Volcanism of the Colorado Plateau - Basin and Range Transition: Implications for Crustal Processes

On the Colorado Plateau-Basin and Range transition in Arizona and New Mexico, basaltic volcanism takes two physiographic forms: (1) Major central composite volcanoes (e.g., San Francisco Peaks) in which basaltic magma differentiates at shallow crustal levels to siliceous and members and (2) large numbers of small cinder cones and a few domes that result from numerous discrete magma batches which apparently had little opportunity for differentiation. This study represents the first look at the petrogenesis of Plateau-bounding volcanic fields, based on rigorous stratigraphic controls, in combination with major and trace-element constraints. The emerging pattern of large volcanic constructs associated with shallow fractional crystallization, and numerous cinder cones associated with limited or no shallow differentiation may provide an analogue for interpreting petrogenetic patterns and/or tectonic settings on Mars.