofacies change from intermittent braided-river red fine-grained sediments of the Qigu Formation to alluvial fan conglomerates of the Kalazha Formation, is widespread along the basin margins. From bottom to top, the Kalazha alluvial fan conglomerates can be divided into six sequences showing a progradation to retrogradation cycle, and they finally retrograde into the lake sediments of the lowermost Cretaceous Qingshuihe Formation. However, within the Junggar Basin, the Kalazha Formation is commonly considered to be absent and the Qingshuihe Formation possesses a basal fluvial coarse-grained sandstone bed (50–100 m), beneath which a widespread unconformity is observed. Stratigraphic correlation suggests that the alluvial fan conglomerates of the Kalazha Formation along the basin margins are equivalent to the basal sandstone bed of the Qingshuihe Formation within the basin. Finally, we conclude that progressive tectonic uplift and climate aridification occurred in the Junggar Basin during deposition of the Qigu Formation in the Late Jurassic, while the basin began to experience a relatively humid climate and underwent rapid subsidence during deposition of the Kalazha Formation in the latest Jurassic-earliest Cretaceous, probably driven by the far-field effects of the short-lived but significant Mongol-Okhotsk collisional orogeny.

The onset of modern central Asian atmospheric circulation is traditionally linked to the interplay of surface uplift of the Mongolian and Tibetan-Himalayan orogens, retreat of the Paratethys sea from central Asia and Cenozoic global cooling. Although the role of these players has not yet been unravelled, the vast dust deposits of central China support the presence of arid conditions and modern atmospheric pathways for the last 25 million years (Myr). Here, we present provenance data from older (42–33 Myr) dust deposits, at a time when the Tibetan Plateau was less developed, the Paratethys sea still present in central Asia and atmospheric pCO2 much higher. Our results show that dust sources and near-surface atmospheric circulation have changed little since at least 42 Myr. Our findings indicate that the locus of central Asian high pressures and concurrent aridity is a resilient feature only modulated by mountain building, global cooling and sea retreat., The onset of modern central Asian atmospheric circulation is often linked to the interplay of late Cenozoic paleogeographic changes and global cooling. Here the authors present sedimentary provenance data from early Cenozoic dust deposits, which indicate long-term stability of the central Asian high pressure system.

The Permian to early Triassic terrestrial successions in the Mahu sag constrain the tectonic evolution of northwestern edge of the Junggar basin. This study analyzes the sequence stratigraphy of the Mahu sag in order to understand the interplay between tectonic process and the sedimentary fill of the basin. It uses detailed analysis of drill cores, geophysical well logs, 2D seismic reflection profiles and isopach maps. Sixteen lithofacies are grouped into three facies associations: fan delta, fluvial delta and lacustrine. The Permian to Triassic strata are organized into two second-order transgressive-regressive (T-R) sequences, further separated into transgressive systems tracts (TST) and regressive system tracts (RST). Based on seismic profiles, paleogeographic facies distribution and isopach maps, two stages of tectonic evolution are recognized: 1) early Permian syn-rift to middle Permian post-rift; 2) late Permian to early Triassic tectonic inversion. During the early Permian, sediments of TST1 record two cycles of depositional system transition from fan delta to deep lacustrine setting within the half-graben structure shown by 2D seismic profiles. At this time, tectonic mechanical subsidence exceeded sediment supply. The middle Permian post-rift stage (RST2) is characterized by gradual and slow peneplanation, which is documented by sediment supply exceeding thermal subsidence, so that the location of depocenter shifted and the depositional system transitioned from lacustrine to fan delta setting. Late Permian-early Triassic tectonic inversion is demonstrated by a striking change of the sediment dispersal patterns along the Hong-Che, Ke-Bai and Wu-Xia fault zones and alluvial fan deposition at the base of TST2. Tectonism is the main factor controlling sediment dispersal, paleogeographic evolution and hence hydrocarbon accumulation, providing a new perspective to oil and gas exploration and development in the Mahu sag.

