碧口地区复理石岩系特征及其构造环境

THE FEATURES AND THE TECTONIC SETTINGS OF THE FLYSCH FORMATION IN THE BIKOU AREA, THE SOUTHERN QINLING

碧口地区晚元古代复理石岩系位于扬子板块西北缘,其主体由下部火山质碎屑浊积岩和上部陆源碎屑浊积岩组成。本文研究了复理石岩系中杂砂岩的岩石学、碎屑模型和岩石化学特征,并与不同板块构造背景下沉积的古代杂砂岩和现代深海砂成分进行了类比。研究表明,复理石岩系形成于沟弧盆系活动大陆边缘构造环境,杂砂岩属大陆岛弧型,物源区为活动大陆边缘的火山—深成岩浆岛弧造山带,源岩为钙碱性长英质火山岩及同源深成侵入岩,沉积盆地为岛弧及俯冲杂岩外侧的古海沟环境。

The late Proterozoic flysch formation in the Bikou area is located in the northwestern margin of the Yantze plate. Its main body is made of the lower part of the volcanic clastic turbidite and the upper part of the terrigenous clastic turbidite. This paper studied the characteristics of graywackes of the flysch formation, and contrasted them with the ancient graywackes deposited under various plate tectonic settings and the modern deep sea sand compositions. The study shows: the flysch was formed in the tectonic setting of the active continental margin; the graywackes belong to continental island arc type; the provenace is the volcanic-plutonic magmatic island arc orogene; the protolith of graywackes dominantly derived from the calc-alkaline felsic volcanic rocks and cogenetic plutonic rocks; the sedimentary basin is the ancient trench or fore-arc setting in the outside island arc and subduction complex.