PRESENT LANDFORMS, ACTIVE TECTONIC ZONES, DEEP STRUCTURES AND UPLIFT MECHANISMS OF THE LONGSHOUSHAN BLOCK ON THE NORTHERN MARGIN OF THE QINGHAI—TIBET PLATEAU

Located in the northern margin of the Qinghai—Tibet Plateau, the Longshoushan Mt. is a small block between Qinghai—Tibet Landmass and Alashan Landmass.Traditional tectonic viewpoint does not consider that the Longshoushan Mt. is a single tectonic block. It is quite evident that there is only a hazy idea about the Longshoushan block. Though there is a very complex tectonic region between Qinghai—Tibet Landmass and Alashan Landmass, the Longshoushan block in the region shows unique tectonic landforms, deep structures and uplift mechanisms. Researching into the relationship between the Longshoushan block and the Qinghai—Tibet and Alashan Landmasses will contribute to the realization of boundary and orogenic belt on the northern margin of the Qinghai—Tibet block. It is a very important scientific subject.The Longshoushan Mt., longer than 150km in NWW direction and wider than 10km, is located on the northern side of Hexi corridor(100 5°～102 5°E,38 5°～39 3°N). It extends from the northwest of Zhangye to Hexibu, and from the south of Chaoshui basin to the north of Minle basin. From west to east, there are the highest peak, Dongdashan Mt.(3616m), the second peak, Dufengding(2937m) and Qianshan peak(2827m), height of the mountains is getting lower and lower, mean height above sea level is over 2000m, and relative height difference is about 1000m. The Longshoushan Mt. provides a natural defence for stopping the southward migration of sandstorm in the Hexi corridor, and forms a topographic step zone from the Alashan Plateau to the Qinghai—Tibet Plateau. In the Longshoushan area, developed landforms, such as planation surface, table\|land, terrace land, are general characters of all geomorphic units. It is shown that the Longshoushan Mt. is a intermittently uplifted block. An astonishingly similar of geometric patterns of Taohualashan Mt. and Hongshihu basin is very interesting natural landscape in the area. It is suggested that Taohualashan Mt. broke away from Hongshihu Basin in secular tectonic movement. The viewpoint is supported by major formation, lithofacies, limitation and style of active faulting. The Longshoushan block consists of two major active fault zones (the northern Longshoushan fault zone and the southern Longshoushan fault zone), the active Pingshanhu—Hongshihu fault basin belt and Taohualashan—Xieposhan tectonic uplift belt. In addition, there are the NNW\|trending West Polamading fault, NWW\|trending Maohudong fault trough, NNE\|trending Daxiahe rift valley and others on the block. the activity and formation style of these structures indicate that the block is acted not only by compressive stress, but also by tensile stress. The northern Longshoushan and southern Longshoushan fault zones are closely related to formation and evolution of the Longshoushan block, the two zones are active fault zones since late Pleistocene and boundary fault zones of the block. The genesis and activity style of the Pingshanhu\|Hongshihu basin are similar to the continental rift, which may be due to the mantle uplift.

THE HIGH RESOLUTION SEISMIC TOMOGRAPHIC IMAGE IN QINGHAI—TIBET PLATEAU AND ITS DYNAMIC IMPLICATIONS

The Qinghai—Tibet plateau and its surrounding areas including Indian subcontinent, Xinjiang, Mongolia, is a largest lithosphere convergence place in the world, which characterized by continent\|continent collision with a thick crust and lithosphere. The high resolution seismic surface wave tomographic inversion has been conducted for studying the 3D velocity structure of crust and upper mantle in those areas. The seismic surface waveform data are from the archives of the CDSN, GSN and GEOSCOPE. About 2400 long period surface waveform recordings are available for both dispersion and waveform tomographic inversion. The block inversion by grid 1°×1°in Qinghai—Tibet plateau and 2°×2°in the surrounding areas were adapted. The resulting maps show the high resolution 3D shear wave velocity variation from earth’s surface to 400km depth.

