Western Tibet Research Articles

Influence of atmospheric circulation on glacier mass balance in western Tibet: an analysis based on observations and modeling

AbstractGlacier changes on the Tibetan Plateau (TP) have been spatially heterogeneous in recent decades. The understanding of glacier mass changes in western Tibet, a transitional area between the monsoon-dominated region and the westerlies-dominated region, is still incomplete. For this study, we used an energy-mass balance model to reconstruct annual mass balances from October 1967 to September 2019 to explore the effects of local climate and large-scale atmospheric circulation on glacier mass changes in western Tibet. The results showed Xiao Anglong Glacier is close to a balanced condition, with an average value of -53±185 mm w.e. a-1 for 1968-2019. The interannual mass balance variability during 1968-2019 was primary driven by ablation-season precipitation, which determined changes in the snow accumulation and strongly influenced melt processes. The interannual mass balance variability during 1968-2019 was less affected by ablation-season air temperature, which only weakly affected snowfall and melt energy. Further analysis suggests that the southward (or northward) shift of the westerlies caused low (or high) ablation-season precipitation, and therefore low (or high) annual mass balance for glaciers in western Tibet. In addition, the average mass balance for Xiao Anglong Glacier was 83±185, -210±185, and -10±185 mm w.e. a-1 for 1968-1990, 1991-2012, and 2013-2019, respectively. These mass changes were associated with the variations in precipitation and air temperature during the ablation season on interdecadal time scales.

Climatic and environmental change in the western Tibetan Plateau during the Holocene, recorded by lake sediments from Aweng Co

Understanding the strength and extent of the Asian summer monsoon (including the East Asian summer monsoon and the Indian summer monsoon) in the Tibetan Plateau (TP) region is crucial for predicting possible changes in the regional eco-environment and water resources under global warming. Due to the lack of well-dated and high-resolution paleoclimate records, long-term monsoon dynamics are still not well understood in the western TP, which is currently influenced by both the Indian summer monsoon (ISM) and the westerlies. Here we present a multi-proxy lacustrine record covering the past 10,500 years from Aweng Co, an alpine lake at the northern limit of the modern ASM in western Tibet. Our results show that the western TP was mainly controlled by the ISM during the Holocene and the regional ecosystem/environment was sensitive to climate change. The climate was the wettest between 10.5 and 7.3 cal kyr BP, when terrestrial plants in the catchment were productive and the biomass of benthic algae was low possibly due to limited sunlight at the lake bottom due to high lake level. From 7.3 to 5.0 cal kyr BP the climate shifted towards drier conditions, resulting in a decline in terrestrial plant cover. Between 5.0 and 3.1 cal kyr BP, the climate became even drier, resulting in a further decline in vegetation cover in the catchment. Between 4.6 and 3.1 cal kyr BP, 100% endogenic dolomite precipitated from the lake water, possibly induced by high Mg/Ca ratios. After 3.1 cal kyr BP, the climate was the driest and frequent centennial-scale droughts occurred. The lake level was low and would have resulted in more light reaching the lake bottom, favoring the growth of benthic algae. The reconstructed lake level change of Aweng Co agrees well with the paleo-shoreline records in the southern TP, demonstrating that the ISM evolution played a key role in lake hydrological processes in this region. A comparison of paleoclimate records shows the ISM reached 34.5° N in the western TP during the Holocene.

Block Tectonics across Western Tibet and Multi-Millennial Recurrence of Great Earthquakes on the Karakax Fault

Block Tectonics across Western Tibet and Multi-Millennial Recurrence of Great Earthquakes on the Karakax Fault

Upper Mantle Heterogeneity and Radial Anisotropy Beneath the Western Tibetan Plateau

AbstractP‐wave radial anisotropy (RAN) tomography of the upper mantle beneath the western Tibetan Plateau is determined using teleseismic arrival time data recorded at 71 temporal seismic stations of the ANTILOPE‐I and Y2 arrays, which reveals a complex deformation pattern in the upper mantle. A high‐velocity anomaly with prominent positive RAN is visible to the south of 31°N, which may reflect the underthrusting Indian lithospheric mantle (ILM). Further north, another high‐velocity zone appears at depths >200 km, which is possibly related to the foundering ILM, or the northward advancing ILM affected by previously attached Tethyan oceanic slab. Considering the continuity of the high‐velocity zones and similarity of the RAN anomalies, we suggest that there is no slab tearing or breakoff at present beneath western Tibet. To the north of 31°N, E‐W trending variations of velocity and RAN at shallow depths (<150 km) suggest that small‐scale convection occurs between 79°E and 81°E, whereas the residue of the Eurasian lithospheric mantle is located in the eastern side. We deem that the formation of the Ya‐Re Rift and Puran Graben was caused by variations of the lithospheric thickness instead of slab tearing or asthenospheric upwelling, considering locations of the rift and the graben and our present results.

