Characteristics of volcanic rocks and associated intrusions based on petrography analysis in Jari-Krondonan Area, Bojonegoro Regency, East Java

Abstract Pandan volcano is one of the dormant Quaternary volcanoes in East Java characterized by several volcanic centers which extend to northern part. This study aimed identify rocks and intrusions Jari - Krondonan area, Bojonegoro as well determine their petrology mineralogical characteristics. Geological observation was conducted obtain primary data collect samples. Thin section samples prepared analyze petrographic aspects. Field shows hills at Mount Jati, Puru, Watu, Lawang sites. Based on field mapping, lithologies research area are andesitic lava intrusion with columnar joint or sheeting structure, surrounded breccia. Andesite porphyritic texture visible phenocrysts glass groundmass. Samples from Watu composed plagioclase hornblende main minerals. Jati Puru pyroxene. Quartz, sanidine, olivine present accessory Plagioclase pyroxene occasionally formed glomerocryst poikilitic texture, play an important role fractionation crystal settling processes. Sieve regular zoning suggest magma mixing. Gabbro metamorphic xenoliths found indicates interaction country rock during rising.