Deep structure and lithospheric shear faults in the East Kunlun-Qiangtang region,northern Tibetan Plateau

The Cenozoic magmatic rocks of shoshonitic series in the eastern Qinghai-Tibet Plateau include potassic alkaline plutonic rocks, volcanic rocks, lamprophyres and acidic porphyries. Analytical results show that these different lithological rocks are extremely similar in Sr, Nd and Pb isotopic compositions with the range of 0.705 187– 0.707 254 for⁸⁷Sr/⁸⁶Sr, 0.512 305–0.512 630 for¹⁴³Nd/¹⁴⁴Nd, 18.53–18.97 for²⁰⁶Pb/²⁰⁴Pb, 15.51–15.72 for²⁰⁷Pb/²⁰⁴Pb and 38.38–39.24 for²⁰⁸Pb/²⁰⁴Pb. They are isotopically similar to the EMII end-member. This indicates that mantle metasomatism must have taken place in their source region. The formation of these particular rocks is related to crustal thinning and mantle upwelling in a large-scale strike-slip and pull-apart fault zone at about 40 Ma in northern and eastern Qinghai-Tibet Plateau     

青藏高原东北缘祁连山西段与东段岩石圈结构差异研究

作为青藏高原东北缘的祁连山,其东段与西段的地貌以及新生代地表变形样式差异显著.在新生代青藏高原向北东扩展这一共同构造背景之下,引起祁连山东段和西段这些差异的深部原因尚不清晰.本文基于一条宽频密集台站观测剖面,利用P波速度结构约束下接收函数和面波频散的联合反演方法给出祁连山东段的壳内及岩石圈地幔结构.结合前人在青藏高原东北缘的研究成果,对比祁连山东段和西段的岩石圈结构,探讨东、西段壳内变形方式的差异,从而揭示引起祁连山东西段这些差异背后的可能原因.东西段岩石圈结构的差异主要有：1) 壳内低速层差异.在20~40 km的深度处,祁连西段(测线BB′)中地壳存在壳内低速物质(3.2~3.4 km·s^-1),而祁连东段(测线AA′)的中地壳并不存在低速层; 2) 岩石圈地幔差异.祁连西段的岩石圈地幔低速异常表现为分块的特征,而祁连东段的岩石圈地幔表现为比较统一的高速体.通过对比研究发现祁连西段壳内强度相对软弱,地壳的缩短变形程度更大,表现为高海拔的山脉以及更厚的地壳,而祁连东段壳内变形及缩短程度相对较弱,表现为地势相对较平坦的临夏盆地和陇中盆地以及较薄的地壳厚度.东、西段壳内强度以及变形方式的差异可能与深部岩石圈地幔的结构相关.

     

The phase velocities of Rayleigh waves and the lateral variation of lithospheric structure in Tibetan Plateau

According to a Sino-U. S. joint project, eleven broadband digital PASSCAL seismometers had been deployed inside the Tibetan Plateau, of which 7 stations were on the profile from Lhasa to Golmud and other 4 stations situated at Maxin, Yushu, Xigatze and Linzhi. Dispersions and phase velocities of the Rayleigh surface waves (10s–120s) were obtained on five paths distributed in the different blocks of Tibetan Plateau. Inversions of the S-wave velocity structures in Songpan-Ganzi block, Qiang-Tang block, Lhasa block and the faulted rift zone were obtained from the dispersion data. The results show that significant lateral variation of the S-wave velocity structures among the different blocks exists. The path from Wenquan to Xigatze (abbreviated as Wndo-Xiga) passes through the rift-zone of Yadong-Anduo. The phase velocities of Rayleigh waves from 10s to 100s on this path are significantly higher than that on other paths. The calculated mean crustal velocity on this path is 3.8 km/s, much greater than that on other paths, where mean crustal velocities of 3.4–3.5 km/s are usually observed. Low velocity zones with different thicknesses and velocities are observed in the middle-lower crust for different paths. Songpan-Ganzi block, located in the northern part of Tibetan Plateau is characterized by a thinner crust of 65 km thick and a prominent low velocity zone in the upper mantle. The low velocity zone with a velocity of 4.2 km/s is located at a depth form 115 km to 175 km. While in other blocks, no low velocity zone in the upper mantle is observed. The value of Sn in Songpan-Ganzi is calculated to be 4.5 km/s, while those in Qiang-Tang and Lhasa blocks are about 4.6 km/s. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,14, Supp., 566–573, 1992.     

