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Zhang, Xiaoran, Chia-Yu Tien, Sun-Lin Chung, Adi Maulana, Musri Mawaleda, Mei-Fei Chu, and Hao-Yang Lee. "A Late Miocene magmatic flare-up in West Sulawesi triggered by Banda slab rollback." GSA Bulletin 132, no. 11-12 (April 8, 2020): 2517–28. http://dx.doi.org/10.1130/b35534.1.
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Abstract Cenozoic magmatism occurs throughout West Sulawesi, Indonesia, yet its detailed evolution remains enigmatic due mainly to the scarcity of precise dating. Here, we report new whole-rock geochemical and zircon U-Pb-Hf isotopic data of plutonic/volcanic rocks and river sediments from West Sulawesi to constrain the petrogenesis and magmatic tempo. The magmatic rocks are intermediate to felsic (SiO2 = 58.1–68.0 wt%), high-K calc-alkaline to shoshonitic (K2O = 2.2–6.0 wt%), metaluminous to weakly peraluminous, and I-type in composition. Trace element concentrations and ratios (e.g., Nb/U = 1.7–4.3 and Ti/Zr < 28), along with negative zircon εHf(t) values (–17.0 to –0.4) and old crustal model ages (TDMC = 2.1–1.1 Ga), indicate a dominant magma source region from the underlying continental crystalline basement. U-Pb dating on zircons from ten magmatic rocks yielded weighted mean 206Pb/238U ages of 7.2–6.1 Ma, best representing the crystallization ages of host magmas, further consistent with the prominent age peaks (7.3–6.3 Ma) defined by detrital zircons from four sedimentary samples. Our new data, combined with available results, allow the identification of a noticeable climax of magmatism (flare-up) at ca. 7–6 Ma, forming a continuous magmatic belt throughout West Sulawesi. Given the absence of contemporaneous subduction and the coincidence of incipient opening of the South Banda Basin during ca. 7.15–6.5 Ma, the Late Miocene magmatic flare-up in West Sulawesi and coeval regional extension in eastern Indonesia are attributed to a resumed episode of Banda slab rollback.
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Usman, Ediar. "THE GEOCHEMICAL CHARACTERISTIC OF MAJOR ELEMENT OF GRANITOID OF NATUNA, SINGKEP, BANGKA AND SIBOLGA." BULLETIN OF THE MARINE GEOLOGY 30, no. 1 (February 15, 2016): 45. http://dx.doi.org/10.32693/bomg.30.1.2015.74.
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A study of geochemical characteristic of major elelemnt of granitoid in Western Indonesia Region was carried out at Natuna, Bangka, Singkep and Sibolga. The SiO2 contents of the granites are 71.16 to 73.02 wt%, 71.77 to 75.56wt% and 71.16 to 73.02wt% at Natuna, Bangka, and Singkep respectively, which are classified as acid magma. While in Sibolga the SiO2 content from 60.27 to 71.44wt%, which is classified as intermediate to acid magma. Based on Harker Diagram, the granites from Natuna, Bangka and Singkep as a co-genetic. In other hand the Sibolga Granite show as a scatter pattern. Granites of Natuna, Bangka and Singkep have the alkaline-total (Na2O + K2O) between 6.03 to 8.51 wt% which are classified as granite and alkali granite regime. K2O content ranges from 3.49 to 5.34 wt% and can be classified as calc-alkaline type. The content of alkaline-total of Sibolga granite between 8.12 to 11.81 wt% and classified as a regime of syenite and granite. The range of K2O is about 5.36 to 6.94wt%, and assumed derived from high-K magma to ultra-potassic types. Granites of Natuna, Bangka and Singkep derived from the plutonic rock types and calc-alkaline magma, while Sibolga granite magma derived from K-high to ultra-potassic as a granite of islands arc. Based on the chemical composition of granite in Western Indonesian Region can be divided into two groups, namely Sibolga granite group is representing the Sumatera Island influenced by tectonic arc system of Sumatera Island. Granites of Bangka and Singkep are representing a granite belt in Western Indonesian Region waters which is influenced by tectonic of back arc.Keywords: magma, geochemical characteristic, major element and Western Indonesian Region Kajian karakteristik geokimia dari unsur utama granitoid di Kawasan Barat Indonesia telah dilakukan di daerah Natuna, Bangka, Singkep dan Sibolga. Kandungan SiO2 granit Natuna antara 71,16 - 73,02%, Bangka antara 71,77 - 75,56%, Singkep antara 72,68 - 76,81% termasuk dalam magma asam. Granit Sibolga memiliki kandungan SiO2 antara 60,27 - 71,44% termasuk dalam magma menengah - asam. Berdasarkan Diagram Harker, granit Natuna, Bangka dan Singkep mempunyai asal kejadian yang sama (ko-genetik), sedangkan granit Sibolga membentuk pola pencar. Granit Natuna, Bangka dan Singkep mengandung total alkalin (K2O+Na2O) antara 6,03 - 8,51% termasuk dalam jenis rejim granit dan alkali granit. Berdasarkan kandungan K2O antara 3,49 - 5,34 %berat, bersifat kalk-alkali. Granit Sibolga mengandung total alkali antara 8,12 - 11,81% termasuk dalam rejim syenit dan granit, dan berdasarkan kandungan K2O antara 5,36 - 6,94% berasal dari jenis magma K-tinggi sampai ultra-potassik. Granit Natuna, Bangka dan Singkep berasal dari jenis batuan beku dalam dan magma kalk-alkalin yang berhubungan dengan penunjaman, sedangkan granit Sibolga berasal dari jenis magma K-tinggi - ultra-potassik sebagai granit busur kepulauan. Berdasarkan komposisi unsur kimia utama, granit di Kawasan Barat Indonesia dapat dibagi dalam dua, yaitu granit Sibolga yang mewakili P. Sumatera, dipengaruhi oleh sistem tektonik busur P. Sumatera. Granit Bangka dan Singkep dapat mewakili suatu jalur granit di perairan Kawasan Barat Indonesia yang dipengaruhi oleh tektonik busur belakang. Kata kunci: jenis magma, karakteristik geokimia, unsur utama, dan Kawasan Barat Indonesia
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Ahnaf, Jemi Saputra, Aton Patonah, and Haryadi Permana. "Petrogenesis of Volcanic Arc Granites from Bayah Complex, Banten, Indonesia." Journal of Geoscience, Engineering, Environment, and Technology 4, no. 2 (June 30, 2019): 104. http://dx.doi.org/10.25299/jgeet.2019.4.2.3171.
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This research aimed to reveal the petrogenesis of granitic rocks of Bayah Complex starting from magma differentiation to exposing event, this research also intended to determine the tectonic environment. The methods carried out in this research include field observation, petrographic analysis using polarized light microscopy, and geochemical analysis using X-Ray Fluorescence (XRF) and Inductively Coupled Mass Spectrometry (ICP-MS).
