中、南天山古生代增生-碰撞事件和变形运动学研究

Paleozoic accretion-collision events and kinematics of ductile deformation in the Central-Southern Tianshan belt

天山山脉是通过早古生代晚期-晚古生代早期的增生和晚古生代晚期的陆-陆碰撞形成的,新生代又受到强烈的陆内挤压隆升与褶皱断裂作用的改造.早古生代晚期的阿齐克库都格-尾亚缝合带以奥陶纪的蛇绿混杂岩、含奥陶纪-志留纪化石的复理石以及高压变质岩和糜棱岩为特征.中天山造山带主要是一个奥陶纪的钙碱性火山岩-深成岩岛弧,而南天山主体是一个弧后盆地.中小型构造形迹及不整合接触关系,提供了一些两期韧性变形的运动学和定年学依据.早期韧性变形发生在400 Ma左右,为从南向北的推覆作用;含麻粒岩的蛇绿混杂岩和石榴石-辉石相韧性变形构造即形成于此期.早石炭世磨拉石不整合沉积在前石炭纪的变质岩和韧性剪切岩石之上.晚期韧性变形发生在晚石炭世-早二迭世,为右旋走滑构造作用;靠近中天山的北天山火山岩中发育有右旋走滑韧性剪切构造.其成因可能与晚石炭世发生的塔里木与西伯利亚两个陆块的碰撞有关.晚古生代花岗岩浆作用和后期构造叠加在早古生代变形形迹之上.结果表明,古生代的两期陆壳增生事件奠定了天山山系的基本构造格架.

The Chinese Tianshan range could have been built by both a late Early Paleozoic accretion and a late Paleozoic collision events. The Aqqikkudug-Weiya late Early Paleozoic suture is marked by Qrdovician ophiolitic melange and Silurian flysch sequence, HP metamorphic relics, and mylonitized rocks. Central Tianshan belt could principally be an Ordovician volcanic arc whereas Southern Tianshan, a backarc basin. Macro- and microstructures along with unconformity provide some kinematic and chronological constraints on a 2-phase ductile deformation. The earlier ductile deformation was marked by a 400 Ma ± north-transporting ductile shearing, yielding granulite-bearing ophiolitic melange blocks and garnet-pyroxene-fades ductile deformation, and the later deformation involved along-strike dextral strike-slip during Late Carboniferous to Early Permian time. The Early Carboniferous molasses were deposited unconformably on the pre-Carboniferous metamorphic and ductily sheared rocks, implying the end of the early orogeny. The large-scale ductile strike-slip along the Aqqikkudug-Weiya zone was possibly caused by the second tectonic event, i. e. , late Paleozoic collision between the northern Tarim block and the southern Siberia block. Late Paleozoic granitic magmatism and superimposed structures overprinted this Early Paleozoic deformed belt. Studied results of geometry and kinematics suggest that the original framework of the Central-Southern Tianshan belts, at least the eastern part of the Tianshan belts, was built by these two phases of accretionary events.