An Elemental Highway: Investigation of a High Nickel Anomaly in Olivine from the Island of Niihau, Hawaii

The study of volcanic geochemistry is one of the main gateways for investigating the Earth’s mantle. One important topic in the field is that of nickel (Ni) in the mineral olivine. While Ni is a compatible element in olivine, its high concentration at a given MgO content is not well understood. A variety of hypotheses have been proposed, including attributing presence of Ni to pyroxenite source melting, contribution from the core, or variation in peridotite source melting. In addition to the other hypotheses, chemical diffusion may also be a mechanism for enriching olivine Ni concentration. Magnesium-iron (Mg-Fe) isotopic measurements have been proposed as a test to see whether chemical diffusion occurs in olivine. Therefore, by taking MgFe isotopic measurements of olivines, high Ni concentration in olivine can be attributed to either chemical diffusion or one of the other hypotheses. To qualify which process led to Ni enrichment in olivine, this project analyzed olivines from basalt samples from the Hawaiian islands of Niihau, Kahoolawe, and Hawaii for major elemental and Mg-Fe isotopic content. Major elemental data have shown that Ni concentration at a given MgO content from olivines of the late-shield Paniau formation on Niihau is highest compared to global data. Mg-Fe isotopic data have shown that the olivines from Niihau follow diffusion models, indicating that chemical diffusion led to a high Ni concentration at a given MgO content. ~27 years of magmatic calibration at Niihau has been estimated by applying a diffusion model to in-situ data of an olivine phenocryst.