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INDONESIA
IJOG : Indonesian Journal on Geoscience
Published by Geological Agency of Indonesia
ISSN : 23559314     EISSN : 23559306     DOI : -
Core Subject : Science,
Earth & Planetary Sciences
The spirit to improve the journal to be more credible is increasing, and in 2012 it invited earth scientists in East and Southeast Asia as well as some western countries to join the journal for the editor positions in the Indonesia Journal of Geology. This is also to realize our present goal to internationalize the journal, The Indonesian Journal on Geoscience, which is open for papers of geology, geophysics, geochemistry, geodetics, geography, and soil science. This new born journal is expected to be published three times a year. As an international publication, of course it must all be written in an international language, in this case English. This adds difficulties to the effort to obtain good papers in English to publish although the credit points that an author will get are much higher.
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Articles 7 Documents
 1 
Search results for , issue "Vol 7, No 3 (2020)" : 7 Documents clear
Peak Metamorphic Conditions of Garnet Amphibolite from Luk Ulo Complex, Central Java, Indonesia: Implications for Medium-Pressure/High-Temperature Metamorphism in the Central Indonesian Accretionary Collision Complex Nugroho Imam Setiawan; Yasuhito Osanai; Nobuhiko Nakano; Tatsuro Adachi; Agus Hendratno; Wahyu Sasongko; Chusni Ansori
Indonesian Journal on Geoscience Vol 7, No 3 (2020)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.7.3.225-239

Abstract

DOI:10.17014/ijog.7.3.225-239Garnet amphibolites, which suggest medium-pressure/high-temperature (MP/HT), are widely recognized in Luk Ulo Complex, Central Java. Their occurrences associated with high-pressure/low-temperature (HP/LT; eclogite, blueschist) metamorphic rocks in the Luk Ulo Complex will provide important constraint on the geodynamic model of Central Indonesian Accretionary Collision Complex (CIACC). This study aimed to estimates P-T metamorphic condition of garnet amphibolite from Luk Ulo Complex by using mineral parageneses, thermodynamic data, and NCKFMASHO pseudosection. Prograde stage assemblages represented by inclusions in the garnet, which are garnet core, zoisite, titanite, apatite, and quartz. Mineral coexistences at the peak P-T condition are garnet rim, magnesio-hornblende, zoisite, titanite, quartz, albite, and phengite. The retrograde stage represented by secondary minerals fill the crack in the garnet and other minerals, which are chlorite and quartz. P-T metamorphic condition of garnet amphibolite can only be interpreted from the peak metamorphic stage. The temperature of the garnet amphibolite is estimated using the garnet-amphibole and garnet-phengite geothermometers. Meanwhile, the pressure condition is estimated from phengite geobarometer. The results were compared to the stability and compositions of the phases in NCKFMASHO pseudosection in order to constrain the peak P-T metamorphic conditions. It is concluded that the peak P-T metamorphic condition for garnet amphibolite is 0.9 - 1.4 GPa and 558 - 606 ºC. The estimated peak P-T metamorphic temperature is higher compared to the previously published gradient geothermal of eclogite and tourmaline-eclogite in the Luk Ulo Complex. The MP/HT (amphibolite) and HP/LT (blueschist and eclogite) metamorphic rocks could have similar metamorphic ages if both footwall and hanging wall had initially very high thermal gradients and the rate of subduction was very slow (10 km/Ma or less).
Lava Discharge Rate of Sinabung Volcano Obtained from Modis Hot Spot Data Estu Kriswati; Akhmad Solikhin
Indonesian Journal on Geoscience Vol 7, No 3 (2020)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.7.3.241-252

Abstract

DOI:10.17014/ijog.7.3.241-252To find out the long term data of Sinabung magma discharge rate and how long a series of eruption will be ended, time series of the volume of magma discharge is required. The dominant eruption product is pyroclastic flow that begins with the growth of the lava dome, so it is important to determine the volume of the lava dome over time. The method of determining the volume of magma issued is carried out by using hotspot data to resolve the problem of prevented visual observations and ground measurements. The heat and volume flux data expressed within a long period for a better view of variations in the Sinabung volcanic activity are based on thermal satellite data. Related lava dome volume and seismic data are also displayed to be compared with the heat and volume flux data. The numbers of thermally anomalous pixels and sum of radiance for all detected pixels at Sinabung during an overpass in the period of 2014 to 2018 have a downward trend. The discharge rates in the period of January 2014 to April 2015, Mei 2015 to March 2016, April 2016 to March 2017, and June 2017 to February 2018 are 0.86 m3/sec, 0.59 m3/sec, 0.36 m3/sec, and 0.25 m3/sec, respectively. Assuming no new intrusion or deformation rate changes, the lava discharge will be in the lowest rate in the early 2020s.
Density Normal Compaction Trend in the Peciko Field, Lower Kutai Basin, Indonesia Agus M. Ramdhan; Neil R. Goulty; Stuart J. Jones; Lambok M. Hutasoit
Indonesian Journal on Geoscience Vol 7, No 3 (2020)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.7.3.253-265

