摘要:
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,该盆地充填较完整晚新生代沉积序列记录着该区构造变形历史,因此对该盆地沉积记录的研究对探讨青藏高原东北缘晚新生代构造活动事件具有重要的意义。通过对天水盆地晚新生代砂岩和含砾砂岩地层中碎屑颗粒磷灰石裂变径迹热年代学研究,推断23.7Ma左右天水盆地北部沉积物源区西秦岭发生了一次与青藏高原隆升有关的构造—热事件,该事件可能导致天水盆地的形成,并开始接受新近系冲积相沉积。约14.1Ma左右天水盆地物源区再次发生构造活动,使西秦岭剥露速率加快和盆地进一步拗陷广泛接受河湖相沉积。通过对剥蚀速率的估算,得出天水盆地沉积记录的23.7Ma和14.1Ma西秦岭北部快速抬升事件的平均剥蚀速率分别达0.34mm/a和1.05mm/a。
Abstract:
An important key site in Tianshui Basin which locates between Liupan mountain and west Qinling, northeast margin of Tibetan Plateau exposed a conformable Cenozoic sedimentary sequence that recorded the exhumation history of this area. So, studying these sediments is very important to reveal the tectonic-heating history of this area. Detrital apatite grain thermochronology was used to examine samples of sandstone and conglomerate, sampled from Yaodian section, Tianshui Basin. With other evidences, we infered two tectonic-heating events occurred at the source regions of the Tianshui Basin. One event, the tectonic uplift of west Qinling, occurred at about 23.7Ma and had the relationship with the Tibetan plateau uplift, which resulted in the formation of Tianshui Basin and to start alluvial deposits in Tianshui Basin. Another tectonic event occured at about 14.1Ma, which made Tianshui Basin was depressed again and came into being broad fluvio-lacustrine deposits. The source region uplifted and were eroded rapidly because of the events. The rough mean exhumation rates were 0.34mm/a and 1.05mm/a ,respectively.
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