FINITE STAIN MEASUREMENT AND SHORTENING ANALYSIS IN THE NORTHERN MARGIN OF QINGHAI—TIBET PLATEAU

Finite strain patterns of rocks The structural styles and crustal shortening in the northern margin of Qinghai—Tibet plateau are examined by systematic finite strain measurements. The finite strain patterns in this area are of following characteristics:① The orientation of & principal axes of strain ellipsoid varies regularly in regard to different tectonic locations. In fact, most of the measured X axes are parallel to the regional structure lines, striking east\|west or approximately east\|west with some X axes trending northeast\|southwest. The measured Z\|axes are approximately at right angle to the regional structure lines, trending north\|northeast or north\|northwest.② The Flinn parameter k is higher in the northern and southern margins of the basin than that in the basin center, indicating that the margins of basin experienced extensional strain and the middle of basin undergo strain.③ Rocks of different age possess different strain state and show k value of 1～2 for Tertiary rocks, 3～4 for Jurassic—Cretaceous rocks. The k value of the basement rocks is the highest of all.

CENOZOIC BASIN EVOLUTION, STRUCTURAL STYLES OF THE QAIDAM AND AN ESTIMATE OF DENUDATION IN ADJACENT MOUNTAIN SYSTEMS, NORTHEAST QINGHAI—TIBETAN PLATEAU

Qaidam basin is located at northeast Qinghai—Xizang (Tibet) plateau, and surrounded by east Kunlun, south Qilian and Altun mountain systems. The purpose of this paper is to study the Cenozoic basin evolutionary stages, structural styles of the Qaidam, and the denudation in adjacent mountain systems through seismic profile interpretation and complemented by field observation. The Qaidam basin has experienced two tectonic stages of Paleogene—early Miocene (65～12Ma) and late Miocene—present (12～0Ma). The former is characterized by differential uplift of the mountains and subsidence of the basin, and the latter by intense compression, wrench, thrusting and folding. The compressional structural styles are mainly distributed in the Circle Hero—Range Depression of southwest Qaidam, such as Nanyishan, Youquanzi, Younan, Youshashan anticline belts and thrust faults. The wrench structural styles of the northern Qaidam include en echelon uplifts (fault—block outcrops) such as Seshitengshan, Luliangshan, Xitieshan and Eimnikshan, which are mainly composed of pre\|Sinian and Paleozoic rocks; en echelon anticlines such as Lenghu—Nanbaxian belts; and en echelon depressions such as Kunteyi, Senan and Yibei depressions, which are mainly composed of Mesozoic and Cenozoic rocks.

STYLE AND CONSEQUENCE OF STRAIN PARTITION IN THE NORTHEAST MARGIN OF QINGHAI—TIBET PLATEAU

The Northeastern margin of Qinghai—Tibet plateau,here refers to the region bounded by Western Qinling fault zone and Longshoushan—Liupanshan tectonic zone, where obliquely compression deformation occurred with the NE\|trending maximum principle axis of stress, with Ordos Massif to the east, Alaxa Block to the north, and Qinghai—Tibet plateau to the southwest. The main structure in this region is Haiyuan—Gulang transpression zone. It consists of a series of active faults: the Haiyuan fault zone, the Tianjingshan fault zone, the Yantongshan fault zone and the Niushoushan—Luoshan fault zone.

THE STUDY AND DISCUSSION ON “DIGITAL QINGHAI—TIBET PLATEAU”

The scientific research on Qinghai—Tibet Plateau has already been the hot and key point on the plateau evolvement, the earth ecological variety, as well as the society harmonious development. The research on Qinghai—Tibet Plateau has the following characteristics:(1) 4\|dimension of time and space: with a vast territory and very deep depth, as well as the big time span.(2) Wide fields and across subjects: including geology, environment, ecology, climate, land, agriculture, forestry, animal husbandry, etc.(3) Theory and practice with profound and lasting influence: the research results can be great function for the direction in understanding the world, ecological environment and the human living conditions.The current issues of the research on Qinghai—Tibet Plateau are as follows:(1) Thousands of papers concerned about Qinghai—Tibet Plateau are lack of quantification data, and the research results are not displayed vividly.(2) The study scopes are more in the portion and less in the whole.(3) There are not enough work of combination of depth study with surface study, the representation in 3\|D is limited.(4) The study of time variation is not enough and there is poor way to show the time series results.(5) There are not enough work in the different specialties intercross, as well as the synthesis study of interdisciplinary subjects and cross subjects.

