Genetic links of crustal radiogenic heating to peraluminous granites

Peraluminous granites are commonly considered to be the product of crustal reworking in continental interiors and have a genetic relationship to Sn-W-rare metals deposits (e.g., Li, Be, Nb, Ta, Cs, Rb), but the heat transfer mechanisms responsible for the formation of peraluminous magmas and the mantle roles in these physical processes remains controversial. To answer these questions, the origin of the Xingluokeng granite in the Wuyi terrain of South China, peraluminous granite hosting large-scale tungsten mineralization, was investigated using zircon UPb and Hf isotopic compositions and numerical modeling of heat transfer with geologically relevant ranges of the ancient crustal thickness and heat production. The strongly negative ${\epsilon }_{\mathrm{Hf}\left(150\mathrm{Ma}\right)}$ values (−25.72 – –7.01) of autocrysic zircons (ca. 150 Ma), varying within those of inherited zircons (600–1000 Ma), suggest no signature of mantle mass input. The Mesozoic upper crust heat production in the Wuyi terrain estimated from fine-grained clastic sediments has an average of 2.9 μW m⁻³, and amphibolite facies to granulite facies rocks, representing the middle-lower crust, have averages of 0.6–4 μ W m⁻³. These values are greater than the global present-day averages for continental crust (upper crust: 1.68 μW m⁻³; middle-lower crust: 0.19–1 μW m⁻³). The high heat production and moderate crustal thickening (∼50 km), together with a normal mantle heat flux, can cause partial melting of metasedimentary rocks in the middle–lower crust within a thermal relaxation period of ∼30–50 Ma. Crustal radiogenic heating also warms the lower crust and the upper mantle and facilitates partial melting of mafic rocks, leaving volumetrically minor mafic dykes coeval with peralumnious granites in the same regions. Therefore, minor mafic dykes are not convincing evidence for the mantle supplying heat or mass for the coeval peraluminous granites. High crustal heat production and crustal thickening is also shared by other regions in the Cathaysia Block, so the above implications may also be applicable to other Mesozoic peraluminous granites in South China.