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.

Electrical Structure and Fault Features of Crust and Upper Mantle beneath the Western Margin of the Qinghai-Tibet Plateau:Evidence from the Magnetotelluric Survey along Zhada-Quanshui Lake Profile

The magnetotelluric （MT） survey along the Zhada （札达）-Quanshui （泉水） Lake profile on the western margin of the Qinghai （青海）-Tibet plateau shows that the study area is divided into three tectonic provinces by the Yalung Tsangpo and Bangong （班公）-Nujiang （怒江） sutures. From south to north these are the Himalayan terrane, Gangdise terrane, and Qiangtang （羌塘） terrane. For the study area, there are widespread high-conductivity layers in the mid and lower crust, the top layers of which fluctuate intensively. The high-conductivity layer within the Gangdise terrane is deeper than those within the Qiangtang terrane and the Himalaya terrane, and the deepest high-conductivity layer is to the south of the Bangong-Nujiang suture. The top surface of the high-conductivity layer in the south of the Bangong-Nujiang suture is about 20 km lower than that in the north of it. The high-conductivity layer within the Gangdise terrane dips toward north and there are two high-conductivity layers within the crust of the southern Qiangtang terrane. In the upper crust along the profile, there are groups of lateral electrical gradient zones or distortion zones of different scales and occurrence indicating the distribution of faults and sutures along the profile. According to the electrical structure, the structural characteristics and space distribution of the Yalung Tsangpo suture, Bangong.Nujiang suture, and the major faults of Longmucuo （龙木错） and Geerzangbu are inferred.

Cu-Ni-PGES MINERALIZATION OF MELANOCRATIC ROCKS IN SOUTHEAST MARGIN OF THE QINGHAI-XIZANG(TIBET) PLATEAU, HKT

The Panxi Rift Zone is a famous metallogenic province in Southwest China. Continental rifting developed in Hercynian period (P 2, 260～250Ma) accompany with a series of basic\|ultrabasic rocks. Various in lithologies, such as layered intrusions (V\|Ti\|Fe formation), small\|sized mafic\|ultramafic bodies (stocks) and large\|scale basalt (Emeishan Basalt) are constituted of a complete melanocratic rock system.Most of Cu\|Ni\|PGE sulfide deposits are related to small\|sized ultramafic rock bodies. It is a perfect possibility for them to be an affinity of basic eruptive lava and for the neck facies. But in ① Panzhihua\|Center Yunnan Province, the Gaojiacun, also Jinbaoshan, as large stratiform basic\|ultrabasic complex used to be thought that is older one intruded to basement rocks in Precambrian. However, new evidences suggest it is similar with the small\|sized ultramafic rock bodies containing Cu\|Ni\|PGE, and also the both are affinity of the Emeishan Basalt; ② Miyi district, Cu\|Pt mineralization was discovered in the Xinjie bedded basic complex, and in where ophitic olivine\|pyroxenite\|peridotite facies are exactly Pt\|bearing layers; ③ Longzhoushan district, we have recently researched basic\|ultrabasic clusters which intruded into fracture zones, and Cu\|Ni\|Pt, Pd mineralization developed at the salbands.Generally, the basalt is poor in PGE and rich in Cu. It is suggested as the result of PGE dispersion\|concentration processing in the melanocratic rock system when rifting happened.

Modeling the Dynamic Gravity Variations of Northeastern Margin of Qinghai-Xizang (Tibet) Plateau by Using Bicubic Spline Interpolation Function

In this paper, the spatial-temporal gravity variation patterns of the northeastern margin of Qinghai-Xizang (Tibet) Plateau in 1992～2001 are modeled using bicubic spline interpolation functions and the relations of gravity change with seismicity and tectonic movement are discussed preliminarily. The results show as follows: ① Regional gravitational field changes regularly and the gravity abnormity zone or gravity concentration zone appears in the earthquake preparation process; ② In the significant time period, the gravity variation shows different features in the northwest, southeast and northeast parts of the surveyed region respectively, with Lanzhou as its boundary; ③ The gravity variation distribution is basically identical to the strike of tectonic fault zone of the region, and the contour of gravity variation is closely related to the fault distribution.

