四川盆地古地温梯度和中-新生代构造热历史

Early Cretaceouspaleocene Geothermal Gradients and Cenozoic Tectonothermal History of Sichuan Basin

摘要:

根据27口井的镜质体反射率剖面,恢复了四川盆地早白垩世末—古新世时的古地温梯度.结果表明,古地温梯度介于20~25℃·km-1,总体呈南部略大于北部、东部大于西部的分布特征.根据古今地温梯度的对比,川西坳陷新生代早期以来地温梯度没有明显的变化,川东和川东北地区晚中生代以来地温梯度下降,而川中和川南地区晚中生代以来地温梯度升高.结合构造演化背景分析,盆地中新生代热历史主要受二叠纪末期的构造热事件、中生代晚期以来岩石圈厚度演化以及现今活动构造的影响.其中,二叠纪末期的构造热事件波及盆地大部分地区;现今活动构造对川南地区有明显的影响;中生代晚期以来的岩石圈厚度演化,可能是控制中新生代盆地大部分地区热历史的主要因素.

Abstract:

Early cretaceouspaleocene geothermal gradients of Sichuan Basin are reconstructed from 27 vitrinite reflectance profiles.Results show that ancient geothermal gradients are between 20~25℃·km-1 and are higher in the eastern and southern regions of the basin than in the western and northern regions. According to comparison of ancient and Current geothermal gradients, geothermal gradients descended in eastern and northeastern but increased in the central and southern regions since the late Mesozoic, while kept unchanged in western Sichuan Basin since the early Cenozoic. According to the tectonic evolution in this area, thermal history of Sichuan Basin in the Mesozoic and Cenozoic was mainly affected by the late Permian tectonothermal event, the evolution of the lithospheric thickness since the late Mesozoic and the recent active tectonics. The late Permian tectonothermal event affected most parts of Sichuan Basin.Current active tectonics have significant impact on southern Sichuan, and the evolution of the lithosphere thickness may be the main factors influencing the MesozoicCenozoic thermal history of Sichuan Basin.