库车盆地白垩系碎屑白云母物源区示踪与构造意义

沉积盆地碎屑岩记录了相邻造山带构造演化及隆升剥蚀的重要信息。本文对库车盆地白垩系砂岩中的白云母进行了电子探针及~(40)Ar/~(39)Ar定年分析,并与天山造山带的数据对比研究表明:库车盆地白垩系砂岩中白云母为多硅白云母,硅原子数小于西南天山蓝片岩及榴辉岩中的多硅白云母,形成时的压力低于目前保留在西南天山蓝片岩中多硅白云母;白垩系砂岩多硅白云母~(40)Ar/~(39)Ar年龄为396.6 Ma,与在低温高压变质带中获得的多硅白云母~(40)Ar/~(39)Ar年龄419~310Ma一致,表明了在白垩纪西南天山低温高压变质岩带已抬升至地表遭受剥蚀,为库车盆地提供大量的物质,也表明了在白垩纪西南天山低温高压变质岩带高度(海拔)高于其南部的哈尔克山,而现今天山地貌形态显示低温高压变质岩海拔低于哈尔克山,这可能是由于新生代天山地区差异隆升剥蚀引起的。

Provenance Tracing of Cretaceous Detrital Muscovite in the Kuqa Basin and Its Tectonic Significance

The clastic rocks in sedimentary basins recorded the information of its adjacent mountain uplifting and tectonic evolution. In this paper the detrital Muscovites from Cretaceous sandstone in the Kuqa basin were analysed by electron microprobe and 40Ar/39Ar dating. A systematic comparison of the geochemical compositions and 40Ar/39Ar ages of Muscovite between Cretaceous sandstone in the Kuqa basin and metamorphic rocks in Tianshan orogen, indicated that Muscovites from Cretaceous sandstone are phengites. The phengites from Cretaceous sandstone has less Si content than them from blueschist and eclogite in southwestern Tianshan, which suggested the pressures in detrital phengites were lower than those preserved in blueschist and eclogite of the present Tianshan. The 40Ar/39Ar phengite age of 396.6 Ma from Cretaceous sandstone is consistent with the ages of 419-310 Ma from the high pressure-low temperature rocks in southwestern Tianshan, which indicated during Cretaceous the high pressure-low temperature rocks had been exhumed at surface and served as the provenance for Kuqa basin. It has been concluded that during Cretaceous the high pressure-low temperature rocks were higher in elevation than the Haerke Mountain which located between the Kuqa basin and the high pressure-low temperature rocks, however, the present geomorphology of the Tianshan indicated that the high pressure-low temperature rocks had lower elevation compared with the Haerke Mountain, which was more likely caused by differential uplift and exhumation of Tianshan in Cenozoic.