EVOLUSI MAGMA BERDASARKAN ANALISIS GEOKIMIA DAN MIKRO TEKSTUR PLAGIOKLAS PADA INTRUSI ANDESIT GUNUNG JULANG DAERAH DESA CINANGSI DAN SEKITARNYA, KECAMATAN CISITU, KABUPATEN SUMEDANG, PROVINSI JAWA BARAT

Abstract

Java Island is part of a volcanic arc archipelago resulting from the subduction of the Indo-Australian plate which moved north under the Eurasian plate. The process of freezing magma into rock can reveal many stories behind it. The distance from subduction to rock formation will also influence what chemical elements accompany it. Andesite intrusions in the research area are part of the magmatism activity which is unique in that it has a different color at each observation location. This makes researchers interested in studying changes in the composition of andesite intrusions, considering that there has been no specific study regarding the genesis of andesite intrusions in the research area by previous researchers. The method used in the research consists of micro-texture analysis and geochemical analysis of rocks using the XRF (X-ray Fluorescence) method. Based on the results of geochemical and microtextural analysis of plagioclase, magmatism activity in the study area has experienced an evolution, this can be seen from the formation of repeated textures in one phenocryst, indicating that there is an increase in high temperatures and interactions with primitive magma and melts rich in Ca caused by the mixing of magma. large scale. because this can happen when magma mixes (magma mixing). In shallow magma chambers, turbulence is also experienced by magma rotation which causes physical and chemical changes as well as recrystallization or the growth of certain micro-textures. This is then supported by geochemical data which shows that the magma differentiation stage occurred at the last stage with a high magma affinity calc-alkaline series.

Keywords: intrusion, magma evolution, geochemistry, micro-texture