Tj. Fagan et al., Formation of feldspathic and metallic melts by shock in enstatite chondrite Reckling Peak A80259, METEORIT PL, 35(2), 2000, pp. 319-329
The enstatite chondrite Reckling Peak (RKP) A80259 contains feldspathic gla
ss, kamacite, troilite, and unusual sets of parallel fine-grained enstatite
prisms: that formed by rapid cooling of shock melts. Metallic Fe,Ni and tr
oilite occur as spherical inclusions in feldspathic glass, reflecting the i
mmiscible Fe-Ni-S and feldspathic melts generated during the impact. The Fe
-Ni-S and feldspathic liquids were injected into fractures in coarse-graine
d enstatite and cooled rapidly, resulting in thin (less than or equal to 10
mu m) semicontinuous to discontinuous veins and inclusion trails in host e
nstatite. Whole-rock melt veins characteristic of heavily shocked ordinary
chondrites are conspicuously absent. Raman spectroscopy shows that the feld
spathic material is a glass. Elevated MgO and SiO2 contents of the glass in
dicate that some enstatite and silica were incorporated in the feldspathic
melt. Metallic Fe,Ni globules are enclosed by sulfide and exhibit Ni-enrich
ment along their margins characteristic of rapid crystallization from a Fe-
Ni-S liquid. Metal enclosed by sulfide is higher in Si and P than metal in
feldspathic glass and enstatite, possibly indicating lower O fugacities in
metal/sulfide than in silicate domains. Fine-grained, elongate enstatite pr
isms in troilite or feldspathic glass crystallized from local pyroxene melt
s that formed along precursor grain boundaries, but most of the enstatite i
n the target rock remained solid during the impact and occurs as deformed,
coarse-grained crystals with lower CaO, Al2O3, and FeO than the fine-graine
d enstatite. Reckling Peak A80259 represents an intermediate stage of shock
melting between unmelted E chondrites and whole-rock shock melts and melt
breccias documented by previous workers. The shock petrogenesis of RKPA8025
9 reflects the extensive impact processing of the enstatite chondrite paren
t bodies relative to those of other chondrite types.