阿拉善地块中元古代诺尔公群的构造变形特征

阿拉善地块作为华北板块的重要组成部分及关键的构造单元,经历了不同时期构造热事件的叠加作用。本文选取阿拉善地块巴音诺尔公地区出露的中元古代诺尔公群进行研究,总结了这些前寒武纪岩石的几何学、运动学及显微构造特征,并对其构造格架、变形期次进行了初步划分。研究表明,中元古代诺尔公群内部至少存在两期变形,早期变形表现为原始层理的片理化过程,形成了区域走向近NE-SW向的片理;而晚期变形则表现为顺片理走向的右行走滑剪切作用。结合前人已有研究成果及年代学资料,认为中元古代诺尔公群的内部变形主要受到石炭纪-二叠纪查干础鲁弧后盆地向阿拉善微陆块之下俯冲作用的控制,俯冲作用造成了NW-SE向的挤压,从而发生了早期片理化,而随后顺俯冲带走向的走滑作用则调节了挤压造成的缩短。

Tectonic deformation characteristics of the Mesoproterozoic Nuoergong Group in the Alxa block

The Alxa block constitutes the westernmost part of the North China Block (NCB). This block has experienced polyphase tectonothermal events and hence serves as a key tectonic unit of the NCB. In this paper, Mesoproterozoic Nuoergong Group in Bayinnuoergong area of eastern Alxa block was selected for studying the tectonic framework and deformation stages of the Alxa block. Based on geometry, kinematics and microstructural characteristics of the Mesoproterozoic Nuoergong Group, the authors recognized two deformation stages. At the first stage, original bedding structure reflected by the ribbon was transformed into foliation, striking in the NE-SW direction. At the late stage, dextral strike-slip shear occurred along the strike of foliation. In combination with previous research results and geochronological data, the authors hold that the deformation structures were controlled by the subduction of Chaganchulu back-arc basin beneath the Alxa block during Carboniferous-Permian period. Due to the intense NW-SE-trending contraction during the subduction, foliation formed and transformed the original bedding structure. After that, dextral strike-slip shear occurred along the strike of the subduction zone and accommodated intense contraction.