The Dynamics of Mantle-melt Extraction Systems: A Field and Theoretical Approach

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).This project is co-supported by the Petrology & Geochemistry and Tectonics programs of the Division of Earth Sciences, and sponsored also by the Office of International Science and Engineering (Africa, Near East, And South Asia Program). This research initiative is designed to study the role of focused melt percolation in the origin of a spectacular ultramafic massif in Morocco, the Beni Boussera ultramafite, that records a depth of origin in excess of 150 km. Intrusions of ultramafic bodies into the lower density continental crust have been documented for a large variety of tectonic settings spanning continental shields, rift systems, collisional orogens, and magmatic arcs. These bodies are intriguing and geodynamically significant because they are denser by 300-500 kg/m3 than their host rocks. Understanding their emplacement mechanism is key to their origin. Detailed field observations and geochemical data of the Beni Boussera ultramafic massif have been used to infer that some of these bodies are composed of km-scale melt percolation features that will be the focus of this project. A new emplacement mechanism has been recently proposed whereby focused flow in the upper mantle produces gravitational instabilities resulting in the emplacement of high-density mantle rocks into low-density crustal sequences. This model predicts that a) many lower crustal ultramafic bodies are km-scale melt channels that reach into the upper mantle and b) confined melt percolation within the upper mantle triggers significant vertical movement of the entire melt extraction systems, influencing local mantle convection patterns. The research plan will combine extensive field mapping with detailed structural and fabric analyses, petrology, geochemistry as well as isotopic fingerprinting. It will also be combined with geologically constrained mass transfer modeling to provide insights on the dynamics of melt percolation zones.