The Tectonic Feature of a Quasi-Trij unction in the Northeastern Corner of Qinghai-Xizang Plateau

Quasi-trijunction is a type of popular structure for certain scale tectonic blocks in a continent. There are two kinds of quasi-trijunction in the conjoining area formed due to rotation of continental blocks. They are the clockwise type and the anticlockwise type of quasi-trij unction. The shape of a quasi-trij unction may be gradually changed associated with block rotation and tectonic evolution, but, sediments and structure in the conjoining area can record the history of tectonic evolution. Thus, studying a quasi-trij unction can reveal regional tectonic evolution.Regional tectonic movement, plane strain partitioning and characteristics of seismic activity can be studied based on kinematics and geometric analysis of a quasi-trijunction.The quasi-trijunction is a surface structure controlled by deep crustal movement. Tectonic activity may be different in three branches. In the quasi-trijunction in the northeastern corner of Qinghai-Xizang Plateau, the NWW-trending Qilianshan-Hexi corridor fault zone

Evolution characteristics of Quaternary tectonic stress field in the north and east margin of Qinghai-Xizang plateau

By inversion of fault slip data for Quaternary tectonic stress field and the analysis of crustal deformation after lateTeriary. we explaincd the evolution of crustal dynamic about the north and east margin of Qinghai-Xizang (Tibet)plateau since Miocenc. From middle or late Miocene to early Pleistocene, the tectonic stress field was featured by amaximum principal compression which was coming from the collision of india Plate continued to the boundaryof the plateau. and was basically of reverse faulting type. Since the late period of early Pleistocene, Pleistocene continuedto push northward and the compressional deformation of the plateau interior increased continuously, meanwhile,N W-SE extension appeared on the east side of the plateau. This formed a favorable condition for the interior block offoe plateau to slide towards east and southeast, causing the faults surrounding the plateau to change from thrust tostrike-slip. -The contemporary tectonic stress field was formed from the late period of early Pleistocene and continuedto present. The direction of maximum principal compressional stress rotated clockwise with respect to the previoustectonic stress held. the stress field was mainly of strike-slip type.

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.

Crust Shortening of the Daliangshan Tectonic Zone in the Cenozoic Era and Its Implications

The Daliangshan tectonic zone is a rhombic area to the east of the Anninghe and Zemuhe fault zones in the middle segment of the Xianshuihe-Xiaojiang fault system along the southeast margin of the Qinghai-Xizang(Tibet)Plateau.Since the Cenozoic era,the neotectonic deformation in the Daliangshan tectonic zone has presented not only sinistral slip and reverse faulting along the Daliangshan fault zone,but also proximate SN-trending crust shortening.It is estimated that the average crust shortening in the Daliangshan tectonic zone is 10.9±1.6 km,with a shortening rate of 17.8±2.2% using the method of balanced cross-sections.The crust shortening from folding occurred mainly in the Miocene and the Pliocene periods,lasting no more than 8.6 Ma.Based on this,a crust shortening velocity of 1.3±0.2 mm/a can be estimated.Compared with the left offset along the Daliangshan fault zone,it is recognized that crust shortening by folding plays an important part in transferring crustal deformation southeastward along the Xianshuihe-Xiaojiang fault system.

青藏高原东北缘晚第四纪活动构造的几何图像与构造转换

青藏高原东北缘所在的柴达木-祁连活动地块内的晚第四纪活动构造可以划分为主边界左旋剪切构造带、块内次级右旋剪切构造带和挤压会聚构造带等三种基本类型。在区域北东向构造应力作用下,块体发生了NE向的挤压缩短、顺时针方向的旋转和向SEE方向的挤出等构造变形。在块体内部形成了挤压推覆构造、次级剪切构造、剪切压扁构造和弧形挤出构造等四种典型的构造转换方式,实现不同方向与不同性质活动构造之间的转换平衡。

青藏高原东北隅似三联点构造特征

在大陆内部，对于一定尺度的构造块体，似三联点构造是一种较普遍的构造形式。由于大陆内部块体旋转的普遍性，似三联点构造可形成顺旋型和逆旋型两种构造型式。随着块体的旋转和构造演化，似三联点逐渐改变原来的形状，在交接构造区内部的沉积和构造变形不断记录着演化过程，因此通过对其研究可了解区域构造演化过程。根据运动学和几何学特点，可以应用似三联点构造的概念研究构造运动和应变的平面分配以及地震活动的规律性。似三联点构造往往是受控于深部构造运动的表层构造形式，三条构造支的活动强度有一定差异。在青藏高原东北隅，北西西向的祁连山左旋挤压构造带和青藏高原东缘右旋剪切带具有深部构造背景，六盘山构造带则偏离深部构造带。

青藏高原隆升及伸展变形中的重力位能

青藏高原在南侧印度板块和北侧欧亚板块的双向挤压下整体抬升 ,边界挤压力所作的功增加了高原内部重力位能 .但高位能态的物质会不断向重力势能最小的平衡态转移 ,并产生流变变形 .由于受南北边界的挤压力约束 ,高原内部的高位能驱使喜马拉雅山和昆仑山之间的地体产生东西向伸展变形 .利用三种不同方法对青藏高原重力位能进行计算 ,结果表明 ,一定流变学条件下 ,青藏高原目前所具有的重力位能可以产生各地体中观测到的地表构造变形速率 .

用双三次样条函数模拟青藏高原东北缘重力场动态图像

用双三次样条模拟了1992～2001年间青藏高原东北缘重力变化时空分布信息,初步研究了本区的重力变化与地震活动及构造活动的关系。结果表明:①在地震孕育过程中,区域重力场出现有规律的变化并产生重力变化异常区或重力变化密集带。②在重力变化显著时段,以兰州为界,测区西北、东南和东北具有不同的重力变化特征。③重力变化与测区主要断裂构造带走向基本一致,重力变化等值线与断裂分布关系密切。

青藏高原南缘现今地球动力学研究

喜马拉雅构造带于新生代时期经历了两代受力条件截然不同的形变。早期造山挤压形变与造山后的引张形变、青藏高原和高喜马拉雅的大幅度抬升。大致低喜马拉雅范围即青藏高原南缘，现今构造活动与青藏高原和高喜马拉雅块断抬升相辅相成。流行的板块聚合动力学模式，即使早新生代发生过，晚新生代以来已经灯熄。东亚大陆现代形变与地震活动的驱动力不可能源于青藏高原南缘被动挤压，而是取决于与高原隆起相关的深部主动动力学过程。

浅谈大陆构造——板块构造的回顾与反思

60年代提出的板块构造理论拓宽了人们的思路,给地球科学带来了活力。但是随着对大陆区域地质调查的深入,发现大陆板块与大洋板块差异很大,用刚性板块运动学理论不能解释大陆内部复杂的构造形变和板内地震活动。J. Dewey(1986)和P. Molnar(1988)相继提出大陆构造及其研究方法。我国青藏高原是一个典型而独特的大陆构造单元,是最强烈的板内形变带和地震活动区,同时是亚洲大气环流的启博器。青藏高原很可能成为新的地球科学理论的诞生地。

青藏高原东北部地区的区域地壳现今构造形变系统 ——陆壳浅源构造地震成因的新认识(英文)

依据青藏高原东北部地区的大震 (MS≥ 7)、大震形变带、活动断裂和活动构造体系的资料 ,以地球系统科学、地质力学、地震地质学、现代地震学的理论和方法为主线 ,对该区内大震的“共性”进行了探讨 ,提出了具有三维空间动态的区域地壳现今构造形变系统的新概念 ,并对该区内地震的形成机制、分布规律等科学问题提出了新的见解 .