UNUSUAL SHOCK METAMORPHISM PRESENT IN A BRECCIA NEAR THE BASE OF THE BLACK DRAGON MEMBER OF THE TRIASSIC MOENKOPI FORMATION, SAN RAFAEL SWELL, UTAH

Fractures in chert, quartz, and other mineral fragments in a breccia present near the base of the Black Dragon Member of the Moenkopi Formation, San Rafael Swell, Utah appear to have been created by a high energy shock wave. Examination of the orientation of the fractures in some of the chert fragments exhibit primarily northwest strikes with steep to vertical dips. In east/west oriented samples several undulating horizontal fractures are observed.

Many observed fractures were filled with mud and silt particles at the time of their formation suggesting the minerals in the breccia were suspended in an unconsolidated silt and mud matrix when fractured. There are no shear planes associated with these fractures.