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KARAKTERISTIK PETROLOGI KOMPLEKS INTRUSI KECAMATAN CIKALONGKULON KABUPATEN CIANJUR JAWA BARAT Firmansyah, Fahmi; Nugroho, Rio Priandri
JGE (Jurnal Geofisika Eksplorasi) Vol 10, No 2 (2024)
Publisher : Engineering Faculty Universitas Lampung

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.23960/jge.v10i2.394

Abstract

Penelitian tentang karakteristik batuan beku dapat berkontribusi pada penelitian lanjut tentang potensi sumber daya lainnya yang terkait dengan fenomena magmatisme, khususnya di lokasi yang memiliki sejarah magmatisme cukup panjang seperti di bagian barat Pulau Jawa. Studi karakteristik petrologi batuan beku pada penelitian ini dilakukan dengan menggunakan sampel yang diperoleh dari Cikalongkulon, Cianjur, Jawa Barat; sebuah lokasi dengan kompleks tubuh intrusi yang membentang hampir Barat-Timur. Dilakukan pengamatan lapangan dan petrografi guna menghasilkan sintesis terkait interaksi antaran tubuh batuan beku dan batuan samping di daerah penelitian. Dari observasi didapati bahwa terdapat metasomatisme yang terjadi akibat proses intrusi andesit terhadap batuan samping. Proses ini terjadi pada rentang suhu 270-320°C yang ditandai oleh kemunculan mineral sekunder berupa klorit, serisit, kalsit, kuarsa, dan epidot. Keberadaan metasomatisme ini juga mengindikasikan bahwa umur tubuh intrusi andesit harus lebih muda dari Miosen Tengah, berbeda dari interpretasi awal pada Peta Geologi Lembar Cianjur yang menempatkan tubuh batuan beku lebih tua dari batuan sedimen di sekitarnya.
Flow dynamics of unsteady pyroclastic density currents (PDC) from Sunda ignimbrite, West Java, Indonesia Ramadhan, Ilmi; Angkasa, Syahreza Saidina; Nugroho, Rio Priandri
Bulletin of Scientific Contribution Vol 19, No 2 (2021): Bulletins of Scientific Contribution : Geology
Publisher : Fakultas Teknik Geologi Universitas Padjadjaran

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.24198/bsc.v19i2.35272

Abstract

Sunda Volcano is the one of several volcanoes in Indonesia which produced ignimbrite deposit from caldera forming eruption. Depending on the volume and considerable thickness of the deposits, Sunda ignimbrite might has been deposited with a variety of flow mechanisms. Heterogeneous deposition mechanism will heavily controlled by numerous parameters such as velocity, rheology, types of flow-boundary zone, or pre-existing topographic influence. According to the deposition parameters, Pleistocene Sunda ignimbrite transportation and deposition mechanisms are still unclear. Here we show detailed observations of each facies and the Unconformity Bounded Stratigraphic Units (UBSU) approach to determine the flow sub-units and flow mechanism of the Sunda ignimbrite. Overall, we found that Sunda ignimbrite consists of five different facies. Forestepping stacking pattern from Sunda ignimbrites also observed from stratigraphic correlation indicates that energy instability occurred during transport and deposition in the PDC. Waxing energy of PDC which occured is caused by the development of granular-flow and fluid-escape dominated flow-boundary zone at the base and body of emplaced PDC. Our results demonstrate how Sunda ignimbrite emplacement mechanism can be affects by pre-existing topography which developed during the effusive eruption of Sunda Volcano. Furthermore, we also found that Sunda ignimbrite deposition has been changed the topography into the gentler relief due to this forestepping pattern of each ignimbrite units. The study of Sunda ignimbrite facies can reveal suitable hazard mitigation and also use to characterize heterogenity in groundwater aquifers and geothermal reservoirs. Moreover, detailed facies analysis and UBSU could give us informations on how explosive eruption at 0.205 M.a take places on the southern flank of Sunda Volcano.
KARAKTERISTIK PETROLOGI KOMPLEKS INTRUSI KECAMATAN CIKALONGKULON KABUPATEN CIANJUR JAWA BARAT Firmansyah, Fahmi; Nugroho, Rio Priandri
JGE (Jurnal Geofisika Eksplorasi) Vol. 10 No. 2 (2024)
Publisher : Engineering Faculty Universitas Lampung

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.23960/jge.v10i2.394

Abstract

Penelitian tentang karakteristik batuan beku dapat berkontribusi pada penelitian lanjut tentang potensi sumber daya lainnya yang terkait dengan fenomena magmatisme, khususnya di lokasi yang memiliki sejarah magmatisme cukup panjang seperti di bagian barat Pulau Jawa. Studi karakteristik petrologi batuan beku pada penelitian ini dilakukan dengan menggunakan sampel yang diperoleh dari Cikalongkulon, Cianjur, Jawa Barat; sebuah lokasi dengan kompleks tubuh intrusi yang membentang hampir Barat-Timur. Dilakukan pengamatan lapangan dan petrografi guna menghasilkan sintesis terkait interaksi antaran tubuh batuan beku dan batuan samping di daerah penelitian. Dari observasi didapati bahwa terdapat metasomatisme yang terjadi akibat proses intrusi andesit terhadap batuan samping. Proses ini terjadi pada rentang suhu 270-320°C yang ditandai oleh kemunculan mineral sekunder berupa klorit, serisit, kalsit, kuarsa, dan epidot. Keberadaan metasomatisme ini juga mengindikasikan bahwa umur tubuh intrusi andesit harus lebih muda dari Miosen Tengah, berbeda dari interpretasi awal pada Peta Geologi Lembar Cianjur yang menempatkan tubuh batuan beku lebih tua dari batuan sedimen di sekitarnya.
Preliminary Result on Optimum Seed Generation Bandwidth for Object-Based Image Segmentation (OBIS) of Porphyritic Igneous Thin Sections Nugroho, Rio Priandri; Widjaya, Victoria Vania Blanca; Roviansah, Mohamad
Jurnal Geologi dan Sumberdaya Mineral Vol. 25 No. 1 (2024): JURNAL GEOLOGI DAN SUMBERDAYA MINERAL
Publisher : Pusat Survei Geologi

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.33332/jgsm.geologi.v25i1.698

Abstract

Crystal size distribution (CSD) analysis is one of many methods for studying the crystallization history of magma. It involves labor-intensive digitation of all crystals, which may prolong the processing of large data sets. This study presents a preliminary result of Object-Based Image Segmentation (OBIS) as a semi-automatic approach in crystal digitation. Five data sets containing 9 photomicrographs of porphyritic igneous rock thin sections were processed using SAGA GIS. The procedure produced an optimum bandwidth equation of y = 38.455 ln(x) + 114, where x is the average size of sampled crystal in mm. Segmentation tests on another sample using the formula returned good and consistent results with important notes on sensitivity to textures which may result in crystal segment separation, such as fractures, veins, and sieve, as well as the inability to separate all groundmass crystals. Even though it shows good results, this formula only applies where the pixel-to-length conversion factor of 562.2 pixel/mm. Keywords: OBIS, SAGA GIS, Optimum bandwidth, Photomicrograph, Porphyritic igneous rock thin section.