Fault activity characteristics in the northern margin of the Tibetan Plateau before the Menyuan Ms6.4 earthquake

Fault deformation characteristics in the northern margin of the Tibetan Plateau before the Menyuan Ms6.4 earthquake are investigated through time-series and structural geological analysis based on cross-fault observation data from the Qilian Mountain-Haiyuan Fault belt and the West Qinling Fault belt. The results indicate： 1） Group short-term abnormal variations appeared in the Qilian Mountain-Haiyuan Fault belt and the West Qinling Fault belt before the Menyuan Ms6.4 earthquake. 2） More medium and short-term anomalies appear in the middle-eastern segment of the Qilian Mountain Fault belt and the West Qinling Fault belt, suggesting that the faults＇ activities are strong in these areas. The faults＇ activities in the middle-eastern segment of the Qilian Fault belt result from extensional stress, as before the earthquake, whereas those in the West Qinling Fault belt are mainly compressional. 3） In recent years, moderate-strong earthquakes occurred in both the Kunlun Mountain and the Qilian Mountain Fault belts, and some energy was released. It is possible that the seismicity moved eastward under this regime. Therefore, we should pay attention to the West Qinling Mountain area where an Ms6-7 earthquake could occur in future.

Joint Inversion of the 3D P Wave Velocity Structure of the Crust and Upper Mantle under the Southeastern Margin of the Tibetan Plateau Using Regional Earthquake and Teleseismic Data

The special seismic tectonic environment and frequent seismicity in the southeastern margin of the Qinghai-Tibet Plateau show that this area is an ideal location to study the present tectonic movement and background of strong earthquakes in China's Mainland and to predict future strong earthquake risk zones. Studies of the structural environment and physical characteristics of the deep structure in this area are helpful to explore deep dynamic effects and deformation field characteristics, to strengthen our understanding of the roles of anisotropy and tectonic deformation and to study the deep tectonic background of the seismic origin of the block＇s interior. In this paper, the three-dimensional （3D） P-wave velocity structure of the crust and upper mantle under the southeastern margin of the Qinghai-Tibet Plateau is obtained via observational data from 224 permanent seismic stations in the regional digital seismic network of Yunnan and Sichuan Provinces and from 356 mobile China seismic arrays in the southern section of the north-south seismic belt using a joint inversion method of the regional earthquake and teleseismic data. The results indicate that the spatial distribution of the P-wave velocity anomalies in the shallow upper crust is closely related to the surface geological structure, terrain and lithology. Baoxing and Kangding, with their basic volcanic rocks and volcanic clastic rocks, present obvious high-velocity anomalies. The Chengdu Basin shows low-velocity anomalies associated with the Quaternary sediments. The Xichang Mesozoic Basin and the Butuo Basin are characterised by low- velocity anomalies related to very thick sedimentary layers. The upper and middle crust beneath the Chuan-Dian and Songpan-Ganzi Blocks has apparent lateral heterogeneities, including low-velocity zones of different sizes. There is a large range of low-velocity layers in the Songpan-Ganzi Block and the sub-block northwest of Sichuan Province, showing that the middle and lower crust is relatively weak. The Sichuan Basin, which is located in the western margin of the Yangtze platform, shows high-velocity characteristics. The results also reveal that there are continuous low-velocity layer distributions in the middle and lower crust of the Daliangshan Block and that the distribution direction of the low-velocity anomaly is nearly SN, which is consistent with the trend of the Daliangshan fault. The existence of the low-velocity layer in the crust also provides a deep source for the deep dynamic deformation and seismic activity of the Daliangshan Block and its boundary faults. The results of the 3D P-wave velocity structure show that an anomalous distribution of high-density, strong-magnetic and high-wave velocity exists inside the crust in the Panxi region. This is likely related to late Paleozoic mantle plume activity that led to a large number of mafic and ultra-mafic intrusions into the crust. In the crustal doming process, the massive intrusion of mantle-derived material enhanced the mechanical strength of the crustal medium. The P-wave velocity structure also revealed that the upper mantle contains a low-velocity layer at a depth of 80-120 km in the Panxi region. The existence of deep faults in the Panxi region, which provide conditions for transporting mantle thermal material into the crust, is the deep tectonic background for the area＇s strong earthquake activity.

