APPARENT SHOCK METAMORPHISM ASSOCIATED WITH A BRECCIA: EVIDENCE SUPPORTING A HIGH ENERGY SHOCK WAVE EVENT AT THE PERMOTRIASSIC BOUNDARY, SAN RAFAEL SWELL, UTAH

In situ fractures and offsets observed in chert breccia fragments, in crystals of zircon (?), quartz and muscovite, and in severely shattered chitin, all support the suggestion of a high energy shock wave event at the Permotriassic boundary in the San Rafael Swell, east-central Utah.

Secondary fractures in chert breccia fragments often exhibit rotation with offset and are commonly bifurcated and filled with diagenetic calcite. Single crystals of zircon (?) and other mineral crystals are fractured and occasionally exhibit rotation with offset. Shattered chitin commonly shows secondary fractures within individual fragments.

Chert breccia fragments and individual mineral crystals were severely shocked in situ before matrix consolidation. Both vertical and horizontal displacements and offsets are observed. Fragmentation of chitin may be explained as resulting from: (1) predation; or (2)high energy shock wave. The chitin fragments studied in this report show no apparent characteristic indicators of predation.

Independent and separate laboratories produced thin sections and identified the chitin in this study: (1) Mesa State College Department of Physical and Environmental Science produced thin sections; (2) Mesa State College Center for Microscopy used a scanning electron microscope with energy dispersive spectrometry (SEM/EDS) to identify and study the chitin; and (3) Colorado School of Mines Department of Geology produced a thin section and used an electron microprobe to identify the chitin.

Chert fragments and individual crystal morphology were studied at the WWG Geol. Research Facility in: (1)thin section with transmitted light; and (2) thick section with reflected light. A Leica DMLP polarizing light microscope with a Clemex imaging system was used in this study.

Seismic waves generated by terrestrial earthquake are not considered here to be sufficiently powerful to cause the severe particle damage observed in this investigation. Bolide impact is a possible cause for such metamorphism.