Petrographic analysis shows that Bayah granitic rocks are composed of quartz, plagioclase, and K-feldspar while the rest are amphibole, biotite, sericite, chlorite, epidote, and opaque. Based on its major oxide concentrations, Bayah granitic rocks classified as granite and diorite-quartz which have high-K calc-alkaline magma. 4 samples of granitic rocks showed the A/N+K+C > 1 molar ratios belonging to the peraluminous S-type granite index while the remaining 1 sample showed a molar ratio of A/N+ K+C < 1 and A/N+K > 1 which classified as metaluminous I-type granite. Accordingly, Bayah granitic rocks are S-type granite which crystallized from sediment-derived magma, the sediments itself estimated sourced from continental especially Malay Peninsula, Indonesian Tin Island, and Schwaner Mountains. During differentiation, the magma undergone crustal contamination reflected by the increase in both SiO2 0.51 wt% and Al2O3 1.95 wt%, and decrease in Fe2O3 + MgO 0.61 wt% from the pure composition of sediment-derived magma. Furthermore, the occurrence of crustal contamination also recognized from high concentrations of Rb and Ba which indicate the interaction of magma with the materials of continental crust.
Regard to the exposing event, Bayah granitic rocks approximated to be exposed due to regional tectonic activity which caused Orogenesa I in the Early Oligocene to the Late Oligocene. Moreover, based on the plot of trace elements especially Rb, Y, Nb, Ta, and Yb on Harker and tectonic discriminant diagrams, Bayah granitic rocks are formed on volcanic-arc active continental margins in accordance with regional tectonic setting.
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Idrus, Arifudin, Federica Zaccarini, Giorgio Garuti, I. Gusti Ngurah Kusuma Wijaya, Yoseph Calasanctius Amita Swamidharma, and Christoph Bauer. "Origin of Podiform Chromitites in the Sebuku Island Ophiolite (South Kalimantan, Indonesia): Constraints from Chromite Composition and PGE Mineralogy." Minerals 12, no. 8 (July 30, 2022): 974. http://dx.doi.org/10.3390/min12080974.
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The presence of PGM associated with the podiform chromitites in the Jurassic–Cretaceous ophiolite of Sebuku Island (South Kalimantan, Indonesia) is reported for the first time. Two types of chromitite have been recognized; one with high-Cr composition (Cr/(Cr + Al) > 0.7) occurs in the deep mantle, the other, high-Al (Cr/(Cr + Al) < 0.6), is located close to the Moho transition zone. The TiO2-Al2O3 relations indicate affinity to IAT and MORB, for the high-Cr and high-Al chromitites, respectively. However, both are believed to have formed by mantle/melt reaction and differentiation of a magma characterized by an initial IAT composition related to an SSZ. Primary magmatic inclusions (<10 μm) of laurite characterized by Ru/Os chondritic ratio are the only PGM found in the high-Cr chromitites, indicating crystallization from undifferentiated magma, at low fS2 in the mantle. In contrast, the high-Al to chondrite, suggesting the increase of fS2 in the evolved melt. Besides laurite, the high-Al chromitite contains a complex assemblage of secondary PGM (Pt-Fe, garutiite, iridium, ruthenium–magnetite aggregates, zaccariniite and unnamed Ru and Mn oxides). These secondary PGM have an irregular shape and occur exclusively in the chlorite matrix sometimes associated with Mn-Ni-Fe-Cr hydroxides. They are interpreted to have formed by desulfuration of primary interstitial PGM sulfides or to have precipitated from secondary fluids during low T alteration. The relative abundance of PPGE in the high-Al chromitite is interpreted as a result of PGE fractionation during differentiation of the parent melt of the chromitites.
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Aryani, L., F. Hakim, A. D. Titisari, G. Nugraha, and C. A. Mahardika. "Preliminary study of the origin of mafic mineral megacrysts in volcanic rocks in the southwestern part of Kulon Progo Mountains, Indonesia." IOP Conference Series: Earth and Environmental Science 851, no. 1 (October 1, 2021): 012031. http://dx.doi.org/10.1088/1755-1315/851/1/012031.
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Abstract The Bagelen district in the southwestern part of Kulon Progo Mountains has a unique aspect in the form of the occurrence of mafic mineral megacrysts in volcanic rocks. This research is conducted to determine the type, the distribution, and the origin of those megacrysts, which are abundant in pyroclastic rocks. Detailed geological mapping on an area of 4 x 4 km with a scale of 1: 25,000 and petrographic analysis were done to explain the geological aspects that led to the presence of mafic mineral megacrysts in the study area. Petrographic analysis shows that the types of mafic mineral megacryst are hornblende, clinopyroxene, and plagioclase. Their features under the microscope observation are oscillatory zoning, half oscillatory zoning, sieve, and breakdown texture. These minerals are found as single crystal fragments and also as clinopyroxene and hornblende cumulate fragments in pyroclastic breccia. Based on mineralogical composition and texture, these mafic mineral megacrysts were formed by fractional crystallization process in the form of crystal settling mechanism. These minerals were initially accumulated in the bottom of magma chamber, then carried upward by rapid magma rising in association with explosive eruption event of Mount Ijo. These minerals were then transported on the surface through the mechanism of pyroclastic flow and were deposited in the valley to form an alluvial fan morphology in the southwestern part of Kulon Progo Dome.
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Harbowo, D. G., B. Priadi, T. Julian, R. N. Amelia, D. J. P. Sihombing, and F. S. Kencana. "A preliminary study on the element abundance in the Hulusimpang Formation, Way Kalianda, Pesawaran, Lampung, Indonesia." IOP Conference Series: Earth and Environmental Science 882, no. 1 (November 1, 2021): 012078. http://dx.doi.org/10.1088/1755-1315/882/1/012078.
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Abstract Hulusimpang Formation.has known as Oligocene-Miocene rocks that consisted of volcanoclastic rock. Its scope was wide, especially in southern Sumatra. This formation is supposed as a prospect host of various hydrothermal mineralization. A preliminary study was carried out to examine the abundance of elements located in Way Kalianda River, Pesawaran, Lampung. This study was conducted by easuring its stratigraphy and analyzing its composition using an X-Ray fluorescence analyzer. The lithologies generally consist of lapilli tuffs, volcanic breccias, interbeded by claystone and sandstone; in addition, it is also frequently found petrified wood and andesitic-lithic fragments. As a result, the significant abundant elements are Fe (35.5%), Si (27.9%), Al (17.4%), K (6.7%), Cl (5.5%), Ti (1.7%), and Ca (1.5%) and also Mn, Ag, P, Mg, Sr, Zr, and Co. It also presents trace elements such as Rb, Zn, Pb, Te, V, Ba, Cr, Sn, Ni, Ga, Nb, Mo, and Eu. These elements are suggested from distal facies of intermediates-magma series Tertiary volcano.
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Gertisser, Ralf, and Jörg Keller. "Temporal variations in magma composition at Merapi Volcano (Central Java, Indonesia): magmatic cycles during the past 2000 years of explosive activity." Journal of Volcanology and Geothermal Research 123, no. 1-2 (April 2003): 1–23. http://dx.doi.org/10.1016/s0377-0273(03)00025-8.
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Putra, Shandiyano, Hamdi Rifai, Riyan Fadila, Ella Destari Ningsih, and Rizaldi Putra. "Distribution of Pyroclastic Deposits around Lake Maninjau Agam District, West Sumatera, Indonesia based on Magnetic Susceptibility." Trends in Sciences 19, no. 7 (March 14, 2022): 3218. http://dx.doi.org/10.48048/tis.2022.3218.
