Formation of feldspathic and metallic melts by shock in enstatite chondrite Reckling Peak A80259

The enstatite chondrite Reckling Peak (RKP) A80259 contains feldspathic glass, kamacite, troilite, and unusual sets of parallel fine-grained enstatite prisms: that formed by rapid cooling of shock melts. Metallic Fe,Ni and troilite occur as spherical inclusions in feldspathic glass, reflecting the immiscible Fe-Ni-S and feldspathic melts generated during the impact. The Fe-Ni-S and feldspathic liquids were injected into fractures in coarse-grained enstatite and cooled rapidly, resulting in thin (less than or equal to 10 mu m) semicontinuous to discontinuous veins and inclusion trails in host enstatite. Whole-rock melt veins characteristic of heavily shocked ordinary chondrites are conspicuously absent. Raman spectroscopy shows that the feldspathic material is a glass. Elevated MgO and SiO2 contents of the glass indicate that some enstatite and silica were incorporated in the feldspathic melt. Metallic Fe,Ni globules are enclosed by sulfide and exhibit Ni-enrichment 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 prisms in troilite or feldspathic glass crystallized from local pyroxene melts that formed along precursor grain boundaries, but most of the enstatite in the target rock remained solid during the impact and occurs as deformed, coarse-grained crystals with lower CaO, Al2O3, and FeO than the fine-grained 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 RKPA80259 reflects the extensive impact processing of the enstatite chondrite parent bodies relative to those of other chondrite types.