Although the basic modes of melt production in the mantle are known (adiabatic decompression and water-fluxing) very little is known about the volumes and rates of magma produced anywhere except mid-ocean ridges. Understanding the physics of active volcanic systems Fluids and Magmas in the Crust and Upper Mantleing of magma production is essential to understanding continental growth. There is abundant evidence that magma production rates vary in space and time by a large amount, although these rates remain poorly quantified.
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Many research facilities are using EarthScope instrument data to produce scientific models and visual representations.
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Fluids and Magmas
A better understanding of deep earth and how the evolution of continental lithosphere is related to upper mantle processes is a primary goal of EarthScope. How and where are forces generated in the upper mantle and how and where are they transferred to the crust are important questions that need answers in order to obtain of this goal.
Melting profile across the Basin and Range. Arrows represent the melting column calculated for each volcanic field based on the most primitive magma compositions. The bottom of the arrow marks the onset of melting at the solidus, and is a function of mantle temperature, while the top of the arrow marks the end of decompression melting, presumably due to the change in rheology near the lithosphere/asthenosphere boundary. East Pacific Rise shows analogous melting calculation for primitive MORB near the Tamayo Fracture Zone assuming melt pooling from a triangular shaped melting regime. Figure after Wang, K., T. Plank, J.D. Walker, E. I. Smith, 2002, A mantle melting profile across the Basin and Range, SW USA, J. Geophys. Res., 107, B1.
Research Questions
- What effect does tectonic deformation have on fluid flow in the crust?
- What is the role of hotspots in evolution of the continents?
- How does tectonic rate (convergence, extension, mantle upwelling) affect magma production?
- Where does melting in the lithosphere occur and what controls magma migration, accumulation, and residence time?
- What is the relation between magma movement, surface deformation, and volcanic eruption?
- Over what temporal and spatial scales do earthquake deformation and volcanic eruptions couple?
- What controls eruption style?
- What are the predictive signs of imminent volcanic eruption? What are the structural, rheological, and chemical controls on fluid flow in the crust?
EarthScope's Contribution
North America contains a diverse range of magmatic systems including the "classic" convergent margin volcanoes of Cascadia and the Aleutians, and the large-volume and wide-spread basalt and caldera-forming silicic eruptions associated with extension in the Basin and Range and the Snake River Plain/Yellowstone magmatic field. How this magma is generated in the mantle and crust are the targets of EarthScope's seismic imaging. Systematic variations in basalt composition across the Basin and Range most likely relate to variations in depth and temperature of melting. Tomographic images of the mantle beneath the western United States, to be provided by USArray, can be compared with geochemical data and volcanic volumes to identify mantle source regions for the magma and address the question of whether varying eruptive volumes are due to geographically varying mantle melting rates or to tectonic controls on magma ascent through the crust.