Southeastern Tibetan Research Articles

Holocene proglacial loess in the Ranwu valley, southeastern Tibet, and its paleoclimatic implications

Glaciers and aeolian sediments are widespread on the Tibetan Plateau. Although glaciations have played an important role in the formation of loess in many glaciated regions in the Northern Hemisphere, proglacial loess on the Tibetan Plateau is rarely reported, and its origin, source, and paleoclimatic implications remain unclear. We have found a small area of proglacial loess deposits in the Ranwu valley, southeastern Tibet. Grain-size, geochemical and geomorphologic evidence, as well as observations of local dust storms, reveal that the outwash sediments of the Laigu glacier (∼30 km long) are the primary source for the local loess. We also found that the glacial wind from this glacier is the main transport vector, and thus speculate that the onset of the Ranwu loess, at ca. 6.6 ka, correlates with the early Neoglacial advance of the Laigu glacier, which generated glacial winds and local dust storms in the closed and deep-incised glacial valley. This is supported by the basal radiocarbon ages of two ice cores and a synthesis of Holocene glacial stadials on the Tibetan Plateau. Loess layers and paleoclimatic proxies indicate two drought stages at ca. 6.6–6 ka and ca. 2.9 ka to the present, corresponding to two well-documented weakened stages of the Indian Summer Monsoon. This study highlights that, although local aeolian sediments always cover a small area, they also have potential to record some clues of regional climate changes in some alpine regions. Much more detailed studies should be done to reveal their specific formation mechanisms and paleoclimatic implications.

Geographic variation in seed traits within and among forty-two species of Rhododendron (Ericaceae) on the Tibetan plateau: relationships with altitude, habitat, plant height, and phylogeny.

Seed mass and morphology are plant life history traits that influence seed dispersal ability, seeding establishment success, and population distribution pattern. Southeastern Tibet is a diversity center for Rhododendron species, which are distributed from a few hundred meters to 5500 m above sea level. We examined intra- and interspecific variation in seed mass and morphology in relation to altitude, habitat, plant height, and phylogeny. Seed mass decreased significantly with the increasing altitude and increased significantly with increasing plant height among populations of the same species. Seed mass differed significantly among species and subsections, but not among sections and subgenera. Seed length, width, surface area, and wing length were significantly negative correlated with altitude and significantly positive correlated with plant height. Further, these traits differed significantly among habitats and varied among species and subsection, but not among sections and subgenera. Species at low elevation had larger seeds with larger wings, and seeds became smaller and the wings of seeds tended to be smaller with the increasing altitude. Morphology of the seed varied from flat round to long cylindrical with increasing altitude. We suggest that seed mass and morphology have evolved as a result of both long-term adaptation and constraints of the taxonomic group over their long evolutionary history.

Zircon U–Pb ages of the Mianning–Dechang syenites, Sichuan Province, southwestern China: Constraints on the giant REE mineralization belt and its regional geological setting

The Himalayan Mianning–Dechang (MD) rare earth element (REE) belt in western Sichuan Province, southwestern China, is approximately 270km long and 15km wide, and contains total reserves of more than 3Mt of light REEs (LREEs), comprising one giant (Maoniuping), one large (Dalucao), two small–medium-sized (Muluozhai and Lizhuang), and numerous smaller REE deposits. The belt occurs within the eastern Indo-Asian collision zone (EIACZ), where its location is controlled by large-scale strike-slip faults and tensional fissure zones. Himalayan carbonatite–syenite complexes consist predominantly of alkaline syenite stocks and carbonatite sills or dikes that host REE mineralization. Previous studies have reported inconsistent ages for alkaline magmatism syenite formation and REE mineralization. Here, we present new results of sensitive high-resolution ion micro-probe U–Pb dating of zircons from syenites from the Dalucao, Maoniuping, Lizhuang and Diaoloushan areas, the first systematic and precise age determinations for these rocks in the MD belt. The new data give concordant ages of 12.13±0.19 and 11.32±0.23Ma for the Dalucao deposit, 22.81±0.31 and 21.3±0.4Ma for Maoniuping, 26.77±0.32Ma for Muluozhai, and 27.41±0.35Ma for Lizhuang. These ages, which should be regarded as maximum ages for the REE mineralization in the study area, can be split into two groups, i.e. 11–12Ma in the southern part of the MD belt and 12–27Ma in the northern part, suggesting a progression of magmatism from north to south. These data suggest that the majority of carbonatite–syenite magmatism within the EIACZ occurred during the main stage of Himalayan metallogenesis. The ages presented in this study suggest that strike-slip shear along the MD belt was initiated at ca. 27Ma and ended ca. 12Ma. This timing is consistent with movements along the adjacent Ailaoshan–Red River strike-slip fault in southeastern Tibet (to the south of the MD belt) and one of the three Cenozoic strike-slip faults in eastern Tibet. Ascent of an asthenospheric mantle diapir beneath the EIACZ in the Cenozoic may have provided a thermal mechanism for the generation of magmas that formed the carbonatite–syenite complexes in the study area. Alternatitvely, the magmas may have been generated by decompression melting associated with the transition from a transpressional to a transtensional regime at 38–40Ma. The precise age results for syenite magmatism in the study area indicate that this transition occurred prior to carbonatite–syenite magmatism and the formation of the MD REE belt, which is consistent with the regional tectonic model.

