Late Mesozoic high-heat-producing (HHP) and high-temperature geothermal reservoir granitoids: The most significant geothermal mechanism in South China

Abstract

Differences in the geothermal regime of continental intraplate regions depend mainly on the amount and distribution of radioactive heat production in crustal rocks. Granitoids are the predominant sources of radioactive heat production and have abundant radioactive heat-producing elements, such as uranium, thorium and potassium. The Mesozoic geology of the South China Block (SCB) is characterized by long-term continental reconstruction, widespread granitoids and super-large ore deposits such as U, W, Mo and Sn deposits and is a typical “hot” continent and so-called Mesozoic large granitic province. Unfortunately, so far, research on the geotherm in the SCB is largely concentrated in geophysics and hydrology, with rare studies on the correlation between the geotherm and granitoids. The peak radioactive heat production rates (RHPRs) are consistent with the Mesozoic magmatic pulse. Notably, the varieties of radioactive heat production from the granitoids are not attributed to the differences in the basement rocks. In contrast to previous studies, this study found that not only A-type granitoids but also I-type and S-type granitoids are high-heat-producing (HHP) granitoids. The RHPRs, heat reservoirs and various batholith sizes in the SCB indicate that the large batholiths generally show high RHPRs and heat reservoirs. The distribution of hot springs is closely linked to the radioactive heat production and size of the intrusions. Additionally, we exclude another possibility of an efficient magma chamber with abundant remnant heat beneath the SCB. On the basis of the calculation and analysis of the amount of granitic radioactive heat production, we suggest that the Mesozoic HHP granitoids and high-temperature geothermal reservoir granitoids are the most significant heat source of the crustal geotherm in the SCB.