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The Divnoe meteorite: Petrology, chemistry, oxygen isotopes and origin
Author(s) -
Petaev M. I.,
Barsukova L. D.,
Lipschutz M. E.,
Wang M.S.,
Ariskin A. A.,
Clayton R. N.,
Mayeda T. K.
Publication year - 1994
Publication title -
meteoritics
Language(s) - English
Resource type - Journals
eISSN - 1945-5100
pISSN - 0026-1114
DOI - 10.1111/j.1945-5100.1994.tb00671.x
Subject(s) - achondrite , plagioclase , olivine , meteorite , geology , partial melting , chondrite , pyroxene , geochemistry , isotopes of oxygen , anorthosite , mineralogy , parent body , basalt , astrobiology , quartz , paleontology , physics
— The Divnoe meteorite is an olivine‐rich primitive achondrite with subchondritic chemistry and mineralogy. It has a granoblastic, coarse‐grained, olivine groundmass (CGL: coarse‐grained lithology) with relatively large pyroxene‐plagioclase poikilitic patches (PP) and small fine‐grained domains of an opaque‐rich lithology (ORL). Both PP and ORL are inhomogeneously distributed and display reaction boundaries with the groundmass. Major silicates, olivine (Fa 20–28 ) and orthopyroxene (Fs 20–28 Wo 0.5–2.5 ), display systematic differences in composition between CGL and ORL as well as a complicated pattern of variations within CGL. Accessory plagioclase has low K content and displays regular igneous zoning with core compositions An 40–45 and rims An 32–37 . The bulk chemical composition of Divnoe is similar to that of olivine‐rich primitive achondrites, except for a depletion of incompatible elements and minor enrichment of refractory siderophiles. Oxygen isotope compositions for whole‐rock and separated minerals from Divnoe fall in a narrow range, with mean δ 18 O = +4.91, δ 17 O = +2.24, and Δ 17 O = −0.26 ± 0.11. The isotopic composition is not within the range of any previously recognized group but is very close to that of the brachinites. To understand the origin of Divnoe lithologies, partial melting and crystallization were modelled using starting compositions equal to that of Divnoe and some chondritic meteorites. It was found that the Divnoe composition could be derived from a chondritic source region by ∼20 wt% partial melting at T ∼ 1300 °C and log(fO 2 ) = IW‐1.8, followed by ∼60 wt% crystallization of the partial melt formed, and removal of the still‐liquid portion of the partial melt. Removal of the last partial melt resulted in depletion of the Divnoe plagioclase in Na and K. In this scenario, CGL represents the residue of partial melting, and PP is a portion of the partial melt that crystallized in situ . The ORL was formed during the final stages of partial melting by reaction between gaseous sulfur and residual olivine in the source region. A prominent feature of Divnoe is fine μm‐scale chemical variations within olivine grains, related to lamellar structures the olivines display. The origin of these structures is not known.