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All Journal IJOG : Indonesian Journal on Geoscience Journal of Geosciences and Applied Geology
Mega Fatimah Rosana
Padjadjaran University
Earth & Planetary Sciences Engineering

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Petrogenesis of Rinjani Post-1257-Caldera-Forming-Eruption Lava Flows Heryadi Rachmat; Mega Fatimah Rosana; Ade Djumarma Wirakusumah; Gamma Abdul Jabbar
Indonesian Journal on Geoscience Vol 3, No 2 (2016)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (2691.244 KB) | DOI: 10.17014/ijog.3.2.107-126

Abstract

DOI:10.17014/ijog.3.2.107-126After the catastrophic 1257 caldera-forming eruption, a new chapter of Old Rinjani volcanic activity beganwith the appearance of Rombongan and Barujari Volcanoes within the caldera. However, no published petrogeneticstudy focuses mainly on these products. The Rombongan eruption in 1944 and Barujari eruptions in pre-1944, 1966,1994, 2004, and 2009 produced basaltic andesite pyroclastic materials and lava flows. A total of thirty-one sampleswere analyzed, including six samples for each period of eruption except from 2004 (only one sample). The sampleswere used for petrography, whole-rock geochemistry, and trace and rare earth element analyses. The Rombonganand Barujari lavas are composed of calc-alkaline and high K calc-alkaline porphyritic basaltic andesite. The magmashows narrow variation of SiO2 content that implies small changes during its generation. The magma that formedRombongan and Barujari lavas is island-arc alkaline basalt. Generally, data show that the rocks are enriched in LargeIon Lithophile Elements (LILE: K, Rb, Ba, Sr, and Ba) and depleted in High Field Strength Elements (HFSE: Y, Ti,and Nb) which are typically a suite from a subduction zone. The pattern shows a medium enrichment in Light REEand relatively depleted in Heavy REE. The processes are dominantly controlled by fractional crystallization andmagma mixing. All of the Barujari and Rombongan lavas would have been produced by the same source of magmawith little variation in composition caused by host rock filter process. New flux of magma would likely have occurredfrom pre-1944 until 2009 period that indicates slightly decrease and increase of SiO2 content. The Rombongan andBarujari lava generations show an arc magma differentiation trend.
Sabang Submarine Volcano Aceh, Indonesia: Review of Some Trace and Rare Earth Elements Abundances Produced by Seafloor Fumarole Activities Hananto kurnio; Ildrem Syafri; Adjat Sudradjat; Mega Fatimah Rosana
Indonesian Journal on Geoscience Vol 3, No 3 (2016)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (1442.696 KB) | DOI: 10.17014/ijog.3.3.173-182

Abstract

DOI:10.17014/ijog.3.3.173-182Geochemical analyses of selected coastal and seafloor samples from Sabang Area revealed abundances of trace and rare earth elements. The selected samples of element abundances were mostly taken from seafloor in the vicinities of active fumaroles either by grab sampler operated from survey boat above fumarole point or by diver directly took the samples on the seafloor especially at Serui - Sabang Bay. Results show that samples closed to seafloor fumaroles demonstrate plenty of trace and rare earth elements. The trace and rare earth elements mean values (n=10) are: Nb (4.33 ppm), La (16.52 ppm), Ce (38.82 ppm), Nd (19.15 ppm), Ce (38.82 ppm), Pr (4.907 ppm), Nd (19.15 ppm), Sm (4.04 ppm), Gd (3.95 ppm), Dy (3.38 ppm), Th (6.432 ppm), and U (4.335 ppm). Negatively, statistical correlations between Fe, Zn, and Ni as the main sulphide elements with sulphur is interpreted that sulphide minerals do not form in the Sabang Sea. Sea water influence in the mineralization process was shown by the good correlations between Fe, Zn, Pb, Ni, and Ba.
Geological and Geomorphological Studies in Parts of Angkola Sangkunur District, South Tapanuli Regency, North Sumatra Mohammad Fachri Azzaenuri; Mega Fatimah Rosana; Cecep Yandri Sunarie; Muhammad Eko Angga Syahputra; Ardiansyah Marbun
Journal of Geological Sciences and Applied Geology Vol 7, No 2 (2023): Journal of Geological Sciences and Applied Geology
Publisher : Faculty of Geological Engineering, Universitas Padjadjaran

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.24198/gsag.v7i2.50440

Abstract

This research focuses on studying geological conditions that develop in the research area which is based on studies related to geomorphology, stratigraphy and geological structures that develop in the research area. In this research, the data used comes from mapping and taking surface data in a research area with an area of 12.5 km2, followed by petrographic analysis to determine the types of rocks found in the research area. The research area is divided into three geomorphological units, namely Sloping Volcanic-Structural Rolling Hills, Steep Volcanic-Structural Hills, and Sloping Volcanic-Structural Rolling Hills. The drainage pattern in the research area consists of parallel patterns in almost the entire area and sub-dendritic flow patterns in the central part of the area. The research area is composed of 3 lithologies, from old to young, namely, andesite, diorite which was formed as an intrusion, and breccia which consists of polymic and monomic breccia with fragments in the form of andesite, diorite, quartz fragments and carbon. The structures in the study area have the main directions northwest-southeast and northeast-southwest, both of which influence the morphology of the study area.
Co-Authors Ade Djumarma Wirakusumah Adjat Sudradjat Ardiansyah Marbun Cecep Yandri Sunarie Gamma Abdul Jabbar Hananto kurnio Heryadi Rachmat Ildrem Syafri Mohammad Fachri Azzaenuri Muhammad Eko Angga Syahputra