Cenozoic volcanism and lithospheric tectonic evolution in Qiangtang area, northern Qinghai-Tibet Plateau

Accompanying with the shortening,thickening and uplifting of the lithosphere,a series of Cenozoic potassic volcanic rock zones are developed in the northern Qinghai-Tibet Plateau.From south to north,the volcanic rocks can be divided into three volcanicrock belts:Qiangtang-Nangqian volcanic belt,Middle Kunlun-Hoh Xil volcanic belt and Western Kunlun-Eastern Kunlun volcanic belt[1].Spatiotemporal evolu-tion of the volcanism and the origins of magmas con-strains on the pulsing uplifting and …     

A review on the lithospheric structures in the Tibetan Plateau and constraints for dynamics

In the last decade, several international joint projects were conducted in the Tibetan Plateau by Chinese, American and French geophysicists and geologists. In the present review, the results from vertical reflections, wide-angle reflections and broadband digital seismic recordings are reviewed and compared. Constraints for the dynamics of continent-continent collision from the lithospheric structures, seismicity, focal mechanism and anisotropy are discussed.The velocities ofPn,Sn, , were accurately determined by using their travel times from local events. They evidenced that the uppermost mantle underneath the Tibetan Plateau was similar to that of the ordinary continental mantle.The reflection profile from INDEPTH-I furnishes convincing evidence that the Indian crust penetrates into the Tibetan lower crust. The results from teleseismic waveform inversion reveal that the Moho discontinuity dips northwards, and an offset of Moho occurs near Bangong suture.The fact that materials within the Tibetan Plateau escape laterally has been proposed by several authors. Recent data and studies provide further convincing evidence that eastward mass transfer does occur, and their paths and natures are investigated.Some authors suggested that the large strike slip faults (Kun Lun, Xianshuihe) in the eastern plateau may be related to the lateral extrusion. However, most of the strike slips are left-lateral, and extrusion could not occur without right-lateral strike slips. Recent observations of the focal mechanisms and geological structure indicate that the earthquakes in the Yanshiping-Changdu belt are left-lateral strike slip. It is the southeast zone of the left-lateral slip faults in the eastern Tibetan plateau. Geological and seismological evidence show that the Bencuo-Jiali belt is the only large right-lateral fault in the eastern plateau. It was proposed that the present eastward extrusion occurs between the Yangshiping-Changdu left-lateral strike slip and the Bencuo-Jiali right-lateral strike slip. The other left-lateral strike slips north of the Yangshiping-Changdu belt are considered to be the fossils of the ancient flow paths.     

Physical structure features of the crust at southeast region of Tibetan Plateau

Chemical reactions of plagioclase, biotite and their single minerals, as well as a mineral mixture of (plagioclase+biotite+quartz), with KCl and (KCl+KHCO₃) solutions were carried out at 150–400°C and 50–80 MPa. Experiments show that alkaline fluid promotes plagioclase’s changing into potash feldspar, while acid fluid helps plagioclase, potash feldspar and biotite alteration form chlorite and sericite. After chemical reaction the acidity-alkalinity of solutions often changes reversely. It was observed that gold dissolved from the tube wall and recrystallized on the surfaces of biotite and pyrite. Therefore the transportation and enrichment of gold are related to the elementary effect of the fluid-mineral interfaces. Fe³⁺-Fe²⁺, as an oxidition-reduction agent, and volatile components Cl^- and CO₂ play important roles in the reaction process     

Teleseismic shear wave splitting and intracontinental collision deformation of the northern Tibetan Plateau and the eastern Tarim basin

Shear wave splitting measurement of teleseismic data has been used to determine the fast polarization directions and delay times for 38 temporary stations and 15 permanent stations from a NW linear seismic array across the eastern Tarim basin(ETB) and the northern Tibetan Plateau(NTP), and 10 permanent stations on both sides of the array. We present an image of upper mantle anisotropy in the ETB and NTP using the 63 new measurements. The results show that the fast directions and delay times have...     

