Current Research in EEPS Seminar – Boda Liu – Department of Earth, Environmental and Planetary Sciences, Brown University
Title: Transport and fractionation of trace elements during melt migration
The topic of this seminar is the effect of melt migration on the transport and fractionation of chemicals in rocky planets. The motivation has two-folds: (1) melt migration is an important step in the cycle of life-essential elements; (2) rock samples as products of melt migration contain information about the heterogeneous nature of the Earth’s interior which are ultimately controlled by long-term planetary evolution. I will demonstrate the coupled geochemical and geodynamic processes beneath mid-ocean ridges as an example of melt migration. Pseudo-2D simulations show a systematic trend of the scattering of isotope ratios of the melt as functions of the size and distribution of internal chemical heterogeneities in the mantle. Applications of the empirical relationship synthesized from current simulations to MORB data suggest that the average size of chemical heterogeneities is 5-8 km. I will also show a 2D model as a platform on which the style of melt migration can be tested against observational constraints from field mapping, geophysical imaging, rock deformation experiments, and geochemical data.
With the accumulated knowledge about melt migration beneath mid-ocean ridges, I will propose an area of research on transport and fractionation of volatiles by processes including but not restricted to melt migration. I will identify the key observation that strongly infers late refertilization or trap of volatiles in the mantle. Conceptual models of volatile trapping beneath mid-ocean ridges and arcs will be sketched within the framework of geodynamics and disequilibrium chemical kinetics.