GEOMORPHIC EVIDENCES FOR CENOZOIC UPLIFT IN THE EASTERN MARGIN OF QINGHAI—TIBET PLATEAU

The uplift history has been becoming the key for the geological science of Qinghai—Tibet plateau. The scholars abroad have reconstructed uplift history of the plateau by studying geological process of the inner globe, they considered that the altitude of the plateau got up to the maximum at 14Ma (M.Coleman et al, 1995; S.Turner et al, 1993)or the plateau got to the present elevation at about 8Ma (T.M.Harrison,1992). The Chinese geologists make use of substitutes of outer environmental elements to deduce that the uplift of Qinghai—Tibet plateau began from 3 4Ma(Li Jijun,1995). It is obvious that there are the different views and controversies about the plateau uplift history.

TECTONIC STYLES IN THE SOUTHWEST QINLING AND RELATIONS WITH DYNAMICS OF QINGHAI—TIBET PLATEAU

Based on the studies of geology and geochemistry, A’nymaque—Mianlue limited oceanic basin is comparable to the Paleo\|Tethys on time, sedimentary, biocoenosis, and the type of ophiolite (Coleman, 1984; Deng, 1984; Xu, 1996;Chenliang, 1999). The A’nyemaqen—Mianlue oceanic basin was one of a northeast branches of Paleo\|Tethys (Zhang Guowei, 1995; 1996) .Our researches on deformations reveal that tectonic styles of the Southwest Qinling orogenic belt is obviously influenced by the dynamics of Qinghai—Tibet plateau.Structural deformation analysis suggested that the southwest part of Qinling have undergone 3 major deformation stages in Mesozoic and Cenozoic. Firstly, rock folding at deep\|middle tectonic level and progressively thrusting shearing characterized the deformation of collision. The thrust tectonics are south\|directed, such as A’nymaque, Wenxian—Kangxian and Mianlue thrusting systems, and the deformations took place in T\-2—T\-3. Secondly, the middle\|tectonic level thrusting and sinistral strike\|slip formed at early intracontinental period (J—K), the thrust tectonics was south\|directed and the regional penetrative left\|lateral slips were NW or NWW. Finally, the east\|west extensional deformations which occurred in late Mesozoic and Cenozoic, a series of north\|south directing basins came into being in this stage, Huixian—Chengxian basin and Lixian basin for example, which overlapped the former deformation styles.

THE PROCESSES OF ATMOSPHERIC IMPURITIES TRANSPORTATION OVER THE QINGHAI—TIBET PLATEAU AS REVEALED BY SEASONAL RECORDS OF SNOW CHEMISTRY

Chemical records were recovered from snow pits samples collected over the two transects (south\|north transect and southeast\|northwest transect) of the Qinghai—Tibetan plateau. It shows that the mean concentration of the major ions over the south regions of Mt. Tanggula is lower than that of the north regions. The flux of major ions over north plateau is over 3 times higher than the south. The cloudy atmosphere of the north plateau is mainly contributed to the local input of dust, while in the south plateau, sea salt ions transported by Indian monsoon is considerable. The continental dust transportation from the north and the marine aerosol transportation from the south reach an approximately equilibrium around Mt. Tanggula regions. Stable oxygen isotopic ratios ( δ 18 O) in precipitation from the south\|north transect shows that, over the north plateau, δ 18 O is positively correlated with temperature, while over south of the plateau the correlation becomes weak and δ 18 O is more correlated with the amount of precipitation.

