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• Dry dense grain flows with crushable grains are intrinsically highly mobile. • Specific packing and elastic body wave are important for the initiation of acoustic fluidization. • This finding is important for the explanation of the behaviour of dense grain flows. High mobility of natural disasters with severe consequences is often reported in large landslides and in earthquake fault ruptures. The mechanism of high mobility keeps to be mysterious to date. In this study, we used high-speed rotary shear experiments under normal stress 1 MPa and with a rotary speed of 2 m/s on grains of four different minerals to show that the tested dry dense grain flows with crushable grains are highly mobile intrinsically. Granular flow quickly weakens to a very low viscosity (about 500 Pa.s), which is independent of grain composition. We find that when flow begins, grains are crushed to a special fractal structure in which most larger grain is surrounded by much smaller grains. This special structure provides a favourable condition for generating and propagating acoustic energy from the abrasion indicated by the scratches on the grains. The scratching generates very high frequency elastic energy (vibration) in the larger grains, which profoundly weakens all grain contacts so that the grain mass flows like a giant flood. Chatter-marked scratches made by smaller grains scouring across boulders in rock-avalanche deposits suggest that the same processes occur in nature. This finding is important for the explanation of the behaviour of dense grain flows at large strains and high strain rates. [ABSTRACT FROM AUTHOR]

Abstract: Paleoelevation reconstruction using oxygen isotopes is making a significant contribution to understanding the Cenozoic uplift of the Himalayas and the Tibetan Plateau. This paper presents new oxygen and carbon isotopic compositions from well dated Tertiary paleosols, lacustrine calcareous carbonates, and marls from the Nianbo (60–54 Ma) and upper Pana Formations (51–48 Ma) of the Linzizong Group in the Linzhou (Penbo) Basin. The sediments of the Nianbo Formation, which are >180 m-thick, were deposited in alluvial fans, braided rivers, fan deltas, and on nearshore to offshore lacustrine settings, whereas those of the upper Pana Formation are >100 m-thick and are comprised predominantly of proximal alluvial fan and braided river deposits. Correlations between the lithofacies and stable isotopic compositions suggest that the basin was mainly a hydrologically open environment. It is confirmed that the and values from Nianbo and Pana Formations have not yet been reset by late-stage diagenesis based on petrographic examination, oxygen isotope of the fossil ostracodes, and tectonic deformation of strata. The paleoelevations are reconstructed using the corrected most negative paleosurface water values. These imply that the Linzhou area had attained an elevation of m during the period of the Indo-Asian collision, i.e., achieved a near-present elevation, and may form an Andean-type mountain range stretching the Gangdese arc before collision. The Gangdese Mountains probably maintained high elevations since at least the Paleocene and could play a crucial role in the climate change in the interior of the Tibetan Plateau during the Early Cenozoic. The paleogeomorphic scenario of the Eocene Tibet is proposed to exist at two high mountains in excess of 4500 m that sandwiched a low elevation basin. [Copyright &y& Elsevier]

Abstract: The timing of uplift of the Tibetan Plateau remains controversial, with estimates varying from Eocene to more recent than Pliocene. In particular, the paleoaltimetry of the Qiangtang terrane, on the central Tibetan Plateau, is completely unknown. Here, we present new stable isotope results of fluvial/lacustrine carbonate cement, pedogenic carbonate and marl from the Kangtuo and Suonahu formations deposited between ∼51 and ∼28Ma in the Heihuling–Bamaoqiongzong area of the northern Qiangtang terrane. The lithofacies associations indicate that the Kangtuo formation was deposited in alluvial fan and fluvial floodplain environments, and the Suonahu formation was deposited in near shore lacustrine, playa-lake and channelized fluvial environments. Carbon and oxygen isotope values, coupled with the sedimentary facies interpretations, point to evaporation and low respiration rates in the Eocene–Oligocene paleosols, suggesting an arid climate in the high Qiangtang area at the time. The δ 18Opsw values of paleo-surface water reconstructed from the lowest (i.e. the least evaporated) δ 18Oc (PDB) values of the unaltered authigenic carbonates are used to make the minimum estimates of the average paleoelevation of the drainage basin. The paleoelevation of the northern Qiangtang terrane is reconstructed as above 5000m by at least the middle Oligocene (28Ma), similar to the present elevation in this area. The aridity and the positive shift in oxygen isotope values of surface waters in our study area may suggest that the high Lhasa terrane established by the middle Oligocene blocked the northward transport of tropical moisture. Maintenance of high elevation (>5000m) from at least the Oligocene to the present suggests that the Qiangtang crust was already thickened by that time, and that underthrusting of India beneath Asia since then has continued to provide additional material while at the same time driving Asian lower crust eastward by crustal flow. [Copyright &y& Elsevier]