Classification and Net Primary Productivity of the Southern China's Grasslands Ecosystem Based on Improved Comprehensive and Sequential Classification System (CSCS) Approach

This research classified vegetation types and evaluated net primary productivity (NPP) of southern China's grasslands based on the improved comprehensive and sequential classification system (CSCS), and proposed 5 thermal grades and 6 humidity grades. Four classes of grasslands vegetation were recognized by improved CSCS, namely, tundra grassland class, typical grassland class, mixed grassland class and alpine grassland class. At the type level, 14 types of vegetations (9 grasslands and 5 forests) were classified. The NPP had a trend to decrease from east to west and south to north, and the annual mean NPP was estimated to be 656.3 g C m−2 yr−1. The NPP value of alpine grassland class was relatively high, generally more than 1 200 g C m−2 yr−1. The NPP value of mixed grassland class was in a range from 1 000 to 1 200 g C m−2 yr−1. Tundra grassland class was located in southeastern Tibet with high elevation, and its NPP value was the lowest (<600 g C m−2 yr−1). The typical grassland class distributed in most of the area, and its NPP value was generally from 600 to 1 000 g C m−2 yr−1. The total NPP value in the study area was 68.46 Tg C. The NPP value of typical grassland class was the highest (48.44 Tg C), and mixed grassland class was the second (16.54 Tg C), followed by alpine grassland class (3.22 Tg C), with tundra grassland class being the lowest (0.25 Tg C). For all the grasslands types, the total NPP of forest meadow was the highest (34.81 Tg C), followed by sparse forest brush (16.54 Tg C), and montane meadow was the lowest (0.01 Tg C).

Reconstructing glacier retreat since the Little Ice Age in SE Tibet by glacier mapping and equilibrium line altitude calculation

Temperate glaciers in the eastern Nyainqêntanglha Range, southeastern Tibet, are highly sensitive to climate change and therefore of particular high interest for research on late Holocene changes of the monsoonal climate in High Asia. However, because of the remoteness of the area, the scarcity of empirical data, and the challenges to remote sensing work posed by cloud and snow cover, knowledge about the glacier dynamics and changes in this region is still very limited. In this study, we applied a remote sensing approach in which 1964 glaciers were mapped from a Landsat ETM+ scene and subsequently parameterized by DEM-supported measurements. Geomorphological evidence, i.e., trimlines and latero-frontal moraines, were used to obtain quantitative data on the glaciers' morphological characteristics and the changes since the Little Ice Age (LIA) maximum glacier advance. Statistical analysis of glacier length change revealed an average retreat of ~27% and a trend toward stronger retreat for smaller glaciers. An evaluation of different methods to calculate equilibrium line altitudes (ELAs) indicates that an optimized toe-to-ridge altitude method (TRAM) is more suitable than other methods in settings with complex topography and a lack of mass balance measurements. A large number of glacier measurements are crucial for high quality of TRAM results, and special attention has to be paid to different glacier characteristics. In order to determine the best-fitting TRAM ratio value and to test the quality of the calculated ELAs, a remote sensing approach was applied: for each investigated glacier, the altitudes of transient snowlines visible in the late summer Landsat scene were measured from the DEM and compared to TRAM results. The interpolated ELA results show a SE–NW gradient ranging from 4400 to 5600m asl and an average ELA rise of ~136m since the LIA. Because of the high spatial resolution of measurements, the ELA distribution reveals topographic effects down to the catchment scale, specifically orographic rainfall and leeward shielding. The interpretation of these patterns reveals that the eastern Nyainqêntanglha Range is influenced by both, the Indian (ISM) and East Asian summer monsoon (EASM). However, the EASM does not reach the western part of the study area. The results indicate that the monsoonal temperate glaciers' high sensitivity to climate change is driven by two double forcings owing to the coincidence of accumulation and ablation phases.