THE TERTIARY STRATIGRAPHIC SEQUENCE OF YANYUAN BASIN IN THE SOUTHEASTERN MARGIN OF THE QINGHAI—TIBET PLATEAU

The Cenozoic Yanyuan basin is located in the huge Longmenshan—Jinpingshan nappetectonic belt along the eastern margin of the Qinghai—Tibet plateau. The basin is the largest and the best\|preserved intraorogenic basin above 2300m ASL.The basin has deposited different kinds of sediments with 1600m in depth. The early Tertiary strata were first named as Lijiang formation in 1961, and later named as Hongyanzi formation. The later Tertiary strata, the lignite\|bearing strata, were once named as Xigeda formation. Li Yougheng(1978) found some mammal fossils in the strata, so they named it Yanyuan formation. The Hongyanzi Formation which thickness is 1022m can be divided into five members according to the lithologic characters. The first one is mainly made of purplish\|red coarse conglomerates. The composition of gravel mainly consists of limestone and purplish\|red sandstone and marl. The second one consists of sandstone interbedded with conglomerate. The member has three cyclic sequences from conglomerate to sandstone. The composition of gravel of this member is mainly limestone. From bottom to top the degree of sorting and roundness tends to be well. In sandstones or sand lenticules the oblique bedding and trough cross\|bedding can be seen. The third one is the member of sandstone and mudstone. The sandstone is light purple while the mudstone is purplish red. Ripple marks can be seen in the sandstone. The forth one consists of conglomerate interbedded with mudstone, The conglomerate and the sandstone assume three cyclic sequences. The composition of the gravel is chiefly limestone. The fifth one is a member of light purple massive conglomerate. The composition of the gravel is limestone. The imbricate structure can be seen in the conglomerate. The strata belong to later Eocene epoch in accordance with the fossils of mammals, plants and ostracoda in it.

PALEOMAGNETIC ESTIMATE OF THE MESOZOIC—CENOZOIC LATITUDINAL DISPLACEMENT OF TERRENES IN THE QINGHAI—TIBET PLATEAU AND ITS SIGNIFICANCE

The Mesozoic—Cenozoic latitudinal displacement amounts of terranes (or blocks) in the Qinghai—Tibet plateau were calculated in paleomagnetism. These terranes (or blocks) include Tarim and Qaidam blocks, East Kunlun, Baryan Har, Qiangtang, Lhasa and Himalaya terranes. The calculated results are listed in table 1. These results show that:(1) There was the latitudinal displacement difference between central area and southwestern area in the Tarim southern margin since the lower Cretaceous. There was a southward latitudinal movement from the beginning of middle Jurassic or upper Jurassic (Zhou Qingjie, 1992). The northward movement amounts of the Tarim northern margin since the Paleocene are greater than that of the Tarim southern margin. Tarim southern margin has moved northward about 1100km since the Paleocene, Tarim northern margin has done about 1700km. Qaidam has moved northward about 3100km since lower\|middle Jurassic. The northward displacement amount of Qaidam since Paleocene is about 810km, near to that of the central area, Tarim southern margin.

CENOZOIC SEDIMENTARY SEQUENCE IN THE KUMUKULI BASIN, XINJIANG AND NEW EVIDENCE ON LATE QUATERNARY UPLIFT OF THE QINGHAI—TIBETAN PLATEAU