Source spectral studies using Lg wave in western Tibet

We investigate the spectral characteristics of Lg wave using 346 waveforms recorded at 24 seismic stations located across Karakoram Fault (KKF) in western Tibet. The tectonic structure of western Tibet is very complex and formed of several blocks, which are separated by distinct suture zones. It is predominated by KKF which is one of the major strike-slip faults in western Tibet. To understand the spatial variation in crustal properties, we subdivide the study region into two parts across the KKF. The analysis of the decay of the spectral amplitudes of Lg waves with epicentral distances allows for the evaluation of the crustal quality factor QLg, which is a direct measurement of attenuation. We have observed a frequency-dependent QLg with strong attenuation in the crust though no variation is observed across the KKF. This is consistent with the reported body wave attenuation study for this region. The corner frequency (fc) is observed to decrease linearly with distance in both sides of the KKF with an effective shift of 2.5 to 1 Hz at 400 km and 1 to 0.7 Hz near 1000 km respectively. The moment magnitude of each earthquake is computed using displacement spectrum and subsequently compared with the reported magnitude.

Detailed mapping of the surface rupture of the 12 February 2014 Yutian Ms7.3 earthquake, Altyn Tagh fault, Xinjiang, China

Large-scale detailed mapping plays a key role in revealing the rupture characteristics and mechanisms of strong earthquakes. Relatively few studies have been performed on the surface ruptures of large earthquakes in central and western Tibet due to its remote nature and high elevation. Based on high-resolution unmanned aerial vehicle (UAV) photography, we mapped the coseismic surface rupture of the 2014 Yutian Ms7.3 earthquake. Along the western Altyn Tagh fault system, the earthquake produced ≈37 km of surface rupture along the South Xor Kol fault (southern section S1), Xor Kol fault (central section S2) and Ashikule fault (northern section S3). Section S1 has a 16-km-long surface rupture with an average sinistral offset of 52±25 cm and a maximum offset of ~90 cm, while section S3 has a 14.2-km-long surface rupture with an average sinistral offset of 36±21 cm and a maximum offset of ~84 cm. A compilation of 5308 cracks yields an average crack width along the southern section of 85±71 cm and a maximum width of ~700 cm; the average width along the central section is 39±21 cm, and the maximum width is 243 cm; and the average width along the northern section is 61±44 cm with a maximum of ~340 cm. In addition, the average cumulative opening across rupture zone is 3.4±2.9 m along the southern section, with a maximum of ~17 m; 4.3±3.6 m along the central section, with a maximum of ~13 m; and 1.7±1.6 m along the northern section, with a maximum of ~6 m. Evidently, the average crack width and cumulative opening decrease towards bends and steps along the fault. A global synthesis of surface rupture distributions corresponding to strike-slip earthquakes indicates that the rupture zone is wider near the complex parts of fault geometries (such as bends, steps and fault bifurcations) than along straight sections, suggesting that the fault geometry has an obvious control on the surface rupture width. The widespread cracks at the intersection between the Xor Kol and South Xor Kol faults may indicate that an extensional regime is more likely to produce distributed offfault deformation, which provides an observational constraint for the numerical simulation of dynamic rupture on a fault. In addition to coseismic surface rupture, the Yutian earthquake also produced a large number of gravity-driven slides on alluvial fans with gentle slopes. The friction efficiency of the water-bearing salt layer beneath fans could decrease the sliding threshold and trigger instability under surface shaking. These distributed deformations and gravity-driven slides reflect the coupling between the rupture propagation and fault geometry and indicate that the rupture may have propagated in two directions along the Ashikule fault after passing through a step. Therefore, the investigation of coseismic surface rupture provides important observational constraints on the dynamic rupture process.

