April-September minimum temperature reconstruction based on Sabina tibetica ring-width chronology in the central eastern Tibetan Plateau,China

Minimum temperatures have remarkable impacts on tree growth at high-elevation sites on the Tibetan Plateau,but the shortage of long-term and high-resolution paleoclimate records inhibits understanding of recent minimum temperature anomalies.In this study,a warm season(April–September)reconstruction is presented for the past 467 years(1550–2016)based on Sabina tibetica ring-width chronology on the Lianbaoyeze Mountain of the central eastern Tibetan Plateau.Eight warm periods and eight cold periods were identified.Long-term minimum temperature variations revealed a high degree of coherence with nearby reconstructions.Spatial correlations between our reconstruction and global sea surface temperatures suggest that warm season minimum temperature anomalies in the central eastern Tibetan Plateau were strongly influenced by large-scale ocean atmospheric circulations,such as the El Ni?o-Southern Oscillation and the Atlantic Multidecadal Oscillation.

Mechanism of Diabatic Heating on Precipitation and the Track of a Tibetan Plateau Vortex over the Eastern Slope of the Tibetan Plateau

Existing studies contend that latent heating(LH)will replace sensible heating(SH)to become the dominant factor affecting the development of the Tibetan Plateau vortex(TPV)after it moves off the Tibetan Plateau(TP).However,in the process of the TPV moving off the TP requires that the airmass traverse the eastern slope of the Tibetan Plateau(ESTP)where the topography and diabatic heating(DH)conditions rapidly change.How LH gradually replaces SH to become the dominant factor in the development of the TPV over the ESTP is still not very clear.In this paper,an analysis of a typical case of a TPV with a long life history over the ESTP is performed by using multi-sourced meteorological data and model simulations.The results show that SH from the TP surface can change the TPV-associated precipitation distribution by temperature advection after the TPV moves off the TP.The LH can then directly promote the development of the TPV and has a certain guiding effect on the track of the TPV.The SH can control the active area of LH by changing the falling area of the TPV-associated precipitation,so it still plays a key role in the development and tracking of the TPV even though it has moved out of the main body of the TP.

The Impact of Atmospheric Heat Sources over the Eastern Tibetan Plateau and the Tropical Western Pacific on the Summer Rainfall over the Yangtze-River Basin

The variability of the summer rainfall over China is analyzed using the EOF procedure with a new parameter （namely, mode station variance percentage） based on 1951-2000 summer rainfall data from 160 stations in China. Compared with mode variance friction, the mode station variance percentage not only reveals more localized characteristics of the variability of the summer rainfall, but also helps to distinguish the regions with a high degree of dominant EOF modes representing the analyzed observational variable. The atmospheric circulation diagnostic studies with the NCEP/NCAR reanalysis daily data from 1966 to 2000 show that in summer, abundant （scarce） rainfall in the belt-area from the upper-middle reaches of the Yangtze River northeastward to the Huaihe River basin is linked to strong （weak） heat sources over the eastern Tibetan Plateau, while the abundant （scarce） rainfall in the area to the south of the middle-lower reaches of the Yangtze River is closely linked to the weak （strong） heat sources over the tropical western Pacific.

Dextral-Slip Thrust Faulting and Seismic Events of the Ms 8.0 Wenchuan Earthquake,Longmenshan Mountains,Eastern Margin of the Tibetan Plateau

