中国西部地壳现今变形特征及其机制探讨

以中国大陆及周边10年来近400个GPS测站的复测资料为基础,获取并绘制了现今地壳水平运动与变形图像,结果表明：青藏块体内西半部南北向只存在微弱的缩短变化（5mm/a左右）,东半部南北向则没有缩短的迹象,南北缩短的区域主要位于青藏块体南缘的喜马拉雅条带（约15mm/a）,北缘中部的柴达木西区（约15mm/a）和青藏块体北面的天山块体及周围地区（约15mm/a）;青藏块体大约有10mm/a的东西拉张,但不均匀,自西向东经历了由弱到强再有所减弱的过程,整个西部地区东边缘的东向运动表现为南强北弱的左旋特征;川滇菱形块体不是逃逸块体而是变形块体;青藏块体东缘及附近地区是东向运动的消减区带,面应变结果显示,青藏块体周边以面收缩为主,内部则以面膨胀为主;其以北的地区以面收缩为主（但压中有张）,面应变的量级为10^-8/a。这样的变形结果,若只靠来处于印度板块的北向挤压是无法解释的。由此并结合最新的地球物理研究成果可推断或证实,地壳下部来自南向的物质涌入是控制青藏块体乃至中国大陆形变的另一大动力源,甚至可能是主导动力源;或者具有深、浅立体活动的某种协同性。

The Characteristics of Present-day Crustal Deformation in Western China and Discussion of Its Mechanism

Based upon re measurement data about 400 GPS stations obtained in last decades in Chinese Mainland and her adjacent area, the images of present day horizontal crustal movement and deformation have been formed. The results indicate, that there is only a little shorten (5 mm/a or so) about SN direction in western part of the Qinghai Tibet plateau, however no shorten evidence is discovered in its eastern part; that constriction in SN direction mostly took place in Ximalaya belt of the south edge which is in the plateau, the magnitude is about 15 mm/a, and the same directional variance happened in the west of Qaidam in the middle of the north edge in the plateau and in the Tianshan area which locates north of the plateau also in its adjacent region, the magnitude is about 15 mm/a too; that there is about 10 mm/a extension in EW direction in Qinghai Tibet plateau; that the eastward movement in east edge of the western China is stronger in south and weaker in north; that the rhombic Sichuan Yunnan Block is not a escape block but a deformation block; that the east edge of the Tibet plateau and its vicinity are decline areas in east direction; the surface strain results show that the constriction is found at the edge around the Qinghai Tibet plateau, surface expanded in its interior and constriction with 10E -8 /a in the north part of Western China.The squeezing in north direction from the India plate can not explain the deformation results. According to the latest geophysical results, we consider the mantle substantial inrush under crust may be another dynamical source that control Tibet plateau motion even the deformation of Chinese Mainland, which perhaps was dominant dynamical source.