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.

Formation and Evolution of the Late Mesozoic-Cenozoic Ruo'ergai Basin,Northeastern Margin of the Qinghai-Tibet Plateau

The Middle Triassic Ladinian-Upper Triassic Norian series in the Mesozoic-Cenozoic Ruo’ergai basin of Songpan area is characterized of large thick shallow marine-deep marine fine grained clastic.The strata are regionally unconformable between each adjacent two of the Middle-Late Triassic fine grained clastic,the Jurassic coal-containing clastic,the Cretaceous-Paleogene variegated coarse clastic。

Gravity evidence of underplating in the northeastern margin area of Qinghai-Tibet plateau

Based on leveling data in 1972 -2011 and relative-gravity data in 1993 -2011, we obtained a longterm vertical crustal-deformation rate of 1.62mm/a and a relative-gravity variation rate of 0.62 × 10^-8 ms^-2a^-1 for the northeastern margin area of Qinghai-Tibet plateau. After removing the contributions from the observed vertical movement and inferred surface denudation, we obtain a gravity-variation rate of 0.73 × 10^-8 ms^-2a^-1 attributable to the mass changes beneath the crust. This positive change suggests that the total mass under the observation stations was gradually increasing. We consider this result to be the gravitational evidence of underplating beneath the study area, and propose that the underplating was caused by collision betwen the Indian plate and Tibetan plateau and by gravitation-potential induced deviatoric stress.

Hydrogeochemistry of River Water in the Upper Reaches of the Datong River Basin,China:Implications of Anthropogenic Inputs and Chemical Weathering

This research investigated anthropogenic inputs and chemical weathering in the upper reaches of the Datong River Basin,a tributary of the upper Yellow River,NW China.Multiple approaches were applied to data from 52 water and 12 soil samples from the Muli,Jiangcang,and Mole basins to estimate the chemical component concentrations and to analyze hydrochemical characteristics,distribution patterns,and origins in this coal mining-affected river basin.Coal mining has enhanced the weathering of the lithosphere in the study region.The total dissolved solids in the river range from 145.4 to 701.9 mg/L,which is higher than the global average for rivers.Ion concentration spatial distributions increase around mining areas.River geochemistry is mainly controlled by coal mining activity,carbonate weathering,and silicate weathering,with variances of 33.4%,26.2%,and 21.3%,respectively.Ca^(2+),Mg^(2+),and HCO_(3)^(-)are mainly due to the dissolution of carbonate minerals(calcite>dolomite);Si and K+are mainly from potassium(sodium)feldspar weathering;and Na+and SO_(4)^(2-)mainly from coal mine production.A conceptual model of the river water ion origins from the study area is presented and management implications for improving the adverse effects of coal mining are proposed.These results provide an important standard reference for water resource and environmental management in the study region.

Dextral strike-slip of Sanguankou-Niushoushan fault zone and extension of arc tectonic belt in the northeastern margin of the Tibet Plateau

Sanguankou-Niushoushan 差错(SGK-NSSF ) 的运动学的特征具有到弧的延期的理解的大意义在西藏高原的东北边缘的构造的带。用地调查和各种各样的数据收集方法，包括大规模地质的印射，典型地形学的测量，并且沉积阶层标明日期， SGK-NSSF 展出明显的右罢工滑倒特征并且因此不是一个左首的罢工滑倒差错，由以前的研究人员相信了，这被决定。这研究的结果证明地质的边界为古生代，中生代，和新生代时代都被差错右地打乱，与是类似的指责的排水量。在地志的效果的消除以后，差错的最大的罢工滑倒排水量被发现是

