Geochemical characteristics of Chu Lai body granitoids in Nui Thanh, Quang Nam

Abstract

Chu Lai body granitoid typically had the gneiss structure. Petrography inclueded biotite and two-mica granitogneiss. The rock consisted of quartz (25 – 30%), plagioclase (28 – 30%), akaline feldspar (30 – 32%), biotite (7 – 8%) and musscovite (3 – 5%). Accessory minerals were zircone, apatite, garnet, etc. Geochemical characteristics were typically high SiO2 (73.89 – 74.38 wt%); high total amount of alkali (Na2O + K2O ̴ 8.28 – 8.89%). Aluminous saturation indexs - ASI (Al2O3/CaO + Na2O + K2O) are more than 1. They have enrichment of the lipthophile elements with high Cs, Rb and Pb indexs; negative anomalies were Nb, Ta and strong Eu, specially. Eu/Eu* values were very low (0.041 – 0.056). The petrographic and geochemical charecteristics showed that Chu Lai rocks were S-granite, formed during the collision tectonic between Indochina and South China block in the early Paleozoic.