恒山中段新太古代高压麻粒岩区的构造特征

Structural Analysis on the Neoarchean High-Pressure Granulite-Bearing Terrain in the Central Hengshan Moutain, North China

恒山中段高压麻粒岩区是华北克拉通新太古代高压麻粒岩最好的露头区之一,北部为强烈重熔的灰色片麻岩区,构造样式以穹窿、近水平韧性剪切带为主,中部以近东西向的右旋走滑剪切带与南部变形变质程度相对较低的岩石单元相接,后者主要的岩石类型为均匀的英云闪长质片麻岩和变质辉绿岩墙。高压麻粒岩以透镜体形式出现在北部。本文通过对恒山高压麻粒岩区构造特征和构造样式的分析,认为高压麻粒岩区主要经历了4期构造变形:①高压麻粒岩透镜体里的逆冲型韧性剪切变形和走滑剪切变形;②向南或南西的伸展变形;③右行走滑剪切;④向东或南东伸展变形。对恒山地区的高压麻粒岩的出露起决定作用的是两次伸展构造运动。

The Hengshan Neoarchean high-pressure granulite terrain is one of the best preserved high-pressure granulite regions in the central North China Block (NCB). This paper shows in detail the characteristics of the high-pressure granulite and describes the various structural forms of this terrain and their distribution in the field. It also gives a tectonic and genetic sequence of this region. It is concluded that the terrain has expierenced four stages of deformation, (1) a ductile shearing during the formation of the high-pressure granulites; (2) a southwestward extensional detachment indicated by the extensive shallow ENE-WSW lineations and horizontal shearing in the northern part; (3) a west-east dextral strike-slipping shearing; and (4) a southeastward extensional detachment characterized by normal faults dipping gently to the southeast in the whole region. The last two extensions finally raised the high-pressure granulites to the upper crust and the whole process probably lasted from 2. 5 Ga to 1. 8 Ga.