Intellectual merit. Volcanoes that form in intraplate fields, although small and (mainly) monogenetic, result from eruptive phenomena ranging from quiet effusion of lava to relatively explosive Strombolian activity and, if external water interacts with ascending magma, hydrovolcanic activity. The generation and eruption of magmas in relatively small batches over dispersed areas, often with evidence for direct ascent from the upper mantle to the surface, suggests a driving process that is hybrid between strong hotspot-style mantle upwelling and scattered pockets of incipient melt that are passively mobilized by tectonic deformation (high- and low-magma flux end members of volcanic fields, respectively).
Integrated approaches involving physical volcanology, petrology, and geochemistry can provide important insights into these processes and the links between magma dynamics at depth and eruption processes on the surface. The lack of long-lived crustal magma reservoirs) allows investigation of the influences of deep magma source(s) and shallow plumbing systems on eruption styles. It is hypothesized that eruption style is influenced by physical and chemical characteristics of magma sources. To test this hypothesis comprehensive data will be integrated from the well-exposed Lunar Crater Volcanic Field (central Nevada). Direct studies of eruptive facies, of exposed shallow conduits (at older, eroded volcanoes), and of abundant mantle xenoliths will provide insights into the magma sources and ascent processes. Existing data on broad geochemicsl trends and age relationships will be integrated with new EarthScope seismic tomography data to provide a framework for understanding: (1) the interplay between pre-existing structure, topography, and vent location; (2) shallow plumbing geometries; (3) shallow controls on magmatic eruption styles, including relationships between eruption style, clast texture and shape, volatile content, and mineral chemistry; (4) spatial and temporal variations in magma sources and magma differentiation processes at individual volcanoes and across the field as a whole; (5) depth of melting and volatile contents of parent magmas; and (6) correspondence between volcano location, melting depths, and upper mantle seismic structure.
Broader impacts. This work will support improvements in volcanic risk assessment, both in terms of the probability (volcano timing and location) of future events and in terms of their consequences (related to eruption processes). The project will also support the training of three Ph.D. students (two of whom are female minorities) and will have a component of international collaboration with the volcanology and geochemistry group at the Universidad Autónoma de México. The proposing team is in communication both with the Shoshone Tribe (Duckwater Reservation) and the Bureau of Land Management so that we can share our results with them and (through BLM) with the public.
The Lunar Crater volcanic field in central Nevada contains more than one hundred Quaternary basaltic cones and maars and related eruptive products and is one of the youngest volcanic fields in the southwestern US. In the northern part of the field many of the volcanic cones and lava flows erupted in the last 100,000 years. Our objectives were to determine the order of eruption of the volcanoes, the source of the magma that eventually erupted to produce the volcanoes, the story of what happened to this magma as it ascended from its source to the surface, and the nature of the source itself, This work was accomplished by detailed geologic mapping of the cones and lava flows, sampling of the basaltic rocks, geochemical analysis of the samples, determiing the age of some of the samples, and finally producing a model that describes the history of the magma from its source to surface. Besides providing an understanding about how basaltic lava fields form, this research also showed that basaltic fields of this type can produce very explosive eruptions and send ash plumes thousands of feet into the atmosphere. If another eruption of this type were to occur at Lunar Crater, ash from the eruption could disrupt air travel across the western US and could cause closures of nearby major international airports (Las Vegas, Salt Lake City, Reno). An event of this type has the potential of producing a severe economic blow to the regional and perhaps national economy. Our study produced a better understanding of the hazards related to the eruptions that commonly occur within this type of basaltic lava field. Another major benefit of this study was the training of both Graduate and undergraduate students. Students at UNLV, Buffalo and Miami University played a major role in this research and received valuable training in their fields of study. Our study showed that the magma that eventually erupted at the surface originally formed at depths of about 70 km in the upper part of the Earth's mantle. The magma rose into the crust and ponded several times before reaching the surface. Eruptions (as mentioned earlier) from cones were explosive and produced significant ash deposits. Interaction of water and magma resulted in several very explosive maar type eruptions. An interesting conclusion is that the source type for volcanoes is more dependent on time rather than location or depth of melting. Two volcanoes located adjacent to one another can have different source characteristics if there is a significant age difference between the two cones. However, two volcanoes spaced a couple of kilometers apart, but similar in age, will have nearly identical chemistry.