Seismicity and focal mechanism in Tibetan Plateau and its implications to lithospheric flow

The Tibetan Plateau is characterized by its high seismicity produced by the continental collision still working at Himalaya. As seismology had made great contribution to the global tectonics in 1960s, it may also provide some improtant clues to the evolution and tectonics in continents. The present paper summarizes the seismicities, focal mechanisms and neotectionics in Tibetan Plateau. The authors suggest a new classification of the seismic belts or zones in the Plateau. The belt from Yadong to Anduo is an active seismic belt. The features of neotectonics and focal mechanisms are different on the west of this belt to the east of it. Most of the earthquakes with focal depthh>70 km in the Plateau situate on this belt. Different to Yuma, Arakan, the earthquakes withh>70 km in Yadong-Anduo belt are less and smaller, their focal mechanisms are normal faults. Appearance of earthquakes with h>70 km suggests that the uppermost mantle in this belt is unstable and the material is hard enough to accumulate strong strain energy. The authors stress the significance of the northwest-southeast striking fault zone of Yanshiping-Changdu. Several large earthquakes occurred in this fault zone are characterized by left-lateral strike slips. It is the southest one of the several left-lateral strike slip zones in the eastern Tibetan Plateau, and may represent the latest produced one of the left-lateral strike slip zones. South to the Bangong-Nujiang suture, the fault zone of Bengcuo-Jiali is a belt of discontinuous right-lateral strike slips with very strong seismicities. The pair-faults of Yanshiping-Changdu left-lateral strike slips and Bengcuo-Jiali right-lateral strike slips provide an evidence of the eastward flow of materials in the lithosphere of Qiang Tang terrain between the pair-faults. Altyn Tagh, Kun Lun and Xianshuihe may represent the residuals of the boundaries of ancient flow paths. Since the sutures and also the cooling effects were produced progressively from the north to south, the flow paths will move progressively southward during the geological times. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica, supp.14, 534–565, 1992.     

藏北高原主要断裂带电性结构特征

对600线的部分测点及2100线的全部测点构成的五道梁—绿草山大地电磁深探测剖面进行了二维非线性共轭梯度反演,得到青藏高原中北部二维电性结构模型.根据该电性结构模型,结合研究区域重、磁及区域地质资料推断了青藏高原中北部主要断裂的位置、产状和切割深度等信息.研究结果表明,青藏高原中北部发育有F1—F16一系列深断裂.其中,F1(苟鲁山克错—囊谦断裂带)和F9(乌兰乌拉湖—玉树断裂带)共同构成金沙江缝合带的北界,是松潘—甘孜—可可西里地块与羌塘—唐古拉地块的分界线;F4、F10—F12共同构成昆仑断裂带,F4(阿尼玛卿断裂带)是南部松潘—甘孜—可可西里地体和北部北昆仑-柴达木地体的分界线;F6、F13—F16为柴北缘断裂带,由南倾的岩石圈深断裂F6和一系列产状相背、北倾的逆冲断裂F13—F16所构成;F7和F8可能反映岩石圈内产状平缓、隐伏的滑脱构造形迹.     

