Petrology and Geochemistry of Intrusive Rocks in the Tanjung Area, South Sulawesi, Indonesia: Implications for Magma Origin, Source Materials, and Geodynamic Setting

Abstract

The origin of magma, source materials, and geodynamic setting of plutonic and volcanic rocks was elucidated by studying the characteristics of the rocks in the Tanjung area, South Sulawesi, Indonesia. The composition of plutonic rocks is dominated by granodiorite, granite, monzonite, and quartz monzonite, whereas volcanic rocks consist of porphyry basalt, amygdaloidal basalt, trachyte, and trachy-andesite. The main minerals in the rocks are quartz, K-feldspar plagioclase feldspars, Hornblende, biotite, pyroxene, and some opaque minerals. Plots of plutonic rock samples with calc-alkaline affinity indicated a typical I-type granitic rock. Meanwhile, plots of volcanic rock samples with calc-alkaline to shoshonitic affinity indicated S- and I-type basaltic rocks. Harker diagrams suggested that the rocks underwent crystallisation fractionation during magma evolution. Plutonic and Volcanic rocks showed enrichment of LILE and LREE and negative Eu anomalies, which resemble continental crust affinity. It is a product of partial melting in the upper continental crust. The geochemical characteristics demonstrate the relationship between the subduction environment and a continental arc.