Other
Scientific paper
Sep 1987
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987jgr....92.e679l&link_type=abstract
Journal of Geophysical Research, Volume 92, Issue B4, p. E679-E696
Other
Scientific paper
Our electron-microprobe studies of four type 3 enstatite chondrites show that olivines and low-Ca pyroxenes with more than 3 wt % FeO are more abundant than previously recognized: 4-8% of clear pyroxene grains and a higher proportion of dusty pyroxenes have Fs 5-20. From scanning electron microscope and electron probe surveys of these four EH3 chondrites, we discovered 542 objects that contain silicates (very largely pyroxene) with >3 wt % FeO 18 chondrules, 381 rimmed or unrimmed graines, and 143 mineral aggregates with Fs 5-27 pyroxene or Fa 3-14 olivine. Aggregates and grains may have been derived from chondrules by comminution. Rims of enstatite with Fs 0-3 on many grains formed by reduction or growth in the nebula or parent body. In two EH4-5 chondrites, we identified 89 FeO-rich objects that are all enstatite grains with Fs 1-10 having FeO-poor enstatite rims, which grew during planetary metamorphism. Two of the 18 FeO-rich chondrules in EH3 chondrites have textures and mineral compositions that are consistent with crystallization of FeO-rich melts, in others these textures are modified by nebula or planetary reduction along cracks and grain edges that formed low-FeO silicates and metallic Fe,Ni. However, several FeO-rich chondrules contain crystals of both high- and low-FeO silicates that appear to have igneous origins but could not have formed by closed system crystallization of chondrule melts. These probably reflect either reduction of chondrule melts by the nebula during crystallization, or collisions of partly molten chondrules having very different FeO concentrations. An origin involving partial melting of chondrule precursor grains seems less plausible.
Keil Klaus
Lusby David
Scott Edward R. D.
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