青藏高原东缘中下地壳流与地壳变形

地壳缩短导致青藏隆升造山是普遍的认识.然而,在青藏东部,越来越多的观测数据和研究支持了中下地壳流与隆升造山的关系.目前,地壳缩短造山机制和中下地壳流造山机制仍然处于争论之中.本文建立了二维黏弹塑性有限元模型,模拟了龙门山断层带的多个地震循环的应变与变形,探讨了无与有中下地壳流情况下,地壳地表的位移、速度与变形的分布和演化;以及有中下地壳流情况下,不同流动范围、速度与黏度对模型结果的影响;并结合地形变观测数据的约束,推测了青藏东缘中下地壳流的流动状态.模拟结果显示,通过对比有和无中下地壳流的模拟结果,发现青藏东部震间的地表垂向速度在变形样式及数值上存在较大差异,即存在地壳流的地表垂向抬升速率显著大于无地壳流;震间在龙门山断层西侧附近产生的垂向凸状隆起随中下地壳流的速度、黏度及通道长度的变化而变化.此外,本文研究结果对青藏其他地区可能存在的地壳流的研究也具有一定的参考意义.     

地壳应变主体单元模型及其与中强地震关系研究

讨论了目前利用GPS观测结果研究块体及其边界带应变状态的研究进展,阐明了与地震相关的块体边界活动构造附近是地壳应变主体区域的认识. 利用Scholz断层能量动态平衡过程,建立了断层周边应变累积与断层面构造力的一般物理关系,据此提出以断裂带为主体的地壳应变主体单元模型. 并利用GPS基准站连续观测资料讨论了模型力学状态演化与2001年11月14日昆仑山口西8.1级地震过程的关系. 结果表明,强烈压剪背景中出现的相对松弛变化,可能有利于触发型中等强度地震的发生.      

挤压型盆地构造热演化模拟研究综述

挤压过程对地质构造和沉积盆地的形成演化具有重要的作用.研究挤压型盆地的构造热演化模拟对认识岩石圈内部应力分布、力学属性和流变结构具有重要意义.本文介绍了挤压型盆地构造模拟的弹性模型、粘弹性模型和深度控制的弹塑性模型,对比了这几种模型的优缺点和适用范围.简单介绍了前人在研究地壳隆升时用到的几种热演化模拟方法.虽然挤压过程的构造模拟已经取得了很大进展,挤压型盆地的热演化模拟则具有很大的发展空间,这应是进一步研究的重点.     

裂谷盆地构造-热演化模拟中几个问题的讨论

裂谷盆地的构造-热演化模拟是在岩石圈尺度计算裂谷盆地形成演化过程中的热历史和沉降史.拉张模型实现了构造和热的完美结合,在描述裂谷盆地沉降和热流演化方面取得了很大的成功.本文使用二维运动学模型,通过有限元方法,在拉格朗日坐标系下进行拉张背景下的构造热演化模拟,探讨了拉张模型中初始地壳、岩石圈厚度、软流圈对流、模型上边界对构造热演化的影响,以及载水和载沉积物两种情况下盆地侧翼抬升的差异.     

剪切生热与花岗岩部分熔融——关于喜马拉雅地区逆冲断层与地壳热结构的分析

本文对影响喜马拉雅逆冲断层地区热结构的三种主要热源（断层的摩擦剪切热,地壳的放射性热和上地幔的传导热）的效应进行了计算分析,在计算中考虑了岩石的流变性造成的剪应力和温度的非线性关系及岩石温度到达熔点时的熔解热.结果表明,尽管地壳的放射性热和上地幔的传导热也可能引起地壳中的部分熔融,但此时熔融将从地壳底部开始发生,这与喜马拉雅地区观测到的地质现象不符;在考虑了剪切断层带的剪切热后,熔融将从断层附近开始发生,因此得到了比较符合实际地质现象的结果.     

剪切生热与花岗岩部分熔融——关于喜马拉雅地区逆冲断层与地壳热结构的分析

本文对影响喜马拉雅逆冲断层地区热结构的三种主要热源(断层的摩擦剪切热,地壳的放射性热和上地幔的传导热)的效应进行了计算分析,在计算中考虑了岩石的流变性造成的剪应力和温度的非线性关系及岩石温度到达熔点时的熔解热.结果表明,尽管地壳的放射性热和上地幔的传导热也可能引起地壳中的部分熔融,但此时熔融将从地壳底部开始发生,这与喜马拉雅地区观测到的地质现象不符;在考虑了剪切断层带的剪切热后,熔融将从断层附近开始发生,因此得到了比较符合实际地质现象的结果.     

