关于华北克拉通燕山期岩石圈减薄的机制与过程的讨论:是拆沉,还是热侵蚀和化学交代?  

Discussion on the lithospheric thinning of the North China craton: delamination? or thermal erosion and chemical metasomatism?

作　　者：邓晋福[1,2,3] 苏尚国[1,2,3] 刘翠[1,2,3] 赵国春[1,2,3] 赵兴国[1,2,3] 周肃[1,2,3] 吴宗絮[1,2,3] 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,北京100083 [2]中国地质大学岩石圈构造,深部过程及探测技术教育部重点实验室,北京100083 [3]中国地质大学(北京)地球科学与资源学院,北京100083

出　　处：《地学前缘》2006年第2期105-119,共15页Earth Science Frontiers

基　　金：国家自然科学基金重点资助项目(40234048);中国地质调查局资助项目(200113900018);国家科学技术部国际合作项目(2001cb711002);IGCP-430项目;教育部211工程项目

摘　　要：关于华北克拉通燕山期岩石圈减薄作用,主要有两种模型:(1)岩石圈拆沉;(2)热侵蚀和/或化学交代。文中主要从岩浆活动与构造变形两个途径,通过(1)燕山带造山幕和结构要素组合以及造山过程的p-T-t轨迹;(2)收缩构造变形、火成岩构造组合和下地壳岩石捕虏体3个独立证据提出陆壳的构造加厚;(3)火成岩成因的壳幔相互作用模型和热模拟等,试图讨论华北地区克拉通有浮力的岩石圈如何转变为密度大的岩石圈,随之发生拆沉作用,而不是热侵蚀或化学交代机制使岩石圈地幔改造为EMI印记实现的减薄作用。大量对流的软流圈物质注入克拉通是诱发陆壳发生局部熔融所必需的条件。底侵玄武质岩浆的加热并弱化先前的冷和强的克拉通地壳,创造一个流变学条件,以使收缩构造变形和陆壳加厚成为可能。陆壳最下部和岩石圈地幔中形成的大量玄武质岩石,在构造加厚作用下,相转变为榴辉岩,致使原先有浮力的岩石圈转变为密度大的岩石圈,随之发生拆沉作用。There are two prevailing models for the lithospheric thinning of the North China craton： （1） delamination, （2） thermal erosion and chemical metasomatism. To assess them, on the basis of both magmatism and tectonic deformation, we have considered the following： （1） structural elements, orogenic episodes, and the P-T-t path of orogenic processes in Yanshan belt; （2） crustal tectonic thickening based on evidence from contractional deformation, igneous rock assemblages and lower crustal xenoliths; and （3） thermal models and models of erust-mantle interaction for igneous petrogenesis. From these considerations we discuss reasons for the transformation of buoyant cratonic lithosphere to a denser one, and favor delamination as the model for lithospheric thinning, rather than thermal erosion and chemical metasomatism. An input of a large amount of convective asthenospheric materials into the craton was needed to make the crust partially molten. Underplating basaltic magma weakened the previous cold and strong crust and facilitated its contractional deformation and thickening. A large volume of eclogite in the lowermost crust and within the lithospheric mantle was produced by the tectonic thickening, transforming the buoyant continental root into a dense one and leading to delamination.

关 键 词：华北克拉通 燕山期 底侵玄武质岩浆 构造加厚 岩石圈拆沉 

分 类 号：P588.1[天文地球—岩石学] P583[天文地球—地质学]