青海共和盆地东北缘中-新生代热演化史:来自沟后杂岩体及当家寺岩体的低温热年代学证据

Mesozoic-Cenozoic thermal evolutionary history of the northeastern margin of the Gonghe basin,Qinghai:Low-temperature thermal chronology evidences from the Gouhou complex and the Dangjiasi pluton

青藏高原东北部中-新生代隆升初始的时间、位置多有争议。共和盆地处于秦岭、祁连、昆仑造山带的结合部,是研究盆-山耦合、构造热演化的理想位置。新近在盆地东北部发现了异常高温的干热岩体,其热源机制和经历的热历史过程是进一步地热藏开发的关键。本文对盆地东北缘青海南山和沟后杂岩体以及盆地内瓦里贡-过马营隆起的当家寺岩体进行了系统的低温热年代学分析,以追溯该区经历的热历史。磷灰石裂变径迹和(U-Th)/He模拟结果显示,当家寺岩体和沟后杂岩体自三叠纪结晶以来,在侏罗纪-白垩纪,经历200~150Ma和135~100Ma两期快速冷却抬升,可能与羌塘地体和拉萨地体依次向北碰撞拼接在青藏高原东北部的远程效应有关。裂变径迹和(U-Th)/He模拟结果显示,沟后杂岩体记录到晚中新世(15~5Ma)的快速冷却事件,而盆地东部当家寺岩体的样品未记录到该期的快速冷却事件,可能是北倾的青海南山南缘逆冲断裂晚新生代再活动使得沟后杂岩体在新近纪晚期快速隆升造成,而当家寺岩体主要受右行走滑-逆冲的瓦里贡断裂的控制,并未发生该时期的快速冷却抬升事件。因此,青藏高原东北部差异隆升、热历史过程不仅受区域构造作用的控制,也明显受不同时期的活动断裂及古地貌的影响。共和盆地东北缘露头岩体热历史过程未见到明显的中新世以来的增热现象,与共和盆地内干热岩存在的增热特征不同。

The timing and location of the initial uplift of the northeastern Tibetan Plateau are debated.The Gonghe basin is located within the interjection of the Qinling,Qilian,and Kunlun orogenic belts,and is an ideal area for studying basin-mountain coupling process and tectono-thermal evolution.Anomalously high temperature hot dry rock(HDR)has been newly discovered in the northeastern part of the basin.Their heat source mechanisms and the thermal history processes they underwent are important for the further development of geothermal resources.We conducted systematic low-temperature thermochronological analysis of field outcrop samples from the Qinghai-Nan Shan and Gouhou complex on the northeastern margin of the basin and from the south and north of the Dangjiasi pluton on the Waligong-Guomaying uplift in the basin to understand the thermal history process in the area.The results of apatite fission track and(U-Th)/He simulations show that the Dangjiasi pluton and the Gouhou complex had experienced two phases(200~150Ma and 135~100Ma)rapid cooling and dramatic uplifting during the Jurassic-Cretaceous since they have crystallized in the Triassic,which may be related to the remote effect of the sequential northward collision and splicing of the Qiangtang and Lhasa terrane in the northeastern Tibetan Plateau.The apatite fission track and(U-Th)/He simulations also show that the Gouhou complex recorded a rapid cooling event in the Late Miocene(15~5Ma),while the samples from the Dangjiasi pluton in the eastern part of the basin did not record a rapid cooling event in the Neogene.This may be caused by the rapid uplift of the Gouhou complex in the Late Neogene due to the Late Cenozoic reactivation of the north-dipping South Qinghai Nan Shan Fault,while the Dangjiasi pluton in the eastern part of the basin was mainly controlled by the dextral strike-slip Waligong fault and did not undergo cooling and uplifting events in this period.Therefore,the differential uplifting and thermal history processes in the northeastern Tibetan Plateau are not only controlled by regional tectonics,but also obviously influenced by active faults and paleo-geomorphologies in different periods.The thermal history of the outcrop samples in the northeastern margin of the Gonghe basin haven’t shown obviously heating process since the Miocene,which is different from the warming characteristics present in the HDR within the Gonghe basin.