博格达山晚石炭纪造山活动的变形地质记录

主要由钙碱性火山岩、火山碎屑岩组成的博格达古岛弧是天山缝合造山带的重要组成部分 ,是一个发育较成熟的山链 ,其演化经历了晚古生代的韧性剪切收缩 ;中生代伸展调整及新生代再造山过程。晚古生代的造山活动在博格达山有很好的地质记录 ,并以显著的韧性剪切变形带的形成和发育同造山的褶皱构造为特点。剪切变形带内同构造的石英脉中的锆石U PbSHRIMP测年结果与山链中花岗岩、辉长岩年龄颇为一致 (311～ 316Ma) ,这个年龄反映在结束洋盆散聚、碰撞焊接的晚华力西期造山过程中 ,博格达古岛弧内存在一次虽不甚强烈 ,但又较为明显的构造岩浆事件 ,其成因可能与引起石炭纪大规模裂陆式喷发的深部断裂构造重新活动有关。

GEOLOGICAL RECORD OF THE LATE-CARBONIFEROUS OROGENY IN BOGEDASHAN, NORTHERN TIANSHAN MOUNTAINS, NORTHWEST CHINA

Bogedashan palaeo island arc composed of calc alkaline igneous rock and volcaniclastic rock is an important component of Tianshan orogenic belt, and it's evolution underwent three main periods:①ductile shear contract (from south to north) in the Late Palaeozoic; ②stretching regularization phase during the Mesozoic ; ③re orogeny in the Cenozoic. There are various geological records about the Late Palaeozoic orogeny in Bogedashan, and the Late Palaeozoic orogeny is characterized by formed ductile shear deformation zone and developed synorogenic folds.The results of zircon U Pb SHRIMP age from syntectonic quartz vein in the shear deformation zone are quite consistent with granite and gabbro dispersing in Bogedashan, the ages represent a stage of tectonic and magmatic event during late Variscan orogeny in Bogedashan Palaeo island arc, and the cause of tectonic and magmatic event is probably related to reactivation of deep faults which led to a large scale Carboniferous volcanic eruption in the island arc.