Geochemical characteristics and genetic model of dolomite reservoirs in the eastern margin of the Pre-Caspian Basin

The widespread Carboniferous KT-I dolomite in the eastern margin of the Pre-Caspian Basin is an important hydrocarbon reservoir. The dolomite lithology is dominated by crystalline dolomite. The δ18O values range from -6.71‰ to 2.45‰, and average 0.063‰, obviously larger than -2.5‰, indicating low-temperature dolomite of evaporation origin. Stable strontium isotope ratios （87Sr/86Sr） range from 0.70829 to 0.70875 and average 0.708365, very consistent with 87Sr/86Sr ratios in Carboniferous seawater. Chemical analysis of Ca and Mg elements shows that the dolomite has 9.1 mole% excess Ca or even higher before stabilization. The degree of order of dolomite is medium–slightly poor, varying in a range of 0.336-0.504 and averaging 0.417. It suggests that the dolomite formed under near-surface conditions. There are two models for the origin of the Carboniferous KT-I dolomite reservoir. These are 1） the evaporation concentration – weathering crust model and 2） the shoal facies – seepage reflux model. The former is mainly developed in restricted platforms – evaporate platforms of restricted marine deposition environments with a representation of dolomite associated with gypsum and mudstone. The latter mainly formed in platform edge shoals and intra-platform shoals and is controlled by dolomitization due to high salinity sea water influx from adjacent restricted sea or evaporate platform.

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.

Episodes of Cenozoic Gold Mineralization on the Eastern Margin of the Qinghai-Tibet Plateau:40Ar/39Ar Dating and Implication for Geodynamic Events

A lot of new gold deposits have been found on the eastern margin of the Qinghai-Tibet Plateau during the past two decades. Among them, three main types of gold deposits have been recognized, including quartz-vein-type, shear- zone-type and porphyry-type. The former two types of gold deposits are mainly hosted within metamorphic rocks, while the latter is related to Cenozoic magmatism. Although all of these gold deposits are believed to have been formed during the uplift process of the Qinghai-Tibet Plateau in the Cenozoic era (Wang et al., 2002b), precise isotopic age constraints have still been lacking until quite recently. This paper presents new 40Ar/39Ar data of some gold deposits on the eastern margin of the Qinghai-Tibet Plateau, which indicate that gold mineralization in the region occurred in response to the episodic stages of the orogenies. Recently obtained 40Ar/39Ar data on quartz and feldspars from several gold deposits, such as the Sandiao deposit, the Baijintaizi deposit, the Pusagang deposits, provide new constraints on gold mineralization on the eastern margin of the Qinghai-Tibet Plateau. Geochronological studies of gold deposits along the Daduhe River indicate that there are three stages of gold mineralization. The early two stages occurred as early as 65.1 Ma in the Shuibaiyang deposit and 58.95 Ma in the Ruoji deposit, while the latter stage occurred as late as 25.35 Ma in Baijintaizi and 24.70 Ma in Sandiao. Isotopic dating of three plagioclases from the Beiya deposit, Zhifanggou deposit and Luobodi deposit and a K-feldspar from the Jinchangqing deposit in Yunnan Province indicates that these deposits were formed at two stages. The Zhifanggou and Jinchangqing deposits have early stage records as old as 58.82 Ma in Zhifanggou and 55.49 Ma in Jinchangqing, but all of the above four deposits in Yunnan have late stage records of 23.18 Ma in Jinchangqing, 24.54 Ma in Zhifanggou, 24.60 Ma in Luobodi and 24.56 Ma in Hongnitang. The above results suggest that the gold deposits on the eastern margin of the Qinghai-Tibet Plateau were formed concentratedly at two main episodes, i.e. the end of the Paleocene (about 58 Ma) and the boundary between the Paleogene and the Neogene (about 25 Ma). The later episode appears to be looks like more important and was coupled with the Sichuan movement, which was extensively activated at that period. The beginning of the Cenozoic Era (about 65 Ma) might be another episode of gold mineralization, but only one deposit (Shuibaiyang) in this study has been proved to have been be formed at this stage and might be earlier than the initial collision between the Indian Plate and the Eurasia Plate. In view of geology, the above three episodes of gold mineralization are associated with three events of tectonic- magmatism and/or fluid events. Even though the gold deposits (for example, the Shuibaiyang deposit, Ruoji deposit and Pusagang deposit) were formed at different episodes, all of them are genetically related to tectonic movements in large- scale shear zones. It looks like theat tectonic events (including large-scale strike-slip) between Paleogene and Neogene had a wide influence upon gold mineralization, with new deposits formed and old deposits enriched or superimposed to be a higher grade by new stage of mineralization. The above data suggest that gold deposits were not only concentrated in some areas, but also formed mainly at different boundaries of geological times, indicating that there existed some peak stages of gold mineralization (metallogenic episodes), and that the gold deposits were formed mainly by episodic mineralization.

