PETROLOGY AND GEOCHEMICAL CHARACTERISTICS OF JATIBARANG VOLCANIC ROCKS IN NORTHERN WEST JAVA AND ITS IMPLICATION OF PALEOGENE VOLKANISM SYSTEM

• Main Author: HUTABARAT (NIM: 32006001); Tim Pembimbing : Prof. Dr. Emmy Suparka; Dr. Ir. Bambang Priadi;, JOHANES
• Format: Dissertations
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/20225
• Institution: Institut Teknologi Bandung

Research studies of petrogenesis of volcanic rocks Jatibarang Formation in the North West Java Basin which a sampling is taken from the rock core drilling in particular in terms of the characteristics of petrology and chemical patterns. Character of magma and order problem tectonic magmatic Jatibarang Formation volcanic rocks is something important enough to be researched in order to complete the evolution of the North Basin of West Java and West Java magmatism. <br /> <br /> <br /> The results of petrographic analysis showed that the rocks are covered in Jatibarang Formation in the North West Java Basin can be divided into volcanic rocks basalt, basaltic andesite, andesite, and tuff. <br /> <br /> <br /> The results of the main chemical elements, trace, and rare earth elements studied area volcanic rocks have SiO2 contents ranging from 47.81% to 63.98%, total alkali (Na2O + K2O) ranged from 3.33% to 7.74% , less than 1.25% TiO2 and calc-alkaline affinity, calc-alkaline to potassic shoshonitic, as well as having the content of MgO, Co, Ni, Cr and Mg # is low. This means Jatibarang Formation volcanic rocks are products magmatism activity associated with subduction zones and the parent magma, molten rock instead of primary sources. The results of the analysis-Pb isotope data indicate that the magma source is a mixture crust and mantle that involves mixing the components of the ocean and sediments. <br /> <br /> <br /> Plot in a variety of discrimination diagrams that illustrate tectonomagmatic volcanic rocks Jatibarang Formation formed arc environment continental type. <br /> <br /> <br /> Analysis of rare earth elements (REE) is a group of lanthanide elements (La, Ce, Nd, Sm, Eu, Gd, Dy, Er, Yb and Lu) to result in normalization kondrit pattern with a negative slope of the light rare earth elements (LREE)) of heavy rare earth elements (HREE) with multiples of 2000 times. This suggests a merger of a higher number LREE enriched fluids associated with subduction in the magma source of the sub-arc mantle. While the multi-element analysis of normalized kondrit overall show positive anomalies in Th and K with marked negative Nb anomalies, this confirms further sign magmatism arc associated with subduction. Based on K-Ar age data that have been determined on one sample and combined with age data that has been carried out by PT. Pertamina, assuming that the age obtained is correct, then there are at least two volcanism stages, ie stage 1 ranged from the oldest age 57.8 ± 1.4 million years until a minimum of 50.3 ± 2 million years shows the duration of at least 7.5 million years, represented by volcanic rocks dominated by pyroclastic tuff deposits (vitric tuff and lithic tuff) which may occur in the terrestrial environment represent volcanism explosive. Phase 2, the maximum age range from 47 million years until the lowest age of 39.19 (example RDG-371946-1947) shows the minimum duration for volcanism 7 million years, represented by lava-dominated volcanic rocks (basalt, andesite and basaltic andesite), and may represent volcanism effusive occurring terrestrial environment. Based on its petrology and geochemistry characteristics, volcanic rocks of Jatibarang Formation are the result of intensive fractionation of the relative cogenetic magma source and show calc-alkaline, potassic calc-alkaline until shoshonitic affinity. Its formation is associated with Northeast-Southwest <br /> <br /> <br /> subduction trend in the Active Continental Margin. This trend is consistent with Pattern of Meratus Belt.