The marginal fault system, which is represented by the Hong–Che (Hongshanzui–Chepaizi), Ke–Bai (Karamay–Baikouquan), and Wu–Xia (Wuerhe–Xiazijie) sub-systems and developed in the northwestern margin of the Junggar Basin, NW China, is a key factor affecting the development characteristics of the Permian–Triassic strata and controlling the hydrocarbon accumulation in the area. In this study, based on the latest two-dimensional and three-dimensional seismic exploration data, regional geological background, and previous research results, the attributes and timing of this structural belt of the NW margin as well as the basin type related to it are clarified. The result shows that the above marginal fault system has dextral strike–slip features and is characterized by a high-angle master fault, branch faults, and short-axis plunging anticlines in an en echelon arrangement. The tectonic deformation is classified into two main periods: late Permian tectonic inversion and late Triassic reactivation. It is found that the late Permian tectonic inversion led to the migration of the depocenter in the Mahu Depression and was induced by the counterclockwise rotation of the Junggar block and West Junggar area relative to the western part of the Chingiz range in the late Paleozoic. The nose structures, fault blocks, and en echelon anticlines derived from the relevant thrust faulting and folding may account for the development of the main structural traps, which play an important role in the hydrocarbon accumulation in the NW margin of the Junggar Basin.

International audience; The Paleogene Lulehe Formation marks the onset of deposition in the Qaidam basin and preserves evidence of the initial topographic growth of northern Tibet. However, limited outcrops impede understanding of the sedimentary features of the Lulehe Formation as well as the tectonic relationship between the basin and surrounding topography. To fill this gap, we investigated core samples along the basin margin and conducted flexural modeling to estimate the topographic load of the Qilian Shan and Eastern Kunlun Shan during the deposition of the Lulehe Formation. Core samples reveal that the Lulehe Formation mainly consists of distal fluvial to marginal lacustrine deposits and proximal fluvial deposits along the southern margin of the basin while characterized by proximal alluvial fan deposits along the northern margin of the basin. Together with evidence for faulting shown on the seismic profiles, we infer that simultaneous deformation within the Qilian Shan and Altyn Tagh Shan during the Paleogene resulted in accumulation of coarse detrital deposits in the northwestern and northeastern Qaidam basin. The simultaneous deformation within the Altyn Tagh Shan and Qilian Shan since the Paleogene supports the idea that deformation in these two regions is kinematically linked. One‐load and two‐load beam flexural modeling indicate that the topographic load generated by both the Eastern Kunlun Shan and the Qilian Shan is responsible for the subsidence of the Qaidam basin during deposition of the Lulehe Formation. Our results highlight the initial relative high topography in the northern Tibetan plateau during the early Cenozoic

The Upper Carboniferous of Bogda Mountain is a critical area for understanding final oceanic closure of the Junggar Ocean in the Central Asian Orogenic Belt (CAOB). The 4 km thick Liushugou and Qijiaojing formations, comprising tuffs and lesser lavas that accumulated in a subsiding marine basin, were studied to understand the architecture and petrogenesis of the volcanic succession. Tuffs, lavas and hypabyssal intrusions are mostly of calc-alkaline composition, ranging from basalt through andesite and dacite to rhyolite, interbedded with rare high-K rocks of basaltic trachyandesite to trachyte composition. Clinopyroxene and Fe Ti oxides are the main fractionating minerals in the calc-alkaline rocks. Plagioclase has altered to albite by sea-floor metasomatism. The rocks are enriched in LILE and show relative depletion in Ta and Nb, suggesting an arc-related origin. The tuffs and lavas pass northward into dominantly trachytic rocks, suggesting a northward subducting, intra-oceanic arc to back-arc system, with polarity contrary to previous literature, that was active from the time of the Kalamaili arc collision (~350 Ma) to shortly after the North Tianshan–Junggar collision (~315 Ma). Following that collision, West Junggar experienced sinistral strike-slip deformation, and related crustal scale faults in Bogda Mountain allowed the rise of basaltic magma, forming pillow lavas and hyaloclastites in a deepening basin. Finally, in the latest Carboniferous, the subduction-related volcanism ended and the Bogda basin was then onlapped by turbidites. The recognition of northward subduction in the Bogda segment of the CAOB has regional implications for final closure of the Junggar Ocean. Comparison with published data from Kalamaili, the Junggar Basin, West Junggar and Arbassy demonstrates three tectonic phases with different volcanism, sedimentation and deformation in different parts of the amalgamating orogen.