Gravity observations along the eastern margin of the Tibetan Plateau and an application to the Lushan MS 7.0 earthquake

This paper introduces relative and absolute gravity change observations in the eastern portion of the Tibetan Plateau. We analyze and discuss a change that occurred in 2010 in the gravity along the eastern margin of the plateau and the relationship between this change and the 2013 Lushan Ms7.0 earthquake. Our results show that： （1） before the Lushan MsT.0 earthquake, gravity anomalies along the eastern margin of the Tibetan Plateau changed drastically. The Lushan earthquake occurred at the bend of the high gradient zone of gravity var- iation along the southern edge of the Longmenshan fault zone. （2） The 2013 Lushan earthquake occurred less than 100 km away from the epicenter of the 2008 Wenchuan earthquake. Lushan and Wenchuan are located at the center of a four- quadrant section with different gravity anomalies, which may suggest that restoration after the Wenchuan earthquake may have played a role in causing the Lushan earthquake. （3） A medium-term prediction based on changes in gravity anoma- lies was made before the Lushan Ms7.0 earthquake, in par- ticular, a prediction of epicenter location.

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.

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.

Present-day Block Movement and Fault Activity on the Eastern Margin of the Tibetan Plateau

The geology and tectonics in the eastern margin of Tibetan Plateau are complex. The main tectonic framework is composed of blocks and faults. Using discontinuous global positioning system survey data for 2008–2014, the velocity field for the Eurasia reference framework was obtained. Based on the velocity field, the present-day velocities of the blocks and boundary faults were estimated. The results reveal that the movement rates of the Chuan-Qing, South China, Chuan-Dian and Indo-China blocks are（17.02±0.60） mm/a,（8.77±1.51） mm/a,（13.85±1.31） mm/a and（6.84 ± 0.74） mm/a, respectively, and their movement directions are 99.5°, 120.3°, 142.9° and 153.3°, respectively. All blocks exhibit clockwise rotation. The displacement rates of the Xianshuihe, Longmenshan, Anninghe, Zemuhe, Xiaojiang and Red River faults are（7.30±1.25–8.30±1.26） mm/a,（10.07±0.97–11.79±0.89） mm/a,（0.96±0.74–2.98±1.73） mm/a,（2.03±0.49–3.20±0.73） mm/a,（3.45±0.40–6.02±0.50） mm/a and（6.23±0.56） mm/a, respectively. The Xianshuihe, Anninghe, Zemuhe and Xiaojiang faults show leftlateral strike-slip movement, while the Longmenshan and Red River faults show right-lateral strikeslip. These characteristics of the blocks and faults are related to the particular tectonic location and dynamic mechanism.

Crustal Uplift in the Longmen Shan Mountains Revealed by Isostatic Gravity Anomalies along the Eastern Margin of the Tibetan Plateau

This study examines the relationship between high positive isostatic gravity anomalies （IGA）, steep topography and lower crustal extrusion at the eastern margin of the Tibetan Plateau. IGA data has revealed uplift and extrusion of lower crustal flow in the Longmen Shan Mountains （the LMS）. Firstly, The high positive IGA zone corresponds to the LMS orogenic belt. It is shown that abrupt changes in IGA correspond to zones of abrupt change of topography, crustal thickness and rock density along the LMS. Secondly, on the basis of the Airy isostasy theory, simulations and inversions of the positive IGA were conducted using three-dimensional bodies. The results indicated that the LMS lacks a mountain root, and that the top surface of the lower crust has been elevated by 11 km, leading to positive IGA, tectonic load and density load. Thirdly, according to Watts＇s flexural isostasy model, elastic deflection occurs, suggesting that the limited （i.e. narrow） tectonic and density load driven by lower crustal flow in the LMS have led to asymmetric flexural subsidence in the foreland basin and lifting of the forebulge. Finally, based on the correspondence between zones of extremely high positive IGA and the presence of the Precambrian Pengguan-Baoxing complexes in the LMS, the first appearance of erosion gravels from the complexes in the Dayi Conglomerate layer of the Chengdu Basin suggest that positive IGA and lower crustal flow in the LMS took place at 3.6 Ma or slightly earlier.

