西藏班公湖-怒江缝合带——深部地球物理结构给出的启示  

Bangong Co-Nujiang suture zone, Tibet-a suggestion given by deep geophysical structure

作　　者：赵文津[1] 刘葵[2] 蒋忠惕[1] 吴珍汉[2] 赵逊[1] 史大年[3] 熊嘉育[1] J.Mechie L.Brown T.Hearn J.R.Guo Seth S.Haines 

机构地区：[1]中国地质科学院 [2]中国地质科学院地质力学研究所 [3]中国地质科学院矿产资源研究所 [4]GeoForschungs Zentrum Potsdam,Potsdam,Germany [5]Department of Geological Sciences [6]Department of Physics,New Mexico University,Las Cruces,NM88003,USA [7]Department of Geological Sciences,Cornell University,Ithaca,NY,USA [8]Department of Geophysics,Stanford University,Stanford,California,USA

出　　处：《地质通报》2004年第7期623-635,共13页Geological Bulletin of China

基　　金：国土资源部(9501207);科技部(97924);美国国家科学基金会(grantEAR9614616);德国研究协会;德国地学研究中心资助

摘　　要：通过跨越缝合带的综合地球物理和地质调查研究,查明了地质上推测的“班公湖-怒江缝合带”的深部结构和构造,提出了下述观点现有资料尚不足以证明,“班公湖-怒江缝合带”是严格意义上的缝合带,而趋向表明是一个老的弧后拉张区,在后来的印度大陆与拉萨地块碰撞挤压过程中,先是沉积了巨厚的第三纪地层,仅在20Ma(?)以来才转变成挤压体制,形成多条逆冲断裂;纳木错-申扎逆冲的蛇绿岩片带代表着侏罗纪洋的主要缝合带位置,在其闭合过程中洋壳与陆壳一起向北发生俯冲,并形成班戈岩带所代表的岩浆弧,在岩浆弧后出现了拉张区;下地壳向北挤压增厚,物理性质不同的上、下地壳之间相互运动而形成了一条缓倾的剪切片理化带,南北长达300km,命名为主羌塘逆冲断裂带(MQT);并使班戈岩片整体向南逆推上去,致使地壳分层增厚;在拉张期伦坡拉小地块向下运动,20Ma以后转变成压缩体制后又开始向上逆推,再加上后期的剥蚀,致使班戈深成岩体出露于地表;唐古拉山、各拉丹冬等年轻的火山岩浆带与地表显示的构造活动无直接关系,推测应是地壳深层作用引起的构造岩浆活动的显示。By an integrated geophysical and geological survey carried out across the Bangong Co-Nujiang suture zone, Tibet, the deep structure of the geologically inferred 'Bangong Co-Nujiang suture zone' has been ascertained, and the following views are put forward: the inferred 'Bangong Co-Nujiang suture zone' is not a suture zone but an old back-arc extensive area, where during the later collision-compression of the Indian continent and Lhasa block very thick Tertiary strata were deposited and a compressional regime and several thrusts were not formed till 20 Ma BP (?). The Nam Co-Xainza ophiolite slab represents the location of the main suture zone of the Jurassic Ocean. During its closing the oceanic crust and continental crust were subducted together northward, forming a magmatic arc represented by the Bangkog rock belt an extensional area at the rear of the magma arc. The northward compression and thickening of the lower crust brought about mutual movement between the upper crust and lower crust of different physical properties, thus forming a shear schistose zone, up to 300 km long from north to south, named as the Main Qiangtang thrust, and furthermore the Bangkog slab was thrust southward wholesale, resulting in crustal stratification and thickening. During the extensional state the small Lunpola block moved downward and again began to be thrust upward after the transformation into the compressional regime at 20 Ma BP. The subsequent erosion exposed the Bangkog pluton. The younger volcanic-magmatic belts such as the Tanggula Mountains and Gêladaindong Mountain have no direct relation with the tectonic activities shown at the surface; it is inferred that they should be manifestations of tectonomagmatic activities caused by deep crustal processes.

关 键 词：西藏 班公湖-怒江缝合带 纳木错-申扎缝合带 主羌塘逆冲断裂带(MQT) 深部热通道 

分 类 号：P542.4[天文地球—构造地质学] P631[天文地球—地质学]