东昆仑阿尼玛卿地区古特提斯火山作用和板块构造体系

The paleo-Tethyan volcanism and plate tectonic regime in the A'nyemaqen region of East Kunlun, northern Tibet Plateau

东昆仑阿尼玛卿蛇绿岩带标志古特提斯洋关闭后的板块缝合带.在该缝合带及周围识别出4套与洋盆扩张和俯冲作用有关的火山岩,由南至北,分别为洋底玄武岩、岛弧火山岩、弧后盆地玄武岩和后碰撞火山岩.板块构造体系说明洋壳俯冲极性从南向北.已有年代学证据表明:阿尼玛卿洋盆的开启时代至少可以早到晚石炭世(308Ma),洋盆关闭可能在早三叠世;岛弧火山岩的时代为晚二叠世(260 Ma);弧后盆地火山岩的时代为早-中三叠世;后碰撞火山岩的时代为晚三叠世.三叠纪沿缝合带及其北部形成了一系列巨大的左旋走滑断裂系,包括东昆仑南缘左旋走滑断裂(200～220 Ma)、阿尔金断裂的早期走滑剪切断裂系(220～230 Ma)以及南祁连南缘巨型左旋走滑断裂(240～250 Ma).认为它们形成于阿尼玛卿古特提斯洋的关闭和斜向碰撞作用,但主要在俯冲板块折返阶段或逆 冲岩片的抬升阶段,其时也是后碰撞岩浆活动和火山喷发阶段.

The A＇nyemaqen ophiolite belt marks the suture after closure of the paleo-Tethys. In this region, four types of volcanic rocks related to ocean-floor spreading and plate subduction have been recognized. They are, from south to north, oceanic floor basalt （OFB）, island arc volcanic rocks （IAV）, back arc basin lavas （BAB） and post-collision volcanic rocks （PCV）. The plate tectonic regime suggests the subduction sense from south to north. The spreading of the A＇ nyemaqen oceanic basin started at least as early as late Carboniferous （308 Ma） and the closure probably took place during early Triassic. The IAV, BAB and PCV were formed respectively in late Permian （260 Ma）, in early-middle Triassic, and in late Triassic. Several large-sized ductile sinistral strike slip fault zones, extending hundreds to thousands of kilometers along the suture or in the north, were initially formed during early to late Triassic. They include the South Margin Fault Zone of East Kunlun （200-220 Ma）, the Altyn Tagh Fault Zone （220-230 Ma）, and the North Qaidarn Fault Zone（240-250 Ma）. These strike slip faults were most likely genetically related to the oblique subduction and collision of the paleo-Tethyan ocean basin, particularly in the period of exhumation of subducted plate or uplift of the overthrust plate, a period when post-collision magmatism and volcanism were active.