New Research Results on Geochemistry and Zircon U-Pb Geochronology of Ankroet Granite in Dalat Zone and Geological Significance

Ankroet granite from the Dalat zone (DZ), Vietnam, is commonly the main petrographic composition of granite and biotite granite, coinciding with the Ankroet complex. The primary rock-forming minerals of the Ankroet granite include plagioclase (30-35%), quartz (30-35%), K-feldspar (25-30%), and biotite (5-7%). Geochemically, they are metaluminous with an average A/CNK value of 0.95-1.04, high SiO2 (73.68-74.14), and low Na2O/K2O < 1. Petrographical and geochemical characteristics of Ankroet granites are classified as A-type granite generated from post-orogenic magmas. Zircons selected from these rocks are characterized by prismatic shape, oscillatory zoning, no luminescent rim, and a high ratio Th/U (0.75-1.78) that are indications of the magmatic origin. We report the first LA-ICP-MS Pb-206/U-238 zircon ages of 87.9 Ma for the Ankroet granite in the DZ in southern Vietnam. This age value is temporally consistent with Late Cretaceous magmatism previously reported in the DZ. Together with other Late Mesozoic magmatic complexes along the DZ, the Ankroet granites are a representative of magmatism linked to post-orogenic magmas beneath the Indochina block during the Late Cretaceous.