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All Journal Jurnal Geologi dan Sumberdaya Mineral (Journal of Geology and Mineral Resources)
Udi Hartono
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Chemistry Earth & Planetary Sciences Energy

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Identification of Adakite from The Sintang Intrusives In West Kalimantan Udi Hartono; Suyono Suyono
Jurnal Geologi dan Sumberdaya Mineral Vol. 16 No. 3 (2006): Jurnal Sumber Daya Geologi
Publisher : Pusat Survei Geologi

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.33332/jgsm.geologi.v16i3.362

Abstract

The Sintang intrusives are widely exposed in West Kalimantan, and as reported by previous workers, consisting of high level intrusives of stocks, plugs, dykes and sills of microdiorite, microgranodiorite, granite/ microgranite, quartz diorite, dacite, andesite, and minor rhyolite and rhyodacite. However, a careful study of published geochemical data gives a result that the rocks are of adakitic type. Considering the tectonic development of the South China Sea and northwest Kalimantan, the adakite was probably originated from magma as a result of melting of the subducted South Cina sea oceanic crust beneath Kalimantan continent. The subduction started in the Late Oligocene when the crust was still young. Keywords : adakite, Sintang, intrusive, Late Oligocene
Petrogenesis of The Sintang Intrusives and Its Implications for Mineralization In Northwest Kalimantan Udi Hartono
Jurnal Geologi dan Sumberdaya Mineral Vol. 16 No. 4 (2006): Jurnal Sumber Daya Geologi
Publisher : Pusat Survei Geologi

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.33332/jgsm.geologi.v16i4.365

Abstract

Arc magmatism is a direct response to tectonic and chemical processes operating in subduction zones. The Sintang Intrusives consist of microdiorite, microgranodiorite, granite/ microgranite, quartz diorite, dacite, andesite, and minor rhyolite and rhyodacite (dacite predominant). Depletion of Nb relative to K and La concentrations are characteristics of the rocks, implying the magma was generated in a subduction zone environment. However, different from magma of other “normal” arcs that were derived from mantle wedges, the magma of the Sintang Intrusives was generated from subducted oceanic crust melting. The result of a careful study of trace element data show that the rocks are of adakite type, characterized by high Sr/Y and Zr/Sm ratios, moderate to strong fractionation of heavy rare earth elements (HREE) and absence of Eu anomalies suggesting melt extraction from garnet-amphibolite sources. By considering the tectonic development in the South China Sea and northwest Kalimantan, it is believed that the magma was probably originated from the melting of previously subducted South China sea oceanic crust (dead slab or fossil subduction) beneath Kalimantan continent in the Late Oligocene - Early Miocene. A compressive tectonic regime in Middle Oligocene, and possibly until Late Oligocene, led to crustal shortening and thickening that facilitated entrapment of arc magma in the Kalimantan crust. The fluid released caused by amphibole breakdown and may have been expelled from older amphibolebearing plutons during compressional tectonics would be significantly important for mineralization. Keywords : Kalimantan, Sintang Intrusives, oceanic crustal melting, mineralization
Posisi Stratigrafi dan Petrogenesis Intrusi Pendul, Perbukitan Jiwo, Bayat, Kabupaten Klaten, Jawa Tengah Surono Surono; Udi Hartono; Sam Permanadewi
Jurnal Geologi dan Sumberdaya Mineral Vol. 16 No. 5 (2006): Jurnal Sumber Daya Geologi
Publisher : Pusat Survei Geologi

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.33332/jgsm.geologi.v16i5.372

Abstract

The Pendul Intrusion consists of andesite, diabas, diorite, and gabbro; that are widely distributed within the Jiwo Hills, south of Klaten, Central Jawa. K/Ar datings of 4 rock indicate that there are two magmatism episodes; Middle Eocene - Early Oligocene (39,82 - 30,04 Ma) and Middle Miocene (17,22 - 13,85 Ma). Trace element concentrations of the Pendul rocks characterize that the magma was originated from subduction environment as a result of mantle wedge melting. The rocks are characterized by low Nb relative to K and La contents. The rare earth element signatures indicate that the Pendul magmas might have come from defferent parent magmas. The Middle Eocene - Early Oligocene parent magmas posses lower rare earth element concentrations than those of the Middle Miocene ones. Keywords: Bayat, Pendul Intrusion, two magmatism episodes, stratigraphy
Co-Authors Sam Permanadewi Surono Surono Suyono Suyono