晚喜山期以来四川盆地构造-热演化模拟

四川盆地位于扬子板块西缘,是我国重要的含油气盆地之一.25 Ma以来的晚喜山期是四川盆地构造-热演化的重要时期,此时,盆地大部分区域受到挤压处于隆升剥蚀的构造动力学环境.本文采用有限元数值模拟方法,基于二维瞬态热传导(含平流项)的基本方程,并引入修正的Airy均衡理论模型,通过覆盖全盆地的八条剖面模拟研究了晚喜山期以来四川盆地的构造-热演化特征,且利用现今大地热流对模拟结果进行了有效约束.模拟结果显示在晚喜山期(~25 Ma)川中地区地表热流较高,为60~64 mW/m²;川西南地区次之,为60~62 mW/m²;川东北地区最低,为50~54 mW/m².该期基底热流,也是川中隆起区热流高,川东北强烈剥蚀区热流低.热流的空间分布特征揭示了四川盆地深部动力学机制.四川盆地晚喜山期以来,抬升剥蚀作用降低了其地表热流和基底热流,其降低幅度与对应的剥蚀速率相关,即剥蚀速率越大,这种降低作用越明显.

Tectono-thermal modeling of the Sichuan Basin since the Late Himalayan period

The Sichuan basin, located in the western margin of the Yangtze block, is one of the most important oil-gas-bearing basins in China. The Late Himalayan period since 25Ma was an important period of tectono-thermal evolution in this basin, during which the basin was in a compressed and uplifted tectonic dynamical environment. In this study, we simulated the tectono-thermal evolution of the Sichuan basin during the Late Himalayan period based on 8 profiles crossing the whole basin. And meanwhile, the simulation results were effectively constrained by the present-day terrestrial heat flow. We used a 2D finite element method to resolve the 2D transient heat conduction equation (including an advection term), and introduced a modified model of the Airy equilibrium theory. The modeling results regionally reveal that the surface heat flow values of the Central Sichuan basin at 25Ma are relatively high, between 60 mW/m² and 64 mW/m²; the values of the southwestern Sichuan are relatively low, between 60 mW/m² and 62 mW/m²; and those of the northeastern Sichuan are the lowest, between 50 mW/m² and 54 mW/m². The spatial variations of the basal heat flow in this period are similar to the surface heat flow. The spatial distribution of heat flow is associated with deep dynamic processes beneath this region. The modeling results indicate that the uplift during the Late Himalayan period reduced the surface heat flow and basal heat flow of the Sichuan basin, and the reduction was influenced by the denudation rate, i.e. the bigger the denudation rate, the lower the heat flow is.