Chemical compositions of detrital feldspars and micas within the Late Triassic and Early Jurassic sequences of northern Kuqa basin, Xinjiang and their implications to provenance tectonics
新疆库车盆地晚三叠世-早侏罗世沉积碎屑矿物成分及其物源区示踪与构造意义

Synkinematic sedimentation analysis is one of the effective approaches to understand the tectonic unroofing process of their provenances and the interrelations of the mountains and related adjacent basins. Sandstone framework analyses have been employed together with the investigations of selected detrital heavy minerals and special minerals such as phengites in previous research to study the interrelationships between Tianshan Mountains and Kuqa basin during Late Mesozoic and Cenozoic. It remains controversial at present that the tectonic uplift and exhumation process of paleo Tianshan Mountains and its contributions to the sedimentation of Kuqa basin in early Mesozoic. 38 detrital feldspars and 26 micas were separated from 15 sandstone samples collected from middle segment of northern part of Kuqa basin for microprobe analysis in order to explore the clues regarding to the provenance features. Chemical compositions of feldspars suggest that they derived dominantly from a provenance mainly composed of metamorphic rocks. 25 micas are phengites and imply that their provenance rocks experienced high-pressure metamorphism. The high-pressure metamorphic belt composed of blue schists and eclogite developed within the Tianshan orogenic belt probably serve as the provenance. The volume of Si within the detrital phengites of this study are lower than those of phengite preserved in blue schists and eclogites in current Tianshan Mountains, which suggest a normal exhumation process of the high-pressure metamorphic belts. This research reveals that at least as early as in Late Triassic and Early Jurassic the high-pressure metamorphic belt have been exhumed at surface and served as the provenance for Kuqa basin instead of the Late Mesozoic. It deserves further study to clarify that the high-pressure belt is Early Paleozoic one in southern Middle Tianshan or the Late Paleozoic one in southern Tianshan Mountains.