International audience; The fall into the Oligocene icehouse is marked by a steady decline in global temperature with punctuated cooling at the Eocene-Oligocene transition, both of which are well documented in the marine realm. However, the chronology and mechanisms of cooling on land remain unclear. Here, we use clumped isotope thermometry on northeastern Tibetan continental carbonates to reconstruct a detailed Paleogene surface temperature record for the Asian continental interior, and correlate this to an enhanced pollen data set. Our results show two successive dramatic (>9 °C) temperature drops, at 37 Ma and at 33.5 Ma. These large-magnitude decreases in continental temperatures can only be explained by a combination of both regional cooling and shifts of the rainy season to cooler months, which we interpret to reflect a decline of monsoonal intensity. Our results suggest that the response of Asian surface temperatures and monsoonal rainfall to the steady decline of atmospheric CO2 and global temperature through the late Eocene was nonlinear and occurred in two steps separated by a period of climatic instability. Our results support the onset of the Antarctic Circumpolar Current coeval to the Oligocene isotope event 1 (Oi-1) glaciation at 33.5 Ma, reshaping the distribution of surface heat worldwide; however, the origin of the 37 Ma cooling event remains less clear.

International audience; Understanding the pre-collisional paleogeography in the NE Tibetan plateau provides insights into the growth mechanisms of the northern portion of the plateau in the Cenozoic. We conducted sandstone petrography analysis and determined U-Pb ages for detrital zircons from Cretaceous sandstone from the Yumen Basin and the northern Qilian Shan. Cretaceous strata in the northern Yumen Basin yield a unimodal age population at 290–240 Ma that indicates primary derivation from Bei Shan. Cretaceous strata in the westernmost Yumen Basin contain zircons of 2.6–2.2 Ga, 2.1–1.7 Ga, 1.4–0.7 Ga, 440–380 Ma and 300–230 Ma, suggesting source derivation from both the Qilian Shan and Bei Shan. Within the northern Qilian Shan, Cretaceous strata yield age populations of 2.8–2.3 Ga, 2.1–1.2 Ga, 480–380 Ma and ca. 270 Ma, indicating derivation from the Qilian Shan. Sandstone composition results show that a sample from the northern Qilian Shan contains more lithic fragments and plots in the recycled orogen field of the quartz-feldspar-lithics (QFL) diagram, while samples from Yumen Basin are more quartz-rich and plot close to the continental block field of the QFL diagram. This compositional difference corresponds to source variation, consistent with the detrital zircon record. Combined with existing sedimentology and low-temperature thermochronology datasets, we suggest the presence of Cretaceous topographic relief in the Bei Shan and Qilian Shan prior to India-Asia collision. Considering >300 km post-Cretaceous left-lateral offset along the Altyn Tagh Fault (ATF) and the consistently similar detrital zircon ages spectra of the samples from the Cretaceous to late Oligocene strata in the Yumen Basin, we infer the paleogeography in the NE Tibetan plateau has been similar from the late Cretaceous to the late Oligocene with ATF termination in the western Yumen Basin instead of having been linked to strike-slip faults in the Alxa or other regions to the east since its initiation.

International audience; Mountains grow upward and outward when the accretion of material outpaces its removal. Mountain building is synergistically influenced by geodynamics, internal structures (crustal and lithospheric), and climate. The northward growth of the Qilian Shan, which occupies a transition zone between the ~4500 m high central Tibetan plateau and the adjacent

The proto-Paratethys Sea covered a vast area extending from the Mediterranean Tethys to the Tarim Basin in western China during Cretaceous and early Paleogene. Climate modelling and proxy studies suggest that Asian aridification has been governed by westerly moisture modulated by fluctuations of the proto-Paratethys Sea. Transgressive and regressive episodes of the proto-Paratethys Sea have been previously recognized but their timing, extent and depositional environments remain poorly constrained. This hampers understanding of their driving mechanisms (tectonic and/or eustatic) and their contribution to Asian aridification. Here, we present a new chronostratigraphic framework based on biostratigraphy and magnetostratigraphy as well as a detailed palaeoenvironmental analysis for the Paleogene proto-Paratethys Sea incursions in the Tajik and Tarim basins. This enables us to identify the major drivers of marine fluctuations and their potential consequences on Asian aridification. A major regional restriction event, marked by the exceptionally thick (

