Geochemical characteristics and Sr-Nd-Hf isotope compositions of late triassic post-collisional a-type granites in Sarudik, SW Sumatra, Indonesia

Abstract

Late Triassic A-type granites are identified in this study in Sarudik, SW Sumatra. We present new data on zircon U–Pb geochronology, whole-rock major and trace elements and Sr-Nd-Hf isotope geochemistry, aiming to study their petrogenesis and tectonic implications. LA-ICP-MS U–Pb dating of zircon separated from one biotite monzogranite sample yields a concordia age of 222.6 ±1.0 Ma, indicating a Late Triassic magmatic event. The studied granites are classified as weakly peralumious, high-K calc-alkaline granites. They exhibit high SiO2,K2O+Na2O, FeO/(FeO + MgO) and Ga/Al ratios and low Al2O3, CaO, MgO, P2O5 and TiO2 contents, with enrichment of Rb, Th and U and depletion of Ba, Sr, P and Eu, showing the features of A-type granites. The granites have zircon εHf(t) values from −4.6 to −0.4 and wholerock εNd(t) values from −5.51 to −4.98, with Mesoproterozoic TDM2 ages (1278–1544 Ma) for both Hf and Nd isotopes. Geochemical and isotopic data suggest that the source of these A-type granites is the Mesoproterozoic continental crust, without significant incorporation of mantle-derived component, and their formation is controlled by subsequent fractional crystallization. The Sarudik A-type granites are further assigned to A2-type formed in post-collisional environment. Combined with previous knowledge on the western SE Asia tectonic evolution, we conclude that the formation of the Late Triassic A-type granites is related to the post-collisional extension induced by the crustal thickening, gravitational collapse, and asthenosphere upwelling following the collision between the Sibumasu and the East Malaya Block.