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地質調查所月報
工业技术院地质调查所
地質調查所月報

工业技术院地质调查所

0016-7665

地質調查所月報/Journal 地質調查所月報
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    Overview of the "Research Cooperation Project on the Exploration of Small-scale Geothermal Resources in the Eastern Part of Indonesia" by the Geological Survey of Japan

    Hirofumi MURAOKAToshihiro UCHIDA
    15页
    查看更多>>摘要：A five-year Indonesia-Japan bilateral research cooperation program, named "Research Cooperation Project on the Exploration of Small-scale Geothermal Resources in the Eastern Part of Indonesia" (ESSEI Project), started in April 1997 and will end in March 2002. This paper gives an overview of the project by the Geological Survey of Japan as an introduction to this special volume. Background information of the project such as the objective, research cooperation regime, research schedule and shared tasks are reviewed. Annual activity and outline results of the Geological Survey of Japan are described.
      原文链接:
    • NSTL

    Geothermal development for supporting the Rural Electrification Program in Indonesia

    Sjafra DWIPA
    8页
    查看更多>>摘要：Indonesia is blessed with abundant geothermal resources. However, only 787 MWe of geothermal energy has been developed as of 2001. To further increase the capacity in Indonesia, we must overcome obstacles like weak cost-competitiveness. Accordingly, a new regulation was issued that shows the government is willing to share the steam development risk and introducing fair competition and more efficient private sector participation. In supporting regional autonomy, the government made stable power supply and rural electrification as its top priorities for expansion of the infrastructure to promote the development of remote islands. The government electrified about 30,394 villages. We look forward to a fruitful cooperation on geothermal development and invite investors for capital investments to keeping momentum of growth.
      原文链接:
    • NSTL

    Geothermal prospects of Flores Island in Indonesia viewed from their volcanism and hot water geochemistry

    Asnawir NASUTIONHirofumi MURAOKAMawardi RANI
    11页
    查看更多>>摘要：Lavas of the Flores volcanic arc have a range of compositions from basalt to dacite but mostly andesite, containing pigeonite and olivine in island arc tholeiitic series and amphibole and biotite in calc-alkaline series. Chemically, the rocks show a wide variety of SiO_2 (51 - 67 wt. percent), Al_2O_3 (14 - 20 wt. percent) and low TiO_2 (<1 wt. percent), together with relatively high Rb, Sr and Ba. These K group elements represent an increase of SiO_2 with increasing depth of the Benioff zone. Strontium isotope ratios of tholeiitic to calc-alkaline lavas are 0.7042 - 0.7045, assumed to be correlated with the depth of the subducted slab across the island. Flores geothermal prospects are situated in young volcanic terrains of andesite and basalt between 500 to 1000 m above sea level (a.s.l.) and associated with post volcanic fractures, faults and caldera structures. Rot water discharges represent a wide variety of chemical water types; sulfate, bicarbonate and chloride waters. Sulfate type is mostly associated with fumaroles and located on high volcanic terrains (700 - 1100 m a.s.l.), indicating the near-surface H_2S oxidation (Ulumbu, Mataloko, Nage and Sokoria). Bicarbonate waters are located at the moderate slope of volcanics (400 - 700 m a.s.l.), shown by Langageda and Sokoria 2. Neutral chloride waters are located at the lower volcanic terrains approximately 5 - 600 m a.s.l., indicating an outflow from geothermal reservoirs with a temperature of 210 to 280 deg C. Geothermal wells that were drilled at the Ulumbu and Mataloko prospects to a depth of 700 - 1800 m and 200 m, respectively have a subsurface temperature of 200 to 240 deg C, indicating that the high sulfate concentration is associated with a vapor-dominated system. The same system probably occurs in the Sokoria field. While the geothermal prospects of high chloride water type are probably associated with hot-water or mixture system (Wai Sano, Wai Pesi, Jopu, Lesugolo and Oka).
      原文链接:
    • NSTL

    Satellite remote sensing data and their interpretations for geothermal applications: A case study on the Ngada District, central Flores, Indonesia

    Minoru URAIHirofumi MURAOKAAsnawir NASUTION
    10页
    查看更多>>摘要：A remote sensing survey was conducted in the Ngada District for geothermal exploration using JERS-1 SAR and OPS, and ASTER VNIR and TIR data. As a result, many small volcanic cones, which have diameters less than 5 km, are seen near the Bajawa in the SAR image. Some volcanic cones are aligned along the north-south direction. Since the SAR has all-weather observation capability, it provides us with details of the volcanic features in the study area, where it is difficult to obtain cloud-free images using optical sensors. Volcanic features are not as obvious in the OPS image compared with the SAR image because of the high sun elevation angle in tropical areas. A small high temperature anomaly is found at the Nage geothermal area using ASTER TIR, which is a new spaceborne sensor having a high spatial resolution. These results demonstrate the advantages and limitations of satellite remote sensing survey for geothermal applications.
      原文链接:
    • NSTL

