东昆仑东段下三叠统洪水川组砾岩源区研究:来自砾岩特征及锆石U-Pb年龄的证据

东昆仑东段下三叠统洪水川组主要分布于东昆南断裂带和东昆中断裂带之间的红水川—托索河一带。笔者分别对出露于宝日禾日俄地区和可可沙地区洪水川组底部层位砾岩的砾石成分、磨圆度和粒度进行综合统计对比分析。结果显示:可可沙地区砾石成分主要为灰岩和变质岩,宝日禾日俄地区砾石成分主要为花岗岩和变质岩。从宝日禾日俄地区花岗岩砾石中获得的LA-ICP-Ma锆石U-Pb年龄为(464.9±9.3)Ma(MSWD=2.9)。砾石特征表明可可沙地区物源来自可可沙地区下伏地层哈拉郭勒组,而宝日禾日俄地区物源主要为早古生代岩浆岩,表明洪水川组底部层位物源主要为加里东期弧岩浆岩,而晚滇西—印支期弧岩浆岩并未提供沉积物质。结合前人资料认为,布青山—阿尼玛卿古特提斯洋于晚二叠世开始向北俯冲,洪水川组为一套弧前盆地的沉积产物,早三叠世早期布青山—阿尼玛卿古特提斯洋处于向北俯冲初始阶段。

Conglomerate source and source area property of Lower Triassic Hongshuichuan Formation in the East Kunlun Mountains: Evidence from conglomerate characteristics and U-Pb dating

The lower Hongshuichuan Formation is mainly distributed around Tuosuo River between Middle Kunlun orogen and South Kunlun orogen in eastern Kunlun Mountains. In this paper, the authors made a comparative study of the conglomerate of Lower Hongshuichuan Formation distributed in Baoriherie area and Kekesha area in components, psephicity and granularity of gravel. The results show that the main components of the gravel are limestone and metamorphic rock in Kekesha area. The main components of gravel in Baoriherie area are granite and metamorphic rock. LA-ICP-MS zircon U-Pb dating of granite yielded magmatic crystallization age of(464.9 ±9.3) Ma(MSWD=2.9) from Baoriherie area. The characteristics of gravel show that the source of the Kekesha area is Halaguole Formation in Qingshuiquan area, whereas the source of the Baoriherie area is Caledonian magmatic rock. These data indicate that the source of Lower Hongshuichuan Formation is Caledonian magmatic rock rather than arc granite of late Hercynian-Indosinian period. Combined with previous data, the authors hold that the Buqingshan-A''nimaqing Ocean began the northward subduction in late Permian, and the Hongshuichuan Formation was a set of sedimentary products in the fore-arc basin. It is held that Buqingshan-A''nimaqing Ocean began its subduction in early Triassic.