Fields of interest: CO2 capture and storage via in situ mineral carbonation in peridotite and basalt; melting and reactive melt transport in the Earth's mantle and lower crust; igneous processes in forming the Earth's crust; density instabilities, ductile deformation and evolution of the lower crust; subduction zone geotherms; and the mechanisms for intermediate depth earthquakes.
Recently, I have added mineral carbonation and hydration in peridotite and mafic rocks to my research program. This is a reactive transport problem, very similar to the work I've done on reactive transport of melt in the upper mantle and lower crust, there are fantastic field areas where active, ongoing mineral carbonation and hydration can be observed, and the physical mechanisms that control key processes are not well understood. We are focusing on understanding processes in natural systems, particularly “reaction driven cracking”, with relevance to engineered geological capture and storage of CO2, stimulation of geothermal reservoirs, in situ mining, and extraction of hydrocarbon resources from tight formations.
For decades, my primary research interest has been in the genesis and evolution of the Earth's crust in the ocean basins, in arcs, and in continents. I approach this topic from the perspective that reactions between melt and rock during transport through the upper mantle are as important as melting, mixing, and crystal fractionation processes in producing different crustal bulk compositions in different tectonic settings. I’ve been fascinated by the stark compositional difference between oceanic and continental crust, and in my research I have gravitated toward end-member examples of magmatic processes: oceanic spreading ridges, and subduction-related volcanic arcs such as the Aleutians where the composition of average lavas and exposed plutonic rocks closely resembles continental crust. In an ongoing effort, I've tried to develop a general theory that explains how reactive melt transport varies along different geothermal gradients, with, 1. mineral dissolution and focusing of flow into high permeability channels in hot, upwelling mantle, 2. diffuse flow where there is a low melt flux into conductively cooled, shallow mantle, and, 3. hydrofracture where high melt flux and crystallization due to cooling clog porosity, leading to ponding of magma and increasing melt pressure. I’ve also become very interested in gravitational instabilities that can remove dense lithologies from the base of the crust, and transport buoyant subducted sediments and felsic igneous rocks from subduction zones back into the crust, and I hope to pursue investigations of metasediments in lower crustal granulite terrains: how do they get down there?
In studying layered intrusions and lower oceanic crust, I’ve tried to understand a few of the many possible mechanisms for forming both compositional and modal layering in gabbros, via injection of layer parallel sills, and via sudden changes in pressure that can modify the assemblage of minerals precipitating from a cooling magma. This research led to general ideas about formation of oceanic crust, via a “sheeted sills” mechanism in which the lower crust crystallizes from many small sills, injected at depths throughout the crust. This end-member process stands in contrast to the “gabbro glacier” hypothesis, in which all oceanic plutonic rocks crystallize in a single, shallow melt lens and undergo ductile flow downward and outward to “fill” the lower crust. A related issue is the mode of cooling of the oceanic lower crust; via conduction with limited, diffuse fluid flow, or via rapid, focused hydrothermal convection. Trying to quantify and constrain these hypotheses, and to determine which processes predominate in different tectonic settings, has motivated a lot of research over the past 15 years.
I've been very fortunate to work with a large number of tolerant geophysicists (Jack Whitehead, Einat Aharonov, Steve Holbrook, Marc Spiegelman, Greg Hirth, Jun Korenaga, Matthew Jull, and others) who have led me into the world of geodynamics. I am grateful to them all, particularly Greg Hirth, with whom I have been able to pursue interdisciplinary studies.
Finally, not that long ago, I was a founding partner of Dihedral Exploration, mineral exploration consultants specializing in field work requiring technical climbing skills. Searching for ore deposits took me to British Columbia, Alaska and Greenland. I've recently started teaching a new course, Earth Resources for Sustainable Development, which covers some of that field, as well as energy resources, water, soil and fertilizer. I’ve been writing general articles and giving public presentations on this topic
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