Evolution of Meso-Cenozoic thermal structure and thermal-rheological structure of the lithosphere in the Bohai Bay Basin, eastern North China Craton

The Meso-Cenozoic thermal structure and thermal-rheological structure of the lithosphere in the Bohai Bay basin are calculated here in this paper, using the Meso-Cenzoic thermal history, crustal layer structure and rheological data. The results show that the lithosphere of the Bohai Bay Basin transformed its thermal structure during the Meso-Cenozoic, from the “cold mantle but hot crust” stage in the Triassic-Jurassic to the “hot mantle but cold crust” stage in the Cretaceous and Cenozoic. The thermal-rheological structure of the Jiyang depression exhibits obvious rheological stratification and changed with time during the Meso-Cenozoic. During the Early Mesozoic, the uppermost of the upper & middle crust and the top of the upper mantle were of thick brittle layers. During the early Early Cretaceous, the brittle layer of the uppermost of the middle crust was thinned, while the uppermost of the upper mantle almost occupied by the ductile layer. During the late Early Cretaceous, the brittle layers of the middle crust and the upper mantle changed into the ductile ones. Then, the uppermost of the middle crust began to occur of the thin brittle layer in the late Cretaceous. During the early Paleogene, the middle crust was of the thin brittle layer. At present, the top of the upper & middle crust and the uppermost of upper mantle are of brittle layers. The lithospheric total strength of the Meso-Cenozoic experienced two weakened stages in the late Early Cretaceous and the early Paleogene, and the strength in the Early Mesozoic was greater than that after the Middle Jurassic. Furthermore, the evolution of the Meso-Cenozoic thermal-lithospheric structure has a good correspondence with the evolution of thermal lithosphere thickness during the destruction process of the North China Craton (NCC), reflecting also the geodynamic process of the eastern NCC destruction caused by the Pacific plate subduction and rollback. The thermal-rheological structure of the lithosphere provides a scientific basis for the studies of the geodynamic process of the basin formation, continental margins and orogenic belts.