Magmatic Conditions as Indicated by Petrological and Mineralogical Aspects in the Tertiary Basaltic Lava, Southeastern Bali, Indonesia
Kondisi magmatik diindikasikan oleh aspek petrologi dan mineralogi pada lava basalt berumur Tersier, di kawasan tenggara Bali, Indonesia. Corr author: [email protected]. https://commons.wikimedia.org/wiki/File:Mount_Agung,_November_2017_eruption_-_27_Nov_2017_02.jpg CCBYSA
by I G.B. Eddy Sucipta, Muhammad Taufik Abdullah, and Purnama Sendjaja
Published onJul 01, 2022
Magmatic Conditions as Indicated by Petrological and Mineralogical Aspects in the Tertiary Basaltic Lava, Southeastern Bali, Indonesia
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Dr. I.G.B. Eddy Sucipta
English
The Tertiary basaltic lava in southeastern of Bali Island present as pillow lava and they have associated with magma series of high-K calc-alkaline in the island arc of volcanic system. Mineralogically, these rocks are composed of olivine and clinopyroxene as main phenocrysts with the plagioclase and magnetite phenocrysts in minor abundants. Their groundmass have the plagioclase, opaque minerals, pyroxene, and volcanic glass that they formed the intersertal texture. Olivine have the forsterite composition (Fo63-92) with normal zoning texture. Pyroxene have augite and diopside composition with normal and reverse zoning. The reverse zoning in the pyroxene phenocrysts have significantly variation of Mg-, Cr-, Ti- and Al-content. Multiple zones have been observed that the reverse zoning formed from core to the first rim, and normal zoning to the next rims. Plagioclase in groundmass have range composition of bytownite to high-K albite. Geothermobarometry of clinopyroxene indicated that the Tertiary basaltic lava in southeastern of Bali Island are formed by cogenetic magma with temperature of 1100o-1300o C and pressure of 3-9 kbar. The magma mixing is important process before the basaltic lava erupted in the marine environment.
Lava basaltik Tersier di bagian tenggara Pulau Bali hadir sebagai lava bantal dan berasosiasi dengan rangkaian magma kalk-alkali K tinggi di busur pulau sistem vulkanik. Komposisi mineral batuan ini tersusun atas olivin dan klinopiroksen sebagai fenokris utama dengan fenokris plagioklas dan magnetit sebagai kelimpahan minor. Masa dasarnya mengandung plagioklas, mineral buram, piroksen, dan kaca vulkanik yang membentuk tekstur intersertal. Olivin memiliki komposisi forsterit (Fo63-92) dengan tekstur zoning normal. Piroksen memiliki komposisi augit dan diopside dengan zonasi normal dan terbalik (reverse). Zonasi terbalik pada fenokris piroksen memiliki kandungan Mg-, Cr-, Ti- dan Al yang sangat bervariasi. Beberapa zona telah diamati bahwa zonasi terbalik terbentuk dari inti ke tepi pertama, dan zonasi normal ke tepi berikutnya. Plagioklas dalam massa dasar memiliki komposisi yang berkisar dari bitownit hingga albit K tinggi. Geotermobarometri klinopirokses menunjukkan bahwa lava basaltik Tersier di tenggara Pulau Bali terbentuk oleh magma kogenetik dengan suhu 1100o-1300o C dan tekanan 3-9 kbar. Pencampuran magma adalah proses penting sebelum lava basaltik meletus di lingkungan laut.
Kata kunci: lava basalt, Bali, magma, petrologi, mineralogi, geotermobarometri.
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