Abstract-Previous X-ray powder diffraction (XRD) studies revealed that shock deformed carbonates and quartz have broader XRD patterns than those of unshocked samples. Entire XRD patterns, single peak profiles and Rietveld refined parameters of carbonate samples from the Sierra Madera impact crater, west Texas, unshocked equivalent samples from 95 miles north of the crater and the Mission Canyon Formation of southwest Montana and western Wyoming were used to evaluate the use of X-ray powder diffraction as a potential tool for distinguishing impact deformed rocks from unshocked and tectonically deformed rocks. At Sierra Madera dolostone and limestone samples were collected from the crater rim (lower shock intensity) and the central uplift (higher shock intensity). Unshocked equivalent dolostone samples were collected from well cores drilled outside of the impact crater. Carbonate rocks of the Mission Canyon Formation were sampled along a transect across the tectonic front of the Sevier and Laramide orogenic belts.

Deformational features from the Sierra Madera impact structure, west Texas, were studied to estimate shock temperature and shock pressure values involved during its formation. Sandstone, limestone, and polymict impact-generated breccia samples occur within the central uplift. The sandstones host several shock-related deformational features including toasted quartz grains and planar microstructures (planar fractures and planar deformation features) in quartz. Zircon mineral grains separated from the sandstone samples provide evidence of shock deformation in the form of planar fractures and granular surface textures. Both sandstone and carbonate within the central uplift contain shatter cones, whereas polymict impactgenerated breccia samples contain shatter cone fragments and clasts of mixed lithology. Most high-temperature features (e.g., high-temperature mineral phases and a melt sheet) typically associated with less eroded structures of similar size are lacking; however, some small (millimeter-size) possible devitrifi ed glass clasts within polymict breccias occur at several locations. Deformational features within zircon mineral grains, shatter cones, and quartz grains with multiple planar microstructures record pressure and temperature conditions during the impact of ~3-20 GPa and postshock temperatures between 350 and >1000 °C. Deformational conditions during the impact event were almost certainly higher, given that erosion has presumably removed most of the more severely shocked rocks.

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