Provenance and paleogeography of the Late Cretaceous Mengyejing Formation, Simao Basin, southeastern Tibetan Plateau: Whole-rock geochemistry, U–Pb geochronology, and Hf isotopic constraints

The Late Cretaceous Mengyejing Formation, which contains the only pre-Quaternary potash salt deposit in the Simao Basin, southeastern Tibet, is thought to be genetically related to the Maha Sarakham Formation in the Khorat Basin. The provenance and paleogeography of these two basins have been under debate, although little diagnostic evidence has been previously published. A combined analysis of whole rock geochemistry, zircon U–Pb chronology, and Hf isotopic compositions was performed to characterize the provenance of the Mengyejing Formation. These formation's sandstones are characterized by moderate chemical index of alteration (CIA) values. These values, together with plots of the Th/U–Th ratios, suggest that certain samples have undergone moderate weathering and sedimentary recycling. The major and trace elements (La/Th–Hf, Th/Sc–Zr/Sc, Eu/Eu*–Th/Sc, TiO2–Fe2O3T+MgO, Al2O3/SiO2–Fe2O3T+MgO, K2O/Na2O–SiO2) indicate that the sedimentary sources were felsic rocks from an active continental margin or continental arc with a minor amount of recycled sediment from a passive continental margin. The Mengyejing Formation contains detrital zircons primarily with U–Pb ages of 2.45–2.57Ga, 1.8–1.9Ga, 740–880Ma, 410–470Ma, and 215–300Ma. The results reveal that the pre-Devonian zircons are derived from the recycled sediments of the Yangtze block originating in the Qinling Orogenic Belt, and they share this provenance with the coeval sediments in the Khorat Basin. The magmatic rocks of the Ailaoshan and Lincang areas are responsible for supplying the Devonian to Triassic detrital zircons. These provenance data combined with published paleocurrent results suggest that the Simao Basin was situated on the western margin of the Khorat Basin during the Late Cretaceous. The basins were connected when marine incursion occurred. We propose that pre-Devonian materials from the southwestern Sichuan Basin first supplied detritus to the Simao Basin and subsequently to the Khorat Basin.

Accumulation of Perfluoroalkyl Compounds in Tibetan Mountain Snow: Temporal Patterns from 1980 to 2010

The use of snow and ice cores as recorders of environmental contamination is particularly relevant for per- and polyfluoroalky substances (PFASs) given their production history, differing source regions and varied mechanisms driving their global distribution. In a unique study perfluoroalkyl acids (PFAAs) were analyzed in dated snow-cores obtained from high mountain glaciers on the Tibetan Plateau (TP). One snow core was obtained from the Mt Muztagata glacier (accumulation period of 1980-1999), located in western Tibet and a second core from Mt. Zuoqiupo (accumulation period: 1996-2007) located in southeastern Tibet, with fresh surface snow collected near Lake Namco in 2010 (southern Tibet). The higher concentrations of ∑PFAAs were observed in the older Mt Muztagata core and dominated by perfluorooctanesulfonic acid (PFOS) (61.4-346 pg/L) and perfluorooctanoic acid (PFOA) (40.8-243 pg/L), whereas in the Mt Zuoqiupu core the concentrations were lower (e.g., PFOA: 37.8-183 pg/L) with PFOS below detection limits. These differences in PFAA concentrations and composition profile likely reflect the upwind sources affecting the respective sites (e.g., European/central Asian sources for Mt Muztagata and India sources for Mt Zuoqiupu). Perfluorobutanoic acid (PFBA) dominated the recent surface snowpack of Lake Namco which is mainly associated with India sources where the shorter chain volatile PFASs precursors predominate. The use of snow cores in different parts of Tibet provides useful recorders to examine the influence of different PFASs source regions and reflect changing PFAS production/use in the Northern Hemisphere.