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Lake Maninjau is an erupting volcano in West Sumatra Province. The results of the eruption have now settled in various places and scattered in all directions due to the transportation process. The process of transporting volcanic material is caused by several factors such as wind and rain. This study aims to analyze the distribution pattern of volcanic material that is scattered around Lake Maninjau, Agam Regency. We have 25 types of samples divided into 3 categories. There are pumice, lava, and ash. This research was conducted at the FMIPA UNP Laboratory using the rock magnetization method. In this study, a Bartington MS2 with MS2B sensor was used by calculating the magnetic susceptibility value based on the mass of the sample. The results of the magnetic susceptibility analysis obtained varied between 74.7×10-8 - 3956.7×10-8 m3/kg which is included in the ilmenite (FeTiO3) group. The highest value of vulnerability was 2800×10-8 - 4000×10-8 m3/kg found at the core of Lake Maninjau ± 5.0 km seen from the green contour map. The lowest magnetic susceptibility values 0 - 800×10-8 m3/kg were found in the western part of Lake Maninjau and the material was deposited at a distance of ± 13 km from the core of the Maninjau caldera. Deposits were also found in the eastern part of Lake Maninjau ± 22.4 km from the core of Lake Maninjau and to the Middle East ± 23 miles from the core of the Maninjau caldera. The white color represents 1600 - 2000×10-8 m3/kg which is included in the moderate magnetic susceptibility value, which is ± 4 km to the southeast of the Maninjau caldera. The benefit that can be taken from this research in the ink industry is the presence of a magnetic mineral distribution map based on suseptibility values and makes it easier to find raw materials for making ink around Lake Maninjau.
HIGHLIGHTS
Lake Maninjau stores various elements contained in the released material. The elements that make up magnetic minerals are Fe, Si, Ca, Al, K, Ti. The collection of several elements forms the raw magnetic mineral
Volcanic material contains the mineral ilmenite which in theory can be used as a raw material for making TiO2 pigments, ferrous metals and chemical compounds containing iron. In the industrial field TiO2 is widely used as a paint pigment, additives in the paper-making process, ceramic raw materials, pharmaceutical industry raw materials and TiO2 is also widely used for photoclinic materials
Superparamagnetic minerals are present in volcanic rock samples resulting from an eruption, the magnetic sensibility values at high frequencies are slightly lower than the magnetic susceptibility values at low frequencies. If there are no superparamagnetic minerals (SP)
It can be assumed that the ancient volcanic eruptions of Maninjau belong to the type of plinia eruption which is highly exposed from magma with high viscosity or acid magma, the composition of the magma is andesitic to rhyolitic
GRAPHICAL ABSTRACT
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Sutarto, Sutarto, Adi Sulaksono, Dema Laksana T., Anggita Mahyudani, Ajimas Setiahadiwibowo P., and Muhammad Nurcholis. "REE content of volcanic rocks and their weathered horizons in the Muria Volcanic Complex, Central Java, Indonesia." Bulletin Mineralogie Petrologie 30, no. 1 (2022): 28–37. http://dx.doi.org/10.46861/bmp.30.028.
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We investigated bedrock samples and their weathered horizons collected from the Muria Volcanic Complex (MVC), Central Java, Indonesia. In addition to petrographic study, samples were analysed using X-ray diffraction (XRD), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), and inductively coupled plasma-mass spectrometry (ICP-MS) for mineral composition, major elements, and trace elements, respectively. Bedrock samples (n = 10) from the MVC have ΣREE ranging from 364 to 739 ppm (avg. 579 ppm). Basanite (n = 2) and phonotephrite (n = 2) are consistently high in ΣREE (659 - 739 ppm) compared with basaltic trachyandesite, trachyandesite, and trachyte. Apatite is the only REE-bearing mineral observed in basanite and phonotephrite (up to ~1 vol.%). The ΣREE is positively corelated with P2O5, which inversely corelates with SiO2. The weathered horizons contain clay minerals that consist primarily of kaolinite ± halloysite. The REE content of the weathered horizons (n = 7) is up to 183 ppm higher than those of the bedrocks. The decrease in CaO and P2O5 indicates a fractionation of apatite at early stage of magma evolution, resulting in the depletion in the ΣREE content in the residual melt. We suggest that apatite is the major host of REE in the MVC alkali-rich, silica-undersaturated volcanic rocks, as evidenced by our petrographic and geochemical data. We also suggest that the increase in ΣREE in the weathered horizon is due to the presence of clay minerals, particularly kaolinite and halloysite.
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Zglinicki, Karol, Krzysztof Szamałek, and Irena Górska. "The Cyclops Ophiolite as a Source of High-Cr Spinels from Marine Sediments on the Jayapura Regency Coast (New Guinea, Indonesia)." Minerals 10, no. 9 (August 20, 2020): 735. http://dx.doi.org/10.3390/min10090735.
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The first detailed mineralogy, geochemistry and origin of heavy minerals in marine sediments along the Jayapura Regency coast on the Indonesian part of New Guinea Island are reported as part of a larger set of investigations conducted since 2009. In these sediments, the following heavy minerals were identified: high-Al and high-Cr spinels, chromian andradite, Mg-olivine, magnetite, mixture of iron (III) oxyhydroxides (limonite) and minerals from serpentine-group minerals (lizardite, antigorite). The heavy mineral fraction of marine sediments contains increased concentrations of metals, including W (up to 257.72 ppm) and Ag (up to 1330.29 ppb) as well as minor amounts of Ni (7.1–3560.9 ppm) and Cr (68.0–5816.0 ppm). The present state of geological knowledge suggests that there are no known prospects for rich Ti, Ni, Co, Cr, Au deposits along the examined part of the Jayapura coast. However, the average content of Ag and W is high enough to provide an impulse for suggested further deposit research. The source of marine sediments is Cyclops ophiolite, which contains a typical ophiolite sequence. Cyclops Mountain rocks have undergone intense chemical weathering processes and the resulting eroded material has been deposited on the narrow continental shelf. The chemical composition of chromian spinels indicates that their source is depleted peridotites from the SSZ (supra-subduction zone) environment of the Cyclops ophiolite. A detailed geochemical examination indicates that the evolution of parental melt of these rocks evolved towards magma with geochemical parameters similar to mid-ocean ridge basalt (MORB).
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Handley, H. K., M. Reagan, R. Gertisser, K. Preece, K. Berlo, L. E. McGee, J. Barclay, and R. Herd. "Timescales of magma ascent and degassing and the role of crustal assimilation at Merapi volcano (2006–2010), Indonesia: Constraints from uranium-series and radiogenic isotopic compositions." Geochimica et Cosmochimica Acta 222 (February 2018): 34–52. http://dx.doi.org/10.1016/j.gca.2017.10.015.
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Patonah, Aton, Haryadi Permana, and Ildrem Syafri. "The Transitional Gabbroic Rocks in Bayah Geological Complex, Western part of Java, Indonesia, Inferred from XRF, ICP-MS, and Microprobe Analysis." Journal of Geoscience, Engineering, Environment, and Technology 6, no. 4 (December 28, 2021): 177–83. http://dx.doi.org/10.25299/jgeet.2021.6.4.7189.
