Title: Manganiferous orthopyroxene and olivine in the Allende meteorite
Abstract: Numerous orthopyroxene grains averaging (in wt.%) 4.2Vo MnO,32.3% MgO and l.4Vo FeO and several olivine grains averaging l.2Vo MnO, 49.5Vo MgO and 9.2Vo FeO occur within a thick relatively coarse-grained rim around an unusually large porphyritic chondrule in the Allende CV3 carbonaceous chondrite. Orthopyroxenes and olivines with such high Mn and low Fe have not previously been reported from meteorites and are rare on Earth, primarily occurring in metamorphosed evaporites and calc-silicate deposits. Relative to opaque matrix, the rim is mildly depleted in refractories, enriched in Cr and Na and greatly enriched in Mn. The bulk enrichments in Cr, Na and Mn in the rim approximately mirror the depletions of these elements in CV chondrules. It thus is possible that the rim acquired, by condensation, volatilized Cr, Na and Mn which were lost from chondrule precursors during heating. The manganiferous orthopyroxene and olivine grew in the Mn-rich rim at elevated temperatures, probably =1000'C. The apparent absence of other grains of MnO-rich pyroxene and olivine within the opaque silicate matrix and other relatively coarse-grained rims in Allende and other CV3 chondrites attests to the unique history of this particular chondrule rim.
Publication Year: 1984
Publication Date: 1984-01-01
Language: en
Type: article
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