Petrogenesis of Late Triassic granitoids in Peninsular Malaysia, Southeast Asia: Implication for crystal-melt fractionation and melt-fluid interaction during granitic magma differentiation

Abstract

Peninsular Malaysia, known as the world’s producer of tin, has drawn great attention to the close affinity between tin mineralization and granitoids during the Permian-Triassic period. This paper reports new petrography, zircon U-Pb ages, whole-rock geochemical and Sr-Nd-Pb-Hf isotopic data of granitoids from the Gerik pluton in Malaysia Main Range province. These samples consist two compositionally distinctive suites, the low silica series (LSS) represented by biotite granites and the high silica series (HSS) represented by tourmaline-bearing granites. They have identical zircon U-Pb ages of 217–215 Ma. The results of petrology and geochemistry indicate that both the LSS and the HSS originated from a mixed source involving igneous protoliths and crustal metasediments. Furthermore, the LSS are best explained as resulting from the AFC process (assimilation and fractional crystallization). By contrast, the HSS display unusual REE tetrad effect, fractionation of twin-elements (low Nb/Ta, Zr/Hf and high Y/Ho) and variable ⁸⁷Sr/⁸⁶Sr_i (0.7058 to 0.7282), clearly showing melt-fluid interaction during the late magmatic stage. We further infer that the magmatic fluids with unradiogenic Sr isotopes are most likely exotic origin and were derived from deep magma reservoir. The external fluids can migrate efficiently to the shallow part of the crust and interact with the highly evolved granitic melts represented by the HSS. Meanwhile, the magmatic fluids may also bring in plenty of fluid-mobile Sn, which finally developed the most abundant hydrothermal vein-type tin deposits in Peninsular Malaysia.