Geothermal evidence of the mesozoic and cenozoic lithospheric thinning in the liaohe depression

Abstract

The Liaohe (辽河) depression is an important part of the Bohai (渤海) Bay Basin, and the Bohai Bay Basin located in the center of lithospheric destruction and thinning in the eastern North China Craton. The North China lithospheric thinning activities have been verified from evidences of structural geology, petrology, geochemistry and geophysics, but there are still some controversies on their timing, mechanism and controlling factors. The sedimentary basin is a thin-bedded geologic unit with a limited distribution in the upper lithosphere, and its formation and evolution represent the shallow response of the deep geodynamic process. Therefore, its thermal evolution is closely related to the deep dynamic conditions. In this article, the Mesozoic-Cenozoic thermal history of the Liaohe depression is reconstructed using the vitrinite reflectance and apatite fission track data. Meanwhile “thermal” lithospheric thicknesses in the Mesozoic and Cenozoic are calculated using the geothermic method on the basis of the above thermal history results. The results show that the Liaohe depression has under- peaks, 81 and 83 mW/m2, respectively, corresponding to two strong rift movements. Accordingly, the depression has experienced two different levels of thinning processes in the Cretaceous and the Paleogene since the Mesozoic, and the “thermal” lithospheric thicknesses were 60 and 50 km, respectively. This may reveal that the depression has experienced two large-scale destructions. The work may provide valuable geothermal evidence for initial revealing the time, process and stage of the lithospheric thinning in the Liaohe depression.