Tertiary to Early Proterozoic gneissic rocks

Gneissic rocks with complex histories, typically with well developed, light-colored granitoid layers and dark-colored biotite- and amphibole-rich layers. Protoliths are of Tertiary to Proterozoic age. This unit includes variably mylonitic gneisses in metamorphic core complexes that have been exhumed from middle crustal levels by large-displacement middle Tertiary normal faults, and gneiss exposed at scattered locations near the Colorado River in southwestern Arizona. These rocks are interpreted to record Proterozoic, Mesozoic, and Tertiary metamorphism and deformation. (15-1800 Ma)
State Arizona
Name Tertiary to Early Proterozoic gneissic rocks
Geologic age Early Proterozoic to Tertiary
Lithologic constituents
Metamorphic > Gneiss (Amphibolite)
Tectonite > Mylonite (Amphibolite)variably mylonitic gneisses
Comments Includes, but is not limited to, gneisses in metamorphic core complexes

Richard, S.M., Reynolds, S.J., Spencer, J.E., and Pearthree, P.A., 2000, Geologic Map of Arizona: Arizona Geological Survey Map 35, 1 sheet, scale 1:1,000,000.

Spencer, J.E., and Reynolds, S.J., 1989, Middle Tertiary tectonics of Arizona and adjacent areas, in Jenney, J.P., and Reynolds, S.J., editors, Geologic evolution of Arizona: Arizona Geological Society Digest 17, p. 539-574.

NGMDB product
Counties La Paz - Maricopa - Mohave - Pima - Pinal - Yavapai - Yuma