Present-day heat flow, thermal history and tectonic subsidence of the East China Sea Basin

Abstract

The East China Sea Basin is located in the convergence area between the Eurasian plate, the Pacific plate and the Philippine Sea plate, and consists of two depressions, the Taibei Depression in the west and the Xihu Depression in the east. Heat flow measurements show that the East China Sea Basin is characterized by present-day heat flow around 70.6 mW/m 2, varying between 55 and 88 mW/m 2. No significant difference in heat flow is observed between the Xihu and the Taibei Depressions. Thermal history reconstruction using vitrinite reflectance suggests that the thermal history was, however, different in the Taibei and the Xihu Depressions. Paleo-heat flow values when the pre-Tertiary formations experienced their maximum temperature at the end of the Paleocene reached a mean of 82 mW/m 2 in the Taibei Depression, much higher than the present-day value. The lower Tertiary sediments in the Xihu Depression experienced maximum temperatures at the end of Oligocene (35.4–23.3 Ma) and reached a mean paleo-heat flow value of 83 mW/m 2. Tectonic subsidence analysis shows that the timing of the major rifting episode was different across the East China Sea Basin. The rifting occurred from the Late Cretaceous (∼65 Ma) to the early Eocene (∼55 Ma) in the Taibei Depression, followed by thermal subsidence from the late Eocene to the end of Miocene (23.3-5.2 Ma). In contrast, in the Xihu Depression the initial subsidence lasted until the early Miocene and thermal subsidence to the end of Miocene. From Pliocene to the present, an accelerated subsidence took place all along the West Pacific margin of Asia. Significant thicknesses of strata were removed from the unconformities in the basin: the mean amount of erosion was 1147 m from the Paleocene and 1208 m above the Oligocene in the Taibei Depression, and 1409 m from the Oligocene in the Xihu Depression.