Petrogenesis study of quaternary volcanic rocks based on petrography analysis in Lubuk Nipis Village, Muara Enim District, South Sumatra

Abstract

This study aims to identify the characteristics of quartz volcanic rocks as well as their existing source and process of formation in the Lubuk Nipis area of Muara Enim Regency, South Sumatera Province. In conducting this study, field observation is required to obtain primary data directly and then petrography analyze is needed to analyze volcanic rock samples obtained during field observation. There are 3 types of rock units generated by volcanic activity during the quaternary period in the study area. The three units of rock are, among others, units of andesite intrusion (Qpva), units of andesite lava (Qhv), and units of tuff lapilli & tuff breksi (Qhv). In units of andesite intrusion visible porphyritic crystal texture with Plagioclase minerals become the most dominating minerals with the emergence of other primary minerals such as Quartz, Feldspar, Biotite, Hornblende and Pyroxene. Andesite lava comes with 2 different types of characteristics, porphyritic and microporfiritic texture. There are also seen the flow texture that shows the lava flow process during the formation of rocks in andesit lava units. While other units of rock that is unit of tuff lapilli & tuff brecchia is a product of pyroclastic fall. This unit has a composition of tuff material that dominates, also present are crystalline materials such as plagioclase, quartz, feldspar, and biotite. Further assisted by the analysis of DEM (Digital Elevation Model) to see the geometry of the spread of volcanic facies, can be interpreted the order of formation of rock units in the study area.