U-Pb zircon age of Diên B́nh granitoid pluton in Bờ Y, Kon Tum province and its implications

Nguyễn Thị Bích Thủy, Nguyễn Thị Xuân, Hồ Thị Thư,                                                              Nguyễn Đức Chính, Trần Đại Dũng, Bùi Thế Anh, Đặng Văn Long


Diên B́nh complex is made up of gabrodiorite, diorite, granodiorite and granite. Most of rocks are medium to coarse grain and display gneissic texture. They are exposed under small or elongated plutons along the Pô Cô Fault. In this study, two biotite rich granodiorite samples were collected from one pluton, which assigned to Diên B́nh complex, in the Bờ Y commune, Ngọc Hồi district, Kon Tum province for age dating. The collected samples are strongly foliated. Petrographically, the rocks are medium - to coarse-grained biotite rich granite and display foliation texture with parallel alignment of biotite and feldspar. The major rock forming minerals are Plagioclase; K-feldspar; Quartz and Biotite. Acessory minerals are zircon, sphene, apatite and opaque minrals. Zircon grains separated from two samples are mostly brown to colorless and sub-transparent, containing black inclusions. They are prismatic in shape and have the length and length/width ratios ranging from 100 to 200 μm and 2:1 to 1.5:1, respectively. All Th/U ratios of analyzed zircons (0.43-1.10) are higher than 0.1 and cathodoluminescent images display oscillatory zoning, indicating magmatic origin. The crystallization age of the granite was determined by zircon U-Pb isotope using a laser beam and measured on an ICP-MS machine and gave the mean 206Pb/238U age value of ca. 470 Ma. This age value of granite indicated the existence of tectono-magmatism and crustal formation during Early Paleozoic time in the study area

Keywords: Granitoid Diên B́nh, U-Pb zircon, Bờ Y -Ngọc Hồi, Early Paleozoic