Abstract

DOI:10.17014/ijog.7.3.253-265The density normal compaction trend is the mandatory parameter in order to calculate contribution of disequilibrium compaction to overpressure, in the presence of unloading to total overpressure. In this paper, mudrock compaction behaviour is studied in the Peciko Field. The density normal compaction trend was constructed in a normally pressured section, where the temperature is <1200C, within the transformation of smectite–illite zone. The compaction trend includes not only vertical effective stress, but also diagenesis, especially smectite-illite transformation, as dependant factor for compaction, both termed as β. This compaction trend is also known as Skempton-Duta compaction model. Quardros-Linares fifth-order kinetic reaction was found that could model smectite-illite transformation in the studied area fairly well. The plot between β and smectite content shows a very good match, confirming that Skempton-Dutta compaction model is valid for the entire range of smectite-illite transformation. In the area where the density log is unavailable, the density normal compaction can be constructed from temperature history acting as a proxy for smectite-illite transformation, with some local calibration.
Geochemical Compositions and Magnetic Susceptibility of Soils from Different Origins: A Case Study in South Lampung, Indonesia Nono Agus Santoso; Mochamad Iqbal; Grandprix Thomryes Marth Kadja
Indonesian Journal on Geoscience Vol 7, No 3 (2020)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.7.3.267-272

Abstract

DOI:10.17014/ijog.7.3.267-272The study of rock weathering into soil is very important in geophysics. The geochemical and magnetic characteristics of soil were investigated in South Lampung using magnetic susceptibility and X-ray Fluorescence (XRF) measurements to identify the rock origin of the soil. The samples consisted of three soil types, those are granite soil, tuff soil in front of ITERA (Institut Teknologi Sumatra, South Lampung), and tuff soil inside ITERA. The tuffs (in front of and inside ITERA) and granite were taken in and around ITERA. The result showed that granite had the highest magnetic susceptibility value, while tuff soil in front of ITERA had the highest FeO content. Each sample can be distinguished by magnetic susceptibility and FeO content to prove that it can be used as a tool to distinguish the rock origin of soil.
Natural Compaction of Semarang-Demak Alluvial Plain and Its Relationship to the Present Land Subsidence Dwi Sarah; Lambok M Hutasoit; Robert M Delinom; Imam A Sadisun
Indonesian Journal on Geoscience Vol 7, No 3 (2020)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.7.3.273-289

Abstract

DOI:10.17014/ijog.7.3.273-289Land subsidence is the lowering of ground surface due to natural and/or anthropogenic processes. Land subsidence in the Semarang-Demak plain has been going on for more than thirty years, however the contribution of natural and anthropogenic causes is relatively unknown. The Semarang-Demak plain has only been formed recently, as a result of rapid sedimentation during the Holocene. The basin mainly consists of underconsolidated thick clay, vulnerable to excessive settlement due to its own weight and additional pressures. The rate of natural subsidence is quantified by modelling the delayed dissipation of measured overpressure and the resulting vertical deformation, resulting in natural compaction rate of less than 0.8 cm/year in Semarang City and more than 0.8 cm/year in Demak Regency. The subsidence computed for parts of the Semarang-Demak plain were compared to the measured geodetic rate, and the relative contributions of natural and anthropogenic causes are derived. Modelling results show that natural subsidence is more significant at the eastern part of the plain (Demak region) with compaction rate reaching 0.9 - 2.2 cm/year that counts for 48 - 92% of the total land subsidence.
The Significance of the Banda Sea: Tectonic Deformation Review in Eastern Sulawesi Adept Titu-Eki; Robert Hall
Indonesian Journal on Geoscience Vol 7, No 3 (2020)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.7.3.291-303

Abstract

DOI:10.17014/ijog.7.3.291-303The geology of eastern Sulawesi is widely known for its complexity due to multiple deformation stages.The geology on land has been studied excessively, but little assessment has been made on the offshore geology, thus the geological evolution of the area remains a subject of controversy. A thorough observation of high multibeam bathymetry dataset offshore and SRTM dataset onshore provides an understanding on the geological features relating to the tectonic deformation. Exquisite morphological features include carbonate buildups and gravitational collapse dominating the shelf areas whereas distinct form of ridges and seamount exists in the offshore. Structural features in this area including the major Tolo Thrust and South Sula Fault varied structural lineations on land with several polygonal extensional faulting and accretionary wedge on the west of the North Banda Sea. The existence of these features may indicate that the area was majorly deformed during Neogene, specifically relating to the opening of the Banda Sea due to the subduction rollback of Banda.
Preliminary Study of Rare Earth Element and Yttrium (REY) Content of Coal In Sangatta Coalfield, East Kalimantan, Indonesia Ferian Anggara; Himawan T.B.M. Petrus; Aulia Agus Patria; Aya Shika Bangun
Indonesian Journal on Geoscience Vol 7, No 3 (2020)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.7.3.305-314

Abstract

DOI:10.17014/ijog.7.3.305-314Kutai Basin is known as one of the most prolific sedimentary coal basins in Indonesia. Coal-bearing sequence in Kutai Basin is mainly Miocene to Eocene in age in which the coal seams are mostly in Miocene strata. Researchers have found that REY concentration in some coals and coal ashes are equal to or higher than that of the conventional deposit, as such coal deposit has become an important source for REY. Moreover, REY recovery as by-product from coal deposits could alleviate the “dirty” into “clean” coal energy. Referring to this shifted paradigm, a study on REY in Indonesian coal has put interest not only for researchers, but also for all stakeholders in this country. In this particular study, Sangatta coalfield in East Kalimantan was chosen as the area to observe the REY concentration. This area has been set due to its interesting geological setting, especially Pinang Dome that might have coal deposit with enriched REY. For the analyzed samples, drill cores were collected and then observed closely using polished section, inductively coupled plasma atomic emission spectroscopy (ICP-AES), and inductively coupled plasma mass spectrometry (ICP-MS). Based on the collected data, the highest REY concentration in coal deposit is located in the nearest part of the Pinang Dome. The REY content in coal deposit is associated with hydrothermal fluids and sediment source. These data suggest that there is a significant effect on Pinang Dome in the REY content in the coal deposit.

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