Mixing model for andesitic volcanism
Andesite and dacite commonly contain partially melted plagioclase, resorted or reacted quartz, and mafic xenolithe (less than 1 mm to 1 m) composed of plagioclase (An/sub 50 to 60/), pyroxene or hornblende, and minor amounts of glass, olivine (Fo/sub 70 to 80/), and plagioclase (An/sub 80 to 90/). Texturally similar xenoliths occur in granodiorite. Petrologic data indicate that the xenoliths represent basalt magma quenched within active silicic magma chambers and that the silicic parent magma is rhyolite. Field relationships suggest that mixing is accomplished by convective stirring in sizeable chambers and that these chambers develop in regions of upward flux of basalt. It is proposed that: (1) basalt magma from the upper mantle provides heat for generating rhyolitic melt in the lower crust, (2) the resulting magma body continues to receive injections of basalt as it rises through the crust, and (3) the influence of tectonic setting on crustal residence time of the magma body controls to what degree the system is homogenized. This model is consistent with elemental and isotopic composition of ingeous rocks and with thermal and hydrodynamic considerations.
- Research Organization:
- Univ. of California, Los Alamos
- OSTI ID:
- 5368586
- Journal Information:
- EOS, Trans., Am. Geophys. Union; (United States), Journal Name: EOS, Trans., Am. Geophys. Union; (United States) Vol. 57:12; ISSN EOSTA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
152000 -- Geothermal Data & Theory
58 GEOSCIENCES
580202* -- Geophysics-- Volcanology-- (1980-1989)
AMPHIBOLE
ANDESITES
ANORTHOSITES
BASALT
CHALCOGENIDES
CONVECTION
ENERGY TRANSFER
GLASS
HEAT TRANSFER
HORNBLENDE
IGNEOUS ROCKS
MAGMA
MATHEMATICAL MODELS
MINERALS
MIXING
OLIVINE
OXIDES
OXYGEN COMPOUNDS
PYROXENES
QUARTZ
RHYOLITES
ROCKS
SILICATES
SILICON COMPOUNDS
SILICON OXIDES
VOLCANIC ROCKS
VOLCANISM