Petrographical, petrogeochemical characteristics, and petrogenesis of the granitoid in the Que Tho area, Quang Nam province

Abstract

Que Tho area is the southwest part of Que Son block in Que Tho commune, Hiep Duc district, Quang Nam province. The granitoid in this area had a relatively isometric block form. The main petrographic composition of this granitoid consists of biotite granodiorite and hornblende biotite granodiorite (phase 2), with diorite (phase 1) present as xenoliths in granodiorite. Its mineral composition mainly was quartz (20−30%), plagioclase (30−40%) and potassium feldspar (25−30%); Colored minerals consisted of biotite (5−10%), amphibole (~5%) and pyroxene (3−5%); typical minor minerals were sphene, apatite, zircon (few). Common post-magmatic metasomatic processes include albitization, microlinization, chloritization, sericitization, and zoisite−epidotization. The average characteristic chemical composition of this granodiorite (%) was SiO2 64.56, TiO2 0.75, Al2O3 15.85, FeO 4.0, Fe2O3 0.45, MnO 0.06, MgO 2.32, CaO 3.95, K2O 3.38, Na2O 3.89, P2O5 0.28; ratio of alkaline K2O/Na2O: 0.86 (<1), The ASI with corundum index was 0.93 (< 1), ratio Rb/Sr 0.19; Ba/Sr 6.63; Ba/Rb 8.4; Th/U 3.99; Zr/Hf 45.87 and Nb/Ta 16.25 and the negative anomaly value Eu was from moderate to strong. The granodiorite belongs to the high aluminum series, calc-alkali series, alkaline type K−Na, high K; I-granite type originated from mantle, formed in the tectonic setting of an intrusive−volcanic arc of an active continental margin and crystallized differently from the mafic magma and influenced by the composition of the crust. The crystallization age of the granodiorite, determined by the LA-ICP-MS U-Pb zircon method, was 279.1± 2.7 million years, corresponding to the Early Permian stage. Compared to the granitoid formations in South Vietnam, the granitoids in the Que Tho area belonged to phase 2 of the Ben Giang−Que Son complex, commonly found in the Kon Tum terrane.