New Mexico Geological Society Annual Spring Meeting — Abstracts

The geologic map of eastern Grand Canyon includes ?670 km² of northeastern Grand Canyon National Park, Kaibab National Forest, and Navajo Nation Reservation. It consists of parts of the Point Imperial, Nankoweap Mesa, Walhalla Plateau, Cape Solitude, Cape Royal, and Desert View 7.5’ quadrangles.

Rocks exposed in the area include Paleoproterozoic basement rocks of the Granite Gorge Metamorphic Suite, the Grand Canyon Supergroup, including the Late Mesoproterozoic Unkar and Neoproterozoic Chuar groups, relatively flat-lying and mildly deformed Paleozoic strata, and Quaternary surficial deposits. Of particular focus in this map is new mapping in the Grand Canyon Supergroup and the structures related to Supergroup deposition, deformation and preservation.

The Grand Canyon Supergroup is one of the best-preserved remnants of Late Proterozoic sedimentary rocks in the southwestern United States. It provides an exceptional record of protracted, multi-phase deformation and intracratonic basin formation. The 1255-1100 Ma Unkar and Neoproterozoic Chuar Group records syn-sedimentary, NW-directed shortening and pencontemporaneous, orthogonal, NE-SW directed extension that are kinematically linked to ‘Grenville-age’ tectonism. The 800-742 Ma Chuar Group records E-W firected extension on N-striking normal faults that are kinematically linked to the incipient rifting of western North America in the Late Neoproterozoic.

Paleozoic rocks in the map area underwent deformation associated with the development of monoclines during the Laramide Orogeny. Laramide-age monoclines preferentially reactivate Proterozoic-age normal faults within the map area. We postulate that Laramide monocline development in the Colorado Plateau region may reflect inversion of the Proterozoic normal faults.