鄂尔多斯盆地中-新生代岩石圈厚度演化——来自地热学的证据

The Mesozoic-Cenozoic evolution of lithospheric thickness in the Ordos basin constrained by geothermal evidence

盆地热历史可以为揭示深部动力学过程提供时间和空间上的连续信息.本文利用镜质体反射率古温标模拟了鄂尔多斯盆地从东到西7口典型井的热历史,并在此基础上计算了盆地中生代晚期、古近纪初期以及现今的“热”岩石圈厚度.结果显示,鄂尔多斯盆地在早白垩世末期经历了一次热流高峰,热流值为73～78 mW/m2,此后的热流值一直降低至今,现今的平均值61.8 mW/m2;早白垩世末期盆地“热”岩石圈厚度也经历了一次减薄高峰,平均“热”岩石圈厚度为65 km左右,此后逐渐增厚至现今的125 km左右.鄂尔多斯盆地现今“热”岩石圈厚度中等,早古生代200 km的厚岩石圈已不存在;早白垩世末期是其地质发展历史的一个重大变革期,此时“热”岩石圈厚度发生减薄,深部构造活动强烈导致浅部盆地拾升剥蚀剧烈,周缘岩浆活动强烈,多种能源矿产形成,这与华北克拉通东部构造转折的时间以及华北克拉通破坏的高峰时限具有一致性.

The thermal history of sedimentary basins can provide continuous information on time and space for the geodynamic process at depths.The heat flow evolution histories of 7wells in the Ordos basin were modeled by using the vitrinite reflectance in this paper.Based on these modeling results,thermal lithospheric thicknesses in the late Mesozoic,the early Paleogene and the present were calculated.The Ordos basin had gone through a heat flow peak in the late Early Cretaceous,when the heat flow reached up to 73～78 mW/m2.After the late Early Cretaceous,the heat flow value gradually reduced to the present 61.8 mW/m2.At the same time,the Ordos basin experienced a thinning process in the late Early Cretaceous,when the average thermal lithospheric thickness was about 65km.Since then the thickness had increased to the present 125 km.The thermal lithospheric thickness at present is in the mid-level and there doesn＇t exist a ＂lithosphere root＂ of 200 km thick.The early Cretaceous was an important geological period of transformation for the Ordos basin,when active tectonic activities at depth led to the strong denudation in the shallow,the intense tectonic-magmatic activities on the periphery of the basin and the generation of many energy resources.The time of heat flow peak in the Ordos basin is consistent with the time when the tectonic system of the eastern North China Craton began to change and the North China Craton destructed.