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.

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.

RELATIONSHIP BETWEEN P-T CONTITIONS OF TWO PHASES OF TAN-LU STRIKE-SLIP SHEAR ZONES AND DELAMINATION OF OROGENIC BELTS ON THE EASTERN MARGIN OF THE DABIE MOUNTAINS

The Tan-Lu fault zone joins the Dabie Mountains on its eastern margin, and offsets the Dabie and Sulu orogenic belts sinistrally for about 500 kin. On the basis of calculation of temperature and pressure experienced by the two phases of the fault zone as well as the thermo-chronological information on mylonite from the earlier and later Tan-Lu fault zones on the eastern margin of the Dabie Mountains, this paper discusses the delamination history and uplifting magnitudes of the Dabie Mountains from earlier Jurassic to earlier Cretaceous. From mineral assemblages, mineral deformation and muscovite-chlorite geothermometry calculation, it is known that the temperature experienced by the two phases of Tan-Lu fault zones are between 40℃ and 450℃, and the confining pressures are between 0.25Gpa and 0.36GPa for the earlier shear zones and 0.24-0.39GPa for the late shear zones. According to the geobarometry of Si-in-phengite and by considering shear heating and tectonic over-pressure, it is concluded that the maximum formation depths for the two phases of the ductile shear zones are not more than 12 kin. Differential formation depths for the two phases of shear zones are 1-2 km at most. At about 190 Ma and 128 Ma, the Tan-Lu fault zone experienced two phases of cooling events. During this period, the eastem margin of the Dabie Mountains experienced a tectonic calm period and no uplifting. According to information from the Tan-Lu fault zone, the uplifting magnitudes of the Dabie orogenic belts are not more than 12 km during the earlier Cretaceous.

NEOTECTONICS ALONG THE EASTERN MARGIN OF THE TIBETAN PLATEAU: INFERENCES FROM BEDROCK RIVER INCISION PATTERNS

The topographic margin of the Tibetan Plateau adjacent to the Sichuan Basin is one of the World’s most impressive continental escarpments, rising from ～600 meters in the basin to peak elevations exceeding 6km across a horizontal distance of only 50～60km. Despite this relief, recent geodetic results (King et al., 1997; Chen et al., 1999) indicate that active shortening across this margin of the plateau is <3mm/a, and is within uncertainty of zero. Recent geodynamic models for active deformation in eastern Tibet (Royden et al., 1997) explain this discrepancy as a consequence of flow of lower crust from beneath the central plateau. These models predict relatively high rates of rock uplift in the near absence of horizontal shortening. Rivers along this margin of the plateau are actively incising into bedrock and afford the opportunity to better resolve the distribution of rock uplift along the margin.

Structural Evolution of the Eastern Margin of Eurasia in Late Mesozoic and Cenozoic

This paper features the structural evolution of the eastern margin of Eurasia in Late Mesozoic and Cenozoic. It is characterized by three stages of development: the riftogenic stage (Jurassic-Early Cretaceous), the platform stage (Late Cretaceous) and the neotectonic one (Paleogene-Quarternary). The boundaries between these stages are distinctly fixed by the geological time limits of planetary range. It is demonstrated that the riftogenic and neotectonic stages were characterized by a high degree of geodynamic activity, and the platform one by a decrease in contrast of tectonic movements. The main river net was formed in the Early Cretaceous and in the Neogene. It experienced a serious reconstruction accompanied by the formation of the Amur River valley being similar to the modern one.

Multi-Stage Basin Development and Hydrocarbon Accumulations： A Review of the Sichuan Basin at Eastern Margin of the Tibetan Plateau

Sichuan Basin is one of the uppermost petroliferous basins in China. It experienced three evolutionary phases which were marine carbonate platform （Ediacaran to Late Triassic）, Indosinian-Yanshanian orogeny foreland basin （Late Triassic to Late Cretaceous） and uplift and tectonic modification （Late Cretaceous to Quaternary）. The present-day tectonics of the Sichuan Ba- sin and its periphery are characterized by three basic elements which are topography, basement type and surface structure, and two settings （plate margin and interior）. Therefore, be subdivided into five units which have different structure and tectonic history. The basin contains five different sets of source rocks with thickness up to 2 500 m. These source rocks were well preserved due to the presence of Middel-Lower Triassic evaporites （〉-200 m） and thick terrestrial sediments filling in the Indosinian-Yanshanian foreland basin （〉3 000 m）. The uplift and erosion since Late Cretaceous has significant influence on cross-strata migration and accumulation of oil and gas. The multi-phase evolution of the basin and its superimposed tectonic elements, good petroleum geologic conditions and diverse petroleum systems reveal its bright exploration prospects.