2001年MW7.8昆仑山地震震后形变观测、机制与青藏高原中北部岩石圈流变:认识与挑战

2001年M_W7.8昆仑山地震是近半个世纪以来青藏高原发生的最大震级地震。同震破裂产生的巨大应力扰动驱动控制着显著震后形变。二十年尺度的大地测量数据记录了地震后长时间、大范围、时空依赖的震后形变演化过程及差异,揭示了昆仑山地震破裂段复杂的断层分段震后运动学特征、分段摩擦性质差异和青藏高原中北部岩石圈流变性质/结构横向各向异性。本文简要回顾昆仑山地震后基于二十年尺度时序InSAR和GPS的震后形变观测方法和时空特征,特别是时空密集的InSAR观测,是该构造区震后GPS观测的重要补充及其不可替代的观测手段;总结大范围震后形变模拟方法及其揭示的震后运动过程、多种动力学机制及其关系。最后总结提出昆仑山地震震后形变20年研究取得的科学认识及尚待深入研究的科学问题,一方面要持续性地对东昆仑断裂带大范围地表形变进行观测研究;另一方面,要不断更新震后形变模型,进一步深化对该断裂带地震周期形变、区域构造对周期形变控制作用、复杂断层运动时空演化机制的认识。      

青藏高原东北缘祁连山中部精细地壳结构研究

现今的青藏高原东北缘祁连山地区是在早古生代构造格架的基础之上,于新生代在欧亚大陆与印度大陆碰撞拼合的远程影响下,重新活化进而隆起成为高原的组成部分.因此,该区域地壳结构的揭示不仅可以获得高原地壳变形方式的关键信息,而且也能对该区域早古生代晚期北祁连洋闭合时的相关构造演化提供重要证据.本文以一条穿过青藏高原东北缘祁连山中部地区的深地震反射剖面为基础,结合前人地质、地球物理资料,通过细致的地质构造解译,获得了青藏高原东北缘祁连山中部地区的精细地壳结构.反射剖面图像揭示了海原断裂西段的深部延伸形态、中地壳的双重构造、以及中下地壳的祁连逆冲断裂系等精细的深部构造.结合前人的地质以及地球物理资料,我们提出早古生代晚期北祁连闭合时的南向俯冲以及新生代以来祁连山地区两次陆内俯冲作用可能造就了现今的祁连山.

     

川滇地区岩石圈温度、化学组分结构研究及对岩石圈减薄过程的认识

川滇地区地处中国大陆西南,对其岩石圈结构的研究是认识该地区构造演化过程的基础.由于不同研究方法存在各自的局限性,导致其所获得的岩石圈结构和可能的构造演化过程仍存在争议.岩石圈温度、化学组分结构是深入认识这些争议性问题的基础.本文基于热动力学模拟和概率密度反演的方法,联合瑞雷面波相速度频散曲线、大地水准面高、地形和地表热流等观测资料,反演了川滇地区岩石圈的温度、化学组分结构.结果表明,川滇地区岩石圈呈现南薄北厚的趋势,其中印支块体岩石圈较薄,为60~80 km,相对起伏较小;川滇菱形块体、江南造山带西缘岩石圈自南（~80 km）向北（~200 km）递增;松潘甘孜块体保持较厚的岩石圈根（~240 km）.印支块体与江南造山带西缘岩石圈地幔以过渡型和难熔型的橄榄岩为主,仍存在部分古老难熔的岩石圈地幔物质;而川滇菱形块体内部为饱满型岩石圈地幔,表明古老、难熔的岩石圈地幔被新的地幔物质所取代.根据现今川滇地区岩石圈温度、化学组分结构,我们推测川滇地区南部的印支块体受印度板块与亚欧板块南北向碰撞的影响,导致该区域岩石圈增厚,并发生以拆沉作用为主的减薄过程,但岩石圈地幔仍以古老难熔的地幔物质为主;拆沉作用所导致的热地幔物质上涌使得川滇菱形块体古老难熔的岩石圈地幔物质由南往北逐渐为新的地幔物质所取代,形成了现今饱满型岩石圈地幔,热侵蚀作用在川滇菱形块体岩石圈减薄过程中占主导地位.

     

Deep lithospheric structure beneath the Polish part of the East European Craton as a result of magnetotelluric surveys

Studia Geophysica et Geodaetica - A fundamental tectonic boundary between the Precambrian East European Craton (EEC) and the younger Phanerozoic mountain belts of Europe runs through Poland....     