Study on spatial clustering characteristics of tuberculosis in China, 2013-2018

Objective: To explore the tuberculosis (TB) clustering areas and changing tendency in China from 2013 to 2018, so as to provide evidence for improving the control and prevention programs on TB. Methods: Spatial distribution of TB in China from 2013 to 2018 was studied using data from TB information management system of Chinese disease prevention and control information system. The SaTScan 9.6 software was used to detect and analyze the TB clusters and relative risks. Likelihood ratio and P value under the scan windows were used as the main index to define the clusters. Results: The TB registration rate declined in China from 2013 to 2018. High-risk clusters were mainly located in western regions of Xinjiang, Tibet, Shaanxi, Sichuan, Chongqing, Yunnan, Guizhou, Guangxi provinces and central and eastern regions of Inner Mongolia, Hubei, Hunan, Jiangxi, Guangdong and Hainan provinces. The number of counties with TB clusters declined slowly, from 1 112 in 2013 to 806 in 2018. In comparison with areas other than the clusters, the RR of TB in the clusters remained at high levels in southern Xinjiang and western Tibet from 2013 to 2018 (RR>3.0). Conclusions: The number of the counties with TB clustering declined slowly from 2013 to 2018, and most of them were located in western and central China. Early detection and health education should be focused on TB patients to prevent the spread of TB. Management programs set for TB patients should be strengthened, especially in the western parts of the country where TB clusters and high relative risks existed.

New evidence of long-distance interaction across the Himalayas: Faience beads from Western Tibet

Abstract Faience beads have been excavated from the Gebusailu site in western Tibet and date back as far as the second half of the 2nd millennium BC. As the earliest faience found on the Tibetan Plateau so far, these beads provide important evidence for the cross-regional exchange in the pre-historic western Tibet. Randomly selected thirteen samples were analyzed by SR-μCT, EPMA and LA-ICP-MS. The CT slices suggested that the structure of the samples was formed on cylindrical core and glazed by cementation. The glaze recipes indicate the samples can be classified as soda-rich faience with pure copper ore, the scrap or oxidation product of the copper metal, as the possible colorant. Those beads were possibly imported from Egypt or somewhere impacted by the Egyptian faience production technology. This implies that the ethnic groups on the plateau or other regions already crossed the Himalayas and integrated into the treasure exchange network of Eurasia, making the decorative luxury commodities penetrate to the Tibetan Plateau in 3500 years ago.

Hydrochemical composition, distribution, and sources of typical organic pollutants and metals in Lake Bangong Co, Tibet.

Lake Bangong Co is a special lake in western Tibet, with characteristics of increased salinity from the eastern area to the western area. Due to its remote location and poor environmental conditions, there are few background data on the water environment of this lake. In this study, the water chemical composition of Lake Bangong Co was studied, and the concentration levels, distribution characteristics, and pollution sources of polycyclic aromatic hydrocarbons (PAHs), phthalic acid esters (PAEs), and metals (As, Pb, Cr, Mn, Cu, Cd, Ni, and Zn) were investigated. The hydrochemical characteristics of the lake showed significant spatial differences. Conductivity, salinity, degree of mineralization, total hardness, Cl-, and SO42- generally increased from the eastern part to the western part. Most water quality parameters met the class III standards of the Chinese surface water standards; however, the Cl- and SO42- concentrations in the western part exceeded the surface water standard limits. ΣPAH and ΣPAE concentrations in lake water have no significant relationship with hydrochemical parameters. Among the 16 target PAHs, 4 PAH monomers with a (5 + 6)-ring were not detected in the lake water. The main sources of PAHs included emissions from biomass combustion, petroleum volatilization, and automobile exhaust. Six PAE monomers were detected at all sampling sites with relatively low concentrations, and di-2-ethylhexyl phthalate (DEHP) and di-n-butyl phthalate (DBP) were the main pollutants. The main source of PAEs was domestic waste, which might be related to increasing human activities in this area recently. In general, the concentrations of metals in the water of Lake Bangong Co were lower than those in the regions affected by anthropogenic activities except As. The results of PCA showed that As, Cu, and Cr mainly originated from natural sources; Pb, Mn, and Cr came from both natural and anthropogenic sources; and Cd was highly likely from anthropogenic sources.

