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Udi Hartono
Pusat Survei Geologi
Chemistry Earth & Planetary Sciences Energy

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ORIGIN OF CRETACEOUS HIGH MAGNESIAN ANDESITES FROM SOUTHEAST KALIMANTAN Udi Hartono; Raden Isnu H. Sulistyawan
Jurnal Geologi dan Sumberdaya Mineral Vol. 20 No. 5 (2010): Jurnal Sumber Daya Geologi
Publisher : Pusat Survei Geologi

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.33332/jgsm.geologi.v20i5.178

Abstract

High magnesian andesites are found in the Cretaceous Haruyan volcanics in Southeast Kalimantan. The rocks have Mg# 67 – 69, but low concentrations of Ni (44 – 60 ppm), Cr (37 – 411 ppm) and, except two samples of 95UH23C and 96UH23, ratios of Sr/ Y are also low. Geochemical and tectonic studies show that the high magnesian andesites were originated from a subduction zone-type magma similar to that of the most “normal” Haruyan volcanics. Two possible origins of the Cretaceous high magnesian andesites are proposed. First, melting of the mantle wedge above the slab to produce a basaltic magma followed by crystal fractionation, especially olivine and pyroxene, during magma ascent to the surface resulted in a derivative magma with low Ni and Cr concentrations. A collision between the pre-Mesozoic Paternoster platform (microcontinent ?) and the Sundaland continent in the Upper Cretaceous-Lower Miocene might cause the magma ascent to pool immediately in the lower crust-upper mantle boundary. The impending magma then reacts with hot mantle peridotite to produce the high magnesian andesites. Secondly, the high magnesian andesite may resulted from a reaction between silicic magma and hot mantle peridotite. The collision may also cause lower crust melting resulted in granitic magma (? The Hajawa Granite), which then reacts with hot mantle peridotite to produce the adakite-type high magnesian magma, such as samples 95UH23C and 96UH23.Keywords : high magnesian andesites, Southeast Kalimantan, origin
IDENTIFIKASI GUNUNG API PURBA DI DAERAH SAPAYA, SULAWESI SELATAN PADA DATA INDERAAN JAUH Sidarto Sidarto; Udi Hartono
Jurnal Geologi dan Sumberdaya Mineral Vol. 19 No. 6 (2009): Jurnal Sumber Daya Geologi
Publisher : Pusat Survei Geologi

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.33332/jgsm.geologi.v19i6.219

Abstract

In Tertiary, the South Arm of Sulawesi Island is a volcanic arc represented by Camba Formation having a relatively wide distribution. Integration of landsat and IFSAR images is able to visualize volcanic morphological features, lithology and volcanic structures that are used to identify ancient volcanoes in Sapaya area and surroundings. The result of geological interpretation on the images indicated there were two ancient volcanoes in this area, involving Sapaya and Bantoloe Volcanoes. The Middle Miocene - Pliocene Sapaya Volcano shows eroded cone feature, consisting of breccia volcanic (proximal facies), tuff (medial facies), and conglomerate (distal facies) units, and the vokanic structures are caldera, and radier intrusion basalts; while the Pliocene Bantoloe Volcano is identified by an eroded cone morphology, consisting of volcanic breccia of Bentoloe (proximal facies), lava Bantoloe (central testes), and diorite showing a deep seated intrusion (central facies). The Sapaya Volcano might be controlled by Tithyan type subduction showing a collision between micro continental which is part of Australian Continent and Eurasian Continent Plates. Keywords: South Arm Sulawesi, morphology, lithology, volcanic structure, ancient volcanoes, landsat and IFSAR Images       
Co-Authors Raden Isnu H. Sulistyawan Sidarto Sidarto