Abstract
We report results from an experimental study of sulfide chemistry
during metamorphism on ordinary chondrite parent bodies. Artificial
LL-chondrite material, composed of silicate, iron metal, and sulfide
grains, was placed in sealed, evacuated silica tubes and heated to
either 500 degrees C or 900 degrees C, These temperatures are representative
peak metamorphic temperatures experienced by type 3 and type 6 ordinary
chondrites, respectively. Rapid sulfur mobilization occurs during
heating and results in the formation of sulfide rims around the metal
grains and sulfur loss from the original sulfide crystals, The newly
formed sulfide rims have two distinct layers that incorporate nearby
silicate grains. We also observe narrow sulfide trails that follow
silicate grain boundaries and connect separate sulfide-rimmed metal
grains. The morphologies of the sulfide rims suggest that vapor transport
is the main mechanism for sulfur mobilization, Sulfur loss is observed
along cracks and crystal boundaries of the initial sulfide grains.
After extensive reaction, patches of iron metal appear at the outer
edges of the sulfide crystals and large pore spaces form throughout
the original sulfides. The experimental metal-sulfide assemblages
resemble those found in low metamorphic grade ordinary chondrites,
This suggests metamorphism is mainly responsible for the observed
metal-sulfide textures in these chondrites. (C) 1997 Elsevier Science
B.V.
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