滇西北金沙江结合带上古生界特征及其古特提斯演化意义

THE UPPER PALEOZOIC IN THE JINSHA RIVER JUNCTION ZONE,NORTHWEST YUNNAN AND IMPLICATIONS FOR THE PALEO-TETHYS EVOLUTION

金沙江结合带的上古生界已发生中浅构造相的强烈变形和低绿片岩相的区域低温动力变质,不同时代、不同位态、不同沉积环境的地层均呈构造岩片状无序堆叠。为提高金沙江结合带上古生界岩石地层、年代地层、生物地层的研究程度,本文从划分构造岩片入手,在各构造岩片中进行岩石地层的划分与对比,将该套地层划分为冉家湾组(D_(1)r)、迪公组(D_(2)d)、柯那组(Dk)、申洛拱组(C_(1)?)、响姑组(CPxg)、喀大崩组(P_(2)k)、奔子栏组(P_(3)b)。在此基础上,分别对各个岩石地层单位的岩石地层、生物地层、年代地层进行研究,最终达到进行时空多重分解、综合复原之目的。金沙江结合带的上古生界划分的7个组,形成于金沙江小洋盆裂解→出现洋盆→裂陷加剧→一度抬升→再次裂解→转向收缩共6个阶段,分别形成于滨海、浅海陆棚、碳酸盐台地、大陆斜坡、洋岛-海山、深海盆地共6种沉积环境。研究金沙江结合带的岩石地层、生物地层、年代地层特征,有助于从沉积作用的角度查明金沙江古特提斯洋的形成与演化特点。

The Upper Paleozoic in the Jinsha River Junction Zone had a strong deformation caused by medium-shallow tectonic activities and a metamorphism of low green schist facies caused by regional low temperature dynamics.The stratigraphic system in this region is very complex and therefore,it is difficult to clarify sequences in each tectonic slice.A detailed study on lithostratigraphy,biostratigraphy,and chronostratigraphy of the Upper Paleozoic in the Jinsha River Junction Zone was carried out based on lithostratigraphic division and biostratigraphic correlation among tectonic slices in this region.The Upper Paleozoic is here composed of seven formations,in ascending order,the Ranjiawan Formation(D_(1)r),the Digong Formation(D_(2)d),the Kona Formation(Dk),the Shenluogong Formation(C_(1)?),the Xianggu Formation(CPxg),the Kadaban Formation(P_(2)k),and the Benzilan Formation(P_(3)b).The lithostratigraphic system and biostratigraphic succession have been newly established to obtain a chronostratigraphic scheme in this region.Thus,a tectonic evolution,which is possibly a part of the Paleo-Tethys,can be established based on a newly established sequence of these seven formations,which can be recognized into six evolutional stages,the splitting to form small oceanic basins,the oceanic basin,the rifting,the temporay uplifting,the second splitting,and the final contraction and closed.These six stages are corresponding to six sedimentary settings,including the coastal,shallow-shelf,carbonate platform,continental slope,ocean island-seamount,and abyssal basin settings.The establishing of the Upper Paleozoic lithostratigraphic,biostratigraphic,and chronostratigraphic sequences in the Jinsha River Junction Zone can provide a comprehensive understanding for the formation and evolution of the Jinsha River Paleo-Tethys Ocean.