International audience; Two debated age models, with a basal age of ~50 Ma versus ~30 Ma, proposed for the depositional age of Cenozoic strata within the Qaidam basin result in a diverse understanding of the initial pattern of deformation in the northern Tibetan Plateau. To evaluate these age models, we integrated isopach maps within the basin with published thermochronology data from surrounding ranges to balance the sediments preserved in the basin with materials eroded in the drainage area. When following the traditional ~50 Ma age model, the total volume of material eroded from the surrounding source area is 4.4±0.3 ×105 km3. Using instead the ~30 Ma age model for the basal Lulehe Formation and related revisions to the basin chronology, the volume of eroded material is calculated at 3.5±0.2×105 km3, which provides a better match to the calculate total volume of solid grains that are preserved in the basin (2.8±0.1×105 km3). However, growth strata revealed in seismic profiles along the Southern Qaidam Thrust suggest reverse‐faulting began during the deposition of Oligocene‐Miocene strata. Following the ~50 Ma age model, the onset time of faulting along the Southern Qaidam Thrust is ~35.5 Ma, consistent with previous thermochronology results. If both age models are correct, then this requires a significant time‐transgressive nature to basin fill that allows for older ages of deposition in the southern part of the basin. This study highlights the need for further effort to determine the depositional age of the strata in the southern and western parts of the Qaidam basin.

The Gongjue basin from the eastern Qiangtang terrane is located in the transition region where the regional structural lineation curves from east-west-oriented in Tibet to north-south-oriented in Yunnan. In this study, we sampled the red beds in the basin from the lower Gongjue to upper Ranmugou formations for the first time covering the entire stratigraphic profile. The stratigraphic ages are bracketed within 53-43Ma by new detrital zircon U-Pb ages constraining the maximum deposition age to 52.51.5Ma. Rock magnetic and petrographic studies indicate that detrital magnetite and hematite are the magnetic carriers. Positive reversals and fold tests demonstrate that the characteristic remanent magnetization has a primary origin. The Gongjue and Ranmugou formations yield mean characteristic remanent magnetization directions of D-s/I-s=31.0 degrees/21.3 degrees and D-s/I-s=15.9 degrees/22.0 degrees, respectively. The magnetic inclination of these characteristic remanent magnetizations is significantly shallowed compared to the expected inclination for the locality. However, the elongation/inclination correction method does not provide a meaningful correction, likely because of syn-depositional rotation. Rotations relative to the Eurasian apparent polar wander path occurred in three stages: Stage I, 33.33.4 degrees clockwise rotation during the deposition of the Gongjue and lower Ranmugou formations; Stage II, 26.93.7 degrees counterclockwise rotation during deposition of the lower and middle Ranmugou formation; and Stage III, 17.73.3 degrees clockwise rotation after 43Ma. The complex rotation history recorded in the basin is possibly linked to sinistral shear along the Qiangtang block during India indentation into Asia and the early stage of the extrusion of the northwestern Indochina blocks away from eastern Tibet.

Lacustrine stromatolites provide high-resolution and sensitive palaeoenvironmental and palaeoclimatic records of their respective drainage basins and beyond. A well-developed stromatolite bed was discovered within the clastic deposits of the Early Miocene Taxihe Formation in the southern margin of the Junggar Basin, north of the Tian Shan Mountains. Their sedimentological features indicate a near-shore stable environment of a shrinking lake. The study of the stable oxygen and carbon isotopes in this stromatolite bed revealed that δ18O V-PDB values range from −11.3‰ to −5. 6‰ and those of δ13C V-PDB from −1.8‰ to 1.7‰. Lower values −10. 2‰ and −8. 2‰, respectively, were determined from nearby lacustrine limestones of Oligocene age. The co-variation and overall increasing trend of the δ18O and δ13C values indicate deposition in a closed basin during a period of aridification. This environmental change can be related to the major uplift of the Tian Shan Mountains, the southern border of the Junggar Basin, during the Early Miocene. Several δ18O and δ13C records of lacustrine stromatolites ranging in age from Oligocene to Middle Miocene were reported: from localities in the Northern Tibetan Plateau and western Qaidam Basin. The similarity of the individual stable isotope records in stromatolites from Northwest China, indicate an underlying regional cause. These stromatolites were deposited during the period of major uplift of the Tibetan Plateau and the Tian Shan Mountains. It is therefore concluded that the stromatolite records provide local snapshots of the effect of this major process on atmospheric precipitation and environmental conditions in Northwest China. Copyright © 2016 John Wiley & Sons, Ltd.