Evidence of crustal ‘channel flow’ in the eastern margin of Tibetan Plateau from MT measurements

Magnetotelluric (MT) survey has been carried out in the eastern margin of the Tibetan Plateau and its neighboring Shimian-Leshan area, Sichuan Province. Analysis of this MT data reveals that the electric structure of the Tibetan Plateau differ much from that of the Sichuan block. In general, the electric re-sistivity of crust beneath the Sichuan block in the east is larger than that of the eastern margin of the Tibetan Plateau in the west. The crust of the plateau is divided into upper, middle, and lower layers. The middle crust is a low resistivity layer with minimum down to 3―10 Ωm about 10―15 km thick. It pre-sumably contains partial melt and/or salt-bearing fluids with low viscosity, prone to deform and flow, producing a "channel flow" under the southeastward squeeze of the eastern Tibetan Plateau. This low-resistivity layer makes the upper crust decoupled mechanically from the lower crust. In the brittle upper crust, faults are dominated by left-lateral strike-slip and thrust motions, leading to surface rising and shallow earthquakes. The low-resistivity layer also cut the Xianshuihe-Anninghe fault zone into two sections vertically. In this region, the thicknesses of upper, middle, and lower crust vary laterally, pro-ducing a transitional zone in the eastern margin of the Tibetan Plateau characterized by thicker crust and higher elevation in the west and thinner crust and lower elevation in the east.

Geochronology and geochemistry of gneissic metagranites in eastern Dabie Mountains:Implications for the Neoproterozoic tectono-magmatism along the northeastern margin of the Yangtze Block

The gneissic metagranites with Neoproterozoic protolith ages are widely exposed along the eastern margin of the Dabie ultra-high-pressure(UHP) metamorphic belt.In this paper,five representative plutons,including Huangzhen,Daba,Shima,Shuanghe,and Sanzusi,were selected for a detailed chronological and geochemical study aiming to identify the nature of the protoliths and to reveal their implications for the Neoproterozoic tectono-magmatic evolution along the northeastern margin of the Yangtze Block.These gneissic metagranites consist mainly of quartz,albite(oligoclase) and K-feldspar,and minor amphibole and biotite,as well as some metamorphic minerals due to the UHP metamorphism,such as phengite,epidote and minor kyanite and garnet.Mafic alkaline minerals(e.g.,aegirine or aegirine-augite) have been observed in some of these plutons.Zircon LA-ICP-MS U-Pb dating results indicate that the protoliths of the gneissic metagranites have been generated in Mid-Neoproterozoic(770-780 Ma),and suffered both ultrahigh-pressure metamorphism in Early Mesozoic and subsequently high-pressure eclogite-facies recrystallization at about 215 Ma.Although the gneissic metagranites generally have high SiO2 contents(70.23%-77.23%) and show metaluminous-weakly peraluminous signatures(ASI=0.90-1.05),there are still some geochemical variances between different plutons.Compared with the Sanzusi pluton,the metagranites from the Huangzhen,Daba,Shima,and Shuanghe have high K2O+Na2O contents(7.76%-9.45%),FeOtotal/(FeOtotal+MgO) ratios(0.82-0.96),HFSEs and Ga concentrations with an average 104×Ga/Al ratio up to 3.07.Combined with the features that the four plutons commonly contain aegirine-augite and have high zircon saturation temperatures(816-918°C),it is suggested that their proto-liths belong to peralkaline A-type granites.The Sanzusi pluton generally contains biotite and epidote generated from metamorphic reaction of amphibole,and is chemically enriched in calcium and depleted in potassium with K2O/Na2O ratios ranging from 0.42 to 0.54,suggesting their protoliths should be ascribed to calc-alkaline granitoids(I-type).The gneissic metagranites in the eastern margin of Dabie Mountains show both arc-and rift-like geochemical signatures,and their protoliths likely have been generated by reworking of the preexisting arc-related crust under an extensional setting,suggesting that the northeastern margin of the Yangtze Block during the Middle Neoproterozoic likely have been under the initial stage of a passive rifting rather than in an active rifting setting typically induced by the upwelling of a mantle plume.

