天水盆地古近纪地层年代及其意义

天水盆地位于青藏高原东北缘六盘山与西秦岭二重要构造带交汇处,该盆地充填的新生代沉积序列记录着该区构造变形历史,因此研究该盆地沉积记录对探讨青藏高原东北缘新生代构造活动事件具有重要意义.通过对天水盆地古近纪砾石层砂质透镜体中碎屑颗粒磷灰石裂变径迹热年代学研究,获得样品地层的最大沉积年龄为24.8士1.5 Ma.结合前人的工作,厘定该套古近纪地层最顶部地层年龄为22～24.8 Ma,并确定天水盆地古近纪沉积物源区在24.8 Ma左右发生了构造冷却事件,推断印度板块与欧亚大陆碰撞的远程效应在古近纪末-新近纪初已传递到青藏高原的最东北缘.

Strata age of palogene sediments in Tianshui Basin and its geological significance

An important key site in Tianshui Basin, located between Liupan Mountain and western Qinling Mountains and at the northeast margin of the Tibetan Plateau exposed, a conformable cenozoic sedimentary sequence that records the exhumation history of this area. So to study these sediments is of great importan- tance in revealing the tectonic history of this region. Detrital apatite grain thermochronology was used to examine samples of conglomate at the top of the palogene sediments from in Yaodian section, Tianshui Basin, and to successfully obtain the oldest depositional age of the studied sediments, which is 24.8~1.5 Ma. With other evidences, the depositional age was determined at 22~24.8 Ma, and a tectonic cooling event occurred at about 24.8 Ma was revealed, which proves that the distant effect of Indian-Asian collision had reached the furthest distal end of NE margin of Tibetan Plateau at late Paleogene-early Neogene.