Lithospheric thermal-rheological structure and shallow thermal response in eastern China

Eastern China (EC) is located in the eastern margin of the Eurasian Plate and has been influenced by the subduction of the Izanagi and Pacific Plate since the Late Mesozoic, resulting in a large amount of tectonic-magmatic activities. After the India–Eurasia convergence, the topography of continental China changed from high-east-low-west to high-west-low-east. At present, the Bohai Bay Basin in EC mainly forms sedimentary basin-type geothermal system, and deep circulation-type geothermal systems mainly occur in southeast coastal China, with thermal springs widely distributed. In the northeastern China, Holocene volcanoes such as Changbaishan Volcano have been formed, together with many thermal springs exposed.

The genesis of shallow thermal anomalies is closely correlated with the thermal-rheological structure of the lithosphere. In this study, we comparatively analyzed the lithospheric thermal-rheological structures of different tectonic units in EC, such as the Bohai Bay Basin, the southeast coastal China, and the Changbaishan Volcano field. We revealed that under the influence of the Pacific tectonic domain, the lithospheric thermal structures differed significantly, and the temperatures at the same depth from high to low are the Changbaishan Volcano field, the Bohai Bay Basin and the southeast coastal China. The rheological structures are significantly weakened in the middle and lower crust in the presence of an intracrustal heat source. The shallow thermal anomalies in the three tectonic units are similar in that the reservoir temperatures are mainly in the range of 100-150°C, and the water sources are all meteoric water. The difference between shallow thermal anomalies corresponds to their lithospheric thermal-rheological structures. The geothermal systems in the sedimentary basin of the Bohai Bay Basin are characterized by wells with a geothermal reservoir depth of 3-5 km. The deep-circulation hydrothermal systems in southeast coastal China are characterized by springs with a circulation depth of 4-7 km, and the hydrothermal systems in the Changbaishan Volcano field are characterized by springs with a circulation depth of 4-5 km. The deep thermal-rheological structure influences the behavioral characterization of shallow thermal anomalies with respect to heat-accumulation patterns. When brittle-ductile transition depth greater than the circulation depth, magma chamber (or partial melting body) and fluid circulation systems are relatively independent, and mass transfer from the magma chamber to the geothermal system may not happen.