西藏雅鲁藏布江一带中生代沉积盆地的演化

经过研究证实,在雅鲁藏布江蛇绿岩的南北两侧,有两套形成于雅鲁藏布江洋底盆地的沉积组合,它们不但形成于不同时代,而且属于不同构造环境下的产物。时代属于晚侏罗世到早白垩世的南侧沉积组合为放射虫硅质岩-层状玄武岩,其沉积特征类似于太平洋洋隆类型,反映了它可能是属于西藏特提斯快速扩张的产物。根据最近所发现的圆笠虫化石确定北侧一套的时代属于中白垩世,它是蛇绿质碎屑岩-枕状玄武岩组合,反映了一种类似于大西洋洋脊类型的、慢速扩张的板块构造环境。它是正常沉积接触关系覆于雅鲁藏布江蛇绿岩套之上。雅鲁藏布江蛇绿岩套是这个时期形成的洋壳的残留体。在晚白垩世时,雅鲁藏布江蛇绿岩被捕获在北部的冈底斯山弧前并且变为冈底斯南缘弧前盆地的基底。随后日喀则群浊积岩在其上堆积。

EVOLUTION OF THE MESOZOIC BASIN ALONG THE YALUNG ZANGBO RIVER, TIBET

It is confirmed that on the both sides of the Yalung Zangbo ophiolite suite two distinguished oceanicbasin sedimentary associations exist. On the south side, the sedimentary association consists of Late Jurassic-Early Cretaceous radiolarites-layered basalts, which resembles the Pacific Rise type and is believed to be theporducts of the rapid-spreading stage of the Tibetan Tethys. On the north side, according to the Orbitolinafossils found recently a Mid-Cretaceous age was established. The sedimentary association consists of ophiol-iti? elastics-pillow basalts and reflects a slow-spreading tectonic setting resembling the Atlatic Ridge type.The Yalung Zangbo ophiolite suite presently observed represents the remnants of the Mid-Cretaceous oceancrust, In Late Cretaceous, the Yalung Zangbo ophiolites were traped at the Gangdise front ar? and turnedinto the basement of the southern Gangdise forearc basin.