Highly evolved rhyolitic glass compositions from the Toba Caldera, Sumatra
The quartz latite to rhyolitic ash flow tuffs erupted form the Toba Caldera, perhaps the largest caldera on earth (100 by 30 kms), provide the unique opportunity to study a highly differentiated liquid in equilibrium with numerous mineral phases. Not only are the rocks very crystal rich (30-50%), but at present a minimum of 15 co-existing mineral phases have been identified. Both whole-rock and glass analyses were made by XRF techniques providing data on both major and trace elements. Whole rock chemistry of individual pumices from the youngest eruption at Toba (75,000 years ago), are suggestive of the eruption of two magma compositions across a boundary layer in the magma chamber. Glass chemistry of the pumices also show two distinct liquid compositions. The more silicic pumices, which have the most evolved glass compositions, are similar to the whole rock chemistry of the few aplitic pumices and cognate granitic xenoliths that were collected. This highly evolved composition resulted from the removal of up to 15 mineral phases and may be a fractionation buffered, univariant composition. The glasses from the less silicic pumices are similar to the whole rock chemistry of the more silicic pumice, thus falling nicely on a fractionation trend towards the univariant composition for these rocks. This set of glass compositions allows an independent test for the origin of distal ashes thought to have erupted from Toba and deposited in Malaysia, the Indian Ocean, and as far away as India.
- Research Organization:
- Michigan Technical Univ., Houghton (USA)
- OSTI ID:
- 6644089
- Report Number(s):
- CONF-8510489-
- Journal Information:
- Geol. Soc. Am., Abstr. Programs; (United States), Vol. 17; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28 Oct 1985
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
AFRICA
CALDERAS
RHYOLITES
VOLCANOES
MINERALOGY
PETROCHEMISTRY
PETROGENESIS
PETROLOGY
ALLANITE
AMPHIBOLE
APATITES
ASHES
BIOTITE
CHEMICAL COMPOSITION
FELDSPARS
GEOLOGIC HISTORY
GLASS
MAGMA
MAGNETITE
ORIGIN
PEROVSKITES
PUMICE
QUARTZ
ACTINIDE COMPOUNDS
CHALCOGENIDES
GEOLOGY
IGNEOUS ROCKS
IRON COMPOUNDS
IRON ORES
IRON OXIDES
MATERIALS
MICA
MINERALS
ORES
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PHOSPHATE MINERALS
RADIOACTIVE MATERIALS
RADIOACTIVE MINERALS
RESIDUES
ROCKS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SILICON OXIDES
THORIUM COMPOUNDS
THORIUM MINERALS
THORIUM SILICATES
TRANSITION ELEMENT COMPOUNDS
VOLCANIC ROCKS
580300* - Mineralogy
Petrology
& Rock Mechanics- (-1989)
580400 - Geochemistry- (-1989)