新疆祁曼塔格地区发现新元古代叠层石

Discovery of Neoproterozoic stromatolites in Qimantag area, Xinjiang Uygur Autonomous Region

在新疆若羌县祁曼塔格地区的水泉子沟附近原蓟县系狼牙山组中首次发现了瘤状通古斯叠层石相似形Tungussia cf.nodosa Semikhatov和有疑问的撕裂贝加尔叠层石Baicalia lacera Semikhatov。它们多呈瘤状、柱状,其总体形态特征可与安徽淮山、辽东地区新元古代地层中分布的Tungussia cf.和Baicalia叠层石以及东昆仑加嗡门地区某些叠层石的特征相类比,相当于华北地区叠层石组合Ⅳ。测得叠层石的寄主岩石全岩Sm-Nd同位素等时线年龄为815±26 Ma。根据该Sm-Nd等时线年龄和叠层石的主要特征以及其它地区相关叠层石的特征综合判断,狼牙山组的地质时代应当归属于新元古代青白口纪,是被动大陆边缘的产物;这个前寒武纪微陆块应由塔里木克拉通(?)解体而来,是Rodinia超大陆的组成部分。本区叠层石的发现及其寄主岩的定年结果,为探讨东昆仑西段的大地构造演化和成岩环境提供了新证据。

Stromatolites of Tungussia cf. nodosa Semikhatov and Baikalia lacera semikhatov were discovered for the first time in the Langyashan Formation of the original Jixian System near Shuiquanzigou, Qimantag area, Ruoqiang County, Xinjiang. The stromatolites are mostly nodular and columnar, and their overall morphological characteristics can be compared with the characteristics of Tungussia cf. and Baicalia stromatolites distributed in Neoproterozoic strata in Huaishan, Anhui and Eastern Liaoning, and some stromatolites in Jiawengmen area of East Kunlun, which is equivalent to stromatolite assemblage IV in North China. Through our work, Sm-Nd whole-rock isotopic isochron age of 815±26 Ma from the host rock of stromatolites is obtained. According to the Sm-Nd isochron age, the main characteristics of stromatolites in study area and other areas, the geological time of Langyashan Formation in Qimantag area should belong to the Neoproterozoic Qingbaikouan Period. Their host rock should expose in passive margin of a Precambrian micro-continent block disintegrated from Tarim Craton(?), which was probably assigned to Rodinian Super-Continent. The discovery of the stromatolites and dating results of the host rock provide new evidence for the tectonic evolution and diagenetic environment in western segment of the East Kunlun Mountains.