中国西部地区沉积盆地热演化和成烃史分析

Thermal evaluation and hydrocarbon generation history of the sedimentary basins in western China

对于揭示大陆岩石圈的地球动力过程及沉积盆地中烃源岩的生烃历史而言 ,热体制都非常重要。中国西部地区的热背景较低 ,但由于各沉积盆地的地质演化历史不同 ,它们的热体制和热历史不一样。利用磷灰石裂变径迹和镜质组反射率等古温度标志参数对塔里木、准噶尔和柴达木盆地的热历史进行模拟 ,结果表明 :柴达木盆地的地热梯度从第三纪以来逐渐变小 ,第四纪又微增 ;塔里木盆地经历了复杂的热演化史 ,二叠纪的火山活动使地热梯度相对较高 ,但新生代地热梯度下降很快 ,现今地热梯度仅约为 2 0℃ /km ;准噶尔盆地的地热梯度和大地热流在其地质演化过程中逐渐减小。不同的热演化史导致不同的生烃史 ,对各盆地主要烃源岩的生烃史模拟结果表明 ,Ro 值为 1 .0 %的生油气高峰期不同 ,从而使各盆地的油气勘探前景存在差异。图 4表 1参 1

Thermal regime is of significant important to reveal the geodynamic processes of continental lithosphere and the generation of hydrocarbon from source rocks in sedimentary basins. There have some lower thermal background in the area of western China. However, the thermal history, modeled from apatite fission track and vitrinite reflectance data, evolved differently because of the different tectonic history in the Tarim basin, Junggar basin and Qaidam basin. The thermal gradient in the Qaidam basin decreased since the Tertiary time, but changed only a little during the Quaternary. The Tarim basin underwent a relative complicated thermal history. The thermal gradient at Permian had a relative high value because of the volcanic activity. It decreased rapidly at the Neocene to Quaternary. The present day's thermal gradient is only 20℃/km. The thermal gradient in the Junggar basin decreased with the geological evolution. The above differential thermal histories resulted in the different hydrocarbon generation in the three basins.