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The onset of mountain building along margins of the Tibetan Plateau provides a key constraint on the processes by which the high topography in Eurasia formed. Although progressive expansion of thickened crust underpins most models, several studies suggest that the northern extent of the plateau was established early, soon after the collision between India and Eurasia at ca. 50 Ma. This inference relies heavily on the age and provenance of Cenozoic sediments preserved in the Qaidam basin. Here, we present evidence in the northern plateau for a considerably younger inception and evolution of the Qaidam basin, based on magnetostratigraphies combined with detrital apatite fission-track ages that date the basin fills to be from ca. 30 to 4.8 Ma. Detrital zircon-provenance analyses coupled with paleocurrents reveal that two-stage growth of the Qilian Shan in the northeastern margin of the Tibetan Plateau began at ca. 30 and at 10 Ma, respectively. Evidence for ca. 30 and 10 to 15 Ma widespread synchronous deformation throughout the Tibetan Plateau and its margins suggests that these two stages of outward growth may have resulted from the removal of mantle lithosphere beneath different portions of the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Provenance analyses provide valuable insights into both the complex interaction between orogenic belts and surrounding sedimentary basins and the role of plate collision in the basin-mountain coupling process. This paper investigates the provenance of the Cenozoic sediments filling the Qaidam Basin (Qinghai Tibetan Plateau, China) by combining petrology, major elements, trace elements, rare earth elements (REEs), and Zircon U Pb dating analysis to provide new insight about the collision of the Indian and Asian plates. The petrographic analysis indicates that the studied sediments are poorly sorted and made of angular to subrounded clasts, suggesting deposition relatively near to the source area. The Chemical Index of Alteration (CIA) of the samples in the study area, which ranges from 68.88 to 74.08, indicates that the study area experienced moderate weathering from the early Eocene to the early Miocene. In addition, Zr/Sc versus Th/Sc shows that most samples did not experience recycling. K 2 O/Na 2 O, SiO 2 , Th, Sc, Zr, La and Co contents indicate that the Cenozoic sediments filling the Qaidam Basin derived mainly from an active continental margin and a continental island arc setting. U Pb dating of detrital zircons denotes that the studied sediments were derived from rocks with five major sets of ages (200–350 Ma, 350–500 Ma, 500–1000 Ma, 1000–1500 Ma, and >1500 Ma), with the two first sets being more common. Based on the regional geology, therefore, these ages indicate that the main provenance source was shifted southwards from the Mesozoic crystalline basement (south Qilian Mountains) in the early-middle Eocene, to the Saishiteng Mountains in the middle-late Eocene, and to Lvliang and Qilian Mountains during the late Eocene-early Miocene. Zircon dating also indicates that the main source area was displaced eastward through time. Finally, it is concluded that the tectonic deformation progressed from west to east in the northern margin of the Qaidam Basin, reflecting a far-field response to the onset of the India-Asia collision. • The sediments mainly derive from source terranes that used to be active continental margin and continental island arc. • Detrital zircon evidence indicates that the Qilian Mountains, instead of the East Kunlun, were the dominant detrital source. • The tectonic deformation during the early Eocene reflected a far-field response to the onset of India-Asia collision. [ABSTRACT FROM AUTHOR]

Abstract: Some rivers on the northern slope of the eastern Kunlun Mountains in the Qaidam Basin, China, show very high concentrations of boron and lithium. Correspondingly, the salt lakes fed by these rivers show an unusual enrichment of boron and lithium, and become an important economic resource. The origin of boron and lithium has long been debated. The aim of this study is to analyze the water chemistry and hydrogen and oxygen isotopic composition of river water to understand the unusual enrichment of boron and lithium in the salt lakes of the Qaidam Basin. Oxygen and hydrogen isotope data show that the source of river water in the winter and summer originates from the Kunlun Mountain ice and snow melt water, respectively. The water chemistry shows that boron and lithium contents are high but little variable with seasons in the Nalenggele River and Wutumeiren River waters. By contrast, other rivers have much lower lithium and boron contents. Moreover, the contents of B3+ and Li+ in the river loads or bed sands show little difference amongst the rivers. This indicates that removal by adsorption or input by surface rock weathering is not the main controlling factor of the B3+ and Li+ variation in the rivers. Rivers with high B3+ and Li+ content are chemically similar to geothermal waters in the Tibetan Plateau. In addition, the source area of the Nalenggele River is located in a collision zone of the Kunlun Mountains and Altun Mountains. Large and deep faults can serve as conduits for geothermal fluids. Thus, deep geothermal waters in the source area can easily migrate to the surface and discharge as springs feeding the rivers. They are an important source of B3+ and Li+ to the rivers. The abnormally high contents of B3+ and Li+ in the Nalenggele and Wutumeiren Rivers also suggest that the geothermal source area may be a future target for boron and lithium resources. [Copyright &y& Elsevier]

