Large granitoid batholith formed by episodic reworking of the continental basement

Large granitoid batholiths contain key information about the formation and evolution of the continental crust, but their growth mechanism and compositional diversity are still not clear. The Neoproterozoic Huangling batholith, one of the largest granitoid batholith in South China, comprises several plutons and covers an area of similar to 970 km(2). The largest trondhjemitic pluton was emplaced at ca. 840 Ma, and its magmatic zircons show large variable Th/U ratios (0.22-1.81) that are strongly correlated with Ti-in-zircon temperatures, zircon U/Yb and Ce4+/Ce3+ ratios. These zircons have negative epsilon Hf (-28.3 to -14.6), variable delta O-18 (4.43-6.99 parts per thousand) and delta Zr-94 values (-0.38 parts per thousand to + 0.21 parts per thousand), as well as moderate zircon saturation temperatures (716-771 degrees C) and high fO(2) (FMQ+1.9). The trondhjemite is therefore proposed to have been derived from the Archean amphibolitic crust and underwent fractional crystallization of zircon, magnetite, apatite and/or titanite. In comparison, one smaller granitic pluton was emplaced at 831 +/- 5 Ma. The magmatic zircons have more radiogenic epsilon Hf (-11.7 to -10.4), constant delta O-18 (6.09-6.66 parts per thousand) and delta Zr-94 values (-0.31 parts per thousand to + 0.06 parts per thousand), and they have slightly higher zircon saturation temperatures (767-803 degrees C) and fO(2) (FMQ+2.9). These geochemical features suggest that the granite was derived from a crustal source with mixed juvenile mafic materials and Archean amphibolitic rocks, and did not experience significant fractional crystallization. The Huangling granitoid batholith was formed by multiple injections of felsic melts with the compositional diversity that probably resulted from heterogeneous protoliths and complex magmatic processes in a prolonged magma evolution system.