MAPPING THE EXTENT OF THE SITGREAVES TUFF USING MULTISPECTRAL ASTER IMAGERY IN THE BLACK MOUNTAINS, NW ARIZONA

The Sitgreaves Tuff (SGT) is a Miocene-aged deposit distributed from near Secret Pass Canyon south to Sitgreaves Pass in the southern Black Mountains, NW Arizona. It post-dates the supereruption of the 18.8 Ma Peach Spring Tuff from the nearby Silver Creek Caldera, ~4 km W of the closest STG exposure (Ferguson et. al., 2013), and may represent the final large-scale explosive activity associated with this supervolcanic system. Our combined field and remote sensing-based examination of the SGT has allowed us to constrain its distribution and lateral correlation in the region.

Previous geologic mapping (Liggett & Childs, 1982) provided the base for identifying SGT extent, guided our mapping, and constrained remotely sensed data that allowed us to refine its distribution. Advanced Spaceborne Thermal Emission and Reflectance Radiometer (ASTER) imagery enabled us to refine contacts and extend the distribution in areas where field data were lacking. ASTER imagery was processed by performing a principal component analysis (PCA), decorrelating the visible to short wave infrared bands, and highlighting spectral differences in the imagery. An ISODATA and k-means unsupervised classification were combined with a Mahalanobis supervised classification trained with field collected data to identify spectral signatures similar to the SGT. We also constructed cross sections from Secret Pass Canyon to Meadow Creek basin (E of Sitgreaves Pass) based upon our field observations, remotely sensed data, and previous mapping (Liggett & Childs,1982).

The SGT is fairly continuous across the central part of the map area, but appears to be more isolated in its occurrence in the north and south where local topography may have controlled its distribution. This is notable near ~35.06° N, 114.35° W where SGT appears to wrap around a possible lava dome of Meadow Creek Trachyte and filled a paleotopographic low (Meadow Creek Basin); the known northern-most extent of the SGT near Secret Pass Canyon may also be topographically controlled where it interfingers with, and pinches out in, rhyolite (dome collapse) breccias of the Flag Spring Trachyte (FST). The interfingering relationship (also present at 35.07° N, 114.38° E) suggests coeval emplacement with the FST. Estimates of the SGT from our mapping suggests that it has a minimum volume of 3-5 km³.