Dextral-slip thrust movement of the Songpan-Garze terrain over the Sichuan block caused the Ms 8.0 Wenchuan earthquake of May 12, 2008 and offset the Central Longmenshan Fault （CLF） along a distance of -250 km. Displacement along the CLF changes from Yingxiu to Qingchuan. The total oblique slip of up to 7.6 m in Yingxiu near the epicenter of the earthquake, decreases northeastward to 5.3 m, 6.6 m, 4.4 m, 2.5 m and 1.1 m in Hongkou, Beichuan, Pingtong, Nanba and Qingchuan, respectively. This offset apparently occurred during a sequence of four reported seismic events, EQ1-EQ4, which were identified by seismic inversion of the source mechanism. These events occurred in rapid succession as the fault break propagated northeastward during the earthquake. Variations in the plunge of slickensides along the CLF appear to match these events. The Mw 7.5 EQ1 event occurred during the first 0-10 s along the Yingxiu-Hongkou section of the CLF and is characterized by 1.7 m vertical slip and vertical slickensides. The Mw 8.0 EQ2 event, which occurred during the next 10-42 s along the Yingxiu-Yanziyan section of the CLF, is marked by major dextralslip with minor thrust and slickensides plunging 25°-35° southwestward. The Mw 7.5 EQ3 event occurred during the following 42-60 s and resulted in dextral-slip and slickensides plunging 10° southwestward in Beichuan and plunging 73° southwestward in Hongkou. The Mw 7.7 EQ4 event, which occurred during the final 60-95 s along the Beichuan-Qingchuan section of the CLF, is characterized by nearly equal values of dextral and vertical slips with slickensides plunging 45°-50° southwestward. These seismic events match and evidently controlled the concentrations of landslide dams caused by the Wenchuan earthquake in Longmenshan Mountains.

Crustal Motion Characteristics in the Eastern Margin of the Tibetan Plateau and Adjacent Regions after the Wenchuan Earthquake

The Wenchuan earthquake has altered the crustal motion characteristics in the eastern margin of the Tibetan Plateau and adjacent regions.Using discontinuous GPS survey data for 2008–2012, the velocity field for the Eurasia reference framework has been obtained, and the general trend of contemporary crustal motion after the occurrence of the Wenchuan earthquake has been studied.In addition, using the velocity field, the block movement velocity has been estimated by least-squares fitting.Furthermore, the properties and displacement rates of main faults have been obtained from the differences in velocity vectors of the blocks on both sides of the faults.The results reveal that there are no obvious changes in the general characteristics of crustal motion in this area after the Wenchuan earthquake.The earthquake mainly changed the rate of the movement of the Chuan-Qing block and caused variation in the movement direction of the South China block.The effect of the earthquake on faults is mainly reflected in variations in fault displacement velocity; there is no fundamental change in the properties of fault activity.The displacement rates of the Xianshuihe fault decreased by 3–4 mm/a, the Longmenshan fault increased by 9–10 mm/a, and the northern segment of the Anninghe fault increased by approximately 9 mm/a.Furthermore, the displacement rates of the Minjiang, Xueshan, Huya, Longquanshan, and Xinjin faults increased by 2–3 mm/a.This implies that the effects of the Wenchuan earthquake on crustal movement can mainly be observed in the Chuan-Qing, South China, and N-Chuan-Dian blocks and their internal faults, as well as the Xianshuihe and Longmenshan faults and the northern section of the Anninghe fault.The reason for this is that the Wenchuan earthquake disturbed the kinematic and dynamic balance in the region.

Last Deglacial Soft-Sediment Deformation at Shawan on the Eastern Tibetan Plateau and Implications for Deformation Processes and Seismic Magnitudes

The eastern margin of the Tibetan Plateau is characterized by frequent earthquakes; however, research of paleo-earthquakes in the area has been limited^ owing to the alpine topography and strong erosion. Detailed investigations of soft-sediment deformation(SSD) structures are valuable for understanding the trigger mechanisms, deformation processes, and the magnitudes of earthquakes that generate such structures, and help us to understand tectonic activity in the region. To assess tectonic activity during the late Quaternary, we studied a well-exposed sequence of Shawan lacustrine sediments, 7.0 m thick, near Lake Diexi in the upper reaches of the Minjiang River. Deformation is recorded by both ductile structures(load casts, flame structures,pseudonodules, ball-and-pillow structures, and liquefied convolute structures) and brittle structures(liquefied breccia, and microfaults). Taking into account the geodynamic setting of the area and its known tectonic activity, these SSD structures can be interpreted in terms of seismic shocks. The types and forms of the structures,the maximum liquefaction distances, and the thicknesses of the horizons with SSD structures in the Shawan section indicate that they record six strong earthquakes of magnitude 6-7 and one with magnitude >7. A recent study showed that the Songpinggou fault is the seismogenic structure of the 1933 Ms7.5 Diexi earthquake. The Shawan section is located close to the junction of the Songpinggou and Minjiang faults, and records seven earthquakes with magnitudes of ?7. We infer,therefore, that the SSD structures in the Shawan section document deglacial activity along the Songpinggou fault.

