Ion Microprobe Evidence for the Presence of Excess Mg in an Allende Anorthite Crystal
نویسندگان
چکیده
An ion microprobe ha~ been. used to observe Mg/"Mg in excess of normal values in anorthite crystals from Allende refractory mclus10ns. In one crystal, Mg excesses up to 40% above normal, correlated with AI/Mg, were. obser_ved. These ~xc~sses are many times larger than those observed by other techniques. T_he _correla~10n with Al(Mg mdicated tha_t the excess '"Mg in the Allende anorthite is uniformly distributed m the anort~Ite. crystal. Analytical procedures and conditions were carefully controlled. Neverthel.ess, small but sig~Ifican~ apparent '"Mg/~fl:ig anomalies in isotopically normal samples were observed m analyses _by ?ne 10n microprobe. A repetition of the isotopic analyses using another ion probe produced normal ratios m the normal samples and confirmed large Mg excesses in the Allende anorthite.
منابع مشابه
Origin of Grossular-bearing Assemblages in Cais from Cv Carbonaceous Chondrites
Grossular is a secondary mineral commonly observed in Al-lende CAIs associated with monticellite, wollastonite, forsterite, anorthite, and wadalite [1–6]. Studies of the 26 Al– 26 Mg systemat-ics in grossular yield (26 Al/ 27 Al) 0 ranging from ~5×10 –5 to <3×10 –6 suggesting grossular formation started almost contempo-raneously with crystallization of CAIs and lasted > 3 My [1–3]. This interpr...
متن کاملSi and Mg Isotope Fractionations in Melilite in Type B Cais
Introduction: Si and Mg isotopic compositions are indicators of evaporation processes experienced by CAIs [1]. Bulk Si and Mg isotopic compositions (up to ~5 permil/amu for Si and ~11 permil/amu for Mg) have been reported by [2]. Isotopic heterogeneity within CAIs is of interest because it may reveal how evaporation processes occurred. It may also reveal if secondary processes such as recondens...
متن کاملHigh Precision Magnesium Isotopic Measurement of Cai Minerals with Low Al/mg Ratio from Allende Utilizing a Nanosims 50l Ion Microprobe
متن کامل
A study of the minor element concentrations of spinels from two type B calcium-aluminum-rich inclusions: An investigation into potential formation conditions of calcium-aluminum-rich inclusions
We have conducted an electron microprobe study of minor element distributions among spinels from two type B 1 calcium-aluminum-rich inclusions (CAIs): Allende TS-23 and Leoville 3537-2. We show that by maintaining the petrologic context (edge, middle, and center of the inclusion plus their host silicate phase), four populations of spinels are resolvable based on their minor element contents. On...
متن کاملMineralogical and geochemical investigations of chromite ores from ophiolite complexes of SE Iran in terms of chrome spinel composition
Ten chromite ores from ophiolite complexes in SE Iran were analyzed mineralogically by XRD, chemically by XRF, and mineral chemistry by EPMA. The identified paragenesis of silicate minerals of chromite ores with the X-ray diffraction is pronounced differently. It consists of secondary phases formed as serpentine, Cr-containing chlorite (kaemmererite), chromic garnet (uarovite) with preserved pa...
متن کامل