Pyroxenes and olivines from a Galapagos spreading center (GSC) rhyodacite record crystal fractionation and magma mixing

Conference · Tue Jan 01 04:00:00 EST 1985 · Geol. Soc. Am., Abstr. Programs; (United States)

OSTI ID:6195349

Mattson, S R; Byerly, G R; Carpenter, P

Phenocrysts and xenocrysts of augite, subcalcic augite, pigeonite, orthopyroxene, and olivine in two glassy rhyodacite dredge samples from 95/sup 0/W on the GSC reflect a complex history of fractional crystallization and magma mixing. The pyroxene compositions can be grouped into clusters reflecting three major sources: a) Fenumber approx. 0.2 from basalt, b) Fenumber approx. 0.5 from rhyodacite, and c) Fenumber approx. 0.6 from rhyolite. Pyroxene Ti/Al ratios of 1:14, 1:7 and 1:3 have Fenumbers suggesting original crystallization from basalt, rhyodacite, and rhyolite melts respectively. These general compositional groups are typical of those produced during fractional crystallization of basalt to rhyolite. At relatively constant Fenumber the augites in any group display a wide spectrum of variation in Wo, Al, and Ti. Basaltic augite core to rim variations exhibit both increases and decreases in Ti at nearly constant Fenumber. A continuous variation in subcalcic augites is present from Fe-augite to Fe-pigeonite. These effects are likely kinetic, perhaps due to rapid cooling rates, but possibly due to supersaturation produced during mixing. Magma mixing may have played an important role in bringing together these contrasting components. The abundance of very-fine-grained basaltic xenoliths and xenocrysts, the glassy rhyolitic inclusions and associated xenocrysts, along with major reverse zoning in Fenumber or major discontinuities in Fenumber in the ferromagnesian phases all point to coexisting melts of radically differing composition.

• Research Organization: Louisiana State Univ., Baton Rouge (USA)
• OSTI ID: 6195349
• Report Number(s): CONF-8510489-
• Conference Information: Journal Name: Geol. Soc. Am., Abstr. Programs; (United States) Journal Volume: 17
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580300* -- Mineralogy
Petrology
& Rock Mechanics-- (-1989)
580400 -- Geochemistry-- (-1989)
ALKALINE EARTH METAL COMPOUNDS
ATLANTIC OCEAN
CHEMICAL COMPOSITION
CRYSTALLIZATION
FRACTIONATION
GEOLOGIC HISTORY
GEOLOGIC STRUCTURES
GEOLOGY
IGNEOUS ROCKS
IRON COMPOUNDS
IRON SILICATES
MAGMA
MAGMATISM
MAGNESIUM COMPOUNDS
MAGNESIUM SILICATES
MINERALS
OLIVINE
OXYGEN COMPOUNDS
PETROGENESIS
PETROLOGY
PHASE TRANSFORMATIONS
PYROXENES
RIFT ZONES
ROCKS
SEA-FLOOR SPREADING
SEAS
SEPARATION PROCESSES
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SURFACE WATERS
TRANSITION ELEMENT COMPOUNDS
VOLCANIC ROCKS