Characteristics of land-atmosphere energy and turbulentfluxes over the plateau steppe in central Tibetan Plateau

The land-atmosphere energy and turbulence exchange is key to understanding land surface processes on the Tibetan Plateau(TP). Using observed data for Aug. 4 to Dec. 3, 2012 from the Bujiao observation point(BJ) of the Nagqu Plateau Climate and Environment Station(NPCE-BJ), different characteristics of the energy flux during the Asian summer monsoon(ASM) season and post-monsoon period were analyzed. This study outlines the impact of the ASM on energy fluxes in the central TP. It also demonstrates that the surface energy closure rate during the ASM season is higher than that of the post-monsoon period. Footprint modeling shows the distribution of data quality assessments(QA) and quality controls(QC) surrounding the observation point. The measured turbulent flux data at the NPCE-BJ site were highly representative of the target land-use type. The target surface contributed more to the fluxes under unstable conditions than under stable conditions. The main wind directions(180° and 210°) with the highest data density showed flux contributions reaching 100%, even under stable conditions. The lowest flux contributions were found in sectors with low data density, e.g., 90.4% in the 360° sector under stable conditions during the ASM season. Lastly, a surface energy water balance(SEWAB) model was used to gap-fill any absent or corrected turbulence data. The potential simulation error was also explored in this study. The Nash-Sutcliffe model efficiency coefficients(NSEs) of the observed fluxes with the SEWAB model runs were 0.78 for sensible heat flux and 0.63 for latent heat flux during the ASM season, but unrealistic values of-0.9 for latent heat flux during the post-monsoon period.

Application of the Material Balance Method in Paleoelevation Recovery: A Case Study of the Longmen Mountains Foreland Basin on the Eastern Margin of the Tibetan Plateau

We applied the material balance principle of the denudation volume and sedimentary flux to study the denudation-accumulation system between the Longmen Mountains （Mts.） and the foreland basin. The amount of sediment in each sedimentation stage of the basin was estimated to obtain the denudation volume, erosion thickness and deposit thickness since the Late Triassic Epoch, to enable us to recover the paleoelevation of the provenance and the sedimentary area. The results show the following： （1） Since the Late Triassic Epoch, the elevation of the surface of the Longmen Mts. has uplifted from 0 m to 2751 m, and the crust of the Longmen Mts. has uplifted by 9.8 km. Approximately 72% of the materials introduced have been denuded from the mountains. （2） It is difficult to recover the paleoelevation of each stage of the Longmen Mts. foreland basin quantitatively by the present-day techniques and data. （3） The formation of the Longmen Mts. foreland basin consisted of three stages of thrust belt tectonic load and three stages of thrust belt erosional unload. During tectonic loading stages （Late Triassic Epoch, Late Jurassic-Early Cretaceous, Late Cretaceous-Miocene）, the average elevation of Longmen Mts. was lower （approximately 700-1700 m）. During erosional unloading stages （Early and Middle Jurassic, Middle Cretaceous and Jiaguan, Late Cenozoic）, the average elevation of Longmen Mts. was high at approximately 2000-2800m.

Paleoglacial and paleoclimate reconstructions during the global Last Glacial Maximum in the Longriba area, eastern Tibetan Plateau

Owing to the remoteness of the Longriba area and the lack of dating records,it is extremely challenging to reconstruct the chronology and extent of the paleoglaciers in this area.In this paper,we combined limited observational data with automated modelling for paleoglacial reconstructions.We first identified a broadly distributed paleoglacier from satellite imagery and field investigation based on the sediment-landform assemblage principle and dated it to 23.1±1.4~19.5±1.2 ka by ^(10)Be exposure dating,corresponding to the global Last Glacial Maximum(gLGM).Then,we reconstructed the extent and ice surface of 171 paleoglaciers formed during the similar period based on geomorphological evidence and‘ice surface profile’modelling.The results showed that the paleoglacial coverage was 426.5 km2,with an ice volume of 38.1 km^(3),in the Longriba area.The reconstructed equilibrium line altitudes(ELAs)based on modelled ice surfaces yielded an average of 4245±66 m above sea level(asl),~725±73 m lower than the present ELA(4970±29 m asl).The temperature was~5.51-6.68℃lower,and the precipitation was~30-34%less in Longriba,during the gLGM compared to the present day.This glacial advance was mainly driven by colder climate that was synchronous with Northern Hemisphere cooling events.