Characteristics of rainfall erosivity based on tropical rainfall measuring mission data in Tibet, China

Rainfall erosivity in Tibet from 2000 to 2010 was estimated based on simplified erosion prediction model using daily rainfall data derived from the Tropical Rainfall Measurement Misssion (TRMM) 3B42 rainfall measurement algorithm. Semimonthly erosive rainfall and rainfall erosivity were validated using weather station data. The spatial distribution of annual rainfall erosivity as well as its seasonal and annual variation in Tibet was also examined. Results showed that TRMM 3B42 data could serve as an alternative data source to estimate rainfall erosivity in the area where only data from sparsely distributed weather stations are available. The spatial distribution of rainfall erosivity in Tibet generally resembles the distribution of multi-year average of annual rainfall. Annual rainfall erosivity in Tibet decreased from the southeast to the northwest. The concentration degree of rainfall erosivity shows an increasing trend from the southeast to the northwest. High rainfall erosivity accompanies low rainfall erosivity concentration degree and vice versa. Rainfall erosivity increased in the middle and western Tibet and decreased in the southeastern Tibet during the 11 years of this study.

Early-summer temperature variations over the past 563 yr inferred from tree rings in the Shaluli Mountains, southeastern Tibet Plateau

We developed a tree-ring chronology (AD 1446–2008) based on 75 cores from 37 Abies squamata Mast. trees from the Shaluli Mountains, southeastern Tibet Plateau, China, using signal-free methods, which are ideally suited to remove or reduce the distortion introduced during traditional standardization. This chronology correlates best with regional temperatures in June–July, which allowed us to develop a June–July temperature reconstruction that explained 51.2% of the variance in the instrumental record. The reconstruction showed seven cold periods and five warm periods. Cold periods were identified from AD 1472 to 1524, 1599 to 1653, 1661 to 1715, 1732 to 1828, 1837 to 1847, 1865 to 1876 and 1907 to 1926. Warm intervals occurred from AD 1446 to 1471, 1525 to 1598, 1716 to 1731, 1848 to 1864, 1877 to 1906 and 1927 to present. The reconstruction agrees well with nearby tree-ring-based temperature reconstructions. Spatial correlation analyses suggest that our reconstructions provide information on June–July temperature variability for the southeastern Tibetan Plateau and its vicinity. Spectral analyses revealed significant peaks at 2–6, 10.7, 51.2, 102.2 and 204.8yr. The temperature variability in this area may be affected by ENSO, the Pacific Decadal Oscillation and solar activity.

Sightings of Gonepteryx amintha thibetana Nekrutenko, 1968 (Lepidoptera: Pieridae: Coliadinae) from Arunachal Pradesh, India: an addition to Indian butterfly fauna erroneously placed in southeastern Tibet earlier

Gonepteryx amintha thibetana, a pierid, is recorded from Eaglenest Wildlife Sanctuary, West Kameng District and Anini, Upper Dibang Valley District in Arunachal Pradesh. This species represents an addition to the butterfly fauna of India, though its type locality, Lalung, originally considered as part of southeastern Tibet, actually falls in West Siang district of Arunachal Pradesh, India

Paleogene sedimentation, volcanism, and deformation in eastern Tibet: Evidence from structures, geochemistry, and zircon U–Pb dating in the Jianchuan Basin, SW China