Preservation of cultural heritage in Tibet : situation and future prospects of the Tholing Monastery

espanolEl Monasterio de Tholing es uno de los monumentos religiosos mas importantes del oeste del Tibet; sus murales muestran el mayor logro artistico de los tibetanos en el contexto cultural y estetico en los dos periodos diferentes de la historia tibetana. Este estudio presenta, en primer lugar, el contexto historico de este monumento, indicando su importancia en el desarrollo de la historia tibetana; en segundo lugar, el valor historico y artistico de los murales del Monasterio de Tholing. Se considera que este importante y valioso monumento debe contar con mayor atencion para su investigacion y preservacion; y ademas, que cumple con los requisitos correspondientes para ser incluido en la Lista de Patrimonio Mundial de la UNESCO. La informacion y promocion sobre este monumento beneficia la industria turistica de la zona. EnglishTholing Monastery is one of the most important religious monuments in western Tibet, and its murals showthe greatest artistic achievement of the Tibetans in the cultural and aesthetic context in the two different periodsof Tibetan history. This article first introduces the historical context of this monument, indicating its importancein the development of Tibetan history. Secondly, both the historical and artistic value of the murals of theTholing Monastery are explained and it is suggested that this monument deserves more attention in preservationand research, and should be included in the UNESCO World Heritage List. Finally, it is considered that thetourist use of the Tholing Monasteries and its Buddhist frescoes could contribute in the future to promote thetourism industry in that area.

Stratigraphic and taxonomic considerations on the Late Cretaceous rudist fauna of Aksai Chin (Western Tibet, China) from the De Filippi Collection

The rudist fauna collected in western Tibet in the Aksai Chin area by the De Filippi expedition in 1914 has been reprised and redescribed. This fauna is composed of Radiolites cf. lusitanicus, Radiolites sp., Gorjanovicia cf. endrissi, ? Sauvagesia sp., Sphaerulites sp., Durania sp., and Gyropleura sp. The rudist-bearing beds belong to the Tielongtan Group of the Tianshuihai terrane. The Turonian-? Coniacian Xiloqzung Formation (Fm.) bear the older rudists (Radiolites cf. lusitanicus, Radiolites sp., Sphaerulites sp., Durania sp.), while younger ages have been determined through microfossil analysis which, compared with the western Neotethys records, suggests an early-mid Campanian age. This allowed to ascribe the younger rudists of the collection (Gorjanovicia cf. endrissi, ? Sauvagesia sp., Gyropleura sp., Radiolites sp.) to the Dongloqzung Formation. Our data confirm that rudist-bearing facies in the Tielongtan Group extend at least up to the middle Campanian. The Aksai Chin rudist assemblage should belong to the Southwestern Asian assemblage of the Eastern Mediterranean Subprovince.

Revealing the scale- and location-specific controlling factors of soil organic carbon in Tibet

Soil organic carbon (SOC) leads to a significant impact on global carbon (C) cycling and soil quality. Variations in SOC are controlled by vegetation, geomorphic, geological and climatic factors, but the dominant environmental differs. In the Qinghai -Tibet Plateau, which contains large amount of low-latitude permafrost, the impact of environmental factors for the variations of SOC may be different due to the unique and complicated geographical condition. In this study, the two-dimension empirical mode decomposition (2D-EMD) is applied to examine the variations of SOC at different scales and locations, and the correlations between SOC and environmental factors are explained. The spatial distribution of SOC in Tibet was decomposed into three intrinsic mode functions (IMFs) under different scales, with spatial variation scales of approximately 7 km, 109 km and 338 km, which represented the small, medium and large scale, respectively. The remaining residual represented the variation trend of SOC across Tibet. The correlations between SOC and environmental factors (elevation, radiation, evapotranspiration and temperature) are distinguished by the physiographic zone at small and medium scales. Temperature is weekly or nonsignificantly correlated to SOC in cold-dry western Tibet at large scale. Normalized difference vegetation index (NDVI) and precipitation influenced SOC mainly at small scales, while the effects of precipitation and evapotranspiration on the distribution of SOC were due to geomorphology and type of permafrost. The combined effect of climate on SOC was larger than other factors at large scale while factors refer to DEM, evapotranspiration, water erosion and NDVI accounted for more contribution at small scale. The results indicated that the environmental factors influence SOC under a combination of scale and location effect. These findings are of great significance for future studies in SOC dynamic modelling under the influence of natural changes and human activities.

