青藏高原东北缘烟筒山构造带二叠系红泉组沉积时代及物源示踪

    Sedimentary age and provenance tracing of the Permian Hongquan Formation in the Yantongshan structural belt on the northeastern margin of the Qinghai-Tibet Plateau

    • 摘要: 青藏高原东北缘烟筒山构造带局部零星出露二叠系红泉组,由于尚未发现古生物化石,该套地层仍缺乏精确的年代学约束。同时,该地区地处北祁连地块、阿拉善地块与鄂尔多斯地块的过渡带,二叠纪沉积物源究竟来自于北东方向的鄂尔多斯地块,还是北部的阿拉善地块,或是西南部的北祁连地块,由于露头的局限性,也一直缺乏系统的沉积学方面证据的支持。以二叠系红泉组底部的凝灰质长石砂岩为研究对象,在碎屑岩锆石U-Pb同位素测年基础上,对该套地层的沉积时代及物源进行了重新厘定。研究认为,二叠系红泉组底部凝灰质长石砂岩碎屑锆石年龄序列主要包括264 Ma、1811 Ma、1928 Ma、2348 Ma、2465 Ma五个峰值,其中264 Ma年龄峰值的锆石为同期火山喷发凝灰质火山灰的产物,代表了该套地层沉积的起始时代,因此红泉组的沉积时代应该归属于中二叠世末—晚二叠世;其碎屑锆石的年龄峰值序列与华北克拉通西部北缘基底隆起带特征较一致,而与阿拉善地块及北祁连地块的年龄峰值序列相差较远,其沉积物源应该与鄂尔多斯地块二叠纪一致,主要来自于北东方向的华北克拉通西部北缘基底隆起带。该研究成果首次厘定了青藏高原东北缘弧形构造带二叠系红泉组的沉积时代,其物源方向的确定为区域岩相古地理的恢复提供了基础地质依据。

       

      Abstract: Restricted by the absence of reliable fossils, the sedimentary age of the Permian Hongquan Formation which was sporadically exposed in the Yantongshan Fault Belt at the northeastern margin of the Tibetan Plateau has always been under dispute.Besides, due to the lack of reliable sedimentary structures in the Permian Hongquan Formation and outcrops, whether the sediments were sourced from the Ordos Block in the northeast, Alxa Block in the north or Northern Qilian Block in the west is undefined.The sedimentary age and provenance of tuffaceous feldspar sandstone at the bottom of the Permian Hongquan Formation were redefined based on zircon U-Pb dating.The results show that the age spectra of the detrital zircons from the taffaceous feldspathic sandstone yields five age peaks at 264 Ma, 1811 Ma, 1928 Ma, 2348 Ma, and 2465 Ma, among which the zircons with the age of 264 Ma mostly come from tephra deposited during the early stage of the Hongquan Period.Therefore, the sedimentary age of the Hongquan Formation is 264 Ma which can be attributed to the late stage of the Middle Permian to Late Permian.The age spectra of the detrital zircons from the Hongquan Formation have similarity with the age spectra of the basement of the western part of the North China Craton, and significant difference with the age spectra of the basement of the Alxa Block and North Qilian Block.Consequently, it is inferred that the sedimentary materials of the Permian Hongquan Formation should come from the Ordos Block in the northeast.This research not only redefines the sedimentary age of the Hongquan Formation in the arcuate tectonic belt at the northeastern margin of the Tibetan Plateau, but also provides solid evidence for the sedimentary source tracing for the reconstruction of the Permian regional lithofacies palaeogeography.

       

    /

    返回文章
    返回