The elevation of Qinghai\|Tibetan plateau is a epoch\|making event in the global evolutionary history, which not only constructed the modern magnificent geomorphic feature, but also influenced far\|reachingly the global climate. The evolutionary models of its uplifting time and scope has been primarily set up, and is waiting to be competed with new discovery and supplement. A comprehensive field geologic excursion on the Cenozoic strata of the Kumukuli basin, Xinjiang, northwest Qinghai\|Tibetan plateau by authors has collected a lot of first\|hand data, and the discovery and dating of the late Pleistocene mammal fossils made an important supplement to the scarcity of late Quaternary fossil recorders in many basins, as well as contributed a great deal to the quantitative study of the researches alike, in the main time, provided new evidences to the uplift of Qinghai\|Tibetan plateau since late pleistocene.Lies in the northwest part of the Qinghai\|Tibetan plateau, and between the Kunlun and Altum Mountain ranges, Kumukuli basin is a intracontinental plateau basin, with a mean elevation about 4000m. Cenozoic strata have a time span from Oligocene to Pleistocene.The stratigraphic and lithologic association displays that the development of Kumukuli basin started at the Oligocene, at the primary uplift stage of the Qinghai\|Tibetan plateau. The Oligocene and Miocene, with a giant thickness and multiple layers of thick conglomerate, is of the products of stronger erosional stage, and a reflection of higher differential in inner geomorphology of the plateau. The aggradation led to the smoothness of the geomorphic feature and fineness of sedimentary particle since Pliocene. Since then, Large scale conglomerate outcroped in the peripheral of the plateau, and differential of geomorphology in the plateau and its peripheral areas became distinct. Kumukuli basin is one of the synchronously developed basin with the plateau, having the most completed Cenozoic sequence with a thickness over 7000m. Its Tertiary sedimentary sequence is basically similar to that of the Ningxia basin, northeastern margin of the Qinghai\|Tibetan plateau, and can be well correlated each other, mutually, they recorded the uplift process of the Qinghai\|Tibetan plateau, and their difference may represent the contrast evolution of the plateau and inhomogeneous differential in geomorphic feature of the plateau and its perimeter respectively. Being two sedimentary basins in separately tectonic units, the former has much thicker strata and coarser particles, for instance, the Oligocene is over 3000m in thickness in Kumukuli basin, however, only about 100m in Ningxia basin. Several uncomformities occurring in Kumukuli basin, namely, between the Quarternary and the Pliocene, the Pliocene and the Middle\|Upper Miocene, as well as the Middle\|Upper Miocene and the Lower Miocene, are the direct effects of horizontal movement accompanied with the process of the uplift of the Qinghai\|Tibetan plateau. Maybe those data imply that the western part of the plateau much stronger in uplift and distinct in horizontal movement than that of the east.

CRUSTAL STRUCTURE IN EASTERN REGION OF QINGHAI—TIBET PLATEAU

A geophysical survey including Magnetotelluric sounding(MT), gravity and geomagnetism was carried out in eastern region of Qinghai—Tibet plateau in 1998. It is to be known from tectonic map that study area was divided into four blocks by three large sutures, but we have very little information on deep\|seated structure which have close relationship with evolution of Tibet plateau, our purpose is to find some deep crustal structure evidences of the blocks and sutures for understanding deep tectonic feature in this region. The geophysical survey region is located in about 97～98°E and 35～26°N, the profile with the length of 760km runs through Bayanhar, Qingtang and Gandise block in NS direction, 349 gravity and geomagnetic data were acquired simultaneously, and 31 MT sites are be placed along the profile with about 18km\|interval to detect electrical conductive feature.

THE UPWARPING AND DOWNWARPING STRUCTURAL SYSTEM OF MOHO—SURFACE IN CHINESE AND NEAR REGION AND THE GENETIC MECHANICS OF QINGHAI—TIBET PLATEAU TECTONIC

Recently, this study group established “the map of MOHO\|surface bathymetric line in Chinese and Near Region" on the basis of latest survey and study of the crustal depth, the preliminary result shows that the regular meridional and latitudinal upwarping and downwarping structural pattern of MOHO\|surface bathymetric line among Eurasian plate and Pacific plate and the Indian plate alternately appears, and which is accreted and coupled with basin ridge structure that exist shallow crustal base, continental crust and oceanic crust and others regular upwarping and downwarping net structure system that possessing different block characters and different scales exist together. Among different structure systems, it occurs that ramp downwarping impetus transform structure belts whose trends is characteristic. Nowadays upwarping and downwarping net structure system is basically modeled in Himalayan orogeny period. It is showed that the Earth revolution way has been changed in this period, which leaded to a new Earth dynamics cycle.The pattern of upwarping and downwarping structure among different structure systems or different structure blocks , and the characters of different trends and different scale transform structure belts, reflects the structure movement way and their conversion law, and reveals the Earth centralized dynamics mechanics that is produced by the revolutionary effect under the environments of aster system. This can be clearly reflected by the change of impetus way between Qinghai—Tibet highland structure system and near structure system.