The Lower Permian volcano-sedimentary Zhesi Group has been investigated in the Hongliuhe and Liuyuan areas in Beishan, China, which is significant for the reconstruction of Late Paleozoic evolution in the southern part of the Central Asian Orogenic Belt. A variety of volcanic facies were distinguished in the Upper Zhesi Group: pillow basalt with interstitial limestone, thin-interbedded limestone and basalt, closely packed pillows, pillow-fragmented hyaloclastite breccia, and peperite. Laser 40 Ar/ 39 Ar whole-rock dating of the basalt yielding an age of 277 ± 11 Ma, as well as Early Permian brachiopod fossils in the limestone interbedded with the basalt, indicate that basalt was erupted in the Early Permian. The identification of the peperite and other facies originating from magma-sediment mingling reveals that the basaltic lava flows were derived from autochthonous basaltic magmatism and formed as part of the Lower Permian succession. The peperite also indicates that these subaqueous basaltic lava flows are not dismembered ophiolitic components, but formed in an autochthonous extensional setting in the Early Permian. The clastic rocks in the Lower Zhesi Group underlying the basaltic flows and peperites in the Hongliuhe and Liuyuan areas show a general fining-upwards sequence, indicating that they were deposited in a progressively deepening basin overlying the Devonian Hongliuhe suture zone. Subaqueous volcanism in a rift basin or basins, accompanied by coeval deposition of carbonate sediment and mud, built up the peperite-bearing volcanogenic-sedimentary successions. From among the various tectonic hypotheses for the Beishan region, this study demonstrates that by Early Permian the region was developing post-collisional rift basins.

Early Carboniferous volcanic rocks in the Batamayineishan Formation overlie unconformably the molasse deposits and the ophiolitic melanges and are restricted in narrow zones along both sides of the Kalamaili orogenic belt in North Xinjiang, southern Central Asian Orogenic Belt. These rocks demonstrate the post-collisional setting in East Junggar commenced in Tournaisian and also mark an important transitional period from the final amalgamation to late Paleozoic voluminous juvenile granitoids in East Junggar. The volcanic rocks are composed of basalt, basaltic andesite, andesite, trachyte and rhyolite. Both mafic and felsic rocks are characterized by enrichments in large ion lithophile elements, light rare earth elements and depletion in Nb and Ta, low initial 87Sr/86Sr and high, positive ɛNd(t). Three groups of mafic rocks have been identified: Shoshonitic group 1 has the highest MgO, CaO, Ni and Cr and the lowest Na2O, Al2O3, La, Ba, La/Yb and Ba/Th with primary magma features; group 2 calc-alkaline and high-K calc-alkaline mafic rocks have the lowest K2O, P2O5, Th and Th/Nb, and the highest TiO2; and group 3 (shoshonitic to potassic alkaline) has the highest K2O, P2O5, La, Ba, La/Yb and Th/Nb, and the lowest TiO2. The A-type-like felsic rocks were derived from the differentiation of the mafic magma. Geological and geochemical evidences indicate that the Batamayineishan Formation was generated from the process of slab breakoff (detachment). Group 1 samples are produced by decompressional melting of the upwelling asthenosphere mainly composed of spinel and garnet (50:50) lherzolite which has been enriched by overlying metasomatized lithosphere during ascent. Group 2 is derived from 5–10% partial melting of shallower spinel-bearing lithospheric mantle induced by the hot rising asthenosphere, where the contribution of slab-derived fluid is predominant. Low partial melting (3–5%) of the mantle wedge and/or thickened lithospheric mantle enriched by slab-derived components generates group 3. Slab breakoff as an important geodynamic process accounts for the post-collisional magmatism between 343.5 Ma–330 Ma, providing a model for post-collisional crust–mantle interaction in the CAOB.

Based on detailed field survey in the western Qaidam Basin, combined with petroleum exploration practices in recent years, this study suggests that the Qaidam Basin is a strike-slip superimposed basin jointly controlled by the left-lateral strike-slip Altyn Tagh and East Kunlun faults. The Altyn Tagh fault acts as the major controlling boundary, while the East Kunlun fault only controls the local evolution of the southern edge of the basin. To the east, the northern Qaidam-Qilian Shan thrust-fold belt passively accommodates the northeastward displacement along the Altyn Tagh fault through NE-SW directed shortening. In the India-Asia collision background, the left-lateral strike-slip faulting along the Altyn Tagh fault initiated from the early Eocene, forcing the Qaidam Basin to move northeastward, causing the thrust and slip deformation of the NW-SE faults in northern Qaidam margin-Qilian Mountain area, and the deposition of the Cenozoic since the Paleogene Lulehe Formation. During the Paleogene, the northern Qaidam Basin developed coarse-grained sediments like that in a foreland basin, forming poor quality source rocks; while the southwestern Qaidam Basin was an extensional sag basin where good quality source rocks deposited. By the early Miocene, left-lateral faulting along the Kunlun fault became active, leading to the formation of a series of en-echelon faults (e.g. the Kunbei fault, the Arlar fault and the Hongliuquan fault). These faults gradually migrated northward, their kinematics changing from left-lateral strike-slip motion to NE-SW transpression. Strike-slip-related structures controlled by those faults (e.g. the Yingxiongling structure) are ideal places for oil and gas accumulation from Paleogene source rocks. To sum up, the Qaidam Basin is a strike-slip superimposed basin jointly controlled by the left-lateral strike-slip Altyn Tagh and East Kunlun faults. The temporal and spatial superimposition of these two strike-slip faults during the Cenozoic controlled the evolution of the basin as well as the oil and gas accumulation. Key words: Qaidam Basin, East Kunlun fault, Altyn Tagh fault, strike-slip superimposed basin, control on oil and gas accumulation

