四川盆地东部构造-热演化:来自镜质体反射率和磷灰石裂变径迹的约束

摘要

利用镜质体反射率(Ro)和磷灰石裂变径迹(AFT)数据,对四川盆地东部不同地区的古地温梯度、古热流、剥蚀量进行了研究.AFT模拟结果表明,四川盆地东部在晚白垩世早期(100～80Ma)开始抬升,抬升剥蚀过程具有一定的阶段性且不同地区存在差异:以约30 Ma为界,重庆北碚地区表现为两期冷却,先期冷却缓慢,后期冷却迅速;川东北持续的冷却过程虽有波动但冷却速率差别较小.依据重建的最高古地温剖面恢复了侏罗系顶部不整合面的剥蚀量,川东北普光地区剥蚀量在2.45～2.85 km,鄂西渝东地区齐岳山复背斜北部剥蚀量较大,达3.65 km,齐岳山复背斜南部剥蚀量2.67 km,川东南地区剥蚀量2.05 km.研究区的构造热演化表现为既存在抬升剥蚀又存在盆地冷却效应的双重作用:由三叠纪至今,研究区地温梯度和热流持续降低,地温梯度由30～38℃/km降低至20～23℃/km;热流由70～85 mW/m2降低至50～55 mW/m2.%Based on the vitrinite reflectance (Ro) and apatite fission track (AFT) data,the tectono-thermal evolution in the eastern Sichuan Basin has been reconstructed and studied in regarding to paleo-temperature gradient,paleo-heat flow and erosion thickness.The AFT modeling result reveals a continuous uplifting since the Early Cretaceous (100-80 Ma) in the stages of regional characteristics in different areas.Two cooling stages,bounded by ～30 Ma,existed in the Beibei & Chongqing areas with marked difference in the cooling rates;on the contrary,there was no obvious difference in the cooling rates in the northeastern Sichuan basin,although cooling rates fluctuated in different stages in this area In addition,the erosion thicknesses of the unconformities on the top of the residual Jurassic have been determined from the maximum paleo-temperature profiles to be 2.45-2.85 km,3.65 km,2.67 km and 2.05 km in the Puguang area,the north of the Qiyueshan anticline,the south and southeastern Sichuan basin,respectively.It is shown that the tectono-thermal evolution is characterized by denudation and cooling since Triassic:the temperature gradient reduced to 20-23 ℃/km from 30-38 ℃/km;and the heat flow reduced to 50-55 mW/m2 from 70-85 mW/m2 in the eastern Sichuan basin accordingly.