温度变化引起跨断层位移测量结果的年周期变化

本文首先给出了北京地区若干跨断层位移测量结果的年周期变化.而后,用二维非线性有限元方法,模拟了温度变化引起的跨断层位移测量结果的年周期变化.计算得到的应变量与野外观测大体一致.结果表明,在地壳介质不均一条件下,地表温度变化足以引起已观测到的种种复杂现象,诸如:存在两类基线,一类是当地表温度升高时增长;另一类是当地表温度升高时缩短.同时,存在两类水准变化,一类是断层热胀系数大的一盘,当地表温度上升时抬升;另一类则相反等等.一般说来,地壳介质是不均一的,因而温度对跨断层位移测量的干扰是不容忽视的.      

大别-苏鲁超高压变质带P-T-t轨迹的动力学模拟

综合现有的地质、地球化学资料以及同位素年龄等研究成果，同时结合新西兰南岛北端陆壳俯冲的最新发现，提出了超高压变质岩的形成四阶段演化模式：板片俯冲形成增生楔、板片俯冲驱动角落流、板片拆离浮力抬升至Moho深度和后期上地壳伸展阶段.以此为定量模拟的出发点，利用二维有限元对大别-苏鲁超高压变质带的形成演化进行了动力学和热演化模拟，追踪超高压变质岩形成演化过程中的质点路径以及对应的P-T-t轨迹.计算的P-T-t轨迹及其空间分布特征均能与实测结果较好吻合.     

汶川M_S8.0地震地表破裂带及其发震构造

震后应急野外考察表明,2008年5月12日汶川MS8.0地震在青藏高原东缘龙门山推覆构造带上同时使北川-映秀断裂和灌县-江油断裂两条倾向NW的叠瓦状逆断层发生地表破裂。其中,沿北川-映秀断裂展布的地表破裂带长约240km,以兼有右旋走滑分量的逆断层型破裂为主,最大垂直位移6.2m,最大右旋走滑位移4.9m;沿灌县-江油断裂连续展布的地表破裂带长约72km,最长可达90km,为典型的纯逆断层型地表破裂,最大垂直位移3.5m;另外,在上述两条地表破裂带西部还发育着1条NW向带有逆冲垂直分量、左旋走滑性质的小鱼洞地表破裂带,长约6km。这一地表破裂样式是近期发生的特大地震中结构最复杂的一次逆断层型地表破裂,地表破裂的长度也最长。利用已有的石油地震剖面,结合余震分布和地表破裂带特征等资料构建的三维发震构造模型表明,龙门山推覆构造带现今和第四纪时期以地壳缩短为主,斜滑逆冲型地震表明青藏高原中东部的水平运动在华南地块与巴颜喀拉地块之间的龙门山推覆构造带上转化为地壳的缩短和隆升     

大别造山带构造演化的数值模拟

利用有限元数值模拟方法,分析了地幔热物质侵入到地壳中对大别地区构造应力场、位移场的影响．数值模拟结果表明:地幔热侵入体在大别地区上地壳内形成张应力区,在与扬子板块水平向挤压共同作用下,造成大别山地区两端挤压、中部拉张的动力环境,同实际观测到的断层表现一致．并进一步讨论了过渡区域可能的演化趋势．      

A thermal model for the distribution in space and time of the Himalayan granites

In southern Tibet, crustal thickening due to the India-Asia collision has led to the formation of two granite belts. One is located at the southern edge of the accretionary wedge of Tethyan sedimentary rocks, close to the contact with basement gneisses of the Tibetan slab. The other is found within the wedge itself, close to the Kangmar thrust trace. Available ages suggest that the granites appeared first in the southern belt and then in the Kangmar belt. This sequence seems to violate the chronology of thrusting. Another feature of the Himalayas is that melting started only about 20 Ma after the onset of thickening, which is much less than the thermal time constant of thick crust. We give a thermal model, based on the assumption of conductive heat transfer, which explains these features. The model relies on the geometry of a sedimentary accretionary wedge bounded by low-angle thrust faults and on the existence of a thermal conductivity contrast between old basement and young sedimentary rocks. The wedge of sedimentary rocks acts as an insulating cap and its southern edge heats up along the contact with basement rocks. On a horizontal cross-section, there is a temperature maximum along this southern edge, which explains why melting starts there. The early thermal evolution is sensitive to local conditions and granites first appear in the vicinity of the most radiogenic parts of the basement. The distribution of granites in space and time is seemingly random, reflecting different melting events in different radiogenic environments in the heterogeneous basement. This model predicts a relationship between radioactivity and age which is compatible with available data. The results emphasize that there are large horizontal temperature variations across a thickened region and that granite ages are not related simply to the timing of tectonic phases.     