Constraining the characters of the upper mantle discontinuities beneath the NE margin of the Tibetan Plateau with a dense broadband seismic array

Based on observations from a dense broadband seismic array located along the northeastern (NE) margin of the Tibetan Plateau in southeastern Gansu Province,we use receiver functions (RFs) to pick the arrival times of P-to-S converted waves and bin the traces in different grids according to the piercing points of the 410 and 660 km discontinuities in the upper mantle.The depths of the two discontinuities are estimated by the ray tracing method with the IASP91 velocity model and a 3-D tomography model.The results indicate the following:(1) The arrival times of the P410s and P660s converted phases are delayed by approximately 1 s than those predicted by the IASP91 model.The mantle transition zone (MTZ) is thicker than that in the global model.(2) The synchronous lags in the P410s and P660s arrival times are consistent with low-velocity anomalies in the upper mantle,which are believed to result mainly from the eastward migration of materials beneath the NE margin of the Tibetan Plateau.(3) Combined with previous tomography results,the depression of the'660'discontinuity and the thickened MTZ are somewhat consistent with the big mantle wedge (BMW) model.However,due to data limitations,more studies are required to explore the BMW in the future.

The Rotational Structure along the Eastern Segment of the Altyn Tagh Fault and Its Implications in Dynamics

As a result of the left-lateral strike-slipping of the Altyn Tagh fault in Neotectonic period, a contra-rotational structure, namely the Zhaobishan vortex structure, has developed at the juncture of the main Altyn Tagh fault and the northern fringe fault of the Qilian Mountains. Preliminary analysis on the deformation and evolution of the Zhaobishan vortex structure. In combination with the previous data, suggests that the tectonic transform between the Altyn Tagh fault and the northern fringe fault of the Qilian Mountains attributes to the deformation of the rotational structure. The existence of a series of rotational structures along the Altyn Tagh fault and on the northeastern edge of the Qinghai-Xizang(Tibet) plateau indicate that as the substance in the northern Qinghai-Xizang (Tibet) plateau moves clockwise around the eastern tectonic knot of the Himalayas, rotational structures become the principal mode on the northern marginal zone of the Plateau of transforming and absorbing tectonic deformation.

近红外高光谱传感器在地震有关气体监测中的应用:以青藏高原东边界为例

为了促进高光谱技术在地震有关气体监测中的应用,本文选取对近地表信息敏感度较强的近红外高光谱传感器TROPOMI的二级产品数据,分析研究了青藏高原东北缘和川滇地区地震相关气体时空特征及其与构造和地震活动关系,评价了近红外传感器在地震有关气体监测中的应用效果和应用前景。结果表明:TROPOMI反演的研究区CH_(4)和CO气体在时间上呈现明显的季节变化,受气候变化、地貌、人类活动等影响;空间上在银川、渭河和四川盆地表现为高值,受地质背景、地形地貌和人类活动等因素影响。目前近红外高光谱传感器在时间分辨率和有效数据量上具有一定的局限性,但是相对于热红外高光谱传感器,近红外传感器可以较好地反映气体与近地表构造的关系。未来随着近红外高光谱传感器的应用和发展,近红外数据可以逐渐弥补热红外传感器数据对近地表信息敏感度低的不足,提高异常与地震关系的判断力。

青藏高原东北缘及邻区岩石圈力学强度的贝叶斯估计

本文基于复合岩石圈挠曲均衡模型,利用布格重力异常和地形数据,采用重力导纳和相关函数联合反演方法,结合贝叶斯统计推理确定最优的岩石圈挠曲参数模型,获取了青藏高原东北缘岩石圈有效弹性厚度Te和载荷比F的空间分布特征及不确定性估计.在此基础上,本文分析了各个构造单元的差异性及其与强震活动的关系,并利用热-流变结构等资料,给出了构造运动可能的深部动力源.研究结果显示:青藏高原东北缘及邻区F呈现大面积低值分布,说明其现今岩石圈挠曲状态主要与地表载荷加载相关.此外,岩石圈有效弹性厚度Te存在显著差异,其力学强度差异与青藏高原向东挤出变形、热结构状态有一定对应关系.本文结果可为定量化研究青藏高原动力学问题提供有效的地球物理依据.