The Low Lake-Level Record according to the Selin Co Stratigraphical Basis and Multi-Proxies during the Last Glacial Maximum in the Central Tibetan Plateau

Objective The lake levels in the eastern and southern Asia are regarded as low lake-level owing to precipitation decreasing based on the records of lake-level fluctuation in the continental interior lakes since the last glacial maximum（LGM）（14C 18±1 kaBP,since 20 kaBP）in the Central Asia.Higher lake-level appeared in the transition belt between western Kunlun Mountain and the central Tibetan Plateau.

Relationship between the regional tectonic activity and crustal structure in the eastern Tibetan plateau discovered by gravity anomaly

The eastern Tibetan plateau has been getting more and more attention because it combines active faults,uplifting, and large earthquakes together in a high-population region. Based on the previous researches, the most of Cenozoic tectonic activities were related to the regional structure of the local blocks within the crustal scale. Thus,a better understanding of the crustal structure of the regional tectonic blocks is an important topic for further study. In this paper, we combined the simple Bouguer gravity anomaly with the Moho depths from previous studies to investigate the crustal structure in this area. To highlight the crustal structures, the gravity anomaly caused by the Moho relief has been reduced by forward modeling calculations. A total horizontal derivative（THD） had been applied on the gravity residuals. The results indicated that the crustal gravity residual is compatible with the topography and the geological settings of the regional blocks,including the Sichuan basin, the Chuxiong basin, the Xiaojiang fault, and the Jinhe fault, as well as the Longmenshan fault zone. The THD emphasized the west margin of Yangtze block, i.e., the Longriba fault zone and the Xiaojiang fault cut through the Yangtze block. The checkboard pattern of the gravity residual in the SongpanGarze fold belt and Chuandian fragment shows that the crust is undergoing a southward and SE-directed extrusion,which is coincident with the flowing direction indicatedfrom the GPS measurements. By integrating the interpretations, the stepwise extensional mechanism of the eastern Tibetan plateau is supported by the southeastward crustal deformation, and the extrusion of Chuandian fragment is achieved by Xianshuihe fault.

Magnetostratigraphy of a Loess-Paleosol Sequence from Higher Terrace of the Daduhe River in the Eastern Margin of the Tibetan Plateau and Its Geological Significance

The eolian deposits distributed in the river valleys in the eastern margin of the Tibetan Plateau （TP） are very useful in neotectonic and paleoclimatic studies. Firstly, the climate in the eastern margin of the TP is mainly controlled by the Indian summer monsoon, and detailed studies on the loess-paleosol sequences in this region can provide valuable terrestrial evidence of past changes in the Indian summer monsoon. Secondly, the river terraces in the eastern margin of the TP are considered to be a sensitive recorder of neotectonism to reflect the timing and amplitude of the TP uplift.

Late Cretaceous K-rich rhyolitic crystal tuffs from the Chuduoqu area in Eastern Qiangtang subterrane:evidence for crustal thickening of the central Tibetan Plateau prior to India–Asia collision

In order to constrain whether the Lhasa–Qiangtang collision contributed to an early crustal thickening of the central Tibetan Plateau prior to the India–Asia collision,we present zircon LA–ICP–MS U–Pb ages,wholerock geochemistry,and zircon Hf isotopic compositions of the newly discovered rhyolitic crystal tuffs from the Chuduoqu area in the eastern Qiangtang subterrane,central Tibet.Zircon U–Pb dating suggests that the Chuduoqu rhyolitic crystal tuffs were emplaced at ca.68 Ma.The Chuoduoqu rhyolitic crystal tuffs display high SiO_(2) and K2 O,and low MgO,Cr,and Ni.Combined with their zircon Hf isotopic data,we suggest that they were derived from partial melting of the juvenile lower crust,and the magma underwent fractional crystallization and limited upper continental crustal assimilation during its evolution prior to eruption.They should be formed in a post-collisional environment related to lithospheric mantle delamination.The Chuduoqu rhyolitic crystal tuffs could provide important constraints on the Late Cretaceous crustal thickening of the central Tibetan Plateau caused by the Lhasa–Qiangtang collision.

