Crust and Upper Structure of Qinghai-Tibet Plateau and Its Adjacent Regions From Surface Waveform Inversion

CRUST AND UPPER STRUCTURE OF QINGHAI-TIBET PLATEAU AND ITS ADJACENT REGIONS FROM SURFACE WAVEFORM INVERSION     

青藏高原及其邻区地壳上地幔S波速度结构

利用CDSN、IRIS、GEOSCOPE等台网33个数字台站及部分数字流动台的长周期面波资料,采用改进的Occam网格反演方法,在获得中国大陆及其邻近区域(5°~55°N,68°~150°E)1°×1°的7~184 s周期Rayleigh波群速度频散的基础上,进一步反演青藏高原及邻区(20°~40°N,75°~105°E)内每个经纬度节点介质的S波速度结构,获得了0~420 km深度地壳上地幔的三维速度分布.研究结果显示:青藏高原不但具有厚壳(60~70 km)和厚岩石圈(超过200 km),而且高原深部结构和速度分布存在明显的横向变化和分区特征.     

Crust and Upper Mantle Electrical Resistivity Structure in the Panxi Region of the Eastern Tibetan Plateau and Its Significance

The Panxi region is located in the frontal zone of positive squeezing subduction and side squeezing shearing between the Indian plate and the Eurasian plate. The long-period magnetotelluric(LMT) and broadband magnetotelluric(MT) techniques are both used to study the deep electrical conductivity structure in this region; magnetic and gravity surveys are also performed along the profile. According to the 2-D resistivity model along the Yanyuan-Yongshan profile,a highconductivity layer(HCL) exists widely in the crust,and a high-resistivity block(HRB) exists widely in the upper mantle in general,as seen by the fact that a large HCL exists from the western Jinpingshan tectonic zone to the eastern Mabian tectonic zone in the crust,while the HRB found in the Panxi tectonic zone is of abnormally high resistivity in that background compared to both sides of Panxi tectonic zone. In addition,the gravity and magnetic field anomalies are of high value. Combined with geological data,the results indicate that there probably exists basic or ultrabasic rock with a large thickness in the lithosphere in the Panxi axial region,which indicates that fracture activity once occurred in the lithosphere. As a result,we can infer that the high-resistivity zone in the Panxi lithosphere is the eruption channel for Permian Emeishan basalt and the accumulation channel for basic and ultrabasic rock. The seismic sources along the profile are counted according to seismic record data. The results indicate that the most violent earthquake sources are located at the binding site of the HRB and the HCL,where the tectonic activity zone is generally acknowledged to be; however,the earthquakes occurring in the HCL are not so violent,which reflects the fact that the HCL is a plastic layer,and the fracture threshold of a plastic layer is low generally,making high stress difficult to accumulate but easy to release in the layer. As a result,a higher number of smaller earthquakes occurred in the HCL at Daliangshan tectonic zone,and violent earthquakes occurred at the binding site of high- and low-resistivity blocks at the Panxi tectonic zone.     

长白山及邻区地壳、上地幔顶部三维速度结构

根据沿长白山布设的宽频带流动地震台站及吉林省地震台网所记录的近震P波走时数据,利用层析成像方法对长白山及邻区（39°N-45°N、122°E-130°E）深至40 km的地壳和上地幔顶部三维速度结构进行了研究。结果表明：地震的发生和分布多集中于断裂等复杂地质构造。利用较高分辨率的地壳、上地幔顶部三维速度结构证实了长白山火山区岩浆囊存在,并推测岩浆囊的位置位于火山口的西南方向,深度为10~40 km。壳内岩浆囊分布对进一步解释、认识火山灾害提供了重要的深部信息。     

秦岭造山带与渭河地堑地电结构研究

秦岭造山带作为典型的陆内复合造山带,发生过强烈的构造变形,与北部的渭河地堑形成独具特色的盆山构造体系,目前其深部结构状态与盆山耦合响应缺乏深层动力学过程的理解,为此以跨越秦岭造山带、渭河地堑布设一条170 km的大地电磁测深剖面,通过宽频带和长周期大地电磁观测,构建秦岭造山带和渭河地堑深部地电结构,研究结果表明:1)秦岭造山带存在多重叠置的巨厚岩石圈,南秦岭与北秦岭地壳尺度存在明显的结构化差异; 2)扬子地块向北楔入到南秦岭岩石圈地幔中,南、北秦岭之间在上地幔存在低阻条带痕迹表明了楔入作用的前缘位置; 3)渭河地堑存在巨厚的沉积盖层,厚度由南向北逐渐减薄,由南侧的7~8 km减到北侧的3~4 km。渭河地堑下地壳至上地幔区域分布的两个低阻块体表明其岩石圈存在明显的电性差异,这种差异性的存在表征了华北地块南向挤压作用背景下软流圈上涌的贡献。     