青藏高原东北缘弧形构造带新生代地层沉积序列及年代学研究进展

青藏高原东北缘弧形构造带新生代的构造变形和沉积充填过程既受到了太平洋板块俯冲的远程效应影响,也受到了青藏高原北东向扩展的控制。确定新生代地层的沉积时代是深入理解青藏高原东北缘弧形构造带内构造变形和沉积充填过程的重要前提,但是目前弧形构造带内新生代地层序列和沉积时代仍存在诸多争议。文章系统研究了弧形构造带内古近纪至新近纪沉积序列和地层时代,结果显示弧形构造带内寺口子组、清水营组、彰恩堡组和干河沟组的沉积时代分别为中晚渐新世、晚渐新世—早中新世、中中新世—晚中新世和晚中新世—上新世。综合分析了古近纪至新近纪不整合界面的形成时代,重新厘定了古近纪—新近纪两期不整合及其大地构造意义,第一期不整合发育在清水营组与彰恩堡组之间,时代为早中新世,指示了青藏高原的北东向扩展到达弧形构造带;第二期不整合发育在彰恩堡组与干河沟组之间,时代为晚中新世,指示了青藏高原北东向扩展对弧形构造带的改造达到高峰。讨论了弧形构造带沉积充填过程与构造演化的耦合关系,新生代盆地的沉积演化过程主要经历了三个阶段:自中渐新世至早中新世,弧形构造带主要受控于早期的滨太平洋伸展构造体系域,处于伸展构造背景;早中新世至晚中新世,构造变形和盆地演化开始受到青藏高原北东向扩展的影响,处于挤压构造背景;晚中新世至上新世,弧形构造带持续快速隆升,并且走滑断裂体系的发育分割了新生代盆地。

青藏高原东南缘自然地理对铁路交通廊道提出的挑战

位于青藏高原东南缘的川藏交通廊道将面临极其复杂的工程环境,全线复杂结构桥梁、超长深埋隧道众多、长大坡道客货共线运行,使其安全高效建设和长期稳定运营面临巨大挑战。首先阐释青藏高原东南缘地形地貌、气候环境、新构造活动以及自然灾害等方面的特征与规律;深入分析高原东南缘独特自然地理对川藏交通廊道提出的挑战及应对策略;最后提出如何改进和强化轨道结构来应对面临的挑战。研究结果表明:①沿线区域大地貌格局以高山峡谷为主体,具山高、坡陡、谷深的险峻地形和极致地貌景观;②沿线各地具有气候垂直分带明显和区域差异大等特点,灾害性天气如雷暴、冰雹、大风、大雪及暴雨频现;③沿线行经青藏高原周缘挤压转换造山带以及向东和南东方向“逃逸”的侧向挤出地体群,区域断裂构造极为发育,断裂活动性强,具有强构造应力和高地热;④沿线区域为高灾害风险区,尤以强震、地震滑坡、高位远程滑坡、冰湖溃决以及大型滑坡堵江事件等致灾因子危险性高;⑤建议采取增加钢轨重量和采用合金轨、强化无缝线路结构稳定性以及轮轨系统动力学性能合理匹配等措施改进和强化现行轨道结构。

