Characteristics of Dioritic Intrusion at Kaligono Area, Kulon Progo Mountains, Indonesia: A Preliminary Study for Petrogenesis Implications

Abstract

This study defines the characteristics of dioritic rock intrusion in the Kaligono area, Kulonprogo Mountains, Indonesia. Previous studies suggest the existence of porphyry deposit system in the mentioned area, hosted by the dioritic intrusion. According to the Geologic Map of Yogyakarta Quadrangle, age of the dioritic intrusion is the Miocene. Study of the intrusion characteristics is very important to gain a better understanding of the geological model associated with the deposit system. This preliminary study focused on determining petrogenesis of the dioritic intrusion. Methods carried out in this study were field data collection, petrographic analysis, and geochemical analysis using ICP-AES (Inductive Coupled Plasma-Atomic Emission Spectrometry) and ICP-MS (Inductively Coupled Plasma Mass Spectrometry) analysis. Petrography analysis showed that igneous rocks in this research area consist of dioritic rock with phorphyritic texture and oscillatory zoning. Based on its geochemical composition, the rock samples can be classified as diorite and granodiorite and calc-alkaline suites. These rocks are enriched in LILEs (Rb, Ba, Sr, and K) and depleted in HFSEs (Nb, Ti, Zr). In addition, REE shows a slight enrichment of light-REE and depletion of HREE. These patterns of the trace elements including REE show a typical pattern of calc alkaline arc. Petrographic observation and geochemical variation indicate that the magma has undergone fractional crystallization.