青藏高原东北缘重力场深部结构及其动力学特征

本文采用欧拉反褶积、场源参数成像(SPI)、场源边界提取(SED)、莫霍面反演、地壳三维可视化等多源方法,对青藏高原东北缘地区的布格重力场进行反演与分析,深入研究该地区的深部结构与变形特征,探讨区域深部孕震环境及动力学机制.研究表明,青藏高原东北缘的布格重力场整体呈负异常值,具有明显的分区性,表现出鄂尔多斯盆地异常值相对偏高、阿拉善块体次之、青藏高原块体极低的特点,其中海源断裂系形成了一条宽缓的弧形重力梯度条带,梯度值达1.2 mGal·km^-1.欧拉结果显示,鄂尔多斯盆地相比于青藏高原块体而言,场源点具有较强的均一性,场源强度值高(密度值高)且深度稳定在25~32 km范围内,而高原块体的中下地壳尺度广泛分布着低密度异常体.SPI图可知,海源弧形断裂系位于“浅源异常”弧形区,反映其地壳较为活跃,易发生中强地震.SED图揭示青藏高原地壳向东北扩展,经过几大断裂系的调节后运动矢量向东或东南转化,SED与GPS、SKS运动特征大致相同,说明地表-地壳-地幔的运动特征有着较强的一致性.青藏高原东北缘地区壳幔变形是连贯的,加之莫霍面由北向南、由东向西是逐渐加深的,因此属于垂向连贯变形机制,不符合下地壳管道流动力学模式.区域形成了似三联点构造格局,其中海源弧形断裂系的深部地壳结构复杂,高低密度异常体复杂交汇,是青藏高原、阿拉善、鄂尔多斯三大块体相互作用的重要枢纽,其运动学特征总体为中段走滑尾端逆冲,而断裂系正处于大型的弧形莫霍面斜坡带之上,具备强震的深部孕震环境,因此大尺度的运动调节与深部孕震条件共同促使了该地区中强震的多发.     

Deep learning-based multi-source precipitation merging for the Tibetan Plateau

Due to its complex and diverse terrain, precipitation gauges in the Tibetan Plateau(TP) are sparse, making it difficult to obtain reliable precipitation data for environmental studies. Data merging is a method that can integrate precipitation data from multiple sources to generate high-precision precipitation data. However, the more commonly used methods, such as regression and machine learning, do not usually consider the local correlation of precipitation, so that the spatial pattern of precip...     

基于背景噪声研究青藏高原东缘三维横波速度结构

本文收集了四川、重庆、甘肃、青海、陕西地震台网的105个宽频带地震台站在2017年8月—2018年8月期间记录的连续波形数据,通过对台站记录的长时间背景噪声进行互相关计算,从而提取出瑞利面波经验格林函数,共获得5416条周期在5~40 s内的基阶瑞利面波频散曲线,用于反演青藏高原东缘地壳和上地幔顶部三维横波速度结构.研究结果表明青藏高原东缘地下速度结构呈现非常明显的横向不均匀性,地下浅层速度结构特征与研究区域的主要地质特征和地块单元非常吻合.青藏高原东缘下方的低速体在向东延伸过程中受到四川盆地刚性地壳的阻挡作用,一部分向南进入川滇地块,并在下方30 km处形成厚度约为15 km的大范围低速异常;另一部分向北延伸,并在塔藏断裂下方上涌和堆积,造成局部莫霍面下沉.此外,青藏高原东缘下方的低速体在东北方向跨越东昆仑断裂带进入柴达木地块,并到达西秦岭断裂带附近.其中,巴颜喀拉地块下方30 km处存在厚度约为15 km大范围的低速体,与青藏高原东缘隆起地形和地壳增厚有一定联系.且该低速体在柴达木地块下方变窄,与祁连地块地下30 km处厚度约为10 km的小范围低速体存在一定的连通性.但祁连地块低速体速度值略高于巴颜喀拉地块低速体速度值,这可能意味着祁连地块低速体相当于巴颜喀拉地块低速体的早期发育阶段.

