查干凹陷中、新生代构造-热演化史

Mesozoic and Cenozoic tectono-thermal evolution history in the Chagan Sag,Inner Mongolia

查干凹陷是中国内蒙古银根-额济纳旗盆地中最具有勘探潜力的凹陷.为了揭示其构造-热演化历史,本文利用35个磷灰石裂变径迹和119个镜质体反射率数据,采用耦合反演的方法恢复了查干凹陷白垩纪以来的热历史.结果显示查干凹陷白垩系具有高的古地温梯度,并且查干凹陷经历了地温梯度快速增加阶段(K1b-K1s),地温梯度高峰阶段(K1y),高地温延续阶段(K2w)和热沉降阶段(Cz)四个构造-热演化阶段.此外,基于热史恢复结果,正演获得查干凹陷高的古地温梯度有利于烃源岩成熟生烃,早白垩世的高古地温梯度控制着该地区的烃源岩有机质的热演化.本文的研究成果可以为下一步油气资源评价和勘探决策提供基础依据.

The Chagan sag has the greatest oil and gas exploration potential among the sags in the Yingen-Ejinaqi Basin,Inner Mongolia.To reveal the tectono-thermal evolution history of the Chagan sag,this article utilized a combination of forward and inversion methods on the basis of 7apatite fission track and 119 vitrinite reflectance data to reconstruct the Mesozoic and Cenozoic tectono-thermal evolution history in the Chagan sag.The results show that the Chagan sag had a high geothermal gradient during the Cretaceous,and it experienced the following 4stages of tectono-thermal evolutions：（1）a rapid geothermal gradient increase stage from the Bayingebi Formation depositional period to the Suhongtu Formation depositional period,during which thegeothermal gradient increased to 46～52℃/km at the end of the Suhongtu Formation depositional period;（2）ageothermal gradient peak stage during the Yingen Formation depositional period,with maximum geothermal gradient ranged from 50 to 58 ℃/km;（3）a high geothermal gradient continuation stage during the Wulansuhai Formation depositional period, with maximum geothermal gradient ranged from 39 to 48 ℃/km;and（4）a thermal subsidence stage during the Cenozoic,during which the Chagan sag is in the uplift and erosion stage due to the Himalayan movement and the geothermal gradient gradually decreased to 31～34 ℃/km at the present day.Moreover,the tectono-thermal evolution was matched with the tectonic evolution and volcanic activities in the Chagan sag.During the Early Cretaceous,the intraplate rift was developed,lithosphere was thinned and multi-phase intense volcanoes were erupted in the Chagan sag,so that a large amount of energy was released to the surface from the deep crust,resulting in a high geothermal gradient during this period.In addition,the high geothermal gradient during the Cretaceous was favorable for hydrocarbon generation,corresponding to a shallow paleogeneration threshold,and the Early Cretaceous geothermal fields controlled the hydrocarbon generation of the Chagan sag.This work may provide new insights for the understanding of the oil and gas exploration potential of the Chagan sag.