Quantification of the concrete freeze–thaw environment across the Qinghai–Tibet Plateau based on machine learning algorithms

The reasonable quantification of the concrete freezing environment on the Qinghai–Tibet Plateau(QTP) is the primary issue in frost resistant concrete design, which is one of the challenges that the QTP engineering managers should take into account. In this paper, we propose a more realistic method to calculate the number of concrete freeze–thaw cycles(NFTCs) on the QTP. The calculated results show that the NFTCs increase as the altitude of the meteorological station increases with the average NFTCs being 208.7. Four machine learning methods, i.e., the random forest(RF) model, generalized boosting method(GBM), generalized linear model(GLM), and generalized additive model(GAM), are used to fit the NFTCs. The root mean square error(RMSE) values of the RF, GBM, GLM, and GAM are 32.3, 4.3, 247.9, and 161.3, respectively. The R^(2) values of the RF, GBM, GLM, and GAM are 0.93, 0.99, 0.48, and 0.66, respectively. The GBM method performs the best compared to the other three methods, which was shown by the results of RMSE and R^(2) values. The quantitative results from the GBM method indicate that the lowest, medium, and highest NFTC values are distributed in the northern, central, and southern parts of the QTP, respectively. The annual NFTCs in the QTP region are mainly concentrated at 160 and above, and the average NFTCs is 200 across the QTP. Our results can provide scientific guidance and a theoretical basis for the freezing resistance design of concrete in various projects on the QTP.

Contribution of external forcing to summer precipitation trends over the Qinghai-Tibet Plateau and Southwest China

在过去的60年中,全球气候经历了快速变暖和短暂的变暖停滞,而中国的区域降水也经历了多样而复杂的变化.本文分析了1961年至2014年外强迫因子对青藏高原和中国西南地区夏季降水趋势的影响.观测数据显示,青藏高原的夏季降水呈增加趋势,而中国西南地区的夏季降水呈减少趋势,这两个相邻地区的夏季降水变化趋势相反.利用CMIP6数据,本文研究了不同外强迫因子对两个区域夏季降水趋势的影响.结果表明,温室气体对青藏高原夏季降水的增加具有显著影响,而气溶胶在中国西南地区夏季降水减少中起主要作用。

Response of Freezing/Thawing Indexes to the Wetting Trend under Warming Climate Conditions over the Qinghai–Tibetan Plateau during 1961–2010:A Numerical Simulation

Since the 1990s,the Qinghai–Tibetan Plateau(QTP)has experienced a strikingly warming and wetter climate that alters the thermal and hydrological properties of frozen ground.A positive correlation between the warming and thermal degradation in permafrost or seasonally frozen ground(SFG)has long been recognized.Still,a predictive relationship between historical wetting under warming climate conditions and frozen ground has not yet been well demonstrated,despite the expectation that it will become even more important because precipitation over the QTP has been projected to increase continuously in the near future.This study investigates the response of the thermal regime to historical wetting in both permafrost and SFG areas and examines their relationships separately using the Community Land Surface Model version 4.5.Results show that wetting before the 1990s across the QTP mainly cooled the permafrost body in the arid and semiarid zones,with significant correlation coefficients of 0.60 and 0.48,respectively.Precipitation increased continually at the rate of 6.16 mm decade–1 in the arid zone after the 1990s but had a contrasting warming effect on permafrost through a significant shortening of the thawing duration within the active layer.However,diminished rainfall in the humid zone after the 1990s also significantly extended the thawing duration of SFG.The relationship between the ground thawing index and precipitation was significantly negatively correlated(−0.75).The dual effects of wetting on the thermal dynamics of the QTP are becoming critical because of the projected increases in future precipitation.