     

藏北高原地震活动性特征及其大地构造意义

藏北高原自新生代以来不仅发生了强烈的火山作用,而且现今的地震活动性仍然强烈.本文收集了2011年前藏北高原区发生的地震事件(源自NEIC)及相应的震源机制解数据(源自GCMT),结合地质与地球物理等相关资料,初步分析表明藏北高原地壳整体上处于伸展应力状态.然而,因区域构造应力场及构造环境差异,将藏北高原地震活动区分为两个地震活动区,即西昆仑地震活动区和藏北中部火山岩区.西昆仑区的地壳应力状态呈东西向伸展,而岩石圈地幔部分主要以南北汇聚为主,表明西昆仑区域下的地壳与岩石圈地幔应力状态是解耦的,而这种解耦机制需要更进一步的研究.而在藏北中部火山岩区的地壳的主张应力场为NNE-SSW的走滑和正断层性质的伸展,尽管缺乏该区域下的岩石圈结构特征认识,但是依据幔源性质的钾质和超钾质火山岩成因模式,认为其下的岩石圈地幔也处于伸展状态,该区域下的地壳与岩石圈地幔同处于伸展应力环境中,表明藏北火山岩区下的结构特征更加复杂,亟待开展相关探测与研究.     

Crustal structure across the Altyn Tagh Range at the northern margin of the Tibetan Plateau and tectonic implications

We present new seismic refraction/wide-angle-reflection data across the Altyn Tagh Range and its adjacent basins. We find that the crustal velocity structure, and by inference, the composition of the crust changes abruptly beneath the Cherchen fault, i.e., ∼100 km north of the northern margin of the Tibetan plateau. North of the Cherchen fault, beneath the Tarim basin, a platform-type crust is evident. In contrast, south the Cherchen fault the crust is characterized by a missing high-velocity lower-crustal layer. Our seismic model indicates that the high topography (∼3 km) of the Altyn Tagh Range is supported by a wedge-shaped region with a seismic velocity of 7.6–7.8 km/s that we interpret as a zone of crust–mantle mix. We infer that the Altyn Tagh Range formed by crustal-scale strike-slip motion along the North Altyn Tagh fault and northeast–southwest contraction over the range. The contraction is accommodated by (1) crustal thickening via upper-crustal thrusting and lower-crustal flow (i.e., creep), and (2) slip-parallel (SW-directed) underthrusting of only the lower crust and mantle of the eastern Tarim basin beneath the Altyn Tagh Range.     

天山-准噶尔地区地震层析成像与壳幔结构

通过对东西天山两条天然地震剖面的远震P波与近震P波走时资料以及2001-2007年新疆地方台网的近震走时资料分析,获得了天山-准噶尔地区的三维地震层析图像.层析反演使用的台站数140个,地震事件1132个,P波走时数24904条.检测板试验结果指出,东西天山剖面、天山轴部和东准噶尔地区P波速度扰动恢复能力相对高.纵波波...     

青藏高原东北缘主要断裂滑动速率及其动力学意义

本文利用青藏高原东北缘地区1991—2015年的GPS速度场资料, 基于弹性球面块体模型获得了区域活动断裂的滑动速率, 并讨论了断裂滑动速率分配的动力学意义。 反演结果表明, 青藏高原东北缘地区主要块体以北东向并兼顺时针旋转运动为主; 区域断裂平均闭锁深度为17 km; 另外, 各主要断裂滑动速率也不尽相同。 其中, 阿尔金断裂、 东昆仑断裂左旋走滑速率为10～12 mm/a, 祁连—海原断裂左旋走滑速率为3～5 mm/a, 鄂拉山断裂、 拉脊山断裂右旋走滑速率为1～3 mm/a。 阿尔金断裂、 祁连—海原断裂、 东昆仑断裂的走滑速率被其端部的山脉隆起和逆冲断裂所吸收和转换, 鄂拉山断裂和拉脊山断裂则起到了调节块体间运动平衡的作用。