白垩纪以来米仓山—汉南穹窿剥蚀过程及其构造意义:磷灰石裂变径迹的证据

Exhumation history of the Micangshan-Hannan Dome since Cretaceous and its tectonic significance:evidences from Apatite Fission Track analysis

报道了米仓山—汉南穹窿一带磷灰石裂变径迹分析结果,以制约该区白垩纪以来的剥蚀-演化历史.露头样品磷灰石裂变径迹年龄分布显示从汉南穹窿南部的核部地区向南至四川盆地北部裂变径迹的年龄逐渐变新,这与米仓山地区逆冲断裂以背驮式扩展的构造样式从汉南穹窿向南经米仓山褶皱-逆冲带发育到四川盆地北缘的构造模式相吻合.热模拟的结果显示米仓山汉南穹窿经历了两期快速的剥蚀,其分别发生在白垩纪(约90 Ma之前)和15 Ma以来.研究区白垩纪的快速剥蚀反映了秦岭大别造山带白垩纪的区域性剥蚀事件,这可能是对临区诸多构造事件(如西伯利亚—蒙古—中朝板块的碰撞,拉萨—羌塘—思茅—印支块体的碰撞,太平洋板块向欧亚板块的俯冲及其相关的岩浆活动)远场效应的响应;约15 Ma以米的快速剥蚀是对青藏高原隆升向东北方向传递的响应.

Apatite Fission Track （AFT） data of the Micangshan-Hannan Dome region is reported in this work. It is shown that AFT ages decrease gradually from the inner part of the Micangshan-Hannan Dome to North Sichuan Basin, which is consistent with the piggyback propagation model of thrusting in the region proposed by previous works based on seismic survey profiles. Thermal history modeling of the AFT data shows that the Micangshan-Hannan Dome experienced two episodes of rapid cooling occurred in Cretaceous （before ~90Ma） and Late Cenozoic （since about 15Ma） respectively. The Cretaceous rapid cooling of this region is coeval with the regional cooling event in Qinling-Dabie Orogen, which is possibly resulted from the far-field effects of tectonic events in the nearby regions （eg. Siberia-Mongolia-Sino-Korean and Lhasa-West Burma-Qiangtang-Indochina collisions, Pacific subduction and Pacific back-arc extension since Early Cretaceous）. The Late Cenozoic rapid cooling since ~15Ma is attributed to the northeastward growth of the Tibetan Plateau.