大陆下地壳层流作用及其大陆动力学意义

大量的地质和地球物理资料表明 ,年轻的大陆构造活动区的下地壳可能因热软化而出现透入性非地震式顺层韧性流动 ,这种下地壳层流作用驱动大陆上地壳发生地震式脆性断块运动 ,形成盆山格局 ,发生圈层耦合。大陆下地壳低粘度物质顺层流动可能是在地幔岩浆底侵作用为下地壳提供热能和添加幔源物质的基础上 ,并在地幔上升派生的重力和剪切力作用下 ,造成大陆下地壳热软化物质从盆地下部的幔隆区顺层流向相邻造山带之下的幔拗区。在下地壳层流过程中 ,地温场和速度场发生变     

Geophysical models for the tectonic framework of the Lake Vostok region, East Antarctica

Aerogeophysical and seismological data from a geophysical survey in the interior of East Antarctica were used to develop a conceptual tectonic model for the Lake Vostok region. The model is constrained using three independent data sets: magnetic, seismic, and gravimetric. A distinct change in the aeromagnetic anomaly character across Lake Vostok defines a crustal boundary. Depth to magnetic basement estimates image a 400-km-wide and more than 10-km-deep sedimentary basin west of the lake. Analysis of teleseismic earthquakes suggests a relatively thin crust beneath Lake Vostok consistent with predictions from kinematic and flexural gravity modelling. Magnetic, gravity, and subglacial topography data reveal a tectonic boundary within East Antarctica. Based on our kinematic and flexural gravity modelling, this tectonic boundary appears to be the result of thrust sheet emplacement onto an earlier passive continental margin. No data presently exist to date directly either the timing of passive margin formation or the subsequent shortening phase. The preserved thrust sheet thickness is related to the thickness of the passive margin crust. Because a significant amount of time is required to erode the thrust sheet topography, we suggest that these tectonic events are Proterozoic in age. Minor normal reactivation of the thrust sheet offers a simple mechanism to explain the formation of the Lake Vostok Basin. A low level of seismicity exists in the vicinity of this tectonic boundary. The existence of a crustal boundary in the Antarctic interior provides new constraints on the Proterozoic architecture of the East Antarctic craton.     

控制碰撞造山带热异常形成的主要因素及其地质作用分析

本文对剥蚀、逆冲断层剪切摩擦和放射性物质富集等因素对造山带热结构和热演化的影响进行了模拟计算以及定量分析,并对热异常与造山带内的若干地质现象之间的关系进行了讨论.在剪切生热模型的计算中考虑了逆冲断层的速度变化及其对热结构的影响,考察了断裂宽度与热结构之间的关系.计算中还考虑了两种热剪切计算模式,即:(1)瞬间推覆就位模式;(2)非瞬间推覆就位模式.从计算与讨论中得出如下认识:造山带后期的剥蚀使整个岩石层加热;剪切摩擦使壳内局部地区升温;放射性物质的富集主要使上部岩石层产生热异常.三者联合作用的结果使岩石层大幅度升温,从而形成造山带内部大范围的与其它地区不同的高温异常以及独特的地质特征.通过计算和讨论,文中认为:重熔型花岗岩和大量的构造岩是造山带内逆断层剪切作用的产物;与逆断层呈平行排列的拉张正断层是造山带在诸因素作用下升温,然后又经剥蚀,物质发生热收缩的结果.在造山带演化后期出现的这种拉张正断层代表造山带解体和向盆地转化的构造面貌.     

拉分盆地形成机制三维数值模拟——以海原断裂带老龙湾盆地为例

拉分盆地是走滑断层系中受拉伸作用形成的断陷盆地.一般在两条平行断层控制下发育.盆地形似菱形,几何形态主要受两条主控走滑断层错距和叠接长度影响.本文以青藏高原东北缘海原断裂带老龙湾拉分盆地第四纪所处的构造环境为基础,参考盆地周围断层几何分布,建立了三维有限元数值模型,模拟该拉分盆地的演化过程;进一步分析了断层力学性质、地壳分层结构等各因素对盆地形成和演化的影响.模拟结果显示,盆地地表沉降伴随有下地壳物质的上涌,此上涌对盆地地表沉降存在阻碍作用.各因素的影响具体表现为:(1)断层力学性质(弹性模量和黏滞系数)越弱,其对构造应力较低的传递效率导致盆地两端差异性运动越明显,从而形成较大的盆地地表沉降和明显的上地壳减薄.(2)平行主控断层的叠接长度反映盆地形成的拉伸作用范围,叠接长度越大,相同的差异性运动在单位面积形成的拉伸应力越小,盆地地表沉降较小.(3)下地壳流变性影响其物质的上涌量,下地壳黏滞系数越小,其对上部拉伸作用的响应越明显,上涌量越大,此上涌对上地壳沉降形成的阻碍作用也越明显.根据老龙湾拉分盆地所处的构造格局,将平行断层的叠接长度取20km,当断层黏滞系数取值为周围基岩的1/10,参考该盆地第四纪构造演化历史,模拟得到的盆地第四纪下沉量与盆地内第四系沉积层厚度在规模上近似,下地壳黏滞系数取值在(2.5~5.0)×1021 Pa·s范围内时,盆地下沉量模拟结果与老龙湾拉分盆地第四系地层厚度吻合较好.     

