Characteristics of material composition and formation age of felsic dyke in Dak Ruong, Kon Ray, Kon Tum and its geological significance

Abstract

The felsic dykes in the Dak Ruong, Kon Ray, Kon Tum areas were 0.5 m to 15 m wide. The observed length was from a few tens of meters to over 1,000 m in the sub−longitude direction and northeast−southwest. The felsic dykes cut through the small−grained biotite granite of the Hai Van complex and the Proterozoic metamorphic formations of the Tac Po formation. The characteristics of the felsic dykes were phenocryst architecture with phenocrysts (5−20%) on a microcrystalline background (95−80%). The common phenocrysts were K−feldspar (35−40%), plagioclase (10−15%) and quartz (35−40%). They included plagioclase, K−feldspar, quartz, biotite, muscovite, sericite and ore. The main accessory minerals included zircon and apatite. The average SiO₂ content was about 75.53 wt%, the total potassium (K₂O and Na₂O) was about 6.66−7.22 wt% belonging to the lime−alkali series, high potassium, corresponding to the S−type granite. In the rare earth element group composition of the felsic dykes, the content of heavy rare earth (HREE) was hihger than that of the light rare earth (LREE). The rare earth elements were normalized with chondrites, giving a negative slope and a strong negative Eu anomaly. The ²⁰⁶Pb/²³⁸U zircon isotopic age results had an average age of 240 ± 2.1 Ma, corresponding to the middle Triassic age, Permian−Triassic period (Indosinian orogen). Their formation could be relaled to the internal extension between the Indochina and South China continental block.