This study investigates the Cenozoic tectono-thermal evolution of the Xihu Sag in the East China Sea Basin, a rift–inversion sub-basin at the convergent boundary of the Eurasian, Pacific, and Philippine Sea plates. The findings have broad implications for hydrocarbon generation and thermal history reconstruction in similar continental margin basins globally. By integrating present-day geothermal data, low-temperature thermochronology, vitrinite reflectance, and fluid inclusion analysis, this study reconstructs the thermal history and source rock maturation processes in the Xihu Sag. The geothermal gradient ranges from 16 to 46 °C/km at depths of 0–4 km, with an average of 31.8 °C/km, and surface heat flow varies between 34 and 88 mW/m², averaging 52.3 mW/m². These thermal regimes show a southeast-high to northwest-low trend, primarily influenced by lithospheric thinning, thermal refraction, and basement morphology. Thermal history modeling reveals a significant cooling event during the Late Miocene (14–7 Ma), corresponding to the Longjing tectonic phase, with progressive southeast-to-northwest deformation. Erosion magnitudes exceeded 800 m in marginal anticline zones, while the central Pinghu Slope Belt experienced denudation rates up to 246 m/Ma. Basin modeling indicates that basement heat flow decreased during the Early to Middle Miocene but increased again during tectonic inversion, significantly influencing source rock maturation. The Pinghu Formation source rocks reached peak hydrocarbon generation by the end of the Miocene. Fluid inclusion data indicate two primary hydrocarbon charging phases (∼15–9 Ma and ∼5–0 Ma), consistent with modeled expulsion stages. This study introduces a robust, multi-parameter integrated framework to rigorously assess the geothermal state, tectonic characteristics, and petroleum generation potential of continental margin basins. This methodological paradigm shift fundamentally advances the approaches to thermal history reconstruction and hydrocarbon exploration, providing a reliable and universally applicable solution for analogous geological settings.
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