内蒙古林西-乌兰浩特地区二叠系极低级变质作用与生烃潜力

Permian very low-grade metamorphism and its potential for hydrocarbon generation in the Linxi-Wulanhaote Area, Inner Mongolia, China

极低级变质作用对年轻造山带构造演化和油气勘探有重要意义,近年来成为地质学家探讨的热点领域。文章以中国东北地区南缘石炭-二叠系为研究对象,探讨了其极低级变质作用的特征。通过对兴蒙造山带东段林西-乌兰浩特地区二叠纪地层的伊利石结晶度、b0值和多型等参数进行测试分析发现,伊利石结晶度Kübler指数在0.175~0.47之间,大多数集中于0.25~0.35,平均值为0.30;样品b0值主要在9.0155~9.0316?之间,平均值为9.0249?;伊利石多型主要为2M1。以上结果表明研究区二叠系林西组和哲斯组主要经历了葡萄石-绿纤石相的极低级变质作用,变质温度200~370℃,压力为中压,同时表明其具有较高的生烃潜力。结合二叠系生烃期研究和区内广泛发育的白垩纪侵入体推测,二叠系极低级变质作用可能发生在早白垩世,且与岩体侵入导致的地温梯度升高有关。

The very low-grade metamorphism has been the focus of research in recent years and has great significance for the study of structural evolution of young orogenic belt and petroleum exploration. The recent studies revealed that the Carboniferous Permian strata in the northeastern part of China mainly underwent very low-grade metamorphism and gradually became a new petroleum exploration layer. This paper launched studies on the illite crystallinity,illite polytype and illite b0 dimension of the Permian System in the Linxi-Wulanhaote Area. The illite crystallinity ranges from 0. 175 to 0. 47,mainly clustering between 0. 25 and 0. 35 with an average of 0. 30. Illite b0 ranges from 9. 0155 to 9. 0316 ?,with an average of 9. 0249 ?. Illite polytype is predominantly 2 M1. Based on the above data,the Permian System in the study area mainly experienced the prehnite-pumpellyite facies very low-grade metamorphism under medium-pressure with metamorphic temperature at 200 ~ 370 ℃,indicating its potential for hydrocarbon generation. Together with the hydrocarbon generation history of the Permian strata and the widespread Cretaceous granites in the study area, the very low-grade metamorphism might occurred during the earlyCretaceous,related to the increase of geothermal gradient caused by the intrusion of granite.