Retention of sodium during chondrule melting

Journal Article · Mon Apr 01 04:00:00 EST 1991 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(91)90152-U· OSTI ID:5586912

Hewins, R H ^[1]

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1. Rutgers Univ., New Brunswick, NJ (USA)

Type I chondrules in unequilibrated ordinary and carbonaceous chondrites tend to be enriched in refractory elements and depleted in volatiles relative to bulk CI. Type II chondrules show chondritic concentrations of major and minor lithophile elements with Na, in particular, at or slightly above the appropriate bulk-rock values. Element ratio diagrams for chondrule bulk compositions show that Type II chondrules plot on a mixing line between forsterite and a Na phase, with Na/Al 1:1, whereas Type I compositions can be explained by mixing forsterite with melilite or CAI or other refractory component with little Na. If their bulk compositions are manipulated, subtracting Ca is diopside and Fe + Mg as olivine, the residue is 90{percent} albite and 10{percent} silica. Albite was incorporated into the precursors of Type II chondrules, which clearly have not been depleted in Na although their initial temperatures overlap with those of Type I. There is no (negative) correlation between Type I liquidus temperatures (1450-1900{degree}C) and Na/Al ratios and hence no indication of Na loss from the melt. If Type I precursors contained albite, the most aluminous chondrules would have suffered the most extreme Na loss, but these have the lowest liquidus temperatures. Their precursors were Na depleted, whereas those of Type II were Na enriched, as a function of the abundance of albite. The simplest way to obtain the bulk compositions of chondrules is to assemble condensates into precursors at different temperatures, and concentration of solids in the nebula or exceptionally rapid heating is required to preserve Na in chondrules after melting. Substantial exchange of Na occurred between chondrules and chondrite matrix during parent-body metamorphism to petrologic type 3.6.

• OSTI ID: 5586912
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Journal Name: Geochimica et Cosmochimica Acta; (United States) Vol. 55:4; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000 -- Geosciences
640106* -- Astrophysics & Cosmology-- Cosmology
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ALBITE
ALKALI METALS
ALKALINE EARTH METAL COMPOUNDS
CHEMICAL COMPOSITION
CHEMISTRY
CHONDRITES
DIOPSIDE
ELEMENTS
FELDSPARS
GEOCHEMISTRY
GEOLOGIC HISTORY
IRON COMPOUNDS
IRON SILICATES
MAGMATISM
MAGNESIUM COMPOUNDS
MAGNESIUM SILICATES
METALS
METEORITES
MINERALOGY
MINERALS
NEBULAE
OLIVINE
ORIGIN
OXYGEN COMPOUNDS
PETROGENESIS
PYROXENES
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SODIUM
SOLAR NEBULA
STONE METEORITES
TRANSITION ELEMENT COMPOUNDS