Seismic attenuation structure across the Karakoram fault in western Tibet

SUMMARY2-D attenuation maps are produced for the crust of western Tibet using local earthquakes which are recorded by an array of 31 broad-band stations operated from 2007 July to 2011 May. Relative contribution of scattering ($Q_{sc}^{-1}$) and intrinsic ($Q_{i}^{-1}$) attenuation have been calculated using Multiple Lapse Time Window Analysis under the assumption of uniform distribution of multiple isotropic scattering and intrinsic absorption in a medium for five different frequency bands centred at 1.5, 3, 6, 12 and 18 Hz, respectively. All the events are selected on the basis of high signal-to-noise ratio having hypocentral distance within 200 km from the respective stations. The obtained Q−1 values show a strong frequency dependent nature which can be correlated to the degree of tectonic complexity and the heterogeneities present in the medium. The intrinsic absorption is found to be the dominant mechanism at all the frequency ranges for all stations except few (WT03, WT07 and WT13) at 18 Hz, which may be correlated with the presence of partial melt, geothermal fluids, hydrothermal springs, mantle-derived fluids and radioactivity in the crust of western Tibet. We have divided the entire area into two regions across the Karakoram fault (KKF) to explore the variations of crustal attenuation properties. The first part covers the northeastern of KKF referred as Region 1 while the second part covers the southwestern of KKF referred as Region 2. The spatial variations of $Q_{i}^{-1}$ across the region exhibit significant differences between Regions 1 and 2 at all the investigated frequencies. Interestingly, Region 1 exhibits higher $Q_{i}^{-1}$ than Region 2 at lower frequencies, whereas $Q_{i}^{-1}$ shows opposite trends at higher frequencies (> 6 Hz) as it shows higher values in Region 2 than Region 1. We find that the obtained values of Q−1 are also in good agreement with the other segments of Himalaya and Tibet as well as different tectonic regions in the world.

Subduction of the Indian Plate and the Nature of the Crust Beneath Western Tibet: Insights From Seismic Imaging

AbstractThe northward extent of subducted Indian plate is a fundamental component of hypotheses explaining deformation and magmatism within the Tibetan Plateau. Yet, these aspects of the plate are debated in west Tibet. Here we report a new three‐dimensional lithospheric structure of seismic velocity and radial anisotropy under west Tibet constructed from Rayleigh and Love wave phase velocity maps at periods of 20–167 and 20–125 s, respectively. Our results show the Indian lithospheric mantle to be subhorizontally subducted under west Tibet across the Bangong‐Nujiang suture to the Qiangtang terrane, as indicated by a prominent fast velocity anomaly accompanied with positive radial anisotropy (Vsh > Vsv). We find a positive spatial correlation of this result with information on the distribution of late Cenozoic potassic‐adakitic rocks in western Tibet. Additionally, we show that the midcrust of west Tibet is characterized by an anomalously low shear wave velocity (3.2–3.4 km/s at ~30‐km depth) and positive anisotropy, which is consistent with an estimated ~3% fraction of partial melt. We suggest that the midcrust of this region is capable of flowing and that its three‐dimensional structure shows it to extend south of the Karakoram fault (KKF), a shear zone interpreted as a barrier to crustal flow. Instead, our results are consistent with the KKF embedded in weak middle crust along with several other structures that display a pattern of distributed deformation in the western portion of the Tibetan Plateau.

Tomographic Imaging of the India‐Asia Plate Collisional Tectonics and Mantle Upwelling Beneath Western Tibet

AbstractTo better understand the lithosphere mantle collision tectonics between the India plate and Asia plate, we determine three dimensional P wave velocity structure beneath western Tibet using 27,439 arrival times from 2,174 teleseismic events recorded by 182 stations of Hi‐CLIMB Project and 16 stations in the north of Hi‐CLMB. Our tomographic images show the velocity structure significantly difference beneath northern and southern Qiangtang, which can further prove that the Longmu Co‐Shuanghu ophiolitic belt is a significant tectonic boundary fault zone. There are two prominent high velocity anomalies and two prominent low velocity anomalies in our images. One obvious high velocity anomalies subduct beneath the Tibet at the long distance near 34°N, whereas it is broke off by an obvious low velocity anomaly under the IYS. We interpret them as northward subducting Indian lithosphere mantle and the low velocity anomanly under IYS likely reflects mantle material upwelling triggered by tearing of the northward subduction Indian lithosphere. The other prominent high velocity anomaly was imaged at a depth from 50 km to 200 km horizontal and up to the northern Qiangtang with its southern edge extending to about 34°N through Hoh Xil block. We infer it as the southward subducting Asia lithosphere mantle. The other widely low velocity anomaly beneath the Qiangtang block lies in the gap between the frontier of India plate and Asia plate, where is the channel of mantle material upwelling.

