Experimental study and TEM characterization of dusty olivines in chondrites: Evidence for formation by in-situ reduction

Details Experimental study and TEM characterization of dusty olivines in chondrites: Evidence for formation by in-situ reduction Experimental study and TEM characterization of dusty olivines in chondrites: Evidence for formation by in-situ reduction

Jan 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003m%26ps...38...81l&link_type=abstract

Meteoritics & Planetary Science, vol. 38, no. 1, p.81-94

Computer Science

13

Scientific paper

An analytical transmission electron microscopy (ATEM) study was undertaken in order to better understand the formation conditions of dusty olivines (i.e., olivines containing abundant tiny inclusions of Fe-Ni metal) in primitive meteorites. Dusty olivines from type I chondrules in the Bishunpur chondrite (LL3.1) and from synthetic samples obtained by reduction of San Carlos olivines were examined. In both natural and experimental samples, micron size metal blebs observed in the dusty region often show preferential alignments along crystallographic directions of the olivine grains, have low Ni contents (typically <2 wt%), and are frequently surrounded by a silica-rich glass layer. These features suggest that dusty olivines are formed by a sub-solidus reduction of initially fayalitic olivines according to the following reaction: Fe2SiO4 = 2Fe + xSiO2 + (1-x) SiO + (3-x)/2O2 in olivine metal in melt in gas in gas Some volatilization of SiOgas may account for the apparent excess of metal relative to silica-rich glass observed in both experimental and natural samples. Comparison with experimentally produced dusty olivines suggests that time scales of the order of minutes usually inferred for chondrule formation are also adequate for the formation of dusty olivines. These observations are in agreement with the hypothesis that at least part of the metal phase in chondrites originated from reduction during chondrule formation.

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