东昆仑地区万保沟群的解体及早寒武世地层的新发现

Disintegration of the Wanbaogou Group and discovery of Early Cambrian strata in the East Kunlun area

通过1∶5万区调工作,初步查明原万保沟群4个组间均以断层(韧性剪切带)为界面,在空间上呈条带状构造岩片态势展布。经填图发现该群实际上仅由火山岩组和碳酸盐岩组构成。并在火山岩组和碳酸盐岩组中分别获得了(1441±230)MaSm-Nd全岩等时线年龄和叠层石化石,确定其时代为中—新元古代;在地质填图中发现该群原上、下碎屑岩组属同物异名现象,笔者及前人获得了早寒武世微古植物化石及小壳动物群化石。据此,对原万保沟群进行了解体,解体后的万保沟群仅由火山岩组和碳酸盐岩组构成,重新厘定为万保沟群,并在群内新建两个正式组级构造地(岩)层单位,即温泉沟组和青办食宿站组。而将原上、下碎屑岩组依据古生物化石、岩石组合特征,重新厘定其时代为早寒武世,并新建立沙松乌拉组。

Through1 ∶ 50000regional geological survey,the authors have preliminarily ascertained t hat all the four rock associations in the original Wanbaogou Group are bounded b y faults or ductile shear zones and distributed as banded tectonic slices.Mappin g has found that the group actually consists merely of volcanic rock association s and carbonate rock associations,in which a Sm-Nd isochron age of1441 ± 230Ma and some stromatolites have been obtainsed.So the two rock association s are determined to be of Meso-to Neoproterozoic age.During recon-naissance mapping,the authors found that the original upper and lower clasti c rock associations of this group are synonymous,from which predecessors and the authors had found Early Cambrian microfossil plants and small-shelly fossils.On that basis,the original Wanbaogou Group is disintegrated.The disintegrated Wanb aogou Group is only composed of the volcanic rock association and carbonate rock association and renamed the Wanbaogou Group-complex,in which two formal formati on-rank tectono-stratigraphic units are established,i.e.the Wen-quangou Formation-complex and the Qingbanshisuzhan Formation-complex.On the basis of the fossils and rock associations,the age of the original upper and low er clastic rock associations are revised and identified to be Early Cambrian and a new formation,the Salawula Formation,is established.