A New Discovery of Ag-Pb-Zn Mineralization via Modern Portable Analytical Technology and Stream Sediment Data Processing Methods in Dajiacuo Area, Western Tibet (China)

Tibet, which is rich in mineral resources, is a treasure trove for geological explorers. However, prospecting work has been slow, especially in the western part, due to the precipitous terrain, changeable climate and low access. Hence, modern advanced field analytical technology and effective data processing methods play significant roles in rapid and efficient exploration in Tibet. In this paper, spectrum-area fractal modeling and portable X-ray fluorescence analysis (pXRFA) were used to identify and verify geochemical anomalies associated with Ag-Pb-Zn mineralization based on a stream-sediment dataset of 39 elements in the Dajiacuo-Xurucuo region of western Tibet. First, staged factor analysis (SFA) was used to obtain the Ag-Pb-Zn-Cd geochemical assemblage. Second, the first-factor pattern obtained using SFA was dissociated by a spectrum-area (S-A) fractal model and a digital elevation model (DEM)-based geochemical model (DGM) was constructed. Finally, the sections of Ag, Cd, Pb, and Zn were obtained using pXRFA. The results show that Ag-Pb-Zn-Cd enrichment zones were mostly located around the contact belt of volcanic rocks and intrusions, or along SE-NW trending faults. Considering the variable terrain and catchment basin, the extension of long axes of Ag-Pb-Zn-Cd anomalies into higher elevation areas that are favorable for Ag-Pb-Zn mineralization should be investigated. Anomaly maps created with the aid of a DGM show promising potential for mineralization in the Dajiacuo-Xurucuo region, and abundant Ag-Pb-Zn mineralization was identified with the assistance of pXRFA in the source areas for the geochemical anomalies in the Dajiacuo. We conclude that SFA and the S-A fractal model constitute a valid tool to identify or verify geochemical anomalies in areas of low-density stream-sediment sampling. The pXRFA can accurately determine the source of geochemical anomalies and improve anomaly verification efficiency.

An investigation of regional variations of coda wave attenuation in western Tibet

Regional variations of coda wave attenuation ( ${Q}_{c}^{-1}$ ) have been analyzed for western Tibet using single isotropic scattering model. A total of 628 local earthquakes, having a source-receiver distance less than 200 km recorded at the Y2 network of broadband stations during 2007–2011, are used for this analysis. All the events are crustal having maximum hypocentral depth up to 40 km. The estimation of ${Q}_{c}^{-1}$ is made at five different frequencies centered at 1.5, 3, 6, 12, and 18 Hz through lapse time windows from 30 to 70 s with an increment of 10 s starting at 1.2 times of secondary wave arrival time. We find a strong frequency-dependent nature of ${Q}_{c}^{-1}$ in this region, which may demonstrate that the medium is highly heterogeneous and tectonically very active. The regional variations of ${Q}_{c}^{-1}$ across the whole region have been performed, and we find a marked contrast across the Karakoram fault (KKF) at different frequencies and lapse time windows, which are consistent with the geotectonic diversity of the region. ${Q}_{0c}^{-1} ({Q}_{c}^{-1} \text {at 1 Hz})$ and frequency-dependent parameter (nc) for each station are also estimated using the power law relation ${Q}_{c}^{-1} = {Q}_{0c}^{-1} f^{-n_{c}}$ . There is a tendency to increase nc with increasing observed ${Q}_{0c}^{-1}$ values, and vice versa. Variations of ${Q}_{0c}^{-1}$ at different lapse time windows and its corresponding apparent depths are also examined. We have observed a certain rise in ${Q}_{0c}^{-1}$ values at a 60-s lapse time window which may be due to the change in velocities, temperature, rock composition variations, and strong heterogeneity in the lithospheric mantle. The obtained values in this study are also found to be well compared with other results reported globally.

