VOLCANO STRATIGRAPHY AND PETROGENESIS BROMO VOLCANO AND SURROUNDING AREA, PROBOLINGGO DISTRICT, EAST JAVA PROVINCE

• Main Author: Nazar Abrory, Achmad
• Format: Final Project
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/36029
• Institution: Institut Teknologi Bandung

Bromo Volcano is an active volcano in East Java Province. The tectonic setting of East Java Province contributes to the geological setting including the magmatism in the area. This research was done to determine the geological aspect, magma series, magma differentiation and the tectonic setting of Bromo Volcano using the principle of volcano stratigraphy and petrogenesis. Remote Sensing analysis and field observation are conducted to identify the geomorphology, stratigraphy, and geological structure. The petrographic and geochemical analysis is used to determine the magma series, magma differentiation, and tectonic setting. This research showed that the research area is part of the volcanic landscapes that has 12 landforms. The volcano stratigraphy of the research area is divided into three Crowns. Those are Tengger Crown, Cemorolawang Crown, and Bromo Crown. Tengger Crown evolved to be Ngadisari Caldera. Cemorolawang Crown consists of Argowulan Hummock and Cemorolawang Hummock which located in Ngadisari Caldera. The Cemorolawang activity ended with the formation of the Sand Sea Caldera. Bromo Crown consists of Widodaren Hummock, Kursi Hummock, Segarawedi Hummock, Batok Hummock, and Bromo Hummock which located in Sand Sea Caldera. Volcanism processes in the research area produced igneous rocks and pyroclastic rocks/deposits. Geological structure in the research area consists of the primary structure and secondary structure. Primary structure consists of sheeting joint, columnar joint, autobreccia, vesicular, parallel lamination, and cross lamination. The secondary structure consists of Ngadisari Caldera Normal Fault and Sand Sea Caldera Normal Fault. Geochemical analysis using trace elements variation diagram shows that the hummocks in the research area came from a magma series which have the same magma source. Magma differentiation processes including crystal fractionation, magma mixing, and assimilation were interpreted based on geochemical analysis using oxide elements variation diagram, plagioclase composition abundance variation, and petrographic textural evidence. The Affinity of the rock suites in the research area categorized as (medium-high K) calc-alkaline originated from magmatism at the active continental margin.