Tectonic Development of the Proterozoic Continental Margins in East Qinling and Adjacent Regions

The East Qinling and adjacent cratonic regions belong to two geotectonicunits,the Sinokorean Subdomain including the Sinokorean Platform and itssouthern continental margin the North Qinling Belt,and the YangtzeanSubdomain comprising the Yangtze Platform and its northern continental mar-gin the South Qinling Belt.The Qinling region may thus be subdivided into twocontinental margin belts separated from each other by the Proterozoic Qinlingmarine realm,which did not disappear until Late Triassic.The convergentcrustal consumption zone,the megasuture between the two belts,lies betweenthe Fengxian-Shangnan line in the north and the Shanyang-Xijia line in thesouth and was much deformed and displaced through Mesozoic intracratoniccollision and compression.In the northern subdomain the Lower Proterozoic is representedby protoaulacogen volcano-sediments,the inner Tiedonggou Group and theouter marginal Qinling Group,which were folded and metamorphosed in theLuliangian orogeny,a general process of aggregation and s     

东秦岭卢氏地区构造控矿的地球化学判据

[摘 要]卢氏地区位于华北陆块与秦岭构造带结合部,具有独特的成矿构造地质背景,已发现矿床、矿点百余处。东秦岭中生代斑岩钼矿及相关的脉型铅锌矿具有明显断裂控矿特征,在断裂的交汇部位、断裂膨大处或拐折处通常可形成大矿和富矿。在卢氏地区这种构造控矿特征得到地球化学判据的支持,水系沉积物测量表明,钨、钼、铅、锌等地球化学异常规模大、强度高,清晰的分带和明显的浓集中心都与区域断裂构造系统有着密切的相依关系。这种钨钼铅锌异常的空间分布成为良好的构造找矿标志,并可为本地区及中国东部进一步开展此类矿床找矿勘查所借鉴。     

西藏高原中南部地壳与上地幔导电性结构

根据2001年国土资源部"十五"青藏专项研究计划项目"西藏高原南部岩石圈电性结构的大地电磁研究"所完成的吉隆-措勤剖面(800线)以及2004年教育部重大项目"藏南雅鲁藏布江缝合带地区地壳三维电性结构及其构造地质学与动力学意义的研究"所完成的定日-措迈剖面(900线)超宽频带大地电磁测深数据,研究西藏高原中南部地壳及上地幔电性结构特征及雅鲁藏布江缝合带导电性结构特征:800线和900线上地壳范围内主要为高阻区,电阻率在200~3000Ω.m之间,顶面大范围出露,底面一般在15~20km深度处,整体上,高阻区底面由南向北逐渐加深,再向北又逐渐变浅,900线高阻体底界深达30km,而800线高阻体底界更深达38km;地下15~45km深度范围内存在一组电性梯度带,该电性梯度带之下存在一组硕大的高导层,其电阻率小于5Ω.m,高导层由规模不等且不连续的高导体构成.雅鲁藏布江以南的中地壳高导体,规模较小,厚度在10km左右,产状略向北倾;雅鲁藏布江以北的高导体,规模较大,厚度在30km左右,产状向北缓倾;相比之下,900线的高导体厚度较小,顶面深度较浅.通过对岩石电阻率影响因素的讨论,推测高导体的成因是部分熔融或含水流体,判断藏南巨厚的中、下地壳的物质状态是热的、软弱的、塑性的.     

西秦岭造山带东段航磁特征及断裂构造格架

本文基于最新高精度1∶5万航磁资料,详细分析了西秦岭造山带东段航磁特征和地质成因,辅以重力资料,新推断或修正了断裂平面位置,探讨了断裂控矿作用和若干典型断裂的地质意义。研究表明,古生界泥盆系、石炭系、二叠系、中生界三叠系碳酸盐岩-沉积碎屑岩是形成平稳负磁背景的主要原因;广泛发育的各类侵入岩,是形成复杂变化、形态各异的叠加异常的主要原因。NWW—EW向、NNE—NE向以及NW向深、大断裂共同构成了全区"南北分带,东西分块"的基本构造格架。NWW—EW向深、大断裂是最早形成的主干断裂,航磁上以不同面貌磁场分界线或醒目的磁场梯度带为特征,属华北、扬子两大板块在新元古代—三叠纪分别沿商丹、勉略缝合带南北向俯冲碰撞的产物,构成了本区一级构造单元的分界线,尤其对泥盆系多金属成矿起决定性控制作用;NNE—NE向深、大断裂应是秦岭强烈陆内造山阶段(晚三叠世—新生代)垂向加积增生作用的产物,对NWW—EW向、NW向断裂具有明显的切割、牵引或阻挡作用,航磁上以连续性较好的线性梯度带或磁场扭转变异带为特征,是区内次级构造单元的界限,对深部矿源物质的运移亦起到一定的疏导作用。     

