大陆下地壳流动:渠流还是层流?  

Continental lower crustal flow:channel flow or laminar flow?

作　　者：李德威[1] 

机构地区：[1]中国地质大学(武汉)地球科学学院和青藏高原研究中心,湖北武汉430074

出　　处：《地学前缘》2008年第3期130-139,共10页Earth Science Frontiers

基　　金：国家重点基础研究发展计划"973"项目前期研究专项(2005CCA05600);国家自然科学基金资助项目(40572113);东方地球物理公司新领域综合研究项目"中国西部盆山耦合与盆山成因研究"

摘　　要：大量的地质、地球物理、地球化学、实验和模拟资料证明大陆岩石圈存在壳内流层,目前创建了渠流和层流两种假说来解释大陆下地壳的流动规律和流动机理。渠流模式是指厚地壳、高地势的造山带或高原中、下地壳低粘度物质在地貌负荷的侧向压力梯度或剥蚀作用驱动下从山根向外侧向扩张。笔者在研究青藏高原的基础上于1992年提出的层流模式是指在大陆边缘俯冲板片脱水熔融和大陆内部地幔柱(枝)底辟上隆的热动力及其相关的重力驱动下的盆山地壳物质循环系统,盆地热软化下地壳物质在重力作用下顺层流向相邻的山根,盆地地壳减薄,造山带地壳加厚,加厚的下地壳部分熔融物质带动深层变质岩向上运动,热-重力派生的垂直主应力形成热隆伸展的变质核杂岩和低角度拆离断层,隆升的山体在重力势能作用下侧向扩张,盆山边界形成逆冲推覆和滑覆构造,同时遭受强烈的剥蚀作用,造山带源粗碎屑沉积物快速堆积在盆缘受下地壳拖曳的壳内有限俯冲坳陷带内。渠流构造和层流构造在大陆板内变形、中下地壳韧性挤出、造山带的挤压和伸展同步转换、中深变质岩的韧性变形及剥露过程、部分熔融及岩浆活动等方面存在相似之处,但是,在发育背景、产出部位、流层边界、流层规模、流动型式、流动体制、流动方向、流动物质、流动效应、流动时间、驱动力等方面存在本质的差异。渠流构造基本上可作为层流构造时空结构中的一个组成部分,层流的驱动力是热能和重力,而不是地表剥蚀作用和山体负荷作用。从全球角度来看,层流只是地球多级物质循环流动系统的一个组成部分。A lot of geological, geophysical and geochemical investigations and the finite element modeling of the continent indicate that crustal flow layers exist in the continental crust. Channel flow model and laminar flow model have been created to explain the flow regularity and flow mechanism. The channel flow model reveals that in the thick crust and high elevation orogen or plateau the low-viscous materials in the middle to lower crust flow outward from mountain root in response to topographic loading or denudation. The laminar flow model proposed by Li Dewei （1992） based on investigation of the Qinghai-Tibet plateau involves a circulative movement of crustal materials with different rheological properties between basin and orogen, lower crust and upper crust driven by the thermal energy related to the upwelling mantle plume diapir in internal continent or the vertical movement of magma upon dehydration of a subduction plate on the active continental margin. Softened or melted substance of the lower crust in a basin flows laterally toward adiacent mountain root driven by gravity, and simultaneously a thin basin crust and a thick orogenic crust are formed. Partially melted magma within the thickened orogenic lower crust drags the vertical movement of metamorphic rocks of lower crust and middle crust because of density inversion, and forms metamorphic core complexes and low-angle detachment fault system acted by vertical main stress induced by thermal underplating of lower crust. Lateral spreading of uplifting mountain results in thrust fault system on the border between mountain and basin, and detritus synchronously produced by erosion of uplifting mountain is transported and deposited along the marginal deep depression in the foreland basin dragged by lower crust flow. The channel flow model is similar to the laminar flow model on the continental intraplate deformation, middle-lower-crust extrusion, detachment fault contemporaneous with thrust fault, exhumation of deep metamorphic rocks, and partial melting of o

关 键 词：下地壳 层流 渠流 循环流 盆山耦合 青藏高原 

分 类 号：P54[天文地球—构造地质学]