西藏康托地区早—中侏罗世木嘎岗日群沉积盆地分析及构造演化研究

Sedimentary Basin Analysis and Tectonic Evolution of the Early-Middle Jurassic Mugagangri Group in Kangtuo Area,Tibet

沿班公湖—怒江结合带中西段出露的早—中侏罗世木嘎岗日群,自创名以来,其代表的年代地层各异,岩石组合宏观上较固定,内部为总体无序局部有序的一套组成成分复杂的构造混杂地层体。通过对木嘎岗日群沉积组合、盆内沉积层序、岩石地球化学、岩相、物源区、碎屑模型、盆地分类及其构造演化分析,将沉积盆地视作一个整体进行地球动力学综合研究。康托地区中特提斯洋盆早—中侏罗世为深海—次深海沉积环境,属被动大陆边缘型弧前深水盆地复理石碎屑沉积组合。沉积构造演化可分为2个阶段:盆地扩张阶段和盆地双向俯冲阶段,包含3个活动期:扩张期、向南俯冲期与双向俯冲期,并将该地区木嘎岗日群地层划分为3个岩性组。

The early-middle Jurassic Mugagangri Group widespread in the middle-western section of the Bangong- co-Nujinag junction zone, the rock association seems like accordance from a macroscopic perspective. However, the chronostratigraphy is inconsistent in different areas since the establishment of Mugagangri Group ; it is a tecton- ic melange with disorder sequence and complex composition. Taking the sedimentary basins as a whole, and ac- cording to features of sedimentary assemblage, sedimentary sequence, rock geochemistry, fithofacies, prove- nance, detrital model, basin classification, and tectonic evolution about the Mugagangri Group, the geodynamic background had been studied. We proposed that the early-middle Jurassic sedimentary environment of Kangtuo ar- ea corresponded to abyssal-bathyal facies of meso Tethys ocean basin; it was a suit of flysch clastic deposits of deepwater in fore-arc basin of passive continental margin. The tectonic evolution was divided into basin spreading period （basin spreading stage）, and basin subduction period （southward subduction stage, bilateral subduction stage）, and the Mugagangri Group can be divided into three lithology groups.