渤海湾盆地中原地区古地温梯度恢复研究

Reconstruction of the paleogeothermal gradient in the Zhongyuan area,Bohai Bay basin,East China

渤海湾盆地中新生代具有叠合盆地多期叠加演化的特点,不同地质时期地温场的恢复具有多解性和不确定性。应用包裹体测温、磷灰石裂变径迹分析、Barker温度函数法、EASY%Ro模拟等方法,通过不同构造单元的最高古地温的恢复,进行不同地质时期的地温梯度恢复。研究表明:(1)包裹体测温、磷灰石裂变径迹分析、Barker温度函数等方法仅适用于欠补偿沉积区古地温及古地温梯度恢复;(2)Barker法计算的地温梯度偏高;(3)而EASY%Ro热史模拟方法是补偿-近补偿沉积区古地温梯度恢复的有效方法;(4)三叠纪、侏罗—白垩纪、古近纪是影响上古生界烃源岩演化的关键时期,地温梯度分别为3.3℃/100 m、4.5℃/100 m和4.0℃/100 m。

The Bohai Bay basin, characterized by multiple phases of geodynamic history, has a complex history of thermal evolution from the Mesozoic to the Cenozoic. This may introduce ambiguity and uncertainty in the reconstruction of the paleogeothermal gradients for the various geologic periods. Using several methods, such as inclusion geothermometry, fission track of apatite, Barker Temperature Function and the model of EASY% Ro,the paleogeothermal gradients are established for geologic periods by reconstructing the paleogeothermal peaks for each tectonic unit. The process of reconstruction of paleogeothermal gradients shows that： （1） inclusion geothermometry, fission track of apatite and Barker Temperature Function may be suitable for paleogeothermal reconstruction only in under-filled sedimentary areas where paleogeotemperature is higher than geotemperature nowadays; （2）the paleogeothermal gradients calculated from Barker Temperature Function may be higher than that from other methods; （3）the thermal history simulation with the model of EASY%Ro may be an effective tool for the reconstruction of paleogeothermal gradients in areas with filled sedimentation; （4） the Triassic, Jurassic-Cretaceous and Paleogene are key periods for the thermal evolution of the Late Paleozoic source rocks, and their geothermal gradients are 3. 3 ℃/100 m, 4.5 ℃/100 m and 4. 0 ℃/100 m respectively.