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Gabbro, is a fossil remnant of oceanic crust in western part of Java, found at Bayah Geological Complex (BGC) and Ciletuh Melange Complex (CMC), Indonesia. It has been studied by using petrographic, X-Ray Fluorescence (XRF), and inductively coupled plasma-mass spectrometry (ICP-MS) and mineralogical (microprobe) analyses. Mineral and geochemical composition of these rocks provide important clues to their origins since the rocks have been deformed and gone through auto metamorphism, beside they contain the economic mineral and or rare earth elements (REE). Gabbroic rocks in these two areas generally shows phaneritic to porphyritic texture, granular texture. These rocks in CMC are dominated by plagioclase (oligoclase to albite), hornblende, pyroxene, partly altered to tremolite, actinolite, chlorite, epidote, and sericite; meanwhile those of BGC dominantly consist of plagioclase, pyroxene, hornblende, some present of chlorite, actinolite, epidote and biotite as secondary minerals. In multi-element diagrams, gabbroic rocks in CMC show strong negative Sr and Zr, but positive Nb anomaly, while those of BGC show strong negative anomaly of Nb and Zr. In addition, based on rare earth elements (REE) diagrams, gabbroic rocks in CMC show depleted of light rare earth elements (LREE) with negative Eu anomaly, while gabbro’s in BGC show enrichment of LREE. These characteristics indicate that GBC’s and CMC’s gabbroic rocks came from different magma sources, one was formed by partial melting of depleted upper mantle reservoir while the other one was formed by partial melting of mantle wedge with active participation of subducted slab in an arc tectonic setting, suprasubduction zone which were formed at started Upper Cretaceous to Paleogene, and they had retrograde metamorphism to epidote amphibolite facies.
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Adi Nugroho, Kevin Setyo, Iwan Setiawan, and Tri Winarno. "Comparison of Granitoid Characteristics West Kalimantan and Karangsambung Based On Mineralogical And Geochemical Aspects." Journal of Geoscience, Engineering, Environment, and Technology 6, no. 3 (September 21, 2021): 152–63. http://dx.doi.org/10.25299/jgeet.2021.6.3.7417.
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Indonesia was included in the ring of fire so that it has various types of tectonic products, one of which is granitoid. Granitoid is very complex rock and many are found in Indonesia. Some of them are found in West Kalimantan and Karangsambung. Basis of the reasearch is there is no research that compares granitoid in two regions. The purpose of this study was to compare rock characteristics and granite petrogenesis of West Kalimantan and Karangsambung. The research method used was collecting data on field, also laboratory analysis of rock samples using a polarization microscope, refraction microscope, and X-Ray Fluorescence analysis. The mineralogical characteristics of each study area tend to be almost the same. The predominant composition of the main minerals is quartz, plagioclase and orthoclase. But specifically the rock samples from West Kalimantan have been altered from phylic-silicification-propylitic. The entire study area contained accessory minerals, namely apatite, zircon, titanite, and for monazite only in the West Kalimantan sample. There was mineralization up to the supergene stage in the presence of the characteristic minerals for the supergene covelite and chalcocytes in the West Kalimantan sample. Geochemical analysis of both regions shows the same magma affinity, namely Calc Alkaline - High K Calc Alkaline. For West Kalimantan, the value of A / CNK <1.1 has a type metaluminious and > 1.1 a type peraluminious. Meanwhile, Karangsambung A / CNK value <1.1 has a type metaluminious. So that West Kalimantan granite has two I-type and S-type. While Karangsambung is I-type. West Kalimantan granite is formed in continental arc granite (CAG) and continental collision granite (CCG). Meanwhile, Karangsambung in Volcanic Arc Granite (VAG). It can be concluded that the granites of the two regions have quite different characteristics even though they belong to a relatively similar tectonic environment.
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Mulyaningsih, Sri, Sutikno Bronto, Arie Kusniadi, Lilis Apriyanti, L. Budiyanto, and Danis Agoes Wiloso. "The Petrology and Volcano-Stratigraphy of The Muria-Peninsula High-K Volcanic Rocks, Central Java, Indonesia." Journal of Geoscience, Engineering, Environment, and Technology 7, no. 2 (June 30, 2022): 69–80. http://dx.doi.org/10.25299/jgeet.2022.7.2.9602.
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The Muria-Peninsula is a Quaternary volcano located in the northern Sunda arc. Its activity was controlled under high potassic and very high potassic magma series resulting in leucite-rich trachyte and pyroxene-rich basaltic-andesite. It is a strato-type volcano that is composed of lava, breccia, and tuff layers, and some dikes have some volcanic craters and maars varying in age and composition. The study area is covering the volcanoes of Muria, Genuk, and Patiayam. This paper aims to describe the petrology, mineralogy, and volcano-stratigraphy of the different volcanic materials. The data and materials were sourced from the primary and secondary data. The methods are field mapping, stratigraphy measurements, collecting samples, thin section analyses, and major element geochemistry using X-Ray fluorescence (XRF). The results describe two groups of volcanic rocks consisting of pyroxene-rich andesitic-basaltic volcanic materials and leucite-rich trachytic volcanic materials. Augite presents in the andesitic basalt together with small grains of olivine and a few anorthite and foid minerals. Aegirine (Na-Pyroxene) is present in the leucite-rich trachyte that is often associated with biotite and hornblende. Na-Ca Plagioclase such as labradorite-andesine is often present in the basaltic-trachy-andesite that is usually rarely leucite. The major elements show high-K volcanic rocks with % K2O is 4-5.9% and very high-K volcanic rocks (with % K2O is between 6-8.24%) and low-K volcanic rocks that contain % K2O is 2-3,9%. There are two groups of high-K to very high-K volcanic materials consisting of silicic-rich volcanic materials (~57-64% of SiO2) and low-silicic volcanic materials (~46-50%). The TAS diagram identifies tephrite, phonolite, and trachyte. Stratigraphic data identifies calcareous sediments of the Bulu Formation as the basement rocks of the Muria trachyandesite. Beds of pumice-rich volcanic breccia of the Ujungwatu Formation are the basement rocks of the basanite-tephrite of the Genuk Volcano, and the tuff of the Ujungwatu is also exposed consisting of the basanite-tephritic-phonolite of the Patiayam Volcano. The leucite-like feldspars are very common in the andesite lava and dikes that compose the crater of Muria. Most of the Muria volcanic materials are rarely in leucite, while some maars contain pumice-rich pyroclastic flows and basaltic lava. The results of the major elemental analysis of the Muria materials indicate that the rock tends to be of medium to high K affinity (~2% K2O). The Genuk and older Muria are consisting of leucite-rich tephrite-phonolite. It was two periods of magmatic series developed in the Muria-Peninsula that was resulting in the high-K to very high-K magmatism and the medium K Kalk-alkaline magmatism.
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Sukadana, I. Gde, Agung Harijoko, and Lucas Donny Setijadji. "Tataan Tektonika Batuan Gunung Api di Komplek Adang Kabupaten Mamuju Provinsi Sulawesi Barat." EKSPLORIUM 36, no. 1 (May 30, 2015): 31. http://dx.doi.org/10.17146/eksplorium.2015.36.1.2769.
