Heat flow, deep temperature and thermal structure across the orogenic belts in Southeast China

Abstract The pattern of heat flow density in Southeast China is presented in the form of heat flow map based on 150 values of heat flow measured in recent years. A two-dimensional numerical solution of the heat conduction equation was used to calculate the temperature field to a depth of 60 km along two geotraverses: the 360 km long Wenzhou-Tunxi (WT) and the 1000 km long eastern segment of the Quanzhou-Heishui (QH). They cross all the major tectonic elements of orogenic belts in Southeast China. The steady-state model was solved using the finite element method. The distribution of heat production was derived from seismic refraction results applying the experimental relationship between seismic velocity ( v p ) and radiogenic heat production ( A ) incorporated with the observed surface heat generation data in the near-surface crust. The thermal conductivity was assigned to be temperature dependent and related to crustal composition. In the upper crust, the temperature field is found to correspond to the regional variation of the surface heat flow, whereas the mantle heat flow is decisive for the temperature field in the lower crust. Low temperatures are typical of the Later Proterozoic orogenic belt and the Early Paleozoic Foreland Fold-Thrust Belt (FTB) (Moho temperature 415–575°C at a depth of 29–37 km). Temperatures increase toward the Triassic orogenic belt, and the maximum increase in Moho temperature and mantle heat flow occurs in the Triassic orogenic belt and its FTB (550–780°C). Low temperatures (400–500°C at Moho) are also calculated in the Coastal Min-Yue Belt supposed to be a Cretaceous orogenic belt. The “thermal” lithospheric thickness varies between 70 and 190 km, decreasing eastward from the Later Proterozoic Jiangnan in the west to the Triassic Zhe-Min orogenic belts. The mantle heat flow values across the orogenic belts in Southeast China range from 24 to 48 mW m −2 accounting for 51–63% of the surface heat flow.