Experimental Quantification of 3D Melt Distribution in Partially Molten Rocks

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Intellectual Merit: This proposal describes an experimental study of melt distribution in partially molten mantle peridotite that will enhance our understanding of the processes of melt generation and transport in the upper mantle beneath oceanic spreading ridges. The 3 main objectives of this project are: 1) to produce texturally equilibrated mono- and polymineralic aggregates containing various amounts of partial melt and to characterize the 3-dimensional (3-D) distribution of melt within these samples and how this changes as a function of melt fraction; 2) to determine the permeability of partially molten rocks based on the experimentally determined 3-D melt distributions; 3) to provide physical constraints on melt migration in partially molten peridotite beneath ocean ridges that will lead to a better understanding of the associated geochemical and geophysical processes. A pilot study indicates that the X-ray synchrotron microtomography will provide valuable 3-D information (such as connectivity) on melt topology, which is a prerequisite for determining the permeability of partially molten rocks. High resolution 2-D SEM microscopy images will be compared to the microtomographic data to assess the fidelity of the latter. Experiments will be carried out at upper mantle conditions using a solid medium piston cylinder device at WHOI. X-ray synchrotron microtomography (Argonne National Laboratory) and Scanning Electron Microscopy (SEM) will be used to quantify melt distribution. Network modeling and the Lattice Boltzmann method will be used to model 3-D complex flow and to provide a quantitative link between the macroscale transport properties and microscale melt distribtution. Incorporation of experimental melt distribution data into the models will facilitate simulation of melt transport and its effects on physical properties of partially molten peridotite at realistic degrees of melting. Broader Impacts of the Proposed Activity: The proposed study will lead to improved models for understanding fluid flow in a number of different geologic systems. Thus, the data will be of interest to scientists in many disciplines. This work will also establish a collaboration between the mantle petrology community and the synchrotron accelerator community that will lead to analytical and theoretical advances. The proposed study will contribute to the professional development of the P.I.s, who are both junior faculty at WHOI, and provide an education and development opportunity for graduate and undergraduate students. In addition to publishing papers in scientific journals, Gaetani and Zhu will work with local high school students and/or undergraduate students to put our experimental results on the internet in a form that will be accessible to a broader audience. Through these education and outreach activities, the proposed research will not only advance our knowledge in basic science, but also serve as platform for cultivating and training researchers of the future.