    Tectonic, volcanic and stratigraphic geology of the Bajawa geothermal field, central Flores, Indonesia

    Hirofumi MURAOKAAsnawir NASUTIONMinoru URAI
    30页
    查看更多>>摘要：Regional geological investigation has been carried out since 1998 to evaluate geothermal resources in the Bajawa City and its surrounding areas of Flores Island as a part of the Research Cooperation Project on the Exploration of Small-scale Geothermal Resources in the Eastern Part of Indonesia (ESSEI Project). Since 4 Ma, volcanic activity occurred in two volcanic terrains: the central area and southern coast. Both of terrains form an element of the en echelon island structure characteristic from Flores to Alor Islands. An 800 m uplift occurred in the two terrains during the past 2.5 million years. In the central area, the Welas caldera formed at about 2.5 Ma. After its post-caldera volcanism, the volcanic activity has been almost extinct. On the southern coast, volcanic activity has continued from 4 Ma to the present. The most conspicuous event was the appearance of the Bajawa rift zone that was related to the north-south left-lateral shear stress accommodated between the north moving Australian accretion block in the east and relatively fixed Sundaland block in the west. The Bajawa rift zone was initiated by the formation of a NNW-SSE elongated volcano probably during 0.8-0.2 Ma. It was followed by the collapse of the eastern flanks from its crest. The collapsed area produced the Bajawa Cinder Cone Complex that consists of more than 60 cinder cones aligned 20 km along the NNW-SSE trending rift zone. Although the majority of volcanic rocks in the study area is basaltic and tholeiitic, all the effusive rocks from the Bajawa rift zone including the volcanic rocks of the elongated volcano and Bajawa Cinder Cones Complex are andesitic, calc-alkaline and very homogenous in composition. This suggests a connected dike swarm ~magma chamber beneath alignments of numerous cones of the Bajawa Cinder Cone Complex. Three steaming grounds and several high temperature hot springs in the study area are closely associated with the Bajawa rift zone magma system as a heat source.
      原文链接:
    • NSTL

    Thermoluminescence dating of volcanic and altered rocks in the Bajawa geothermal area, central Flores Island, Indonesia

    Isao TAKASHIMAAsnawir NASUTIONHirofumi MURACKA
    8页
    查看更多>>摘要：Ages of volcanic and altered rocks distributed in the Bajawa geothermal area were determined by thermoluminescence (TL) dating. All volcanic rock samples are collected from formations younger than 0.15 Ma by K-Ar dating but their fixed ages have not been determined. Separated quartz and plagioclase are used for dating. Ages for eight volcanic rocks range from 32-160 ka. The youngest age of 32 ka is obtained for Mt. Keli Inerie, a large active stratovolcano. Ages of 72-160 ka are first reported for small stratovolcanos that are characterized by clear craters at the summits and linearly arranged. Most acidic white colored alteration halos have been formed at low temperatures, generating no quartz. Only Nage, Mataloko and Rakalaba alteration zones have yielded samples for TL dating using quartz. The obtained TL alteration age range are 12-54 ka, 28-33 ka and 44 ka for Nage, Mataloko and Rakalaba, respectively. Ages of volcanic rocks are expected for a heat source in most geothermal fields in the Bajawa geothermal area. Young alteration ages also suggest the existence of reservoirs beneath this area.
      原文链接:
    • NSTL

    Geochemistry of volcanic rocks in the Bajawa geothermal field, central Flores, Indonesia

    Hirofumi MURAOKAAsnawir NASUTIONMinoru URAI
    13页
    查看更多>>摘要：Multi-components of 46 volcanic rocks were analyzed from the Bajawa geothermal field, central Flores, Indonesia. Twenty six samples were taken from the Bajawa rift zone volcanic rocks including numerous cinder cones called the Bajawa Cinder Cone Complex. The results show that tholeiitic basalt to dacite are rather common in the field, but the Bajawa rift zone volcanic rocks are calc-alkaline andesite and extremely homogeneous throughout the samples in major and minor components. The plot of the Bajawa rift zone volcanic rocks to pseudoternary diagrams reveals that their cluster is constrained by the phase boundaries and equilibrated at about 3 kbar or 10 km depth. This depth corresponds with the bottom of the oceanic crust in this region, and the rift type magmatism might have caused such a shallow depth magma generation. The homogeneity of the Bajawa rift zone magma is ascribed to its short path from the magma source region to the surface and its non-stop rising as a dike swarm.
      原文链接:
    • NSTL