Mineral Geochemistry of Apatite in the Jiama PorphyrySkarn Deposit,Tibet and its Geological Significance

The Jiama deposit,a significant porphyry-skarn-type copper polymetallic deposit located within the Gangdese metallogenic belt in Tibet,China,exemplifies a typical porphyry metallogenic system.However,the mineral chemistry of its accessory minerals remains under-examined,posing challenges for resource assessment and ore prospecting.Utilizing electron microprobe analysis and LA-ICP-MS analysis,this study investigated the geochemical characteristics of apatite in ore-bearing granite and monzogranite porphyries,as well as granodiorite,quartz diorite,and dark diorite porphyries in the deposit.It also delved into the diagenetic and metallogenic information from these geochemical signatures.Key findings include:(1)The SiO_(2) content,rare earth element(REE)contents,and REE partition coefficients of apatite indicate that the dark diorite porphyry possibly does not share a cogenetic magma source with the other four types of porphyries;(2)the volatile F and Cl contents in apatite,along with their ratio,indicate the Jiama deposit,formed in a collisional setting,demonstrates lower Cl/F ratios in apatite than the same type of deposits formed in a subduction environment;(3)compared to non-ore-bearing rock bodies in other deposits formed in a collisional setting,apatite in the Jiama deposit exhibits lower Ce and Ga contents.This might indicate that rock bodies in the Jiama deposit have higher oxygen fugacity.Nevertheless,the marginal variation in oxygen fugacity between ore-bearing and non-ore-bearing rock bodies within the deposit suggests oxygen fugacity may not serve as the decisive factor in the ore-hosting potential of rock bodies in the Jiama deposit.

Geochronology and Geochemistry of Ore-related Granitoids in the Giant Gariatong Rb Deposit,Tibet and Implications for Rb Metallogeny in China

Rubidium(Rb)deposits mostly occur in the South China and Central Asia orogenic belts and are often closely associated with highly differentiated granites.This study investigates a newly-discovered giant Rb deposit at Gariatong in the Central Lhasa terrane in Tibet.Detailed field studies and logging data revealed that the Rb mineralization mainly occurs in monzogranite and is related to greisenization.LA-ICP-MS U-Pb dating of zircon yielded ages of 19.1±0.2 Ma and 19.0±0.2 Ma for greisenized monzogranite and fresh monzogranite,respectively.The monzogranites are characterized as strongly peraluminous,with high contents of SiO2,Al2O3,K2O and Na2O as well as a high differentiation index.They are enriched in light rare earth and large ion lithophile elements with significant negative Eu anomalies and depleted high fieldstrength elements.Petrological and geochemical features of these ore-related monzogranites suggest that they are highly fractionated S-type granites,derived from remelting of crustal materials in a post-collisional setting.The geochemistry of zircon and apatite points to a low oxygen fugacity of the ore-related monzogranite during the magma’s evolution.The discovery of the Gariatong Rb deposit suggests that the Central Lhasa terrane may be an important region for rare metal mineralization.

Present-day Upper-crustal Strain Rate Field in Southeastern Tibet and its Geodynamic Implications:Constraints from GPS Measurements with ABIC Method

The Earth’s surface kinematics and deformation are fundamental to understanding crustal evolution.An effective research approach is to estimate regional motion field and deformation fields based on modern geodetic networks.If the discrete observed velocity field is obtained,the velocity related fields,such as dilatation rate and maximum shear strain rate,can be estimated by applying varied mathematical approaches.This study applied Akaike's Bayesian Information Criterion(ABIC)method to calculate strain rate fields constrained by GPS observations in the southeast Tibetan Plateau.Comparison with results derived from other three methods revealed that our ABIC-derived strain rate fields were more precise.The maximum shear strain rate highlighted the Xianshuihe–Xiaojiang fault system as the main boundary for the outward migration of material in southeastern Tibet,indicating rotation of eastern Tibet material around the eastern Himalaya rather than whole extrusion along a fixed channel.Additionally,distinct dilatation rate patterns in the northeast and southwest regions of the fault system were observed.The northeast region,represented by the Longmenshan area,exhibited negative dilatational anomalies;while the southwest region,represented by the Jinsha River area north of 29°N,displayed positive dilatational anomalies.This indicates compression in the former and extension in the latter.Combined with deep geophysical observations,we believe that the upper and lower crusts of the Jinsha River area north of 29°N are in an entire expanding state,probably caused by the escape-drag effect of material.The presence of a large,low-viscosity region south of 29°N may not enable the entire escape of the crust,but instead result in a differential escape of the lower crust faster than the upper crust.