对雅鲁藏布江缝合带嘎学组和泽当组的新认识

New recognition of Gaxue Formation and Zedang Formation in Yalu Tsangpo Suture Zone

在1∶5万区域地质调查的基础上,对雅鲁藏布江缝合带北带与蛇绿岩相伴产出的嘎学组和泽当组进行了综合研究,并就其岩石地球化学参数及构造环境与蛇绿岩进行了对比。结合相关古生物及同位素年龄资料,初步认为嘎学组和泽当组火山岩与蛇绿岩是不同时代、不同成因类型的产物,嘎学组和泽当组形成于晚侏罗世—早白垩世与洋内俯冲相关的洋内弧构造环境,为洋板块地层序列的前弧玄武岩类(FAB型);在后期俯冲碰撞过程中,嘎学组和泽当组主体被改造成混杂岩,或呈断夹片(块)状残存于混杂岩带中,表现为俯冲增生杂岩带的构造组合样式。该认识对合理恢复并建立雅鲁藏布江缝合带北带洋板块地层序列具有重要的地质构造意义。

On the basis of the 1∶50000 regional geological survey,the authors comprehensively studied Gaxue Formation and Zedang Formation in North Yalu Tsangpo Suture Zone,and compared their petrogeochemical parameters and tectonic environment with ophiolite.Combined with paleontological and high-precision isotope dating analysis,it is preliminarily considered that Gaxue Formation,Zedang Formation and ophiolite are products of different genetic types.Gaxue Formation and Zedang Formation were formed in the intra-oceanic arc tectonic environment from late Jurassic to early Cretaceous,and belonged to the front arc basalt(FAB type)which was the standard oceanic plate stratigraphic sequence.In the late subduction and collision process,the main body of Gaxue Formation and Zedang Formation was transformed into melange or existed in the melange belt in the form of a broken clip(block),mainly as the structure styles in subduction and accretionary complex zones.This understanding is of great geological tectonic significance for the rational restoration and establishment of the northern belt oceanic plate stratigraphic sequence of Yalu Tsangpo Suture Zone.