The Cenozoic tectonics of southeastern Tibet feature several large-scale strike-slip ductile shear zones along block boundaries and complex rotation and internal deformation of the blocks that are widely thought to be the result of India–Eurasia collision. The way in which we can match the rotation and internal deformation with the strike-slip movement remains an open issue. The easternmost of these shear zones, the 1000-km-long Ailao Shan/Red River sinistral shear zone, consists of three segments, and the gaps between the segments are occupied by the Chuxiong and Jianchuan Basins. Geologic data from these basins may provide positive constraints on the nature of Cenozoic deformation of continental crust of southeastern Tibet, but few data are available. This paper documents structural, geochronological, and geochemical results to constrain the tectonics of the Cenozoic Jianchuan Basin, eastern Tibet. Detailed field observations along a transect across the Jianchuan Basin revealed a horizon of volcanic rocks that overlies thick massive Eocene mudstones and siltstones, and which in turn is overlapped by coarse-grained Oligocene sandstones and conglomerates. The Late Eocene volcanics are shoshonitic and high in magnesium, and they consist of trachybasalts, trachyandesites, and trachydacites. In situ zircon U–Pb dating demonstrates that the volcanism was short-lived from 35 to 36Ma. Structural data reveal that some of the basement of the Jianchuan Basin has been uplifted, and then thrust over the Cenozoic sediments. Mudstone dikes developed along the main fault plane, and diapirs developed along other minor fractures of the hanging wall. Except for a few gentle folds, no solid-state deformation-induced structures are found in the Cenozoic strata, whereas syndepositional structures are common. These observations suggest that the basement uplift, thrusting, and sedimentation were coeval. Widespread pervasive NW–SE striking vertical fracture-cleavages in the basement suggest that the syndepositional uplift and thrusting were caused by NE–SW directed compression. These structures are distinct from ductile deformational features associated with the sinistral Ailao Shan shear zone. Available data revealed that the ductile shearing lagged ca. 10Ma behind the NE–SW compression. Our data thus suggest that deformation was widely distributed within continental block(s) at an early stage of the India–Eurasia collision, and then localized into some ductile shear zones likely due to block rotation. New zircon U–Pb geochronology and geochemistry of the igneous rocks in the basement show that these igneous rocks formed during the Early Triassic and the earliest Middle Triassic, and not as previously thought during the Late Triassic; they are therefore probably part of the Jomda–Weixi arc rather than the Yidun arc.

Modeling and analysis of lake water storage changes on the Tibetan Plateau using multi-mission satellite data

Estimation of the water storage changes in the lakes of the Tibetan Plateau (TP) is essential for an accurate evaluation of climate change in this alpine region and its impact on the surrounding hydrologic environment. Because of the remoteness and poor accessibility of these alpine lakes, and a lack of lake bathymetric data, estimating their mass budget over the TP poses a considerable challenge. However, the integration of optical remote sensing images, satellite altimetry data, and gravimetry data makes it possible to monitor the overall variations in lake water storage in this extensive region. The ICESat/GLAS altimetry data used in this study reveal that most of the lakes in the TP showed a significant upward tendency (0.2–0.6m/year) in water level between 2003 and 2009, particularly those lakes that are supplied with a large proportion of glacial meltwater. A series of lake area data derived from Landsat MSS/TM/ETM+imagery over the past four decades indicate that during the 1970–1990 period most of the lakes experienced severe shrinkage, with only some of those in central and western Tibet undergoing expansion. During the 1990–2011 period, in contrast, the majority of the lakes on the TP displayed a remarkably expansion tendency. The total lake area increased from 35,638.11km2 in the early 1970s to 41,938.66km2 in 2011. Based on the statistical relationships between the extent of the lake surface area and lake water levels from 2003 to 2009, an empirical model for each of the region's 30 lakes is established to estimate the lake water level from the corresponding area data, thereby reconstructing time series of lake level data for each lake from the 1970s to 2011. Based on time series of lake area and water level data, a time series of lake water volume is also reconstructed. The results show that total lake water storage increased by 92.43km3 between the early 1970s and 2011, with lakes with an area larger than 100km2 accounting for 77.21% of the total lake water volume budget. Moreover, the GRACE signals confirm a similar spatial pattern in water mass changes, i.e., a significantly positive water mass balance in the north and center of the TP and mass loss in southeastern Tibet and along the Himalayas. The water mass budget (6.81km3/year) derived from satellite gravimetry signals in the Chiangtang Plateau are in good agreement with the estimated rising rate of 6.79km3/year of lake water storage in this region based on the empirical model developed in this study. The mechanism of lake water storage changes is discussed and analyzed with reference to previous studies.

