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Abstract

Whether active fractures are thermal anomalies is a cutting-edge scientific issue in geothermics. Geothermal measurements of the San Andreas Fault reveal no heat flow anomaly, and then the "heat flow paradox" was proposed. The Tan Lu Fault Zone (TLFZ) is the most important fault in eastern Asia and is still active currently. We have carried out extensive geothermal measurements in the south-central TLFZ: the heat flow in the southern TLFZ is concentrated in the range 55-65 mW/m²; the highest heat flow site LZSD (93 mW/m²) is determined by the high heat production rocks, so the southern TLFZ is not a thermal anomaly. In contrast, the heat flow value in the middle section of the TLFZ is over 80 mW/m², which is likely to be a thermal anomaly zone. Simulations and calculations show that the heat generated by the fault activity is not significant (1-6 mW/m²). Detailed two-dimensional temperature field simulation work also confirms these conclusions. The differences in the present-day thermal state of the TLFZ are the result of differences in the influence of tectono-thermal events in different regions, with the "Craton destruction event" at the late Early Cretaceous having altered the property of lithosphere in East China (Lower Yangtze Craton and the north part of the eastern North China Craton), while the south part of the eastern has only undergone the lithospheric thinning process. The difference in paleo-lithosphere thickness is likely the main reason for the different thermal state of the TLFZ.