ANISOTROPY OF MAGNETIC SUSCEPTIBILITY STUDY OF FLOW AND DEPOSITIONAL PROCESSES IN THE PEACH SPRINGS TUFF, KINGMAN, ARIZONA

During mid-Miocene time, the Peach Springs Tuff (PST) was deposited in the pre-existing Kingman, Arizona, paleo-valley, which was bounded to the north and south by the Cerbat and Hualapai Mountains. Anisotropy of magnetic susceptibility (AMS) results from PST deposits on isolated topographic highs indicate that flow directions and magnetic rock fabrics are mainly controlled by paleotopography, such that the PST underwent different depositional and flow processes upon interacting with a gently sloping Granite Ridge and steeply sloping Scoria Cone. Stratigraphic measurements indicate the PST was density stratified prior to interacting with paleotopography, containing a lower, dense portion and upper, dilute portion. Variable flow directions, inferred from AMS, and transition from lithic- to pumice-rich ignimbrite on the Granite Ridge shows that the local roughness of the topographic high exerted a drag force on the current that encouraged deposition and blocking of the denser underflow. Deposition from a well-developed depositional system on the Ridge was replaced by turbulence near the Granite Ridge crest. AMS fabrics on the lee side point to grain-fall and/or vortex-induced flow and deposition as a result of flow separation. Strong AMS fabrics in down current deposits suggest that density stratification was reestablished after the current cleared the topographic high. AMS flow directions and fabrics at the Scoria Cone indicate that as the PST impacted against the steep topographic high, the lower underflow was laterally diverted along the lower parts of the Cone while the turbulent transport system overtook the crater rim. It is interpreted that deposition at the crater rim and down current areas resulted from a dilute, turbulent transport system, while deposition along the lower flanks of the Scoria Cone resulted from a denser, more lithic-rich current.