    Geology, geochemistry and geochronology of the Bajawa area, central Flores, Indonesia: Geologic structure and evolution of the Bajawa depression

    Masami OTAKEHiroshi TAKAHASHITakehiro KOSEKI
    13页
    查看更多>>摘要：The Bajawa area is located in the central part of Flores Island in eastern Indonesia. The area is widely underlain by Pliocene to Pleistocene voluminous volcanic products and includes a depression called the Bajawa depression. It extends 13-16 km east-west and is more than 12 km north-south with well-preserved steep cliffs up to 300-400 m in height at the western margin. Stratigraphy of the study area consists of older volcanic rocks (V1), Bajawa volcanic rocks (Bv), products of cinder cone (C1, C2), Aimere tuff (At) and products of the Inerie volcano (Ie) in ascending order. Evolution of the Bajawa area is divided into four stages: (1) In the Pliocene to Early Pleistocene, the Bajawa area became a site of intense volcanic activity to form a broad volcanic edifice that comprised the older volcanic rocks (V1) ranging from basalt to andesite in the tholeiite series. (2) Bajawa depression occurred on the central highland of the volcanic edifice formed during stage 1. Displacement of subsidence is estimated to have been more than 400 m. (3) The depression was widely filled by Bajawa volcanic rocks (Bv) consisting of andesite lavas and volcaniclastic rocks. Subsequently, andesitic cone volcanism occurred along linear fractures and formed some cinder cones (C1, C2). This volcanism was caused by calc-alkaline magma. (4) A large stratovolcano (Inerie volcano) consisting of tholeiitic andesite (Ie) grew at the southwestern margin of the depression. Based on the lineament on the satellite imagery, alignments of the cinder cones and linear discontinuities of resistivity, it is considered that the formation of the Bajawa depression results from the subsidence of the pre-depression rocks that is segmented by north-south, northwest-southeast and northeast-southwest trending faults. The north-south trending fault in the western part may be interpreted as the bounding fault that defined the western rim of the subsidence.
      原文链接:
    • NSTL

    2001 fissure-forming eruption of Inie Lika volcano, central Flores, Indonesia

    Hirofumi MURAOKAKasumi YASUKAWAMinoru URAI
    8页
    查看更多>>摘要：A phreato-magmatic eruption occurred at the Inie Lika volcano, Flores Island, Indonesia during January 11-16, 2001 after 95 years of quiescence. This event and consequent fissure formation were described. Inie Lika volcano forms a northern part of the Bajawa Cinder Cone Complex extending over 16 km in the NNW-SSE direction. Ash fall continued for six days and steam discharge continued for two months after the incipience of the eruption. It should be noted that the eruption formed a N16 deg W trending fissure, about 20 m wide and 300 m long, suggesting tensile rifting caused by a thin magmatic dike invasion into a shallow depth.
      原文链接:
    • NSTL

    Geochemical characteristics of hot spring water in Bajawa area, central Flores, Indonesia

    Masaaki TAKAHASHIMinoru URAIKasumi YASUKAWA
    17页
    查看更多>>摘要：Water and gas samples taken from hot and cold springs, streams, rainfall and fumaroles were analyzed geochemically to assess the geothermal resources of the Bajawa area, central Flores Island, eastern part of the Nusa Tenggara Islands, eastern Indonesia. Five pro spective manifestation areas, Mataloko, Nage-Keli Tiworiwu-Wolo Bobo, Soka, Mengeruda, Gou-Tukapela, are near three active volcanoes, Inerie, Inie Lika and Ebulobo and more than 30 monogenetic volcanoes. One hot spring, Mbay, is near the northeastern seashore. Temperatures of the hot springs were >90 deg C at the Mataloko, >75 deg C at the Nage, >70 deg C at the Keli Tiworiwu, >60 deg C at the Mbay and 40 to 45 deg C at the other areas. Geochemical characteristics of most hot water were acid sulfate type, except for Nage hot water, which is acid sulfate-chloride type. Origin of dissolved sulfate and chloride of acid hot springs was relatively low temperature volcanic gases containing hydrogen sulfide gases and interstitial water in acid alternation zone. However, dissolved sulfate and chloride of Nage hot springs may be from high temperature volcanic gases, which contain hydrogen chloride and sulfur dioxide, and interstitial water in the acid alternation zone and volcanic ash.
      原文链接:
    • NSTL