Evolution of the Cenozoic thermal lithosphere of the Jiyang Sub-basin, Bohai Bay Basin: Implications for the lithospheric thinning mechanism

The Jiyang Sub-basin is an important sub-tectonic unit of the Bohai Bay Basin (BBB), which thinned by over 100 km during the Meso-Cenozoic. Changes in the thermal lithospheric thickness, of the Jiyang Sub-basin in the Cenozoic, were assessed using data from 131 single boreholes, together with the thermal history and layered crustal structure. From these, basement subsidence, stretching factor and strain rate were calculated for each borehole. The results show that the Jiyang Sub-basin experienced a peak of lithospheric thinning during the Cenozoic. In the early Cenozoic, the thickness of the lithosphere was about 80–100 km, and the strain rate was mostly low, 10⁻¹⁶–10⁻²² s⁻¹, indicating a weak extensional environment. At the peak of the lithospheric thinning (50 Ma to 35 Ma), the thermal lithosphere thickness was 70–55 km, the tectonic subsidence was about 1000 m, the lithospheric strain rate was higher about 10⁻¹⁵–10⁻¹⁶ s⁻¹, the stretching factor had also increased rapidly to 1.1–1.2. The thinning of the lithosphere in the Eocene is interpreted as a product of collective movements of the Indian, Pacific, and the Philippine Sea plates, although the effect of the Pacific plate was small as - the Izanagi-Pacific mid-ocean ridge is still young age (0–10 Ma). Knowledge of the history of the Cenozoic lithosphere in the Jiyang Sub-basin is of great significance for understanding the tectonic evolution of the BBB and of the North China Craton.