Recent Trends in Satellite-Derived Chlorophyll and Aerosol Optical Depth Together with Simulated Dimethylsulfide in the Eastern China Marginal Seas

The biogenic compound dimethylsulfide(DMS)produced by a range of marine biota is the major natural source of re-duced sulfur to the atmosphere and plays a major role in the formation and evolution of aerosols,potentially affecting climate.The spatio-temporal distribution of satellite-derived chlorophyll_a(CHL)and aerosol optical depth(AOD)for the recent years(2011-2019)in the Eastern China Marginal Seas(ECMS)(25°-40°N,120°-130°E)are studied.The seasonal CHL peaks occurred during late April and the CHL distribution displays a clear zonal gradient.Elevated CHL was also observed along the northern and western coastlines during summer and winter seasons.Trend analysis shows that mean CHL decreases by about 10%over the 9-year study period,while AOD was higher in south and lower in north during summertime.A genetic algorithm technique is used to calibrate the key model parameters and simulations are carried out for 2015,a year when field data was available.Our simulation results show that DMS seawater concentration ranges from 1.56 to 5.88 nmol L^(−1) with a mean value of 2.76 nmol L^(−1).DMS sea-air flux ranges from 2.66 to 5.00mmol m^(−2) d^(−1) with mean of 3.80mmol m^(−2) d^(−1).Positive correlations of about 0.5 between CHL and AOD were found in the study region,with higher correlations along the coasts of Jiangsu and Zhejiang Provinces.The elevated CHL concentration along the west coast is correlated with increased sea-water concentrations of DMS in the region.Our results suggest a possible influ-ence of DMS-derived aerosol in the local ECMS atmosphere,especially along the western coastline of ECMS.

Spatial Distributions and Potential Sources of Long Chain(C_(30),C_(32)1,15-)Alkyl Diols in Surface Sediments from Eastern China Marginal Seas

Long chain alkyl diols have shown important potential for the reconstruction of sea surface temperature,productivities and upwelling conditions in marine or lacustrine environments.However,little is known about the distribution and sources of the diols in eastern China marginal seas(CMS),which are areas of important organic carbon sink.Here the contents of C_(30) and C_(32)1,15-diols were analyzed in 181 surface sediments from eastern CMS.The similar distribution pattern and strong linear correlation between C_(30) and C_(32) diols indicated that they had similar biological source,with a dominance of C_(30) diol.Their contents ranged from 7-2726 ng g^(-1) for C_(30) diol and 5-669 ng g^(-1) for C_(32) diol,and both showed higher values mainly in the mud area of the Yellow Sea,while the TOC normalized contents showed a more obvious seaward increasing trend.The similar distribution pattern and significant positive correlation between diols and the other marine biomarkers(brassicasterol,dinosterol,C_(37) alkenones) indicated C_(30) and C_(32) diols in eastern CMS were mainly from marine algae.This conclusion was also supported by principal component analysis(PCA).Our results also showed that sediment diol contents were generally related to marine productivity,suggesting that diols could be applied for marine productivity reconstruction in eastern CMS.

Lithospheric Electrical Structure across the Eastern Segment of the Altyn Tagh Fault on the Northern Margin of the Tibetan Plateau

Project INDEPTH （InterNational DEep Profiling of Tibet and the Himalaya） is an interdisciplinary program designed to develop a better understanding of deep structures and mechanics of the Tibetan Plateau. As a component of magnetoteUuric （MT） work in the 4th phase of the project, MT data were collected along a profile that crosses the eastern segment of the Altyn Tagh fault on the northern margin of the plateau. Time series data processing used robust algorithms to give high quality responses. Dimensionality analysis showed that 2D approach is only valid for the northern section of the profile. Consequently, 2D inversions were only conducted for the northern section, and 3D inversions were conducted on MT data from the whole profile. From the 2D inversion model, the eastern segment of the Altyn Tagh fault only appears as a crustal structure, which suggests accommodation of strike slip motion along the Altyn Tagh fault by thrusting within the Qilian block. A large-scale off-proffie conductor within the mid-lower crust of the Qilian block was revealed from the 3D inversion model, which is probably correlated with the North Qaidam thrust belt. Furthermore, the unconnected conductors from the 3D inversion model indicate that deformations in the study area are generally localized.