U-PB ZIRCON AGE OF DIÊN B̀NH GRANITOID PLUTON IN BỜ
Y, KON TUM PROVINCE AND ITS IMPLICATIONS
Nguyễn Thị
Bích Thủy1, Nguyễn Thị Xuân2, Hồ
Thị Thư1, Nguyễn Đức Chính2,
Quách Đức Tín1, Trần Đại Dũng1,
Bùi Thế Anh2, Trần Bá Duy2, Đặng
Văn Long3
1General Department of Geology and Minerals of Vietnam
;
2Vietnam Institute of Geosciences and Mineral Resources; 3Hồ
Chí Minh University of Science
Corresponding
author: thuynguyendcks@yahoo.com
Abstract: 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
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