Detrital Zircon Fission-Track Thermochronology of the Present-Day River Drainage System in the Mt. Kailas Area, Western Tibet: Implications for Multiple Cooling Stages of the Gangdese Magmatic Arc

It is still controversial how the high elevation of the Tibetan Plateau established after the Indian-Asian collision during the Cenozoic. The timing of Gangdese magmatic arc exhumation and uplift history would provide useful message for this disputation. We present six zircon fission-track (ZFT) data from modern river sand in the western Tibet, around the Mt. Kailas, to decipher the long-term exhumation histories of the Gangdese magmatic arc. The data suggests that all the Gangdese magmatic arc rocks experienced rapid cooling during the Eocene (∼46’35 Ma) and Oligocene (∼31’26 Ma). The movement along the north-south trending extensional fault and dextral strike-slip Karakoram fault induced the adjacent rocks exhumed at the Middle Miocene (∼15’16 Ma) and Late Miocene (∼10’11 Ma), respectively. According to the minimum and central AFT ages for each sample, the fastest exhumation rate is about 0.4 km/Ma, with average long-term exhumation rates on the order of ∼0.3 km/Ma since the Oligocene. This result supports the outward growth model for plateau forming, indicating the southern margin of the Gangdese magmatic arc attained high elevation after the Oligocene.

Dietary exposure to arsenic and human health risks in western Tibet

The health effects of drinking water exposure to inorganic arsenic are well known but are less well defined for dietary exposure. The rising concerns of arsenic risks from diet motivated this study of arsenic concentrations in highland barley, vegetables, meat, and dairy products to evaluate arsenic exposure source and to assess health risks among rural residents of Ngari area, western Tibet. Total arsenic and arsenic speciation were measured by inductively coupled plasma mass spectrometry (ICP-MS) and high-performance liquid chromatography combined with ICP-MS (HPLC-ICP-MS) respectively. Average total arsenic concentrations of 0.18 ± 0.21 (n = 45, median: 0.07 mg·kg−1), 0.40 ± 0.57 (n = 17, median: 0.15 mg·kg−1), 0.21 ± 0.16 (n = 12, median: 0.17 mg·kg−1), and 0.18 ± 0.08 (n = 11, median: 0.22 mg·kg−1) were observed in highland barley, vegetables, meat, and dairy products, respectively. Inorganic arsenic was determined to be the main species of arsenic in highland barley, accounting for about 64.4 to 99.3% (average 83.3%) of total arsenic. Nearly half (44.4%) of the local residents had ingested >3.0 × 10−4 mg·kg−1·d−1 daily dose of arsenic from highland barley alone, above the maximum oral reference dose recommended by the United States Environmental Protection Agency (USEPA). The inorganic arsenic daily intake from highland barley was 3.6 × 10−4 mg·kg−1·d−1. Dietary exposure to inorganic arsenic alone increased the cancer risk probability to 5.4 in 10,000, assuming that the inorganic arsenic in highland barley has the same carcinogenic effects as that in water.

Molecular Phylogeography and Evolutionary History of the Endemic Species Corydalis hendersonii (Papaveraceae) on the Tibetan Plateau Inferred From Chloroplast DNA and ITS Sequence Variation

In response to past climatic changes, the species with different habits or adaptive traits likely have experienced very different evolutionary histories, especially for species that restricted to high mountain areas. In order to trace how Quaternary climatic oscillations affected range distributions and intraspecific divergence of such alpine plants on the Tibetan Plateau, here, we investigated maternally inherited chloroplast DNA (cpDNA) markers and biparentally inherited nuclear ribosomal internal transcribed spacer (ITS) DNA variations and aimed to explore the phylogeographic history of the endemic alpine species Corydalis hendersonii Hemsl. (Papaveraceae). We sequenced four cpDNA fragments (trnS-trnG, trnT-trnL, atpH-atpI, and psbE-petL) and also the nuclear (ITS) region in 368 individuals from 30 populations across the species' range. The network and phylogenetic analysis based on cpDNA variations identified 15 chlorotypes that cluster into three distinct clades. However, our nuclear DNA results demonstrated that there were four genetic/geographical groups within C. hendersonii. Some common and highly divergent cpDNA and ITS haplotypes were distributed in the populations of central and northeastern Tibetan Plateau, and the highest nucleotide diversity and genetic differentiation were detected in the central region. Demographic tests further indicated that the populations of southwestern and western Tibet may have experienced recent range expansion, which most likely occurred during the last glacial maximum (LGM) and continued its expansion after the beginning of the Holocene. These two different groups of this species may have derived from potential refugia that existed in the central and/or northeastern regions of Tibet during recent interglacial periods. In addition, our AMOVA analyses detected high genetic differentiation along with the whole sampling range. Also, distinct phylogeographic structures were detected among populations of C. hendersonii based on both of cpDNA and ITS variation. These findings shed new light on the importance of climatic oscillations during Quaternary and complex local topography as causes of intraspecific diversification and demographic changes within cold-tolerant herbs in the Tibetan Plateau biodiversity hotspot.