青藏高原周缘的河流纵剖面特征及其对构造地貌演化的启示

河流水系是改造地表地貌的主要外动力,其形态样式记录了造山带和高原的生长和演化。目前对于青藏高原周缘的河流剖面研究主要集中在南缘、东南缘及东缘。相比而言,对于流经高原其他边缘河流的纵剖面特征仍然缺乏分析,不同位置的高原边缘河流发育是否存在相似性或差异性及其内在原因尚未开展相关研究。选取青藏高原北缘西昆仑—阿尔金地区、东北缘祁连山地区、东南缘三江地区和南缘喜马拉雅等典型区域,通过开展河流地貌对比研究,利用河流纵剖面的关键地貌参数定量分析了高原周边地貌边界带的空间特征及相关的构造与气候因素。结果表明,在青藏高原周缘地貌边界带上,河流陡峭度指数最大值与区域地形起伏最大区域一致,河流流经高原边缘时陡峭度有显著升高,而在高原边缘两侧陡峭度均相对较低,且河流向高原内部的溯源侵蚀十分有限,而且河流裂点均出现在区域地形起伏较高的地貌部位。其中青藏高原北缘、东北缘与南缘,地形起伏最大的区域与构造边界所围限的高原边界一致,并大致对应最新构造活动的强隆升区,而青藏高原东南缘的高原边界较模糊,地形起伏度变化最明显的区域出现在雅砻逆冲断裂两侧,与前人提出的古高原边界一致,暗示该区河流裂点的形成可能与雅砻逆冲断裂的早期活动有关。基于研究结果认为,对于青藏高原这样大尺度或经历长时间构造演化过程的地貌单元,基于稳态假设下的河流形态分析高原隆升时间可能存在较大偏差。青藏高原东南缘的高海拔低起伏地貌面可能是在较平缓的内流水系作用下形成的,在随后的河流袭夺等过程中演变为现今的外流河状态。

青藏高原东缘应力场及地下工程灾害风险研究

青藏高原东缘广泛发育着深大活动断裂带,强烈控制着高原东缘区域应力场。本文基于收集的178个点位1181组原位应力数据,通过数值模拟反演得出青藏高原东缘活动断裂影响下青藏高原东缘地应力场,结果表明,青藏高原地应力场呈现出明显的非均匀性特征,应力量值由西向东逐渐减小。然后,利用ArcGIS分析青藏高原东缘埋深100~2000 m岩爆及大变形趋势,岩爆集中产生于次级板块内部,岩爆范围基本不随深度变化;而大变形产生于次级板块边界,并随深度增加面积逐渐向板块内部扩大;岩爆及大变形风险等级随埋深呈现规律性变化。最后,通过二郎山隧道隧址区以及双江口水电站两个工程实例探讨了本研究在工程建设中对岩爆及大变形趋势预测的适用性,结果表明,本文给出的青藏高原东缘地下工程灾害趋势与基于强度应力比方法获得的岩爆倾向性以及工程实例中岩爆现象基本一致。

青藏高原东北缘龙首山晚新生代多阶段构造隆升的盆地记录

龙首山地区位于青藏高原与阿拉善地块的结合部位,其盆山演化过程和断裂带扩展模式的恢复对揭示青藏高原新生代北东向生长具有重要意义。本文基于龙首山南北两麓3个新近系沉积剖面的构造特征和5个砂岩样品的碎屑锆石U-Pb同位素LA-ICP-MS年龄结果,重建了青藏高原东北缘龙首山地区晚新生代的盆山演化过程。研究结果显示,龙首山地区晚新生代沉积-构造演化经历了3个主要阶段:(1)~14Ma,龙首山南缘断裂带活化,阿拉善地块南缘沿此断裂逆冲于张掖盆地之上,张掖盆地开始接收阿拉善地块的物源;(2)~5Ma,龙首山南缘断裂带的次级断裂开始发育,使龙首山南侧山麓白垩系开始剥露并为张掖盆地提供物源,同时,龙首山北缘断裂带活化并导致潮水盆地发生挠曲沉降,接收龙首山的物源;(3)5~2.5Ma,龙首山北缘断裂带的次级断裂开始发育,导致龙首山北麓白垩系开始剥露并为潮水盆地提供物源。通过对龙首山周缘盆地沉积相和物源开展分析,本研究反演了龙首山地区中新世以来的断裂带活动和山体隆升过程,表明在14~2.5Ma,随着龙首山南缘断裂、北缘断裂的活化和次级断裂的发育,龙首山经历了3次强烈的隆升,这对揭示青藏高原北东向的扩展过程具有重要的指示意义。