ON THE RELATIONSHIPS BETWEEN THE SUMMER RAINFALL IN CHINA AND THE ATMOSPHERIC HEAT SOURCES OVER THE EASTERN TIBETAN PLATEAU AND THE WESTERN PACIFIC WARM POOL

The relationships between the summer rainfall in China and the atmospheric heat sources over the eastern Tibetan Plateau and the western Pacific warm pool were analyzed comparatively, using the NCEP/NCAR reanalysis daily data. The strong (weak) heat source in summer over the eastern Tibetan Plateau will lead to abundant (scarce) summer rainfall in the Yangtze River basin, and scarce/abundant summer rainfall in the eastern part of Southern China. While the strong (weak) heat source in summer over the western Pacific warm pool will lead to another pattern of abundant (scarce) summer rainfall in the middle-lower reaches of the Yangtze River and scarce (abundant) summer rainfall in Southern China and in the region of northern Jiangsu to southern Shandong. Comparatively, the heat source over the eastern Tibetan Plateau affects a larger area of summer rainfall than the heat source over the western Pacific. In both cases of the heat source anomalies over the eastern Tibetan Plateau and over the western Pacific, there exist EAP-like teleconnection patterns in East Asia. The summer rainfall in China is influenced directly by the abnormal vertical motion, which is related closely to the abnormal heat sources in the atmosphere. The ridge line of the western Pacific High locates far south (north) in summer in the case of strong (weak) heat sources over the two areas mentioned above.

Seismogenic Capability of the Northeastern Segment of the Longmenshan Thrust Zone and its Tectonic Role at the Eastern Tibetan Plateau

Objective The occurrence of the devastating Wenchuan earthquake not only caused huge economic loss and deaths but also raised a question whether or not it would trigger any destructive earthquakes on its neighboring segments in the Longmenshan Thrust Zone （LTZ） in the future.

Anthropogenic Aerosol Pollution over the Eastern Slope of the Tibetan Plateau

In this study, a combination of satellite observations and reanalysis datasets is used to analyze the spatiotemporal distribution, classification and source of pollutants over the eastern slope of the Tibetan Plateau(ESTP). The aerosol optical depth(AOD) over the ESTP is extremely large and even larger than some important industrialized regions and deserts. The main aerosol component over the ESTP is sulfate, followed by carbonaceous and dust aerosols. Local emissions related to human activity directly contribute to the accumulation of sulfate and carbonaceous aerosols over the Sichuan Basin. In addition, in spring, abundant carbonaceous aerosols emitted from forest, grassland and savanna fires in Southeast Asia can be transported by the prevailing southwesterly wind to southern China and the ESTP. The dust AOD over the ESTP peaks in spring because of the transport from the Taklimakan and Gobi deserts. Additionally, the high aerosol loading over the ESTP is also directly related to the meteorological background. Due to the special topography, the terrain-driven circulation can trap aerosols in the Sichuan Basin and these aerosols can climb along the ESTP due to the perennial updraft. The aerosol loading is lowest in summer because of effective wet deposition induced by the strong precipitation and better dispersion conditions due to the larger vertical temperature gradients and ascending air movement enhanced by the plateau heat pump effect. In contrast,the aerosol loading is greatest in winter. Abundant anthropogenic aerosols over the ESTP may generate some climatic and environmental risks and consequently greatly influence the downstream regions.

A Late Quaternary Climate Record Based on Multi-Proxies Analysis from the Jiaochang Loess Section in the Eastern Tibetan Plateau,China

We compared the stable carbon isotopic records from a loess transect of the Jiaochang in the eastern Tibetan Plateau, spanning the last -21,000 years, with multiproxy data for pedogenesis, including magnetic susceptibility, clay fraction, Fed/Fet ratio, carbonate and total organic carbon content, in order to probe the mechanisms of δ^13C values of organic matter and Late Quaternary climate variations in the eastern Tibetan Plateau. Our results indicate that there is no simple relationship between δ^13C of organic matter and summer monsoon variations. The change in δ^13C values of organic matter （in accordance with the ratios of C3 to C4 plants） results from the interaction among temperature, aridity and atmospheric pCO2 level. Drier climate and lower atmospheric pCO2 level contribute to positive carbon isotopic excursion, while negative carbon isotopic excursion is the result of lower temperature and increased atmospheric pCO2 level. Additionally, our results imply that the Tibetan monsoon may play an important role in climate system in the eastern Tibet Plateau, which specifically reflects frequently changing climate in that area. The results provide new insights into the forcing mechanisms on both the δ^13C values of organic matter and the local climate system.

