Trace element geochemistry and U-Pb dating of zircon inclusions in sapphire from Southern Vietnam

Doan Thi Anh Vu^1,2, Elena Belousova³, Abhisit Salam¹, Alongkot Fanka¹^,4, Chakkapphan Sutthirat^1,*

¹Department of Geology, Faculty of science, Chulalongkorn University, Thailand
²Faculty of Geology, University of science, VNU-HCM, Vietnam
³ARC Centre of Excellence for Core to Crust Fluid Systems (CCFS) and GEMOC National Key Centre, Department of Earth and Environmental Sciences, Macquarie University, Sydney, Australia
⁴Applied Mineral and Petrology Special Task Force for Activating Research (AMP STAR), Department of Geology, Faculty of Science, Chulalongkorn University, Bangkok, 10330 Thailand

* Corresponding author e-mails: c.sutthirat@gmail.com; chakkaphan.s@chula.ac.th

Abstract

Trace element geochemistry of zircon inclusion in sapphire from Southern Vietnam shows a large variation in Hf (1.1 to 2.7 wt%), Y (779 – 4220 ppm), Th (329 – 5199 ppm), U (224 – 3587 ppm), and ∑REE (706 – 2710 ppm) abundances with clearly positive Ce and mildly negative Eu anomalies observed in chondrite-normalized REE patterns. These characteristics suggest that the majority of the host sapphires were crystallized from evolved felsic melt at the lower crustal levels. The U-Pb zircon dating yields the ages ranging between 35.5 ± 1.6 Ma and 14.7 ± 0.29 Ma for Krong Nang sapphire, 5.9 ± 0.13 Ma for Binh Thuan sapphire, 5.6 ± 0.07 Ma for Dak Nong sapphire, and 5.5 ± 0.08 Ma for Di Linh sapphire. Except the Krong Nang sapphire, these ages are coeval with the alkali basalt eruptions in Southern Vietnam. This implies the crystallization of sapphire during early stages of the basaltic magmatism. Sapphire and associated minerals were extensively transported from different depths to the surface during the later stages of basalt magmatism (≤5 Ma).

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