Heat flow, heat production, thermal structure and its tectonic implication of the southern Tan-Lu Fault Zone, East–Central China

We present new heat flow and heat production data to constrain the lithospheric thermal structure along the southern Tan-Lu Fault Zone (STLFZ), a continuous active deep crustal fault zone in East Asia, and use these thermal data to infer how the thermal structure of the STLFZ influences regional focal depths. We report five new high-quality heat flow measurements derived from temperature–depth profiles at five well sites and detailed thermal conductivity measurements of 13 outcrop samples and 115 dry core samples from five wells along the STLFZ. We analyze these new data in combination with published data to derive a thermal profile along the STLFZ and map the 350 °C isotherm along the STLFZ, which correlates well with the maximum depth of recorded seismicity. The results indicate that: (1) the thermal gradient along the STLFZ increase from 22.2 °C km–1 in the south to 34.8 °C km–1 in the north; (2) heat flow values are in the 44.0–75.4 mW m–2 range along the STLFZ, with a mean value of 59.9 ± 10.5 mW m–2; (3) the highest heat flow value is located in Lu-Zong Basin, with extremely high radioactive heat production of 15–20 μW m–3 in the upper crust that may be related to local ore bodies; and (4) the bottom boundary of the shallow-earthquake seismic zone in the STLFZ coincides with the 350 °C isotherm.