­­REMOTELY-SENSED DISTRIBUTION OF THE MIOCENE-AGED PEACH SPRING TUFF SUPERERUPTION DEPOSIT IN THE SOUTHERN BLACK MOUNTAINS OF NW AZ

The Peach Spring Tuff (PST) formed during an 18.78 Ma supereruption from the Silver Creek Caldera in the southern Black Mountains (SBM), NW AZ. Although the PST is absent immediately surrounding the caldera (e.g., Williams et al., 2014; GSA abs), it is present toward the southern end of the range (Gray et al., 1990; USGS Bull). Assessment of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) imagery of the SBM suggests the PST can be identified using spectral-matching techniques from compositionally different tuffs and rock units allowing us to further constrain its presence in this region. To elaborate, spectral analysis of the PST, a single cooling unit, indicates three spectral zones are uniquely mappable in the SBM using Visible and Near-infrared (VNIR) (15 m/pxl) and Short-wavelength Infrared (SWIR) (30 m/pxl) bands, possibly due to different degrees of resistance to weathering, which, in turn, may represent different degrees of welding and/or mineralogies. 7-3-1 RGB band combination images, emphasizing wavelengths of 2.262-0.807-0.556 micrometers, respectively, displayed the most qualitatively noticeable differences between the PST zones and surrounding rocks. Using spectral plotting of ground-truthed areas, Google Earth, and mapping by Gray et al. (1990), we determined if PST was present at locations based on the color displayed in the RGB scheme and the reflectance and absorbance peaks. The complete PST unit as a whole had characteristic reflectances at 2.15 and 2.25 micrometers with absorptions at 2.20 and 2.35 micrometers. The PST spectral zones could then be recognized by the reflectance and absorption intensities of image-collected spectra. Our results are consistent with Gray et al’s. (1990) distribution of the PST, but also help to further differentiate it from areas they have mapped as undivided. The Warm Springs (34°54'22"N, 114°19'16"W) and Caliche Springs (informal name; 34°55'51"N, 114°13'27"W) areas within the SBM displayed the most complete PST spectral zone “stratigraphy. This study in conjunction with others provides further framework to help establish a more complete volcanic stratigraphy of the southern BM and thus offer further insight into the complex volcanic history this area.