CHARACTERISTICS OF THE TRIASSIC CLAY MINERALS IN ABA AREA,NORTHERN SICHUAN,AND ITS GEOLOGICAL IMPLICATIONS
Liu Weixin1, Wang Yanbin2, Qin Jianzhong1
1. Wuxi Research Institute of Experimental Geology, China Petroleum & Chemical Corporation, Wuxi, Jiangsu 214151; 2. School of Resources and Security, China University of Mining and Technology, Beijing 100083
The Triassic is extensively distributed in Aba area,northern Sichuan,where is located in the eastern part of the Qinghai-Xizang Plateau.The Triassic diagenesis and diagenesis evolution stages were critical for oil and gas exploration in the region.Based on analyses of the clay mineralogy,diagenetic-metamorphic mineral assemblages,illite crystallinity and vitrinite reflectance(Ro),with the indicatrixes comprehensively discussed for discriminating diagenesis and very low-grade metamorphism,different diagenesis stages were recognized,and the main conclusions were as follows.The Triassic at central part near Tangke was still at later diagenetic stage with diagenetic temperature being 200～212 ℃,illite crystallinity(IC)≥0.42(Δ2θ);The Triassic in the periphery areas was at very low-grade metamorphic stage with diagenetic temperature being 212～222 ℃,illite crystallinity(IC)<0.42(Δ2θ).The vitrinite reflectance(Ro) had same evolutional characters.The boundaries between different diagenetic stages were proposed.The differential diagenesis and its evolution in the northern Sichuan area could be reasonably explained by long-range effect of tectonism.The structural movement exerted lesser effect at the central part and stronger effect on the periphery of Aba area,so that the very low-grade metamorphism occurred only along the marginal areas.