Geochemistry, zircon UPb ages and Hf isotopes of Tra Bong granitoid from Kontum massif, central Vietnam, and its petrogenetic significance

Abstract

Tra Bong granitoid, distributed in the northern area of Kontum, primarily consists of diorite and granodiorite. The main rock-forming minerals contain plagioclase (26–60 %), K-feldspar (8–22 %), quartz (15–33 %), biotite (3–7 %), and hornblende (9–20 %). The accessory minerals are sphene, apatite, zircon, and magnetite. Tra Bong granitoids are characterized by SiO₂ (58.83–65.8 %), total alkali (6.68–8.03 %), and A/CNK (0.80–0.90). They show high-K and relative enrichment of large-ion lithophile elements (Sc, Rb, and K), and the relative depletion of Nb, Ta, and Ti elements. The P₂O₅ content decreases with increasing SiO₂, and Th increases with Rb, a trend typical of I-type granites. All observed petrographic and geochemical characteristics suggested that the Tra Bong granitoid is typical of the I-type granite, formed in a subduction zone. The UPb crystallization age ranges from 254.5 to 255.0 Ma, coinciding with the Late Permian-Early Triassic magmatic activity, which was previously reported in the Truong Son belt. The ε_Hf(t) value together with the Hf zircon model ages (T_DM2) ranges from 1011 to 1159 Ma. The Tra Bong granitoid is a result of partial melting Mesoproterozoic mafic-intermediate magmatic rocks, with a minor amount of metasedimentary crust remelting. In conjunction with other Permian-Triassic magmatic rocks along Truong Son belt and the Song Ma suture, the Tra Bong granitoid represents magmatic activity related to subduction-collision of the Indochina and South China blocks and closure of Paleo-Tethys Ocean in the Late Permian-Early Triassic, along the Song Ma suture.