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Kompleks batuan gunung api Adang di daerah Kabupaten Mamuju, Sulawesi Barat secara lebih detail dapat dikelompokkan menjadi tujuh, yaitu kompleks Tapalang, Ampalas, Adang, Malunda, Karampuang, Sumare, dan Labuan Rano. Komplek Adang merupakan salah satu komplek gunungapi utama yang masih dapat diidentifikasi bentukan morfologinya dengan baik. Komplek ini tersusunatas batuan gunung api basa hingga intermediet yang memiliki nilai laju dosis radiasi cukup tinggi yang disebabkan oleh kandungan mineral radioaktif di dalamnya. Keterdapatan mineral radioaktif pada batuan basaltik-andesitik belum pernah dijumpai di Indonesia sehingga hal ini menjadi sangat menarik untuk dilakukan penelitian terutama tataan tektonika pembentukan batuan komplek gunung api tersebut. Tujuan penelitian ini adalah untuk menentukan tipologi magmatik yang terkait dengantataan tektonikanya dengan pendekatan geokimia batuan gunung api menggunakan analisis X-Ray Fluorescence (XRF). Batuan gunung api Adang merupakan hasil dari proses vulkanisme suatu komplekgunung api yang memiliki pusat erupsi dan beberapa kubah lava. Batuan tersebut tersusun atas batuan trachyte-phonolite, dengan afinitas magmatiknya ultrapotasik, Dari data tersebut dapat diinterpretasi bahwa tataan tektonika magmatologinya adalah active continental margin(ACM). Magma asal yang membentuknya dari aktivitas gunung apinya dipengaruhi oleh kerak benua mikro barat daya (South West/SW) Sulawesi. Adang volcanic complexlocated in Mamuju Region, West Sulawesi can be grouped more detail into seven complexes that are Tapalang, Ampalas, Adang, Malunda, Karampuang, Sumare, and Labuan Rano. Adang complex is one of the main volcanic complexes that still can be identified with good morphological formations. This complex is composed of alkaline volcanic rocks with basic to intermediates composition that have high value of radiation dose rate caused by their radioactive mineral content. Radioactive mineral occurrences on the basaltic-andesitic rocks has never been found in Indonesia, so it becomes very interesting to do research mainly tectonic settings of the volcanic rock complex formation. The purpose of this study is to determine magmatiic typology related with the tectonic setting based on volcanic rock geochemistry using X-Ray Fluorences (XRF) analysis. Adang volcanic rock is the result of a complex process of volcanism having a volcanic center and several lava domes. They are composed of phonolite to dacite rock, with ultrapotassic affinity, interpretation of data concluded that tectonic setting of magmatism formed in active continental margin (ACM). Magmatism source from vulcanic activities influenced by South WestSulawesi micro-continental crust.
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Voigt, Annika, Michael Cassidy, Jonathan M. Castro, David M. Pyle, Tamsin A. Mather, Christoph Helo, Mirzam Abdurrachman, and Idham Andri Kurniawan. "Experimental Investigation of Trachydacite Magma Storage prior to the 1257 Eruption of Mt Samalas." Journal of Petrology, July 25, 2022. http://dx.doi.org/10.1093/petrology/egac066.
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Abstract The caldera-forming Samalas eruption of the Samalas-Rinjani volcanic complex on Lombok, Indonesia, in 1257 CE ranks as one of the most explosive and sulfur-rich eruptions of the last thousand years. Along with other significant events (e.g., Tambora 1815, El Chichón 1982), Samalas 1257 forms a class of powerful eruptions of magmas of intermediate alkaline composition which remain relatively understudied. This study aims to better understand the pre-eruptive magma reservoir conditions and volatile storage capacities of intermediate alkaline systems, using the 1257 Samalas eruption as a case study. Systematic partial-equilibrium experiments were run to constrain potential magma reservoir conditions (25–200 MPa and 850–1000°C) by examining changes in the chemistry and textures of experimental glass and mineral products. Natural trachydacite pumice from the 1257 Samalas eruption was used as the experimental charge for a series of water-saturated experiments run in cold-seal pressure vessels, buffered at an oxygen fugacity ƒO2 of NNO/NNO+1 log units. Assessing the match between natural and experimental glass compositions and mineral phases and textures, reveals that pre-eruptive magma reservoir conditions were between 875°C and 930°C and ca. 100–150 MPa (4.5 ± 1 km depth). Breakdown of experimental amphibole at pressures below 75 MPa, and plagioclase instability at 950°C/100 MPa, provide the strongest constraints on phase stabilities that are consistent with the magma storage region. In the observed temperature and pressure range, the natural compositions of plagioclase, amphibole and orthopyroxene are replicated in experimentally precipitated rims. Clinopyroxene and high anorthite plagioclase (An>64) in the natural mineral assemblage could not be replicated in the experiments, implying that these compositions most likely did not grow in the shallow pre-eruptive reservoir of Mt Samalas. The pre-eruptive storage depths of trachydacite magma are significantly shallower than the postulated magma storage at the currently-active basaltic-andesite magmatic system at Rinjani, and thus monitoring magma storage depth may be a useful indicator of changing magma composition in the future. Our findings show that highly explosive, VEI 7 eruptions of intermediate alkaline magma can be fed from a relatively limited range of storage pressures (100–150 MPa), suggesting accumulation of magma in one place, rather than the rapid extraction of magma from a vertically-extensive, transcrustal magma system.
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Bernard, Olivier, Caroline Bouvet de Maisonneuve, Laurent Arbaret, Kazuhide Nagashima, Jeffrey Oalmann, Arief Prabowo, and Antonius Ratdomopurbo. "Varying processes, similar results: How composition influences fragmentation and subsequent feeding of large pyroclastic density currents." Frontiers in Earth Science 10 (September 14, 2022). http://dx.doi.org/10.3389/feart.2022.979210.
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Unlike their silicic counterparts, mafic eruptions are known for being on the low-end of the explosivity spectrum with eruption styles commonly ranging from effusive to Hawaiian fire fountaining. However, there are increasing discoveries of large mafic Plinian eruptions, sometimes generating ignimbrites, suggesting that this phenomenon might not be so uncommon. So, what processes lead a mafic magma to fragment violently enough to generate extensive ignimbrites?We sampled pumices from ignimbrites and PDCs with a compositional range from basaltic-andesite (Curacautín ignimbrite, Volcàn Llaima, Chile), andesite (Marapi, Indonesia) to trachyte (Gunungkawi ignimbrite, Batur, Indonesia). We use SEM imagery and X-ray Microtomography on pyroclasts from these deposits to characterize phenocryst, microlite and vesicle textures. From vesicle number densities we estimate fragmentation decompression rates in the range of 0.4–1.6 MPa/s for the three deposits. With a combination of EPMA and SIMS analyses we characterise pre-eruptive storage conditions. Based on the bulk and groundmass compositions, the storage temperature (1,050–1,100°C), pressure (50–100 MPa) and phenocryst content (1.0–2.5 vol%), we conclude that the basaltic-andesitic Curacautín magma was at sub-liquidus conditions, which allowed fast and widespread disequilibrium matrix crystallization (0–80 vol%) during ascent to the surface. Combined with the important decompression rate, this intense crystallization led to a magma bulk viscosity jump from 103 up to >107 Pa s and allowed it to fragment brittlely. Conversely, for the Marapi PDC and Gunungkawi ignimbrite, similar decompression rates coupled with larger initial bulk viscosities of 105–106 Pa s were sufficient to fragment the magma brittlely. The fragmentation processes for these latter two deposits were slightly different however, with the Marapi PDC fragmentation being mostly driven by vesicle overpressure, while a combination of bubble overpressure and intense strain-rate were the cause of fragmentation for the Gunungkawi ignimbrite. We conclude that mafic ignimbrites can form due to a combination of peculiar storage conditions that lead to strongly non-linear feedback processes in the conduit, particularly intense microlite crystallization on very short timescales coupled with intense decompression rates. Conversely, the high viscosity determined by pre-eruptive storage conditions, including temperature and volatile-content, are key in controlling the formation of more evolved magmas PDCs'.
