摘要
自从大陆整合以来作为一个整体的青藏高原继续受着印度板块向北俯冲的影响,也必定不断地改造着原各地体的结构构造,形成了高原整体意义上东西向的差异。这种差异与原本各地体的组成、结构和东西向延伸不一致。这不仅表现在南北向断裂构造跨各单个地体范围的出现,而且,逐步形成了东西的分区。这种分区突出地表现在区域重力与磁场的特征上,这不仅是局部的岩石磁性与密度变化的结果,而且是由于印度板块向北俯冲过程中,在其前缘的不同部位上经受的压力不同,以及地块的隆升与扩张作用的差异造成了高原东西各区段的地壳组分与厚度的变化。青藏高原的南北向断裂构造并非地壳上层的局部断裂,它具有深层的原因。由于印度板块向北推进的过程中不是均匀地齐头并进,而是在帕米尔高原以东的青藏高原范围内存在着推进速度和俯冲深度的差异,随着高原隆升的加剧高原本身出现断裂,自中新生代以来就存在着一定差异,所以南北向的断裂构造比目前地表见到的多些,而且具有较大的深度,Moho面的深度和地壳厚度都受南北向断裂的控制,并形成了区域重磁场的变化。同时,高原的东西向拉张作用也使南北断裂带发育加剧。
The Qinghai-Tibet Plateau as an integral unit has continued to be affected by northward subduction of the Indian plate since the assembling of the continent; so certainly the structures of various original terranes have been constantly reworked. As a result, the differences of the plateau as a whole in the E-W direction have been formed. These differences are not in agreement with the constitutions, structures and east-west extensions of the various original terranes. This is not only manifested in the appearance of the N-S-trending fault structure across various individual terranes, but also in the gradual division in the E-W direction. This division is highlighted by the features of the regional gravity and magnetic fields, which is not only the result of the sectional rock magnetism and density variations but also the result of the variations in crustal composition and thickness of various areas and segments in the east and west parts of the plateau caused by different compressions undergone by different parts of the leading edges of the northward subduction of the Indian plate and the differences in block uplift and expansion. Based on the above, the paper analyzes the cause for the E-W division of the Qinghai- Tibet Plateau.The N-S-trending fault structure on the Qinghai-Tibet Plateau is not a local fault in the upper crust but is of deep origin. In the course of northward pushing, the various parts of the Indian plate did not keep abreast of each other. There were differences in pushing speed and subduction depth within the limits of the Qinghai-Tibet Plateau east of the Pamir Plateau. Due to the acceleration of the uplift of the Qinghai-Tibet Plateau, faults appeared on the Qinghai-Tibet Plateau itself. Because the differences have existed since the Miocene, more N-S-trending faults are found at the earth＇s surface and they extend to greater depths. The Moho depth and crustal thickness are both controlled by these faults, causing the variation in the regional gravity and magnetic fields. At the same time, the E-W extension of the plateau also affects the N-S-trending fault belt.
出处
《中国地质》
CAS
CSCD
2006年第4期912-919,共8页
Geology in China
基金
国土资源部科技专项计划项目(2001010103)资助。
关键词
青藏高原
重磁异常
东西向分区
南北向构造特征
Qinghai-Tibet Plateau
gravity and magnetic anomalies
division in the east-west direction
characteristics of N-S-trending structure