Abstract We used thermogravimetry to determine that the frictionally heated sliding surface reached ∼850 °C at the base of the 1.16 × 10 9 m 3 Daguangbao landslide, triggered during the 2008 M s 8.2 Wenchuan earthquake. Optical and electron microscope images reveal evidence of dolomite thermal decomposition, hot fluid penetrating fine cracks and dynamic recrystallization of minerals. A high-speed rotary shear apparatus simulated the rapid sliding and provided data on very low frictional resistance (friction coefficient, μ ≈ 0.05) during shearing above 1 m/s. Electron-probe analysis of samples from the experiments showed lime and magnesia from thermal decomposition of dolomite. Some of the sheared minerals formed a dynamically recrystallized layer ∼0.1 mm thick, and its viscous resistance would have contributed to the low apparent friction during high-speed sliding. A further explanation, however, was very high pore-fluid pressure from hot supercritical CO 2 (and superheated steam at a partial pressure of >10 MPa in the field situation with groundwater). These friction-reducing mechanisms are not mutually exclusive and both were present simultaneously at the landslide base. Highlights • The 1.16 × 10 9 m 3 Daguangbao landslide achieved a friction-induced basal temperature of ∼850 °C. • The high temperature decomposed the dolomite and produced hot vapor. • Superheated steam and CO 2 provided a high basal pore-fluid pressure. • Hot lime and magnesia of decomposition formed a superplastic layer. • Superplastic layer decreased viscous resistance to already low frictional resistance. [ABSTRACT FROM AUTHOR]

Abstract Active thrust faulting at the front of the Qilian Shan accommodates the northeastward growth of the Tibetan Plateau, however, the lifespan of individual faults and their slip history on different timescales remain largely unknown. Here, we show that the main range-bounding thrust fault of the western Qilian Shan has accrued tectonic slip at an almost constant rate during the last ∼200 ka, and possibly since fault initiation in the mid-Miocene. Our finding is based on 10Be ages from a flight of five deformed fluvial terraces along the Hongshuiba river, which constrain the vertical slip rate of the Qilian Shan frontal thrust to be 1.2 ± 0.1 m/ka during the last 200 ka. With a fault dip of 30 ± 5 ° constrained by seismic reflection data, we obtain a horizontal shortening rate of 2.0 ± 0.3 m/ka. This value is consistent with both the short-term shortening rate of 1.7 ± 0.3 mm/a derived from GPS data and the long-term shortening rate of 2.1 ± 0.4 m/ka, which is based on a balanced geological cross-section. The latter provides a total shortening estimate of 25 ± 3 km since the thrust fault initiated 12 ± 2 Ma ago. The agreement between the shortening rates on the range of timescales between 100 and 107 years suggests that the western Qilian Shan frontal thrust has slipped at a steady rate since its initiation and implies that this fault is the main structure responsible for the growth of the western Qilian Shan. Highlights • 10Be ages for five river terraces constrain slip rate of Qilian Shan frontal thrust. • 10Be-based shortening rate is consistent with a balanced cross-section and GPS data. • Shortening on Qilian Shan frontal thrust proceeded at steady rate since mid-Miocene. • New sampling strategy for exposure dating of loess-covered fluvial terraces. [ABSTRACT FROM AUTHOR]

The northernmost exposures of sub-Himalayan Cenozoic strata in the Hazara–Kashmir syntaxial region of north Pakistan comprises the Paleocene–Eocene marine strata in the lower part and Oligocene–Miocene nonmarine strata in the upper part. This study provides the detrital zircon U–Pb geochronology of the Cenozoic strata in this area. The strong resemblance of U–Pb age spectra of Paleocene Hangu, Lockhart and Patala formations with those of Himalayan strata indicate an Indian plate provenance. The first appearance of <100 Ma detrital zircon U–Pb ages within the lower most part of the Early Eocene Margalla Hill Limestone indicates a shift from an Indian to Asian provenance. Geologic mapping shows the existence of a disconformity between the lower and upper most part of the Patala Formation, which is interpreted to have been formed by the migration of a flexural forebulge through this region. We consider the upper most part of the Patala Formation to have been deposited within the distal foredeep of the foreland basin. The Indian to Asian provenance shift and the presence of a possible foreland basin forebulge provide strong evidence that India–Asia collision was underway in northern Pakistan at ca. 56–55 Ma. [ABSTRACT FROM AUTHOR]