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Whitley, Sean, Ralf Halama, Ralf Gertisser, Katie Preece, Frances M. Deegan, and Valentin R. Troll. "Magmatic and Metasomatic Effects of Magma–Carbonate Interaction Recorded in Calc-silicate Xenoliths from Merapi Volcano (Indonesia)." Journal of Petrology 61, no. 4 (April 2020). http://dx.doi.org/10.1093/petrology/egaa048.
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Abstract Magma–carbonate interaction is an increasingly recognized process occurring at active volcanoes worldwide, with implications for the magmatic evolution of the host volcanic systems, their eruptive behaviour, volcanic CO2 budgets, and economic mineralization. Abundant calc-silicate skarn xenoliths are found at Merapi volcano, Indonesia. We identify two distinct xenolith types: magmatic skarn xenoliths, which contain evidence of formation within the magma; and exoskarn xenoliths, which more likely represent fragments of crystalline metamorphosed wall rocks. The magmatic skarn xenoliths comprise distinct compositional and mineralogical zones with abundant Ca-enriched glass (up to 10 wt % relative to lava groundmass), mineralogically dominated by clinopyroxene (En15-43Fs14-36Wo41-51) + plagioclase (An37-100) ± magnetite in the outer zones towards the lava contact, and by wollastonite ± clinopyroxene (En17-38Fs8-34Wo49-59) ± plagioclase (An46-100) ± garnet (Grs0-65Adr24-75Sch0-76) ± quartz in the xenolith cores. These zones are controlled by Ca transfer from the limestone protolith to the magma and by the transfer of magma-derived elements in the opposite direction. In contrast, the exoskarn xenoliths are unzoned and essentially glass-free, representing equilibration at sub-solidus conditions. The major mineral assemblage in the exoskarn xenoliths is wollastonite + garnet (Grs73-97Adr3-24) + Ca-Al-rich clinopyroxene (CaTs0-38) + anorthite ± quartz, with variable amounts of either quartz or melilite (Geh42-91) + spinel. Thermobarometric calculations, fluid-inclusion microthermometry and newly calibrated oxybarometry based on Fe3+/ΣFe in clinopyroxene indicate magmatic skarn xenolith formation conditions of ∼850 ± 45°C, < 100 MPa and at an oxygen fugacity between the NNO (nickel–nickel oxide) and HM (hematite-magnetite) buffer. The exoskarn xenoliths, in turn, formed at 510–910°C under oxygen-fugacity conditions between NNO and air. These high oxygen fugacities are likely imposed by the large volumes of CO2 liberated from the carbonate. Halogen- and sulphur-rich mineral phases in the xenoliths testify to infiltration by a magmatic brine. In some xenoliths, this is associated with the precipitation of copper-bearing mineral phases by sulphur dissociation into sulphide and sulphate, indicating potential mineralization in the skarn system below Merapi. The compositions of many xenolith clinopyroxene and plagioclase crystals overlap with that of magmatic minerals, suggesting that the crystal cargo in Merapi magmas may contain a larger proportion of skarn-derived xenocrysts than previously recognized. Assessment of xenolith formation timescales demonstrates that magma–carbonate interaction and associated CO2 release could affect eruption intensity, as recently suggested for Merapi and similar carbonate-hosted volcanoes elsewhere.
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Linn Zaw, Kyaw, Lucas Donny Setijadji, I. Wayan Warmada, and Koichiro Watanabe. "Petrogenetic interpretation of granitoid rocks using multicationic parameters in the Sanggau Area, Kalimantan Island, Indonesia." Journal of Applied Geology 3, no. 1 (September 2, 2015). http://dx.doi.org/10.22146/jag.7180.
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Granitoid rock compositions from a range of tectonic environments are plotted on a multicationic diagram, based on major and trace element geochemistry and K-Ar dating. This shows that there is a different tectonic nature, rock affinity and suites. The basement granitoid rocks are ranging from diorite to granite composition. They appear to the products of crystallization differentiation of a calc-alkaline magma of island affinity and range to metaluminous granites, granodiorite and tonalite. The tectonic setting has two kinds which are subduction and post-subduction. The geochemical interpretation, origin and melting of mechanism and tectonic setting shows the types of granitoid are M and I-M type. The basement of granite and granodiorite are a segment of island arc that were happened the Sintang Intrusion as post subduction or syn-collision tectonic setting.
Keywords: Petrogenetic, tectonic, affinity, Sintang Intrusion, Kalimantan
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Alfianti, Hilma, Philipson Bani, Mamay Sumaryadi, Sofyan Primulyana, Mita Marlia, Ugan B. Saing, Nia Haerani, and Hendra Gunawan. "Bromo activity over the last decade: consistent passive degassing and source magma evolution." Geoscience Letters 9, no. 1 (March 19, 2022). http://dx.doi.org/10.1186/s40562-022-00221-2.
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AbstractBromo is among the very active volcanoes in Indonesia and is known for its recurrent and long-lasting eruptive manifestations. Past volcanic gas studies have revealed Bromo as one of the principal sources of volcanic degassing in Indonesia. This high degassing from Bromo volcano is further characterized in this work, based on more than 10 years of intermittent ground-based gas measurements, combined with daily SO2 mass, captured by the OMI sensor. Over the past decade, Bromo has released 0.7 Tg of SO2 into the atmosphere, representing 3% of the volcanic degassing budget of Indonesia and 0.3% of the global volcanic SO2 emission budget outside eruptive periods. Results also reveal that 18.8 Tg of H2O, 2.0 Tg of CO2, 0.1 Tg of H2S, and 0.005 Tg of H2 were released from the Bromo volcano in one decade. About 81% of these gases are released passively between eruptive events. The chemistry of the eruptive products, sampled between 2001 and 2019, indicate that Bromo volcanic activity is sustained by a basaltic-andesite to basalt trachy-andesite magma source with a transition from medium-K to high-K composition. Such an evolution associated to a C-rich gas likely resulted from a low partial melting and sediment contribution to the genesis of the source magma. New magma injections into the reservoir and fractional crystallization have further amplified the changes of magma composition. Finally, we speculate that the shallow reservoir replenishment, in response to the continuous strong degassing is the driving mechanism behind the Bromo frequent eruptive events.
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Wibowo, Haryo Edi, Mitsuhiro Nakagawa, Takeshi Kuritani, Ryuta Furukawa, Oktory Prambada, and Agung Harijoko. "Petrological and geochemical study of Sundoro volcano, Central Java, Indonesia: Temporal variations in differentiation and source processes during the growth of an individual volcano." Journal of Petrology, August 18, 2022. http://dx.doi.org/10.1093/petrology/egac083.
