A new record of Late Permian granitoid in Tra Phu - Tra Bong area, Quang Ngai (Kontum massif) and its tectonic implications

Tra Bong area in Quang Ngai province is located between the southern Tam Ky - Phuoc Son suture zone and the northern Kontum massif, which has recently been of broad interest to geologists. The area includes several stages of magmatic intrusions and extrusions from different origins and ages. The granitoid samples in this study are mainly granodiorite and weakly orientated medium - grained biotite granite collected in the Tra Phu, Tra Bong area. Their mineral composition is characterized by an assemblage of plagioclase, K - feldspar, quartz, hornblende, and biotite. Geochemically, they show a moderate to high SiO2 content (63.65 – 69.41 wt %), Na2O+K2O (6.65 – 8.24 wt %) and indicate A/CNK ratios of < 1.1, low TiO2, MnO, MgO and P2O5. The samples fall within the volcanic - arc field (volcanic - arc granites) , corresponding to I - type granite. The LA - ICP - MS U - Pb zircon ages for these rocks are between 255 – 252 Ma that indicate the timing of magmatic emplacement during Late Permian. The geochronological results indicate that Tra Phu granitoids in the studied area are younger than previously assumed (Ordovician - Silurian). This finding confirms that they formed during the convergence of the South China and Indochina blocks as well as the Indosinian Orogeny.