SUMARRY
Petrogeochemical
characteristics of the Bù Dình sub-volcanic granitoid massif
in Thanh
Hóa, Viet Nam and its geological implication
Nguyễn
Thị Xuân, Bùi Thế Anh, Đỗ Quốc Bình, Bùi Thanh
Vân,
Tạ
Đình Tùng, Nguyễn Đức Chính
The sub-volcanic
granitoid of Bù Dình massif is located in Lang Chánh district, Thanh Hóa
province, covering an area of nearly 50 km2.
The basic petrographic composition of the rock is porphyritic granite and
coarse - medium to small grained granodiorite. In the rocks, the content of
plagioclase mineral (mainly andezin) is equal or more than potassium feldspar.
The rocks belong to medium K, calc-alkaline series and are dominant in sodium
(K2O/Na2O <1). The concentrations of La, Ce, Sm and Nd
elements are usually 20-70 times higher than those of the Chondrite.
Furthermore, the rocks are characterized by medium fractionation between light
- and heavy rare earth elements ((La /Yb)N = 12.8 -28.3). Bù Dình sub-volcanic
granitoids have high SiO2 content (>73%) and very low MgO with
Mg# values of ca. 10 to 28, indicating the crustal origin of magma. Our new
analytical results pointed out a similarity in petrography, mineralogy and
geochemistry of the Bù Dình granitoids to those of the sub-volcanic granitioid
of the Sông Mã complex and formed in the tectonic setting of plate collision.
Keywords: Red River Shear Zone, Tân
Hương granite, zircon U-Pb isotope.