U-Pb zircon LA-ICP-MS and Hf composition in granitogneiss of Chu Lai body and its implication of the Kontum massif, central Vietnam

Abstract

The Chu Lai granitogneiss is widespread throught the Northern Kontum massif. The Chu Lai body is located in the W-SW of the Nui Thanh Townlet (Nui Thanh Dists., Quang Nam Prov.). On an areas of ~ 300 km2. The Chu Lai intrusion mainly consists two mica gneiss, it is light grey and have porphyritic textures. Its major minerals include plagioclase (25÷40%), K-feldpar (20÷40%), quartz (25÷35%), biotite (5÷13%) and mustcovite (0÷6%). Accessory minerals are apatite, zircon, orthit. Garnet and tourmaline are occiasionally found. Zircons separated from a granitogneiss sample colleted in Chu Lai body are generally euhedral to subhedral, dark gray and prissmatic in shape with 100÷300 µm, with length/witdth ratios from 1:1÷1:3. There are many Neoproterozoic - Cambrian ages among the zircon cores in the Chu Lai samples, and these are regarded as inherited zircons. The LA-ICP-MS zircon age is 431 Ma, corresponding to the Silurian. The Chu Lai granitogneiss strongly negative zircon εHf (-4.2÷-11.4) and complex inherited zircon components, characteristics of typical S-type granite. Hf model ages TDM2 1.5÷1.9 Ga, suggests that the Chu Lai granitogneiss was derived from partial melting of old crustal basement rocks, probaly Paleoproterozoic in age.