【作者】 何建坤； 刘金朝；

【Author】 HE Jian-Kun~a,LIU Jin-Zhao~b a.Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100101,China b.Department of Geophysics,Peking University,Beijing 100871,China

【机构】 中国科学院地质与地球物理研究所； 北京大学地球物理系；

【摘要】 应用不可压缩非牛顿粘性流体的本构关系,对造山带同挤压期下地壳流变及其与上地壳构造伸展的动力学关系进行了二维有限元数值模拟。结果表明,在板块侧向挤压下,当造山带山根下陷和地表隆起达一定程度后,地壳不同层圈岩石将发生复杂的粘性流变。流变的运动学方式和分布范围不仅与时间有关、同时还受地壳厚度转变带形态的制约。在构造挤压和山体荷载达到弹性平衡状态后,地壳流变首先发生在造山带下地壳山根,但经一定的Maxwell时间后,地壳流变将不断局限于造山带前缘的厚度转变带。这一流变方式的变化是导致造山带浅部地壳动力学转变的主要原因。它造成造山带内上地壳最小主应力从近水平挤压不断转化为近水平拉张,由此使造山带在前陆发生挤压冲断的同时,山体的核部发生上地壳的拉张伸展。最后,应用这一结果讨论了青藏高原南缘南北向地壳伸展的动力学性质。更多还原

【Abstract】 In attempt to reveal the mechanical relation between lower-crust ductile flow and upper-crust extension in collisional orogenic belt,the present paper makes numerical simulation using the Finite Element Method(FEM),which is based on stress-strain consti-tution of incompressional Non-Newtonian rheology.Results show that,under the tectonic compression and the gravitational loading conditions,the crust in mountain-building process undergoes complex ductile flow.Kinematics of ductile flow is time-dependent,and influenced by the shape of the crust transition zone(CTZ) between orogenic belt and frontal stable plate.Under the mechanic balance of tectonic compression and gravitational loading,the ductile flow is facilitated first in mountain root. However after several Maxwell times,it will be localized narrowly to the CTZ,where the flow pattern is featured by a downward flow near the mountain side and an upward flow near stable-plate side.This flow pattern causes stress partition and displacement differentiation spatially in orogenic belt.In details,the minimum principle stress in upper crust near the mountain center will change from hori-zontal compression to horizontal tension.The magnitude of tensile stress is mainly related with the height of mountain belt above reference surface.It indicates that crustal extension in syn-collision orogenic belt has a mechanic relation with gravitational collapse,but the extension is probably intensified further by lower-crust ductile flow.For this consideration,it is concluded that mechanics of compression-extension coupling in orogenic belt is derived from the lower-crust ductile flow that is initiated by the gravitational loading and horizontal tectonic compression.Using model result,the north-south crustal extension in the southern Qinghai-Xizang Plateau has been discussed.更多还原