大别—苏鲁区残余超高压构造及其动力学意义

RELIC UHP STRUCTURES IN DABIE-SULU REGION, CHINA: STRUCTURAL EXPRESSION AND GEODYNAMIC SIGNIFICANCE

根据构造学及岩石学研究并结合已有同位素年代学资料地质意义分析证明 ,现在观察到的大别 -苏鲁超高压变质带的区域构造框架 ,主要是在三叠纪中朝与扬子克拉通碰撞期后( 2 0 0～ 170Ma)伸展体制和角闪岩相条件下形成的 .残余的同碰撞及超高压构造只保留在较大的榴辉岩及其他超高压变质岩体内部 .以湖北省麻城县乘马岗和何家湾、安徽省岳西县碧溪岭及江苏省东海等地区的榴辉岩为例 ,分析描述了具弱面理的块状榴辉岩、超高压剪切带和A型褶皱等残余超高压构造 .强调指出 ,只是这些早期的构造记录才反映大陆碰撞阶段的构造环境及相对运动学特征 .据此提出一个运动学模型 ,表示三叠纪 ( 2 40～ 2 10Ma)扬子克拉通向北俯冲于中朝克拉通之下并与其发生斜向碰撞的动力学格局 .

Structural and petrological research combined with the geological analysis of the isotopic dating references available now is used in this paper to demonstrate that the present day observed tectonic framework of the ultrahigh pressure (UHP) metamorphic belt in the Dabie Sulu region was formed dominantly in an extensional process at 200-170?Ma, on amphibolite facies conditions, following the Triassic collision between the Sino Korean and Yangtze cratons. The relic syn collision and UHP structures are preserved in the relatively large eclogite and other UHP metamorphic rock masses. Examples of the eclogite drawn from the Chengmagang and Hejiawan in Hubei Province, the Bixiling in Anhui Province, and Donghai in Jiangsu Province, are used to analyze and describe such relic UHP structures as the massive eclogite with weak foliations, the UHP shear zones and A type folds. It is stressed in the paper that only early UHP relic structural records may reflect the tectonic environment in the continental collision stage, and the corresponding relative dynamic features. On this basis, a kinematic model is proposed to represent the dynamic framework of the northward subduction of the Triassic (240-210?Ma) Yangtze craton under the Sino Korean craton and of their corresponding oblique collision.