青藏高原及周边地区下地壳地球物理异常及成因

青藏高原及周边地区下地壳普遍发育电性高导层、波速低速层和热流密度值异常区.下地壳电性结构和速度结构明显具有纵向分层和横向分块的特点,其热流密度值具有明显的南北条带性和东西分块性.下地壳高导层、低速层和热流密度值异常区与青藏高原及周边地区各构造单元有一定的匹配性,异常区的形成与青藏高原和周边盆地耦合过程中下地壳岩石的热软化以及韧性流动有关.下地壳层流是下地壳岩石热软化和韧性流动的结果,青藏高原的隆升是层流作用的表现,目前层流作用的动力来源于恒河盆地下地壳,层流方向由恒河盆地流入青藏高原.     

秦岭造山带大型-超大型矿床密集区构造定位与勘查新思路--热水沉积成矿盆地分析与研究方法之三

采用构造 -沉积 -成矿综合分析方法对秦岭造山带大型 -超大型矿床的地质背景及构造定位进行了研究 ,认为秦岭泥盆纪聚矿沉积盆地位于两类大陆构造环境中 ,即秦岭微板块板内聚矿沉积盆地及秦岭微板块北缘被动陆缘上聚矿沉积盆地 ,这些聚矿盆地均属伸展盆地。提出秦岭造山带大型 -超大型矿床定位模式及新勘查思路。     

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.     

秦岭中段印支期花岗质岩浆作用与造山过程

据新测得的41个样品的秦岭中段花岗质岩石锆石U-Pb同位素年龄数据,结合近期发表的秦岭花岗岩年代学和岩石成因的研究资料,将秦岭中段印支期花岗质岩浆作用分为早期(248～216Ma)、中期(215～201Ma)和晚期(200～195Ma)3个阶段。早期阶段形成于勉略洋闭合过程,发育于洋壳向北俯冲到浅表地壳碰撞过程;中期阶段形成于扬子克拉通北缘与华北克拉通南缘北秦岭岛弧杂岩的同碰撞到造山带垮塌过程;晚期阶段形成于碰撞后造山带拆沉作用。因此,秦岭中段印支期花岗质岩浆作用较为完整地记录了造山带的演化过程。     

Research of the Conductive Structure of Crust and the Upper Mantle beneath the South-Central Tibetan Plateau

With the super-wide band magnetotelluric sounding data of the Jilong (吉隆)-Cuoqin (措勤) profile (named line 800) which was completed in 2001 and the Dingri (定日)-Cuomai (措迈) profile (named line 900) which was completed in 2004,we obtained the strike direction of each MT station by strike analysis,then traced profiles that were perpendicular to the main strike direction,and finally obtained the resistivity model of each profile by nonlinear conjugate gradients (NLCG) inversion. With these two models,we described the resistivity structure features of the crust and the upper mantle of the center-southern Tibetan plateau and its relationship with Yalung Tsangpo suture: the upper crust of the research area is a resistive layer with resistivity value range of 200-3 000 ?·m. The depth of its bottom surface is about 15-20 km generally,but the bottom surface of resistive layer is deeper in the middle of these two profiles. At line 900,it is about 30 km deep,and even at line 800,it is about 38 km deep. There is a gradient belt of resistivity at the depth of 15-45 km,and a conductive layer is beneath it with resistivity even less than 5 ?·m. This conductive layer is composed of individual conductive bodies,and at the south of the Yalung Tsangpo suture,the conductive bodies are smaller with thickness about 10 km and lean to the north slightly. However,at the north of the Yalung Tsangpo suture,the conductive bodies are larger with thickness about 30 km and also lean to the north slightly. Relatively,the conductive bodies of line 900 are thinner than those of line 800,and the depth of the bottom surface of line 900 is also shallower. At last,after analyzing the effect factors to the resistivity of rocks,it was concluded that the very conductive layer was caused by partial melt or connective water in rocks. It suggests that the middle and lower crust of the center-southern Tibetan plateau is very thick,hot,flabby,and waxy.     

