Equilibration Temperatures of Iron and Magnesium in Chondritic Meteorites

Abstract

The distribution coefficients for Fe(++) and Mg(++) were calculated from new microprobe analyses of coexisting olivine, orthopyroxene, and calcic pyroxene in chondritic meteorites. Interpretation of the data shows that (i) the equilibration temperatures were of the order of 850 degrees C, and (ii) the olivineorthopyroxene partition does not reflect ideal behavior. This equilibration temperature is much lower than previous estimates.

The Oro Grande, New Mexico, Chondrite and Its Lithic Inclusion

“…Electron microprobe traverses across individual grains indicate that the major phases, olivine and orthopyroxene, are homogeneous within the precision of the analyses (to.5% of the amounts present); this is compatible with classification of the meteorite into petrologic group 5 (Van Schmus and Wood, 1967 The distribution coefficient, KD' for the Fe H and Mg of the orthopyroxene and clinopyroxene is 0.60 and is similar to that of many other ordinary chondrites as reported by Van Schmus and Koffman (1967). According to Kretz (1963), the equilibration temperature for a KD of 0.60 is about 790°C.…”

Implications of Poikilitic Textures in Ll‐group Chondrites

“…4. There is no compositional difference between olivine chadacrysts and the one large, anhedral olivine, Wiik, 1969 Van Schmus and Koffman, 1967). CaO over 1.0 wt % in orthopyroxene was also observed by Dodd (1974) in similarly-textured lithic fragments in the St. Mesmin chondrite.…”

Olivine zoning and retrograde olivine-orthopyroxene-metal equilibration in H5 and H6 chondrites

“…Van Schmus and Koffman (1967) recognized that chondrite orthopyroxene-diopside Fe-Mg exchange temperatures might reflect closure temperatures during cooling rather than peak metamorphic temperatures. More dramatically, chemical zoning in taenite (γ, face-centeredcubic) and kamacite (α, body-centered-cubic) are the result of taenite-kamacite equilibration during cooling (Wood 1967).…”