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Abstract Volcanic rocks of the Java sector of Sunda arc have a wide range of isotopic compositions that indicate significant addition of subjected sediment. What processes control these geochemical characteristics is a topic of long-standing debate. Here we report Sr-Nd-Pb radiogenic isotope ratios and geochemical data from stratigraphically well-constrained rocks of Sundoro volcano in central Java that represent the volcano’s activity since 34 ka. The rocks range from basalt (51 wt.% SiO2) to andesite (63 wt.% SiO2) and are dominated by basaltic andesite. We divide them into magma types A, B, and C, having low, medium, and high 87Sr/86Sr and Pb isotopic ratios, respectively. According to various differentiation indices, the three magma types have separate, parallel 87Sr/86Sr, Ba/Zr, and La/Yb trends, and disparate Pb isotopic trends. The dominant process of intracrustal differentiation appears to be magma mixing, in which each of the three magma types represents the mixing of a distinct mafic end member and a distinct felsic end member. The distinct geochemical profiles of these magma types indicate that the three mafic end-members are genetically unrelated and that their differences may represent characteristics of their magma sources. On the basis of trace element ratios (Ba/Yb and La/Yb) and Sr-Nd-Pb isotopic compositions, we estimate that magma types A, B, and C represent mantle wedge materials fluxed by ~1%, ~1.5%, and ~2% slab-derived materials containing 50%, 55%, and 65% sediment component, respectively, reflecting increasing proportions of sediments and increasing slab flux. Geochemical data from Merapi volcano, interpreted using the same approach, reveal a similar increase in the slab-derived flux to the magma source, raising the possibility that such short-lived variations in magma genesis, perhaps related to the subduction of bathymetric relief features, characterize the unusual magmatism beneath the volcanic front of the central Java sector of the Sunda arc.
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Li, Weiran, Fidel Costa, and Kazuhide Nagashima. "Apatite crystals reveal melt volatile budgets and magma storage depths at Merapi volcano, Indonesia." Journal of Petrology, October 27, 2020. http://dx.doi.org/10.1093/petrology/egaa100.
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Abstract Magma volatile budgets and storage depths play a key role in controlling the eruptive styles of volcanoes. Volatile concentrations in the melt can be inferred from analyses of glass inclusions, which however may not be present in the investigated rocks or may have experienced post-entrapment processes that modify their volatile records. Apatite is becoming an alternative robust tool for unraveling the information of magmatic volatiles. Here we report a comprehensive dataset for the concentrations of volatiles and major elements in apatite crystals in the rocks from two eruptions with contrasting eruptive styles: the 2006 (dome-forming) and 2010 (explosive) eruptive events at Merapi volcano (Java, Indonesia). We obtained two-dimensional compositional distributions and in situ concentrations of H2O, CO2, F, Cl, and S in 50 apatite crystals occurring at various textural positions. The CO2 concentrations we report are probably the first ones from natural volcanic apatite. Using the volatile concentrations in apatite and existing thermodynamic models and geothermobarometers, we have calculated the volatile abundances of the pre-eruptive melts of the two eruptions. We find that the apatite from the 2006 and 2010 deposits have a similar compositional range of volatiles, with a bimodal distribution of F-H2O-CO2 contents. The apatite included in amphibole has higher H2O (0.9–1.0 wt.%) and CO2 (Type equation here.≥2400 ppm), but lower F (0.9–1.4 wt.%), compared to crystals included in plagioclase, clinopyroxene, or in the groundmass (H2O: 0.4–0.7 wt.%; CO2: 40–900 ppm; F: 1.7–2.3 wt.%). Using these volatile concentrations and apatite-melt exchange coefficients we obtained two distinct ranges of H2O-CO2-S-F-Cl concentrations in the melt. Melts in equilibrium with apatite included in amphibole had 3–8 wt.% H2O, ≥8000 ppm CO2, 340–2000 ppm S, whereas melts in equilibrium with apatite included in anhydrous minerals and in the groundmass had lower H2O (1.5–4 wt.%), CO2 (60–2500 ppm), and S (10-130 ppm). We calculated the melt H2O-CO2 saturation pressures and found that they correspond to two main magma storage depths. The shallow reservoir with melts stored at ≤10 km below the crater agrees with the depths constrained by melt inclusions, as well as the geodetic, geophysical, and seismic tomography studies from the literature. We have also found a significantly deeper melt storage zone at ≥25–30 km recorded by the C- and H2O-rich apatite in amphibole and barometry calculations using amphibole and high-Al clinopyroxene, which matches with the depths reported in seismic tomography studies. The high CO2/H2O and CO2/SO2 concentrations of the deep melt can help to explain the sharp increase in these ratios in fumarolic gas that were sampled just before the eruption in 2010. Supply of deep volatiles to the shallower magma column before the eruption in 2010 could have increased the magma buoyancy, and thus led to higher magma ascent rates and associated eruption explosivity. Evidence for the faster pre-eruptive magma ascent in 2010 than 2006 is also found on the diffusion distance of Cl in apatite microlites.
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Sutawidjaja, Igan S., Mega F. Rosana, and K. Watanabe. "Magma Chamber Model of Batur Caldera, Bali, Indonesia: Compositional Variation of Two Facies, Large-Volume Dacitic Ignimbrites." Indonesian Journal on Geoscience 2, no. 2 (August 25, 2015). http://dx.doi.org/10.17014/ijog.2.2.111-124.
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Fitri Yudiantoro, Dwi, Intan Paramita Haty, Wahyu Budi Santosa, Angelina Delaira Lukita, Friska Mesy Ayu Pratiwi, Muhammad Irvingia Al Farizzi, and Mohammad Siraj Riyadurrizqy. "KARAKTERISTIK BATUAN BEKU GUNUNG API KENDIL BERDASARKAN ANALISIS PETROGRAFI, KECAMATAN KEJAJAR, KABUPATEN WONOSOBO, PROVINSI JAWA TENGAH." PROSIDING SNAST, November 12, 2022, B30–37. http://dx.doi.org/10.34151/prosidingsnast.v8i1.4112.
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Indonesia is located at the three world's active tectonic plates. These tectonics interact with each other formed a subduction zone that controls the volcanic arc, known as the Ring of Fire. The Quaternary volcanic arc on Java Island has the youngest age, and the volcanic process is still ongoing. Dieng Volcano Complex which consists a complex of stratocones, parasitic vents, and explosion craters are one of the quartenary volcanoes. The research area of Mount Kendil is one of the quaternary volcanic chain trending northwest-southeast in the Dieng Volcano Complex. The purpose of this study is to identify and determine the characteristics of igneous rocks, including texture and mineralogy composition, from the the Kendil volcanism in the past. The research method using primary data with surface geology and petrographic thin section analysis. The results in sample one there are pyroxene, plagioclase, and hornblende embedded in volcanic glass. In sample two minerals such as hornblende, pyroxene, and plagioclase embedded in volcanic glass. The third sample minerals are biotite, plagioclase, and hornblende embedded in volcanic glass. Based on the analyzed data, it can be concluded therewas an evolution of magma from mafic to intermediate. Mafic magma marked by the pyroxene minerals as indicator and intermediate magma marked by hornblende and plagioclase. This research is expected to add information and enrich the literature that discusses the evolution and characteristics of magma in the Mount Kendil area.
