东天山南北两侧早二叠世沉积演化的差异性对比

Correlation of the Early Permian sedimentary evolution between north side and south side of East Tianshan Mountains

在前人研究成果和野外地质调查的基础上,系统研究了东天山南北两侧(准噶尔东缘和吐哈北缘)早二叠世沉积序列、岩相组合、古流向及盆地演化。研究表明,早二叠世准噶尔盆地东缘石人子沟组和塔什库拉组发育枕状玄武岩、流纹岩等双峰式火山岩建造和海相砂、泥质及碳酸盐岩复理石相沉积,并含有大量的海相生物化石,指示了海相裂谷盆地环境。吐哈北缘发育依尔希土组,以安山岩、流纹质火山岩及火山碎屑岩夹陆相碎屑岩为主,表现为陆相裂谷盆地环境。东天山南北两侧古流向及物源显示,东天山北侧,早二叠世古水流指向东南方向,在其南侧古水流指向西北部凹陷区,并且物源主要来自下伏前二叠纪岩石建造,表明早二叠世时期东天山博格达地区为汇水沉积区,且由东至西分别发育陆相和海相裂谷盆地,至早二叠世末期整体演化为陆相坳陷盆地。而导致东天山南北两侧早二叠世沉积环境迥异的原因是,石炭纪博格达裂谷东段祁家沟-天池地区和西段吐哈北缘地区演化的差异,造成随后的闭合阶段中东段早闭合、沉积环境"突变",西段晚闭合和沉积环境"渐变"的不同过程。

Based on the previous study and new geological data, the authors made a comparative study of sedimentary sequences, lithofacies and paleocurrents of the Early Permian period on the south side and north side of East Tianshan Mountains and discussed the possible evolution of the basins. The Early Permian Shirenzigou Formation and Tashenkula Formation, developed on the north side of East Tianshan Mountains, were mainly composed of pillow basalt, rhyolite, carbonate flysch deposits, siltstone with marine fos- sils, etc. and suggested a marine rift basin, The Taoxigou Group and Yierxitu Formation on the south side of East Tianshan Mountains contain andesite, rhyolite and pyroclastic rocks interbedded with non-marine clastic rocks, implies a continental（non-marine） rift basin. Provenance analysis shows that paleocurrents in SE direction existed in the north of East Tianshan Mountains. On the contrary, paleocurrents in the south showed a northwest direction and provenances were from the underlying Pre-Pernlian lithological associa-tions. It is suggested that the Bogeda area was a depositional center in East Tianshan Mountains in the Early Permian period and ma- rine rifts were located in the north of East Tianshan Mountains and non-marine rifts were dominantly in the south. However, they were integrated into a large non-marine basin in late Early Permian. Researches indicate that the difference in sedimentary environ- ment between the north side and south side of East Tianshan Mountains was mainly caused by different evolution processes in the east and west of Bogeda rift in the Carboniferous period.