Mormon Mountain Volcanic Field (House Mountain)

Mormon Mountain Volcanic Field (MMVF), located in northern Arizona, is a Cenozoic volcanic field situated in the transition zone between the Basin and Range and the Colorado Plateau near the southwestern margin of the latter. It covers an area of ~3500 km2 formed of multiple basaltic flows, monogenetic cinder cones, and north-west trending fissure volcanoes, overlying the Permian Coconino sandstones. Rock types include calc-alkaline andesites, dacites, and rhyolites, and a spectrum of basaltic lithologies ranging from alkaline olivine nephelinite and olivine tholeiite with the most abundant being basanite and alkali olivine basalt. An occurrence of note in the field is at House Mountain shield volcano in the Verde Valley on the north-eastern side of the transition zone. This structure is composed at its base of sub-horizontal mildly alkaline hawaiitic lava flows, overlain by a thick sequence of steeper dipping basaltic lapilli scoriaceous tuffs, tuff breccias, and aggolomerates. A cinder cone is covered by an upper section of hawaiite, mugearite, benmoreite, and basaltic andesite lava flows. Intruding the shield are a suite of minor intrusives, with compositions including basanitic nephelinite, ijolite, and nepheline monzosyenite. These intrusives are confined to the north part of the volcano and take the form of mappable scale dykes, smaller scale dykes, schlieren, and ocelli. Near to House Mountain, occurrences of the intrusive rock types can be found at Lee Mountain and Casner Butte. A map of occurrences in the MMVF along with whole rock major and trace element data can be found in Gust and Arculus (1986), with specific information on House Mountain including a simplified geological map of the volcano and geochemical data for both whole rock and mineral chemistry in Wittke and Holm (1996).