Magma Evolution in The Formation of Lava Tube at Goa Lawa Purbalingga

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Abstract

Abstract. Goa Lawa Purbalingga is an eruption trace of Slamet Volcano. Currently used as a tourist destination. Geologically, it is an interesting phenomenon to study in more depth regarding the dynamics of magma evolution. The dynamics of the Plagioclase Mineral were measured using petrographic analysis and then confirmed using rock chemical analysis. Rock samples were taken in a structured manner from the bottom to the top, referring to the earlier of the eruption process to the later of the eruption process. In this way, the changes that occur in the magma from the beginning to the end of the eruption can determine the direction of its evolution. From this research, an understanding was obtained that morphologically the Goa Lawa area is included in the Slamet Volcano Lava Flow Ridge morphological unit. Which is composed of the Slamet volcana Lava rock group which consists of Scoria Basalt Lava. In Goa Lawa there are 5 layers of lava. In order from bottom to top, also meaning from Old to Young, there are Lava A, Lava B, Lava C, Lava D, and Lava E. The chemical composition of the lava ranges from SiO2 content values ​​of 50.53 to 51.35, still included in Basalt. The position of the depth where the initial magma melted did not significant dynamics, at a depth of 150 km. The mineralogical and chemical characteristics of the lava have not changed significantly and are still in the basaltic range, so the character of the magma has not changed, it has low viscosity and effusive eruption.