Lateral variation in seismic velocities and rheology beneath the Qinling-Dabie orogen

The Qinling-Dabie orogen is an important tectonic belt that trends east-west and divides continental China into northern and southern parts.Due to its strong deformation,complicated structure,multiphase structural superposition and the massive exposed high and ultrahigh metamorphic rocks,its tectonic formation and geodynamical evolution are hot research topics worldwide.Previous studies mainly focused on the regional geological or geochemical aspects,whereas the geophysical constraints are few and isolated,in particular on the orogenic scale.Here,we integrate the available P- and S-wave seismic and seismicity data,and construct the rheological structures along the Qinling-Dabie orogen.The results demonstrate that:(1)there are strong lateral variations in the crustal velocity between the western and eastern sections of the Qinling-Dabie orogen,indicating the different origin and tectonic evolution between these two parts;(2) the lateral variations are also manifested in the rheological structure.The rigid blocks,such as South China and Ordos basin(North China Craton),resist deformation and show low seismicity.The weak regions,such as the margin of Tibet and western Qinling-Dabie experience strong deformation and accumulated stress,thus show active seismicity;(3) in the lower crust of most of the HP/UHP terranes the values of P-wave velocity are higher than the global average ones;finally(4) low P- and S-wave velocities and low strength in the lower crust and lithospheric mantle beneath Dabie indicate lithospheric delamination,and/or high temperature,and partial melting condition.     

纵贯中国东部一条新的巨型构造带

本文从地貌、地质、地球物理和地震活动等方面,论证了一条由地垒、地堑系组成的、纵贯中国东部的巨型活动性深断裂带。 这是一条以张扭性为主、差异升降强烈的追踪断裂带。它控制着沉积岩相、地貌水系和岩浆活动,尤其是作为一条超基性岩带,可为寻找有关矿产提供标志;同时也是一条构造地震带     

Seismotectonic Study on the West Part of the Interaction Zone Between Southern Tianshan and Northern Tarim

The interaction zone between southern Tianshan and northern Tarim is located at the northeast side of Pamir. It is a region with high seismicity. We constructed a seismotectonic model for the west part of this zone from geological profiles, deep crust seismic detection and earthquake focal mechanisms data. Based on the synthesized geological features, deep crust structure, and earthquake focal mechanisms, we think that the main regional tectonic feature is that the Tianshan tecto-lithostratigraphic unit overthrusts on the Tarim block. The Tianshan tectonic system includes the Maidan fault and thrust sheets in front of the fault; The Tarim tectonic system includes the underground northern Tarim margin fault, conjugate faults in basement and overthrust fault in shallow. The northern Tarim margin fault is a high angle fault deep in the Tarim crust, adjusting different trending deformation between Tianshan and Tarim. It is a major active fault that can generate large earthquakes. The other faults, such as the Tianshan overthrust system and the Tarim basement faults in this area may generate moderately strong earthquakes with different styles.     

Dynamic processes in the system of interacting geospheres at the Earth’s crust-atmosphere boundary

Results of various instrumental observations of geodynamic processes in the Earth’s crust and geophysical fields at the crust-atmosphere boundary in the Oka area of the Nelidovo-Ryazan tectonic structure and adjacent fractures and in the zone of the Gornyi Altai earthquake of September 27, 2003, are presented. The correlations between the geophysical fields are determined from the results of processing and analysis of microseismic vibrations, the emanation field of natural radon, and variations in the electric field in ground and the magnetic field in the surface atmospheric layer. Tidal deformations of the crust were considered as external effects enhancing the interactions between the geospheres. It is noted that tectonic faults determining the block structure of the crust are recognizable as anomalous variations in the geophysical fields and their high cross-correlation.     

Numerical modeling of the development of southeastern Red Sea continental margin

The Red Sea continental margin (RSCM) corresponds to a wide hinge zone between Red Sea and Arabian plate. This margin has been studied through geological and geophysical observations primarily in regard to the evolution of Red Sea rift. This margin is characterized by occurrence of thin sediments, significant onshore uplift, tectonic subsidence of the offshore sedimentary basin, active faulting and seismicity. Studies indicate that sedimentary sequences of the margin are deformed by faults and folds resulti...