METALLIC MICROSPHERULES AND SHOCK METAMORPHISM CHARACTERISTICS IN A BRECCIA SUPPORT A HIGH ENERGY SHOCK WAVE EVENT AT THE PERMOTRIASSIC BOUNDARY, SAN RAFAEL SWELL, EAST-CENTRAL UTAH

In situ magnetic/metallic microspherules, fractured crystals of zircon(?), quartz, muscovite plus fractured chert and chitin, all support the suggestion of a high energy shock wave event at the Permotriassic boundary.

Oriented thin sections show fractures in euhedral crystals that are commonly offset vertically as well as horizontally. Shattered chitin and chert breccia clasts commonly exhibit secondary tension fractures within individual fragments. These fractures are often filled with diagenetic calcite and/or matrix-derived silt particles. Chert breccia fragments are commonly fractured with segment rotation. Fractures in these particles do not extend into the surrounding siltstone/mudstone matrix suggesting these objects were suspended in an unconsolidated groundmass.

Metallic/magnetic microspherules are associated with these fractured particles in a breccia unit. The microspherules range in size from 6um to 44um, are primarily iron, amorphous to precursor crystalline, and show some evidence of having been molten.

Seismic waves generated by terrestrial earthquake are not considered sufficiently powerful to cause the particle damage observed in this investigation. A high energy shock wave produced by an aerial bolide blast or by bolide impact is a possible explanation for the shock metamorphism characteristics observed in this study.