Neotectonics of the Eastern Margin of the Tibetan Plateau: New Geological Evidence for the Change from Early Pleistocene Transpression to Late Pleistocene-Holocene Strike-slip Faulting

We present in this paper some new evidence for the change during the Quaternary in kinematics of faults cutting the eastern margin of the Tibetan Plateau. It shows that significant shortening deformation occurred during the Early Pleistocene, evidenced by eastward thrusting of Mesozoic carbonates on the Pliocene lacustrine deposits along the Minjiang upstream fault zone and by development of the transpressional ridges of basement rocks along the Anninghe river valley. The Middle Pleistocene seems to be a relaxant stage with local development of the intra-mountain basins particularly prominent along the Minjiang Upstream and along the southern segment of the Anninghe River Valley. This relaxation may have been duo to a local collapse of the thickened crust attained during the late Neogene to early Pleistocene across this marginal zone. Fault kinematics has been changed since the late Pleistocene, and was predominated by reverse sinistral strike-slip along the Minshan Uplift, reverse dextral strike-slip on the Longmenshan fault zone and pure sinistral strike-slip on the Anninghe fault. This change in fault kinematics during the Quaternary allows a better understanding of the mechanism by which the marginal ranges of the plateau has been built through episodic activities.

Crustal flow beneath the eastern margin of the Tibetan plateau

In large continental orogens, an important research topic is the behavior of deep crustal and upper mantle deformation, and the flow styles of ductile material. The morphology of the eastern margin of the Tibetan plateau, adjacent to the Sichuan basin, is characterized by very steep relief with high mountain ranges. The crust beneath this region slows the velocities in the middle and lower crust. We have adopted a relatively dense network to inverse the detailed structure of the crust and upper mantle along the eastern margin of the Tibetan plateau and Sichuan basin, using teleseismic data via receiver function analysis. The results are in-line with the hypothesis that viscous crustal material is flowing beneath the eastern margin of the Tibetan plateau and that this process drives overlying crustal material around the strong and rigid Sichuan basin. When the viscous material hits this obstruction, flows are divided into two or more branches with different directions. The upper part of the upwelling viscous flow produces the pressure to intrude the upper crust, thereby driving uplift of mountain ranges and high peaks. In contrast, the lower part of the downwelling viscous flow produces the pressure to intrude the lower crust and upper mantle to deepen the Moho discontinuity, causing observed crustal thickening.

Seasonal and spatial distribution of trace metals in alpine soils of Eastern Tibetan Plateau,China

The distribution of trace metals in remote alpine region is an effective way to understand the impacts of regional human activity and vegetation on the alpine ecosystem. In this study, the concentrations of cadmium(Cd), copper(Cu), lead(Pb), and zinc(Zn) in the soils of Gongga Mountain, Eastern Tibetan Plateau, were investigated to reveal their seasonal and spatial distribution and enrichment state, and to decipher the effects of atmospheric deposition and vegetation on their distributions among five vegetation zones. The results showed that the concentrations of Cd, Pb, and Zn were higher in the O horizon than in other horizons despite the seasonal changes, whereas Cu was enriched in the C horizon. The enrichment states of the metals studied in the soils decreased in the order of Cd > Pb > Zn > Cu. Cd and Pb were mainly sourced from atmospheric deposition; Zn was from both atmospheric deposition and parent materials, whereas Cu was mainly from parent materials.Seasonally, the trace metals were generally higher in May and December but lower in September, implying the impact of vegetation on the distribution of trace metals under the plant uptake and the litter decomposition. Spatially, the higher enrichment of Cu, Pb, and Zn in the soils existed in the mixed broadleafconiferous forests and coniferous forests(approximately 3000 m above sea level). The results suggested that atmospheric deposition and biological processes are main factors controlling the seasonal and spatial distribution of trace metals in the soils of the remote alpine ecosystem.