New Research Results on U-Pb Zircon Isotope Age of Ta Cu Granodiorite in Dalat Zone and Geological Significance
Le Duc Phuc, Pham Minh, Pham Trung Hieu, Trinh Nguyen Hung Vi
Abstract
Ta Cu granodiorites from the Dalat Zone, Southern Vietnam, have typical composition of granodiorite, coinciding with the Dinh Quan complex. The granodiorites are composed of plagioclase (45–50%), quartz (20–25%), orthoclase (15–20%), hornblende (5–7%), and biotite (5–7%). Geochemically, they are metaluminous with an average A/CNK value of 0.89- 0.96, low SiO2 (61.68-62.14) and high Na2O/K2O> 1. Petrographical and geochemical characteristics of Ta Cu granodiorites are classified as I-type granite generated from arc-related magmas. Zircons selected from these rocks are characterized by prismatic shape, oscillatory zoning, no luminescent rim, and have high ratio Th/U (0.35–1.11) that are indications of the magmatic origin. We report the first LA-ICP-MS 206Pb/238U zircon ages of 116 Ma for the Ta Cu granodiorite in the Southeastern Dalat Zone in Southern Vietnam. This age value is temporally coeval with Early Cretaceous magmatism previously reported in the Dalat Zone. Zircon ꜪHf(t) values +4.0 to+13.0, whole-rock ꜪNd(t) values -2.0 to +0.2, and average model ages (TDM2) 652 Ma to 957 Ma indicate that the Ta Cu granodiorites were derived from the remelting of Neoproterozoic mantle-derived melt with a minor input of crustal materials. Together with other Late Mesozoic magmatic complexes along the Dalat Zone, the Ta Cu granodiorites are a representative of magmatism linked to Pacific Ocean subduction beneath the Indochina block during the Early Cretaceous.