The morphological characteristics of glacial deposits during the Last Glaciation, taking the Parlung Zangbo River Basin as an example

Moraine morphology is a mark of climate change.Previous field investigations have found that the moraine of last glacial has a uniform pattern.Ten glacial deposits in the Parlung Zangbo River basins,southeast Tibetan Plateau,were selected to study the deposit characteristics of the Last Glaciation,to reveal the climate change process reflected by the glaciation.It is found that a huge moraine ridge deposited by ancient glacier in MIS(marine isotope state) 2 of the last glacial,which can be mentioned as the main moraine ridge.The main moraine ridge indicates that it was formed under a longtime sustained and stable climate.There are at least two but smaller moraine ridges in external extension or in the bottom of the main moraine ridge,which indicate that climate of the ice age before MIS 2 was more severe but the duration was relatively short.These phenomena may reflect the climate in the ice age of MIS 4 and / or MIS 3.In the valley between the inside of the main moraine ridge and the modern glacier there are many moraine ridges usually,of which the scale is small as compared with the main moraine.Some of the moraine ridges may be recessional moraine,but the influence of Younger Dryas or Heinrich t events should be noteworthy.The moraine ridges of Neoglaciation and Little Ice Age can be identified near the terminus of modern glacier.With high-precision system dating,one can restore the curve of climate change by studying the shape,scope and scale characteristics of glacial deposits in southeastern Tibet,which is helpful to understand the relationship between global oxygen isotope curve and climate change.

A new species of the genus Scutiger (Anura: Megophryidae) from southeastern Tibet, China

A new species of the genus Scutiger (Anura: Megophryidae) from southeastern Tibet, China

Glacial dammed lakes in the Tsangpo River during late Pleistocene, southeastern Tibet

Lacustrine and alluvial terraces and sediments record the extent of at least three stages of late Pleistocene glacially dammed lakes, along the Tsangpo River at the Dazhuka-Yueju gorge, the Zangga-Gyaca gorge and the Grand Bend gorge, in southeastern Tibet. Analysis of lacustrine samples in the Tsangpo River valley by Optically Stimulated Luminescence and pollen analysis showed that the three dammed lakes in the Tsangpo River valley occurred during the early stage of the last glaciation, the later stage of the last glaciation (the Last Glacial Maximum), and the Neoglacial.

Rock slope stability evaluation in static and seismic conditions for left bank of Jinsha River Bridge along Lijiang-Xamgyi’nyilha railway, China

Jinsha River Bridge is located along the Lijiang-Xamgyi’nyilha railway on the southeastern Tibet plateau; it is an area with a high prevalence of earthquakes. The bridge abutments were designed to be constructed in river bank slopes, where rocks are controlled by two sets of joint planes that significantly influence the stability of the left bank slope. According to the engineering-geological conditions and the characteristics of discontinuities, strength properties of the rock mass were obtained based on Barton model and direct shear test. Numerical analyses were performed using FLAC3D software to examine the slope’s response to seismic loading. Then in order to evaluate the damage trends of the rock mass under the different loading conditions, a calculation model based on the geological parameters and slope stability was simulated and analyzed using the discrete element numerical simulation program UDEC (Universal Distinct Element Code), and the effect of degradation of discontinuities on the slope stability was investigated. The results show that the destruction of rock mass under the gravity, bridge foundation, and seismic load are mainly concentrated within 30 m depth of slope, and the slope under loading may slide along joint planes. In addition, the dynamic analysis by amplification of the input loading indicates that instability occurs to the bank slope at a height of about 200 m, and rock blocks will fail under seismic load. Therefore, to prevent the slope from deformation under the engineering loading and strong earthquakes, the bridge foundation should be strengthened.

