Experimental Investigation of Mantle Heterogeneity: Behavior of Ga, Ge, and First-row Transition Elements (FRTE) During Partial Melting of Pyroxenite and Spinel Peridotite

Earth's mantle is its largest layer by mass and volume and is ultimately the source of most of the magmas generated near Earth's surface. The chemistry and mineral composition of the rocks in Earth's mantle also serve as a time capsule that records events from the time of Earth's formation and its subsequent evolution caused by the recycling of near-surface materials back into the mantle through the processes of plate tectonics. This project is an experimental investigation of the chemistry of magmas that can be generated in Earth's mantle by different types of rocks that are likely to be found there. High pressure and high temperature experiments will be performed to investigate how the first-row transition elements (FRTE; Sc-Zn on the periodic table) and Ga and Ge behave during the formation of magmas in Earth's mantle. These elements are particularly useful for identify the types of rocks that may be melting to generate magmas. The results of this project will increase scientific knowledge of how magmas are formed on Earth and, through comparison with the chemistry of natural samples, will increase our understanding of the distribution of different rock types in Earth?s interior. Broader impacts of this research include support for an early-career researcher at a primarily undergraduate institution. The project will support training of a female graduate student who will gain expertise in formulating scientific questions, designing and performing experiments, analysis using several analytical methods, and interpretation and dissemination of experimental results. This project will also foster collaboration between the experimental lab at the University of Minnesota Duluth and the geochemistry and cosmochemistry lab at Florida State University, where analyses will be performed.

This research is an experimental study of the partitioning of FRTE between mantle minerals and melts, which will improve geochemical tools for identifying the source lithology of basaltic magmas. Experiments containing melts and either peridotite or pyroxenite mineral residues will be performed in a piston cylinder apparatus at conditions of mantle melt generation (pressures of 1.5 and 3 GPa and temperatures from 1270 to 1450 °C). These experiments will be doped with FRTE and Ga and Ge. The concentrations of these elements in the experimental run products (quenched melts and minerals) will be analyzed by laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS). These analyses will yield partition coefficients for each element of interest between each mineral and coexisting melt. The project will aim to improve constraints on the concentrations and ratios of FRTE in melts generated by partial melting of peridotite and pyroxenite in Earth's mantle. Model melt compositions will be generated using these new experimental constraints and compared with the chemistry of natural basalts to better understand how lithological heterogeneity in the mantle is expressed in the chemistry of basaltic magmas. Better constraints on the source lithology of natural basalts will improve estimates of the abundance and distribution of recycled lithologies in Earth's upper mantle.