Technical description: USArray data are significantly advancing knowledge of the structure and physical properties of the upper mantle beneath the southwestern US. For the Colorado Plateau (CP), there is evidence that the upper mantle may be substantially modified by gravitational destabilization of dense domains as drips/delaminations and/or by thermal rejuvenation +/- melt invasion of the lithosphere where it is juxtaposed against the asthenosphere. This project is focused on evaluating these scenarios by determining conditions of melt generation and segregation associated with lithosphere destabilization across the north- and southwestern transition zones of the Colorado Plateau. The overarching goals of this study are (1) providing intensive parameters for melting conditions and (2) gaining insights into the lithologic heterogeneity in zones of melting. New data being acquired in this study include: (1) estimates of magmatic water contents from analyses of nominally anhydrous clinopyroxene and melt inclusions in olivine and; (2) pressures and temperatures of melting and clinopyroxene crystallization; (3) estimates of source oxygen fugacity; and (4) limits on the role of lithologic heterogeneities in the mantle from minor element characteristics of olivine and from trace element and isotopic characteristics of whole rocks (especially Hf and Os isotopes). These data are being considered along with seismic anisotropy observations from USArray to evaluate scenarios for the dynamics of melting beneath the CP and for the structure and evolution of lithosphere beneath the Colorado Plateau and its transition zones.
Broader impact and significance: Just as seismic waves can reveal heterogeneities in the physical properties of Earth's interior, compositional features of volcanic rocks can reveal heterogeneities in its chemical properties. From these twin approaches, insights into the interdependence and evolution of the physical and chemical properties are possible. This project is using the chemistry of lavas and minerals associated with profound changes in the Earth's outer shell to learn about the pressures, temperatures, and chemical compositions - especially fluids - of magma sources responsible for enigmatic volcanism. The results are helping to elucidate the origin of continental melting and to better interpret seismic models for the structure and dynamics of the North American plate. The project is providing professional training for two graduate students in the collection and interpretation of novel high quality geochemical data. It is also fostering collaborations between the principal investigator and scientists at three other universities. The results of this study will be shared professionally at national and international conferences as well as in peer-reviewed publications. Insights into the origin of CP-related volcanism will also be disseminated to naturalists at Sunset Crater and El Malpais National Monuments.