The Altyn Tagh fault, located in the northern Tibetan Plateau, is a large left-lateral strike-slip fault heavily responsible for the growth and formation of the plateau during Cenozoic time. Despite its significance, the initial timing and kinematic patterns of movement along the Altyn Tagh fault remain highly debated. Here, we present a detailed analysis of the stratigraphy and geochronology of three key lithologic sections (Tula, Anxi, and Caishiling) along the Altyn Tagh fault to better understand this kinematic history. By correlating stratigraphic contacts and lithology with the U-Pb age spectra of Mesozoic samples within the western Qaidam Basin, we find the Altyn Tagh fault has experienced a total of ∼360 km of displacement during the Cenozoic. By combining seismic profile data with geologic observations, we divide the activity along this fault into two distinct stages of motion: (1) an initial stage, which occurred between early Eocene (ca. 49 Ma) and mid-Miocene time (ca. 15 Ma) and resulted in ∼170 km of offset, and (2) an early stage, which began in the late Miocene Epoch and continues into the present, resulting in ∼190 km of offset along the fault. We identify the Tula and Anxi sections as piercing points along the western segment of the Altyn Tagh fault and define these regions as residual parts of the original Qaidam Basin. These estimates suggest that motion along the Altyn Tagh fault has accelerated from an average left-lateral strike-slip rate of ∼5.0 mm/yr during initial stage faulting to a rate of ∼12.6 mm/yr between the late Miocene Epoch and present day.

Several solutions have been proposed to explain the long-standing kinematic observation that postcollisional upper crustal shortening within the Himalaya and Asia is much less than the magnitude of India-Asia convergence. Here we implement these hypotheses in global plate reconstructions and test paleolatitudes predicted by the global apparent polar wander path against independent, and the most robust paleomagnetic data. Our tests demonstrate that (1) reconstructed 600–750 km postcollisional intra-Asian shortening is a minimum value; (2) a 52 Ma collision age is only consistent with paleomagnetic data if intra-Asian shortening was ~900 km; a ~56–58 Ma collision age requires greater intra-Asian shortening; (3) collision ages of 34 or 65 Ma incorrectly predict Late Cretaceous and Paleogene paleolatitudes of the Tibetan Himalaya (TH); and (4) Cretaceous counterclockwise rotation of India cannot explain the paleolatitudinal divergence between the TH and India. All hypotheses, regardless of collision age, require major Cretaceous extension within Greater India.

The Late Mesozoic&ndash, Cenozoic topographic and climate evolution of Central Asia remains highly debated. The final retreat of the proto-Paratethys Sea from the western Tarim Basin is thought to correspond in time with the onset of tectonic uplift in the Pamir, Tian Shan and Altai ranges, as well as with regional aridification. The oxygen and carbon isotope compositions of the sediment deposits in the various Central Asian basins have already been used to decipher both the topographic and climatic changes that occurred in that region during the Cenozoic, generally concentrating on one sedimentary section and/or on a limited time range and either using multiple-type samples including sandstone calcitic cements, marine carbonates, fossils, or paleosols. In order to get a homogeneous dataset, minimizing variations in the isotopic composition of the material depending on its type and/or depositional environment, we selected only calcareous paleosols sampled in several continuous sections covering a wide time range from the Late Jurassic to the Pliocene. Our sampling also covers a wide area encompassing the whole Tian Shan region, which allows detecting regional variations in the &delta, 18O and &delta, 13C values. We show that the influence of the distance to the proto-Paratethys Sea on the paleosol &delta, 18O record was not significant. Besides local factors such as the occurrence of large lakes that can have a significant effect on the isotopic composition of the calcareous paleosols, the long-term evolution of both the &delta, 13C values possibly reflects the hypsometry of the river drainage systems that bring water to the basins. However, as it is commonly accepted that the &delta, 18O of soil carbonates is controlled by the &delta, 18O of in-situ precipitation, this last conclusion remains to be further investigated.

