Developing a New Model to Investigate the Dynamics of Melt Generation beneath Mid-Ocean Ridges

The global mid-ocean ridge system is the largest volcanic system on Earth. Magma generated by decompression of upwelling mantle beneath the ridge axis creates the oceanic crust and the heat associated with magma emplacement drives biological activity and hydrothermal circulation. This, in turn, modulates chemical exchange between the oceans and the lithosphere. This research develops models and modeling software for melting beneath mid-ocean ridges in order to predict (1) the total amount of melt produced and (2) composition of the melts. Such information is important for predicting the style of volcanic eruption on the seafloor, as well as determining the flux of elements and volatiles (e.g., CO2) from the Earth?s mantle into the shallow crust, oceans, and atmosphere. The proposed project will provide support for an MIT/WHOI Joint Program graduate student and several WHOI undergraduate summer student fellows. In addition, the new software that will be developed for this project will maximize the utility of the research by making the source codes of the new software publicly accessible via the NSF-funded Computational Infrastructure for Geodynamics (CIG).

This research develops a new, open-source mid-ocean ridge basalt (MORB) melting model with enhanced predictive capabilities that capture the key physics/thermodynamics of melting, and couples this model with other 3-D geodynamic models to address outstanding questions in MORB genesis. The new model will incorporate: (1) melting near cpx-out, (2) Cr-Al spinel melting reactions, (3) the effects of small amounts of H2O on mantle melting, (4) melting in the presence of garnet, (5) variable melt productivity as a function of pressure, and (6) tracking of trace element concentrations. The models will be used to exploit a wide range of experimental data published over the last two decades. Coupled with geodynamic models, the melting model will be used to investigate local and global variations in mantle potential temperature, mantle composition, and the length-scales and patterns of melt migration at mid-ocean ridges. Resulting models will be used to: determine the relative roles of mantle temperature, melt productivity, and mantle composition (including volatiles) on melting beneath mid-ocean ridges; explore the influence of the geometry of the melting region (as controlled by axial thermal structure) and the patterns of melt migration on key observables such as crustal thickness and major and trace element chemistry; and investigate the relative roles of high-pressure fractional crystallization and melt-wall rock reaction in controlling MORB and abyssal peridotite chemical compositions.