Black smoker hydrothermal heat flux

Vigorous hydrothermal venting on the ocean floor is one of the most remarkable geologic processes on Earth. Here, circulating fluids provide nutrients for unique ecosystems, form massive sulfide deposits, and influences the chemistry of the Earth’s crust and oceans. While both magma input and crustal permeability are recognized as controlling factors in facilitating focused hydrothermal circulation, their relative importance remains poorly understood. My current work focuses on applying 3D full-waveform imaging to map crustal permeability beneath black smoker fields on the Endeavour segment of the Juan de Fuca Ridge. We find that black smoker heat flux is rate-limited by an evolving, highly heterogeneous crustal permeability structure. Furthermore, our results show a more spatially complex permeability structure than is commonly assumed by current numerical or analytical models. Thus, our seismic images can inform future models of hydrothermal flow, thereby improving our understanding of these complex hydrothermal systems.

Magmatic focusing at mid-ocean ridges

At fast-spreading mid-ocean ridges the generation of oceanic crust arises from the focusing of mantle-generated melt from a broad, partially molten zone at depth to a narrow axial magmatic system. Owing to the inaccessibility of mid-ocean ridges and the underlying mantle, much of what we know pertaining to magmatic focusing stems from numerical simulations and observations from ophiolites—ancient, subaerially exposed oceanic crust and mantle. Nevertheless, the mechanics of melt focusing remain unclear. Both numerical simulations and field investigations, however, support one mechanism: high-porosity decompaction channels near the base of oceanic lithosphere. Until now, however, no evidence of shallow mantle, seismic reflections supporting the existence of such features has been reported.

Currently, I am analyzing seismic reflections near the East Pacific Rise that arise from features within the uppermost mantle. I have used reflection coefficient analyses, tomographic imaging, and finite-difference modeling to constrain the physical properties, geometry, and location of the subcrustal reflector. On the basis of the results, we infer the observed reflectivity originates from a geographically extensive, intermittent system of sub-horizontal dunite channels formed in situ near the base of the lithosphere. Our results support a previous interpretation of the origin of replacive dunites, in which they form sub-horizontally in response to melt flux within high-porosity decompaction channels.