PETROLOGICAL CHARACTERISTICS AND COOLING DYNAMICS OF MOUNT PARANG AND MOUNT BONGKOK INTRUSION, PURWAKARTA, WEST JAVA

Abstract

Mount Parang and Mount Bongkok in Purwakarta represent well-exposed intrusive bodies in West Java. However, studies on their magmatic dynamics and crystallization history remain limited. This paper presents the petrological characteristics and crystallization dynamics of both bodies, based on petrographic observations and Crystal Size Distribution (CSD) analysis of plagioclase crystals. Field and petrographic observations reveal that both mountains are composed of andesite with phenocrysts of plagioclase, hornblende, and pyroxene, and show evidence of magma mixing and assimilation. CSD analysis indicates that the magma forming Mount Parang crystallized over a period of no less than 11.74–16.59 years. Meanwhile, the crystallization duration for the magma forming Mount Bongkok is estimated to be at least 10.93–18.95 years.