Magma Chamber Model of Batur Caldera, Bali, Indonesia: Compositional Variation of Two Facies, Large-Volume Dacitic Ignimbrites

Igan S. Sutawidjaja, Mega F. Rosana, K. Watanabe

Abstract


DOI:10.17014/ijog.2.2.111-124

Batur is one of the finest known calderas on Earth, and is the source of at least two major ignimbrite eruptions with a combined volume of some 84 km3 and 19 km3. These ignimbrites have a similar compositions, raising the question of whether they are geneticaly related. The Batur Ignimbrite-1 (BI-1) is crystal poor, containing rhyodacitic (68 - 70wt % SiO2), white to grey pumices and partly welded and unwelded. The overlying Batur Ignimbrite-2 (BI-2) is a homogeneous grey to black dacitic pumices (64 - 66 wt % SiO2), unwelded and densely welded (40 - 60% vesicularity), crystal and lithic rich. Phase equilibria indicate that the Batur magma equilibrated at temperatures of 1100 - 1300oC with melt water contents of 3 - 6 wt%. The post-eruptive Batur magma was cooler (<1100oC) and it is melt more water rich (> 6 wt % H2O). A pressure of 20 kbar is infered from mineral barometry for the Batur magma chamber. Magmatic chamber model is one in which crystals and melt separate from a convecting Batur magma by density differences, resulting in a stratified magma chamber with a homogeneous central zone, a crystal-rich accumulation zone near the walls or base, and a buoyant, melt-rich zone near the top. This is consistent with the estimated magma temperatures and densities: the pre-eruptive BI-1 magma was hoter (1300oC) and more volatile rich (6 wt % H2O) with density 2.25 g/cm3 than the BI-2 magma (1200oC; 4 wt % H2O) in density was higher (2.50 g/cm3). Batur melt characteristics and intensive parameters are consistent with a volatile oversaturation-driven eruption. However, the higher H2O content, high viscosity and low crystal content of the BI-1 magma imply an external eruption trigger.


Keywords


Batur caldera; ignimbrite; rhyodacite; dacite; melting zone; magma chamber model

References


Baker, F., 1979. Trondhjemite: Definition, environment and hypotheses of origin. In:Baker, F. (ed.), Trondhjemites, dacites and related rocks. Elsevier, Amsterdam, p.1-12. DOI:10.1016/B978-0-444-41765-7.50006-X

Blake, S. and Ivey, G. N.,1986. Magma-mixing and withdrawal dynamics of stratified reservoirs. Journal of Volcanology and Geothermal Research 27, p.153-178. DOI:10.1016/03770273(86)90084-3

Deer, W. A., Howic, R. A., and Zussman, J.,1992. An Introduction to the Rock-forming Minerals, 2nd edition. Harlow, UK: Longman.

de Silva, S. L. and Wolff, J. A.,1995. Categorized magma chamber; magma chamber geometry influence on the sidewall convective fractionation. Journal of Volcanology and Geothermal Research 65, p.111-118.

Le Maitre, R. W. (ed.), 1989. A frozen classification Rocks and Glossary. Oxford: Blackwell.

Marinelli, G. and Tazieff, H., 1968. L’ignimbrite et la caldera de Batur (Bali, Indonesie). Bulletin Volcanologique, 32, p.89-120. DOI:10.1007/BF02596587

Marsh, B. D., 1981. On the crystallinity, probability of occurrence, and rheology of lava and magma. Contributions to Mineralogy and Petrology, 78, p.85-98. DOI:10.1007/BF00371146

O’Connor, J. T., 1965. A classification of quatrz rich igneous rock based on feldspar ratios. US. Geological Survey Professional Paper,

B525, p.79-84.

Peccerillo, R. and Taylor, S.R., 1976. Geochemistry of Eocene calc-alkaline volcanic rocks from the Kastamonu area, northern Turkey.

Contribution to Mineralogy and Petrology, 58, p.63-81. DOI:10.1007/BF00384745

Reubi, O. and Nicholls, I.A., 2004. Magmatic evolution at Batur volcanic field, Bali, Indonesia:petrological evidence for polybaric

fractional crystallization and implications for caldera-forming eruptions. Journal of Volcanology and Geothermal Research, 138, p.345-369. DOI:10.1016/j.jvolgeores.2004.07.009

Sutawidjaja, I.S., 1990. Evolution of Batur caldera, Bali, Indonesia. A thesis of MSc, Victoria University of Wellington, New Zealand, unpublished.

Sutawidjaja, I.S., 2009. Ignimbrite analyses of Batur caldera, Bali, based on 14C dating. Indonesian Journal of Geology, 4 (3), p.189-202. DOI:10.17014/ijog.vol4no3.20094

Watanabe, K., Yamanaka, T., Harijoko, A., Saitra, C., and Warmada, I.W., 2010. Caldera activities in North Bali, Indonesia. Journal of SE

Asian Applied Geology, 2 (3), p.283-290.

Wheller, G.E. and Varne, R., 1986. Genesis of dacitic magmatism of Batur volcano, Bali, Indonesia: Implications for the origin of stratovolcano calderas. Journal of Volcanology and Geothermal Research, 28, p.363-378. DOI:10.1016/0377-0273(86)90031-4


Full Text: PDF

Refbacks

  • There are currently no refbacks.


Creative Commons License
Indonesian Journal on Geoscience by https://ijog.geologi.esdm.go.id/index.php/IJOG/index is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

 

Indexing Site :

Follow us on:


shopify visitor statistics
View My Stats