International audience; A Cenozoic structural inversion event from transtension to transpression involving salt tectonics has been uncovered in the Yingxiong Range, the western Qaidam Basin. Seismic reflection data show that there are two common structural styles in the Yingxiong Range: (1) the positive flower structure; (2) the thrust-controlled fold at shallow depth and the positive inverted flower structure at deep levels, which are separated by a salt layer in the upper Xiaganchaigou Formation. The Yingxiong Range experienced a first stage of transtension in the Eocene, induced by the Altyn Tagh Fault, and a second stage of transpression from the early Miocene to present, jointly controlled by the Altyn Tagh and Eastern Kunlun Faults. The Eocene transtension produced numerous NW-striking right-stepping en-échelon transtensional normal faults or fractures in the Yingxiong Range. At the same time, evaporites and mudstone were deposited in the vicinity of these faults. In the early Miocene, the Eocene transtensional normal faults were reactivated in a reverse sense, and the thrust-controlled folds at shallow depth started to form simultaneously. With transpression enhanced in the late Cenozoic, positive flower structures directly formed in places without evaporites. The Cenozoic transtension to transpression inversion of the Yingxiong Range is the result of strike-slip superimposition controlled by the Altyn Tagh and Eastern Kunlun Faults in time and space.

The right-stepping en-echelon Kunbei fault system, consisting of the Hongliuquan, Arlar, XIII, and Kunbei faults, features importantly in the tectonic evolution of the southwest Qaidam basin. The 3D seismic cross-section interpretation and key horizon similarity attribute analysis show that the NWW-striking Arlar fault is composed of two steeply dipping faults (F1 and F2) in cross-sectional view, and branches eastward into two west-dipping faults (F5 and F6) in map view. The fact that the strata above T 2 (the base of the early Miocene Xiayoushashan Formation) become dramatically thinner toward the high points of the Arlar fault suggests an early Miocene initiation (ca. 22.0 Ma) for this fault. As indicated by the windowed amplitude-related attribute maps, the Arlar fault and F5 (one branch of the Arlar fault) have cumulative sinistral offsets of ∼8.6–8.7 km and ∼5.2–5.4 km, respectively. These considerably greater strike-slip components, in conjunction with the respective maximum true dip-slip displacements of

Paleomagnetic dating of the India-Asia collision hinges on determining the Paleogene latitude of the Lhasa terrane (southern Tibet). Reported latitudes range from 5°N to 30°N, however, leading to contrasting paleogeographic interpretations. Here we report new data from the Eocene Linzizong volcanic rocks in the Nanmulin Basin, which previously yielded data suggesting a low paleolatitude (~10°N). New zircon U-Pb dates indicate an age of ~52 Ma. Negative fold tests, however, demonstrate that the isolated characteristic remanent magnetizations, with notably varying inclinations, are not primary. Rock magnetic analyses, end-member modeling of isothermal remanent magnetization acquisition curves, and petrographic observations are consistent with variable degrees of posttilting remagnetization due to low-temperature alteration of primary magmatic titanomagnetite and the formation of secondary pigmentary hematite that unblock simultaneously. Previously reported paleomagnetic data from the Nanmulin Basin implying low paleolatitude should thus not be used to estimate the time and latitude of the India-Asia collision. We show that the paleomagnetic inclinations vary linearly with the contribution of secondary hematite to saturation isothermal remanent magnetization. We tentatively propose a new method to recover a primary remanence with inclination of 38.1° (35.7°, 40.5°) (95% significance) and a secondary remanence with inclination of 42.9° (41.5°,44.4°) (95% significance). The paleolatitude defined by the modeled primary remanence—21°N (19.8°N, 23.1°N)—is consistent with the regional compilation of published results from pristine volcanic rocks and sedimentary rocks of the upper Linzizong Group corrected for inclination shallowing. The start of the Tibetan Himalaya-Asia collision was situated at ~20°N and took place by ~50 Ma.