Sandstone petrographic and U–Pb detrital zircon analyses of Upper Triassic sedimentary rocks from the northern margin of India (Tethyan Himalaya Sequence) and southern margin of Eurasia (Lhasa terrane) provide new constraints on the Mesozoic paleogeography of Neo–Tethyan Ocean basins. The Upper Triassic Nieru Formation of the Tethyan Himalaya Sequence (THS) near Lazi city (∼29°N, 87.5°E) is dominated by Indian-affinity, Precambrian detrital zircons, which are typical of the majority of the THS. However, the Upper Triassic Langjiexue Formation of the THS exposed to the east (at 90–93°E longitude) includes significant populations of Permian to Early Jurassic (291–184 Ma) detrital zircons for which there is no known Indian source. In addition, the Upper Triassic Nieru Formation near Kangma town (∼28.5°N, 90°E), located ∼200 km to the southeast of Lazi city, yielded detrital zircon age spectra that are similar to those of Langjiexue Formation. Based on detrital zircon age spectra comparisons, we propose that both the Langjiexue and Nieru formations were derived from continental crustal fragments that were adjacent to the northwestern margin of Australia. Furthermore, we suggest that these THS units, and age-equivalent strata in Northwest Australia, West Sulawesi, Timor and West Papua, comprised a Late Triassic submarine fan along the northern Australian shelf. The Upper Triassic Mailonggang Formation in the southern Lhasa terrane (35 km northeast of Lhasa city, ∼30°N, 91.5°E) is dominated by Permian detrital zircons, which were likely derived from proximal Lhasa terrane sources. The Mailonggang Formation differs from all age-equivalent strata in the Tethyan Himalaya; therefore we interpret that it was separated from Greater India by the Neo–Tethyan Ocean. [ABSTRACT FROM AUTHOR]

• More negative δ 2 H wax values from Gyirong paleosediments than from modern soils. • Higher GDGT-based paleotemperatures in the Gyirong Basin than at present. • Similar differences between basin floor and mountain altitudes using isotopic and GDGT altimeters. • Better applicability of GDGT altimeters under warmer and wetter environments. • A lower-altitude Himalayas (basin floor at ∼2.5 km asl) before the Mid-Pliocene. Contradictory paleoaltitudinal histories of the Himalayas arrived at using isotopic paleoaltimeters and ecological evidences have constrained our further exploration of the geodynamic mechanisms driving the India-Eurasia collision and the resultant interaction between tectonic uplift and climate change. In this study, based on evidence derived from glycerol dialkyl glycerol tetraethers (GDGTs), the hydrogen isotopes of leaf wax n -alkanes (δ 2 H alk), we estimated the paleoaltitude of the Gyirong Basin (GB), central Himalayas, for the 7.0∼3.2 Ma period. The paleoaltitudinal reconstruction based on δ 2 H alk values (∼6.3 km above sea level (asl)) was consistent with that of the revised δ 18 O c values (∼5.6 km asl), and higher than the present-day altitude (∼4 km asl). The reconstructed paleotemperatures based on brGDGTs (14.2 ± 4.5 °C for the lake surface; 7.5 ± 3.3 °C for terrestrial organic matter source areas) were consistent with the ecological evidences, indicating a low-altitude paleoenvironment. This proves that a systemic bias exists between the isotopic paleoaltimeters and the ecological evidence, rather than a problem with specific indicators. The reconstructed paleoaltitudinal differences between the δ 2 H alk and δ 18 O c values are similar to those of brGDGT reconstructions, seemingly representing the paleoaltitudinal differences between the source areas of terrestrial organic matter inputs and the lake surface, and suggesting that the isotopic palaeoaltimeters do not specifically record the higher-altitude parts of the basinal topography. Further paleoenvironmental analysis indicated that the warmer and wetter environment present during the Late Miocene to Mid-Pliocene would, on the face of it, be better suited to the application of brGDGT paleothermometers, and this in turn would potentially lead to a systemic overestimation by isotopic paleoaltimeters. We therefore adopted the paleoaltitudinal reconstructions which used brGDGTs and concluded that the lake surface of the GB during the Late Miocene to Mid-Pliocene was 2.5 ± 0.8 km asl, and that the surrounding mountains exceeded 3.6 km asl in height, implying that the central Himalayas underwent a rapid uplift of ∼1.5 km after the Mid-Pliocene. [ABSTRACT FROM AUTHOR]