Radiogenic heat production in the lithosphere of Sulu ultrahigh-pressure metamorphic belt

The Chinese Continental Scientific Drilling (CCSD) project is located at the Sulu ultrahigh-pressure metamorphic (UHPM) belt. It offers a unique opportunity for studying the radiogenic heat production of both shallower and deeper rocks. Based on the concentrations of radiogenic elements U, Th and K on 349 samples from main hole of CCSD (CCSD MH), pilot holes and exposures, we determined radiogenic heat productions of all major rock types in the Sulu UHPM belt. Results show the mean values of orthogneiss and paragneiss are respectively 1.65 ± 0.81 and 1.24 ± 0.61 µW m− 3. Due to different composition and grade of retrogressive metamorphism, the eclogites display significant scatter in radiogenic heat production, ranging from 0.01 to 2.85 µW m− 3, with a mean of 0.44 ± 0.55 µW m− 3. The radiogenic heat production in ultramafic rocks also varies within a large range of 0.02 to 1.76 µW m− 3, and the average turns out to be 0.18 ± 0.31 µW m− 3. Based on the measurements and crustal petrologic model, the vertical distribution model of heat production in Sulu crust is established. The resulting mean heat production (0.76 µW m− 3) contributes 24 mW m− 2 to the surface heat flow. 1-D thermal model indicates that the temperature at the Moho reaches above 750 °C, and the thermal thickness of the lithosphere is ~ 75 km, in good agreement with the geophysical results. The high teat flow (~ 75 mW m− 2) together with thin lithosphere presents strong support for the extension events during the late Cretaceous and Cenozoic.