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Titisari, Anastasia Dewi, David Phillips, and Hartono Hartono. "GEOCHEMICAL VARIATIONS ON HOSTED VOLCANIC ROCKS OF CIBALIUNG EPITHERMAL GOLD MINERALISATION, BANTEN – INDONESIA: IMPLICATIONS FOR DISTRIBUTION OF SUBDUCTION COMPONENTS." Journal of Applied Geology 6, no. 1 (September 2, 2015). http://dx.doi.org/10.22146/jag.7216.
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Subduction of the Indo-Australian Plate beneath the Eurasian Plate formed at least seven magmatic arcs in Indonesia. One of the magmatic arcs is the Neogene Sunda-Banda arc hosts various style of gold mineralisation such as Cibaliung epithermal gold mineralisation. Major and trace element data for host volcanic rocks to the Cibaliung epithermal gold mineralisation is provided by this study to identify the magmatic arc system and the distribution of subduction components. Enriched LILE (Large Ion Lithopile Element) and LREE (Light Rare Earth Element) compositions for basaltic andesite – rhyodacitic samples from the Cibaliung district are characteristic of calc-alkaline arcs. In this typical volcanic arc, the subduction component can be shown to make a dominant contribution to its content of LILE such as Rb, K, Th, and Ba enriched (more than 88%) relative to the mantle and within plate inputs. The incompatible elements (Hf, Zr, and Nb) cannot be observed in the subduction component and thus assumed to be derived from trace element enriched sub-continental lithosphere. These incompatible elements are defined as conservative elements therefore it suggests that the magma occurrence is related to a hydrous slab component. Keywords: Subduction, Indo-Australian plate, magmatic arcs, volcanic rocks, Cibaliung, epithermal gold.
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Gao, Meng-Hao, Ping-Ping Liu, Sun-Lin Chung, Qiu-Li Li, Bin Wang, Wei Tian, Xian-Hua Li, and Hao-Yang Lee. "Himalayan zircons resurface in Sumatran arc volcanoes through sediment recycling." Communications Earth & Environment 3, no. 1 (November 17, 2022). http://dx.doi.org/10.1038/s43247-022-00611-6.
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AbstractUnderstanding the processes of subducted sediment recycling in subduction zones is vital to decipher Earth’s crust-mantle interactions. This study uses along-arc geochemical variations and zircon U-Pb-Hf-O isotopes of Quaternary arc basalts and andesites on Sumatra Island, Indonesia to assess the mode of sediment recycling in subduction zones. The Hf-O isotopes of inherited zircons of the basalts and andesites near the Toba Caldera indicate that some of them were derived from subducted terrigenous sediments mainly sourced from the (eastern) Himalaya. Hybridization of the subducted sediments with the mantle also accounts for the enriched Sr-Nd isotopic compositions of arc volcanic rocks near the Toba Caldera. Thermodynamic modeling indicates that the subducted sediments did not melt on the slab surface. Rather, geochemical evidence supports their formation as diapirs that rise buoyantly through the hot mantle wedge and contribute to ~30 to 45% of the magma source of the arc volcanic rocks near Toba.
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van Hinsberg, Vincent J., Kim Berlo, Daniele L. Pinti, and Bassam Ghaleb. "Gypsum Precipitating From Volcanic Effluent as an Archive of Volcanic Activity." Frontiers in Earth Science 9 (November 2, 2021). http://dx.doi.org/10.3389/feart.2021.764087.
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Records of volcanic activity are a key resource in volcano monitoring and hazard mitigation. The time period for which such records are available and the level of detail vary widely among volcanic centers and there is, therefore, a need for supplementary sources of this information. Here, we use growth-zoned gypsum as a mineral archive of the activity of Kawah Ijen volcano in East-Java, Indonesia. Gypsum precipitates where water seeps from the crater lake and hydrothermal system, and it has formed a 100 m long cascading plateau. A 19 cm plateau cross-section was analysed for minor and trace elements using laser-ablation ICP-MS. Absolute ages were assigned to this transect based on 210Pb dating. This 210Pb age model was corrected for variations in the 210Pb0 resulting from fluctuations in the volcanic radon flux by using 84Kr/36Ar and 132Xe/36Ar. The age model indicates that the transect covers a period from 1919 ± 12 to 2008 ± 0.2. Gypsum-fluid partition coefficients (D) permit the gypsum compositions to be converted to the concentrations in the fluid from which each growth zone grew. The D-values also show the compatibility of the elements in the gypsum structure, and identify the LREE, Sr, Pb, Tl, Ni, Co, Cu, Zn, Cd, Sb, Th, and Mo as least susceptible to contamination from rock fragment and mineral inclusions, and therefore as most reliable elements of the gypsum record. Compositional variability in the timeseries correlates with known element behavior in the Kawah Ijen system and shows three element groups: the LREE, Sr, and Pb that represent rock-leaching; Cu, Zn, and Cd, which have previously been linked to immiscible sulfide destabilization in a deep-seated basalt; and Sb, Tl, and As which point to a contribution from the shallow system and evolved magma. Moreover, the gypsum record shows that episodes of unrest and quiescence have a distinct compositional signature in Kawah Ijen seepage fluids, and can be distinguished. Thus, we show that gypsum is a sensitive recorder of volcanic activity and can provide detailed information on the state of the magmatic-hydrothermal system in the past.
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Utami, S. B., F. Costa, Ph Lesage, P. Allard, and H. Humaida. "Fluid Fluxing and Accumulation Drive Decadal and Short-Lived Explosive Basaltic Andesite Eruptions Preceded by Limited Volcanic Unrest." Journal of Petrology 62, no. 11 (October 8, 2021). http://dx.doi.org/10.1093/petrology/egab086.
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Abstract Some volcanoes are known for repeatedly producing explosive but short-lived eruptions (< half a day) every decade or so. These eruptions are often preceded by limited unrest signals and short run-up times to eruption (a few hours to months), and thus they are difficult to anticipate. Some well-documented examples are the 1990 and 2014 eruptions of Kelud volcano in Indonesia, or the 2015 Calbuco eruption in Chile. Here we interrogate the rock record and obtain insights into the processes and pre-eruptive conditions that led to the 1990 Kelud eruption, which we integrate with monitoring data (seismicity, lake temperature and hydro-acoustics, sulfur emissions) towards a conceptual model for this type of events. Mineral-melt geothermobarometers indicate that the basaltic andesite magma carried a crystal cargo from as deep as 15–19 km, and reached volatile saturation at 4–9 km with 2–4 wt.% water in the melt. The textures and compositional zoning of orthopyroxene and plagioclase do not support intrusion of more primitive magma as the driver for the eruption, and we instead propose that pre-eruptive fluid accumulation and high-temperature fluid fluxing from depth (likely dominated by CO2) played a major role in priming the eruption to occur. Such pre-eruptive gas accumulation is also supported by mass balance calculation of the emitted excess SO2 gas. Mg-Fe diffusion profiles in reversely zoned pyroxenes constrain timescales of weeks to months before eruption for fluid addition to the reservoir, and such events may be recorded in the monitoring signals, especially in the change of hydroacoustics and water lake temperature, and probably in the seismic swarms. We propose that fluid exsolution and accumulation in the shallow reservoir plays a crucial role in modulating and triggering short-lived explosive eruptions with brief unrest at Kelud and probably other volcanoes worldwide.