北祁连山东段海原一带海原群变质岩原岩恢复及其构造背景

对海原群的岩石组成、原岩性质和构造环境的研究表明,海原群中云母片岩、石英片岩的原岩是泥质岩、杂砂岩等,大理岩、石英岩的原岩为白云岩—灰岩、石英砂岩或硅质岩,绿片岩和角闪岩的原岩为基性火山岩或次火山岩,蛇纹岩的原岩为超镁铁质岩。变质沉积岩的形成构造环境判别结果表明,它们形成于活动大陆边缘,介于岛弧与稳定陆缘之间。变质基性火山岩主要亦介于岛弧拉斑玄武岩与板内玄武岩之间,部分显示洋脊玄武岩的特征。认为海原群形成于岛弧—弧后盆地的构造环境。

Reconstruction of protoliths of metamorphic rocks and tectonic setting of the Haiyuan Group in the Haiyuan in the eastern segment of the North Qilian Mountains, China.

Study of the composition and nature of the protoliths of metamorphic rocks in the Haiyuan Group and their tectonic setting shows that: the protoliths of mica schist and quartz schist of the Haiyuan Group are argillaceous rocks and graywacke; the protoliths of marble and quartzite are dolostone-limestone, quartzose sandstone or siliceous rocks; the protoliths of greenschist and amphibolite are basic volcanic rocks or subvolcanic rocks; the protoliths of serpentinite are ultramafic rocks. Tectonic setting discrimination of metasedimentary rocks indicates that they formed in an active continental-margin environment, between the island arc and the stable continental margin. Metabasic volcanic rocks are also mainly intermediate between island-arc tholeiite and within-plate basalt and partly show the features of mid-ocean basalt. On that basis, combined with the features of the rock association of the Haiyuan Group, it is thought that they formed in an island arc-back arc basin.