Topographic Constraints on Deviatoric Stress Field in the Indo-Eurasian Collision Region: Seismo-Tectonic Implications

The deviatoric stress field are computed from the inversion of Gravitational Potential Energy (GPE) for the Indo-Eurasian plate collision region including the Himalaya and the Tibet Plateau. The resulting stress pattern in combination with stress and strain rates obtained by inverting, respectively, the focal mechanism solution of large earthquakes and GPS derived plate motions are used to study the nature of the present-day deformations. A narrow belt bordering the Himalayan collision zone from the south is characterized by strong compressive stresses. The variations in stress pattern along this belt coincide with arc-normal ridges extending into the Himalaya and are able to explain arc-parallel segmentation of seismicity. Gravitational collapse seems to play an important role in the southeastern Tibet Plateau. Depth sensitivity of the seismic derived stresses and GPS derived surface strain rates coupled with evidence of arcuate shaped high electrical conductivity favour strong ductile flow around the Eastern Himalaya Syntaxis (EHS) at mid-crustal depth. The deflection of crustal flow indicted by the viscous resistance offered by the rigid Sichuan basin adds to the traction stresses to cause clockwise rotation of the block around EHS.

Demography and speciation history of the homoploid hybrid pinePinus densataon the Tibetan Plateau

Pinus densata is an ecologically successful homoploid hybrid that inhabits vast areas of heterogeneous terrain on the south-eastern Tibetan Plateau as a result of multiple waves of colonization. Its region of origin, route of colonization onto the plateau and the directions of introgression with its parental species have previously been defined, but little is known about the isolation and divergence history of its populations. In this study, we surveyed nucleotide polymorphism over eight nuclear loci in 19 representative populations of P.densata and its parental species. Using this information and coalescence simulations, we assessed the historical changes in its population size, gene flow and divergence in time and space. The results indicate a late Miocene origin for P.densata associated with the recent uplift of south-eastern Tibet. The subsequent differentiation between geographical regions of this species began in the late Pliocene and was induced by regional topographical changes and Pleistocene glaciations. The ancestral P.densata population had a large effective population size but the central and western populations were established by limited founders, suggesting that there were severe bottlenecks during the westward migration out of the ancestral hybrid zone. After separating from their ancestral populations, population expansion occurred in all geographical regions especially in the western range. Gene flow in P.densata was restricted to geographically neighbouring populations, resulting in significant differentiation between regional groups. The new information on the divergence and demographic history of P.densata reported herein enhances our understanding of its speciation process on the Tibetan Plateau.

E–W extension and block rotation of the southeastern Tibet: Unravelling late deformation stages in the eastern Himalayas (NW Bhutan) by means of pyrrhotite remanences

In the Himalayan chain the collision of India into Eurasia has produced some of the most complex crustal interactions along the Himalayan–Alpine Orogen. In NW Bhutan, middle to late Miocene deformation has been partitioned between conjugate strike-slip faulting, E–W extension along the Yadong-Gulu graben and kilometre-scale folding. To better understand the late deformation stages and their implications for the evolution of the eastern Himalayas, the palaeomagnetism in the erosional remnant of the Tethyan Himalayan rocks outcropping in NW Bhutan has been studied. Their position to the south of the trace of the inner South Tibetan Detachment, to the south of the Tibetan Plateau offers a unique possibility to study the Tertiary rotation of the Himalayas. Pyrrhotite is the carrier of the characteristic magnetisation based on 270–325 °C unblocking temperatures. The age of the remanence is ca. 13 Ma indicated by illite 40K/40Ar cooling ages and a negative fold test. Small circle intersection method applied to the pyrrhotite components shows a ca. 32° clockwise rotation with respect to stable India since 13 Ma. We suggest that this clockwise rotation is related to strain partitioning between NE-directed shortening, sinistral-slip along the Lingshi fault, and east–west extension. This represents a field-based explanation and a minimum onset age for present-day eastward motion of the upper-crust of SE-Tibet and NE-Himalayas.

A new species of the genus Scutiger (Anura: Megophryidae) from southeastern Tibet, China

A new species of Scutiger Theobald, 1868 is described from Medog, southeastern Tibet, China. Scutiger wuguanfui sp.nov. is distinguished from congeners in the following combination of characters: (1) large adult size, female is much largerthan male; (2) maxillary teeth absent; (3) male with a pair of pectoral glands and a pair of axillary glands, axillary glandssimilar to pectoral glands, all of them covered by black spines in breeding season; (4) in breeding male, nuptial spines ondorsal surface of firs and second fingers, and inner side of third finger; (5) male with an internal single subgular vocal sac,a pair of slit-like openings of vocal sac near corners of the mouth. This new species is currently known only from the type locality.