U-Pb ages and Hf isotopic composition of zircon and bulk rock geochemistry of the Dai Loc granitoid complex in Kontum massif: Implications for early Paleozoic crustal evolution in Central Vietnam

摘要

The northern Kontum massif in central Vietnam, one of the most key tectonic and metallogenic terrenes of the Indochina block, consists of numerous volcano-plutonic complexes including the Dai Loc granitic complex that formed an essential part of the early Paleozoic batholith of the massif. Rocks of the Dai Loc complex are granodiorite and granite in composition. Geochemically, the rocks are of sub-alkaline affinity and belong to high-potassium series. These rocks have moderate Aluminum Saturation Index (ASI) values of 0.76-1.19 and low Mg# values of 23-39. Zircon grains separated from the rocks have high ε_(hf)(t) values and old Hf model ages (Tdm) which varying from -0.7 to +4.8 and 0.9 to 1.1 Ga, respectively. All these characteristics, in conjunction with trace element features, suggest generation by partial melting of crustal source rocks with additional input of mantle-derived material. Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) zircon U-Pb analytical results from two samples revealed emplacement ages of the granite at 423 ± 2.2 and 427 ± 9.9 Ma. Our geochronological data provide evidence for early Paleozoic crustal evolution in Central Vietnam.