The nonmarine, at present hypersaline Qaidam basin of Western China comprises a ca. 8-17 km thick sedimentary fill, which is dominated by Eocene to Recent clastic rocks. These successions were folded due to ongoing India-Eurasia convergence from late Miocene onwards until today. Shortening also resulted in enhanced fluid flow and precipitation of sulphate minerals in subvertical tension gashes, which are mainly filled by celestine and fibrous gypsum. The orientation of subvertical veins is similar over most parts of the western Qaidam basin and indicates NNE-SSW to N-S shortening (present-day coordinates) dissimilar to the NE-motion direction deduced from recent geodetic (GPS) data. In deeper stratigraphic levels of anticlinal cores, tension gashes composed of fibrous gypsum subparallel to bedding demonstrate fluid overpressure during their formation at a shallow structural level, below the conversion temperature of gypsum to anhydrite. We interpret all these veins as near-surface precipitates from sulphate-rich brines during an advanced stage of folding. The 87Sr/86Sr ratios of a synsedimentary celestine layer and a celestine vein at the abandoned Dafengshan mine are 0.711414 and 0.711418, respectively, and are similar to those from Oligocene and Miocene limestones (0.711578 to 0.711679). Although the source area is highly heterogeneous in composition, these data indicate, therefore, in accor- dance with previous observations on clastic rocks, only a very minor change in the average 87Sr/86Sr ratio of the source region from Oligocene to Quaternary times. [ABSTRACT FROM AUTHOR]

Abstract: During 2006 to 2007, a small array of broadband seismic stations was deployed across the eastern Qaidam–Kunlun border. Receiver functions derived from this data set show a coherent P-to-S converted phase from the Moho at ~65km to ~58km below sea level (b.s.l.) from south to north beneath the Kunlun mountains. The Moho is observed at ~45km b.s.l. beneath the Qaidam basin. A sharp offset of ~15km in the Moho depth is observed just beneath the Qaidam–Kunlun border. The close correlation between the surface topography and the sharp Moho offset substantiates the view that the Kunlun crust is weaker than that of the Qaidam basin and thickens vertically in response to compression between India (through the Tibetan plateau) and the Qaidam basin. Furthermore, a strong steeply north-dipping converted phase can be seen from ~5 to 15km b.s.l. north of the North Kunlun Fault, which is likely a major south-directed thrust fault partially responsible for the thickening of the Kunlun crust. [Copyright &y& Elsevier]

The timing and mechanism of the changes in the stress/strain field direction on the northeastern Tibetan Plateau are controversial, which limits our understanding of the tectonic evolution of the northeastern Tibetan Plateau and the Altyn Tagh Fault (ATF). Here, we conducted a detailed anisotropy of low-field magnetic susceptibility analysis of successive fluvial-lacustrine sediments deposited since the early Oligocene at Eboliang in the middle-western Qaidam Basin. Magnetic fabrics of the upper part (the Qigequan Formation) are predominantly considered to be primary sedimentary magnetic fabrics, while those of the lower-middle parts (the Shangganchaigou to Shizigou Formations) are mainly pre-folding, layer-parallel shortening induced embryonic tectonic fabrics. The magnetic lineation revealed ~50° successive clockwise rotations of the compressional strain orientations from nearly N-S to NE-SW in the middle-western Qaidam Basin during ~15–7 Ma. The nearly N-S compressional event is consistent with the generally N-S-directed India-Asia collision and thus was attributed to its far-field effects, whereas the post-mid-Miocene transition of ~50° clockwise rotations of the compressional strain orientations is consistent with the tectonic deformation in the basin interior. This transition lagged far behind that in the northern Qaidam marginal thrust belt (NQMTB), which began in the early Oligocene. The laterally diachronous transition in compressional strain orientation and deformations in the middle-western and northern Qaidam Basin were most likely due to the two-stage, sinistral strike-slip faulting of the ATF, with confined sinistral shear occurring along the ATF and partially transferred into the NQMTB during the early Oligocene to middle Miocene, while distributed sinistral shear occurred on the northeastern Tibetan Plateau beginning in the middle Miocene. A bidirectional propagation of compressional strain variation and tectonic deformation from the northern Qaidam Basin since the early Oligocene is proposed to reflect the tectonic evolution of the northeastern Tibetan Plateau. • Magnetic fabrics from lower-middle parts of the Eboliang profile were mostly induced by prefolding, layer-parallel shortening • Magnetic lineation revealed ~50° successive clockwise rotations of compressional strain orientations during ~15–7 Ma • Diachronous transitions in compressional strain were attributed to two-stage strike-slip faulting of the Altyn Tagh Fault [ABSTRACT FROM AUTHOR]

Abstract: Forty-one apatite fission track ages (AFT) were determined on samples collected along a N–S section of the eastern Kunlun Mountains across the Middle and South Kunlun Faults between Buqingshan and Dulan. Measured AFT ages lie between 25±2 and 130±10Ma, and all are significantly younger than their host rock formation or sediment deposition ages. Modelling the AFT data identifies a two stage regional cooling history that spans the last 100Myrs. The earliest cooling phase occurred between the late Jurassic and early Tertiary and involved a moderate level of cooling between 20 and 40°C, equivalent to average exhumation rates of =15m/Myr. The second phase of cooling took place from ∼20Ma with cooling rates increasing tenfold. Average exhumation rates for this period are estimated to be in the range of ∼100–150m/Myr. The first stage of protracted cooling is consistent with regional evidence from the Qiantang and Lhasa terrans where previous studies have noted low rates of denudation in relation to a back-arc extensional setting. The more recent acceleration in cooling seen in the Kunlun data coincides with an increase in sedimentation rates in the adjacent Qaidam Basin. This points to a phase of Neogene uplift and increased erosion of the Kunlun Range, although contemporaneous monsoon strengthening may also have had a role. [Copyright &y& Elsevier]