Deep Background of Wenchuan Earthquake and the Upper Crust Structure beneath the Longmen Shan and Adjacent Areas

By analyzing the deep seismic sounding profiles across the Longmen Shan,this paper focuses on the study of the relationship between the upper crust structure of the Longmen Shan area and the Wenchuan earthquake.The Longmen Shan thrust belt marks not only the topographical change,but also the lateral velocity variation between the eastern Tibetan Plateau and the Sichuan Basin.A lowvelocity layer has consistently been found in the crust beneath the eastern edge of the Tibetan Plateau, and ends beneath the ...     

Deep Background of Wenchuan Earthquake and the Upper Crust Structure beneath the Longmen Shan and Adjacent Areas

Abstract: By analyzing the deep seismic sounding profiles across the Longmen Shan, this paper focuses on the study of the relationship between the upper crust structure of the Longmen Shan area and the Wenchuan earthquake. The Longmen Shan thrust belt marks not only the topographical change, but also the lateral velocity variation between the eastern Tibetan Plateau and the Sichuan Basin. A low-velocity layer has consistently been found in the crust beneath the eastern edge of the Tibetan Plateau, and ends beneath the western Sichuan Basin. The low-velocity layer at a depth of ~20 km beneath the eastern edge of the Tibetan Plateau has been considered as the deep condition for favoring energy accumulation that formed the great Wenchuan earthquake.     

西秦岭金龙山卡林型金矿床地质-地球化学及矿床成因研究

金龙山金矿床位于南秦岭造山带的复理石褶冲带中,赋矿围岩为碎屑岩-碳酸盐建造,矿化明显受地层岩性与韧-脆性构造发育程度的控制。矿床稀土元素地球化学研究表明,地层岩石、矿石和热液矿物的轻重稀土分异程度和特征参数基本一致,表明成矿流体应主要来自于赋矿地层。铅同位素研究表明,地层岩石、矿石和热液矿物均具有较高的放射性成因的铅同位素组成,且均落入南秦岭造山带的泥盆系范围内,暗示铅也主要来自赋矿地层。对前人已有的碳-氧-硫-氢同位素组成和流体包裹体数据综合分析表明,碳和氧应主要来自海相碳酸盐的溶解作用,硫主要来自海相硫酸盐的热化学还原反应;从成矿早阶段到晚阶段,成矿流体的δ18O及δD值向大气降水线＂漂移＂,指示成矿流体以盆地建造水和变质水为主,在晚阶段有大气降水加入。金龙山金矿床与卡林型金矿床的矿床地质-地球化学特征相似,应属于卡林型金矿床,其形成于秦岭造山带陆内造山作用过程中,多层次陆壳叠置加厚的地球动力学背景,是陆内碰撞造山作用的产物。     

新疆富蕴--库尔勒剖面接收函数方法获得的地壳上地幔结构成像

利用远震接收函数方法处理宽频地震探测数据获得富蕴-库尔勒剖面地壳上地幔结构转换波成像.中天山南缘断裂下方自南向北Moho转换界面具有向北倾斜的特征,且此转换界面有间断,深度逐步由50 km加大到60～70 km.北天山北缘断裂北部下方相对连续的转换界面明显以较小的幅度向南俯冲延伸到80～90 km深度.中天山南缘断裂到乌鲁木齐之间,除间断、斜交和叠置的Moho转换界面外,还可见其他转换界面.乌鲁木齐以北,进入准噶尔盆地Moho转换界面相对平缓深度在50 km上下,最深处靠近天山附近.天山Moho面的加深、重叠以及地震发生的深度表明本区天山构造活动较强,天山的山根深度近100 km.相对于天山西段本区南北向的推挤作用明显减弱.     

新疆富蕴--库尔勒剖面地震层析图像与地壳上地幔的速度结构

利用在2002~2004年新疆天山地区富蕴—库尔勒布设的流动地震台,经过连续两年的观测所采集的数据,挑选远震P波到时数据,进行了地震层析反演处理,获得此剖面地震层析图像推断地壳上地幔的速度结构。反演结果表明,富蕴—库尔勒剖面上塔里木板块向北的推进相对于西部有所减弱,在西部表现强烈的造山作用,向东逐步减缓,在天山的底部不过100km上下。地震活动集中在此范围内。岩石圈物质移动方向发生变化部分向东推移,自然也降低了天山的隆升作用,从而造成天山西段和东段的差异。在本剖面范围内天山的Moho面结构复杂有重叠、斜插特征,深度最大在天山地区达80km,准噶尔盆地和本剖面范围内塔里木盆地北部Moho面深度为40~50km。     

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 mainland China 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 lowvelocity 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 forthe area's strong earthquake activity.