合肥盆地热演化特征

Analysis of characteristics of thermal evolution in Hefei basin

通过 5口钻井 2 3个样品镜质体反射率 (Ro)数据的统计分析 ,运用镜质体反射率 -深度 (Ro-H)剖面斜率及其对应地温梯度的筛分对比方法 ,综合研究了合肥盆地中新生代的热演化特征。结果表明 ,盆地不同区块二叠系、下侏罗统和下白垩统的Ro数值大小存在较大差异 ,介于 0 .82 %～ 2 .70 % ,但其相应的Ro-H剖面斜率均显著大于上白垩统和下第三系 ,表明上、下白垩统之间存在明显的间断。下白垩统的地温梯度分布在 70 .80～ 130 .90℃ /km ,相对稳定区接近 70 .80℃ /km ,表明早白垩世存在一次规模较大的区域性构造 -热事件。上白垩统和下第三系Ro集中分布在 0 .4 0 %～ 0 .74 % ,地温梯度为38.30℃ /km。晚第三纪以来 ,盆地整体抬升冷却 ,地温梯度降至现今的 2 7.5 0℃

Based on statistical analysis of vitrinite reflectance ( R o) data of 23 mudstone samples from five wells in Hefei basin, the thermal evolution characteristics of the basin during Mesozoic and Cenozoic are comprehensively studied by sieve correlating the slope of vitrinite reflectance vs. depth profile ( R o H ) and the corresponding geothermal gradients. The R o values of the Permian, Lower Jurassic and Lower Cretaceous in different blocks of the basin vary significantly and range from 0.82% to 2.70%, while the slopes of the corresponding R o H profiles are remarkably larger than that of the Upper Cretaceous and Lower Tertiary, indicating an obvious hiatus between the Lower and Upper Cretaceous. The geothermal gradient in the Lower Cretaceous ranges between 70.80?℃/km and 130.90?℃/km, and that in relatively stable area is near 70.80?℃/km, which indicate that there have been a relatively large regional tectonic thermal event during the Early Cretaceous. The R o of the Upper Cretaceous and Lower Tertiary distribute narrowly between 0.40% and 0.74% and the geothermal gradient is 38.30?℃/km. The basin has been uplifted, as a whole, and cooled down since Late Tertiary, lowering the geothermal gradient to the current 27.50?℃/km.