The final hurdle in major element diffusion chronometry in olivine: addressing the accuracy problem one proton at a time

The proposed project seeks to solve an important issue in the field of geology: the inaccuracy in determining the timing of magmatic processes leading to volcanic eruptions, using a common mineral called olivine. Olivine is found in many rocks on Earth, including those that make up the planet's mantle. The movement of elements such as iron and magnesium within olivine can be used to determine the timing of geological events. However, there is a significant problem with this method which is that even small amounts of water in the olivine structure can greatly increase the rate at which elements diffuse within it. This means that if there is water present in the olivine, the timing determined using the mineral may be inaccurate, leading to false predictions and assessments of associated hazards. The goal of this project is to address this problem by determining exactly how water affects the movement of elements within olivine. This will be done through a two-step experimental plan. Firstly, the tracer diffusivity of magnesium in single crystals of pure forsterite (a type of olivine) will be determined as a function of the water content. Secondly, the diffusivity of iron-magnesium in natural olivine as a function of water content will be studied. The results of this project will have significant implications for the field of geology, as they will allow for more accurate determinations of the timing of magmatic processes leading to volcanic eruptions. This, in turn, will have an impact on volcano eruption forecasting and the assessment of associated hazards. The goal of the project is to improve the accuracy of diffusion chronometry, a technique used to determine the timing of geological events such as volcanic eruptions. To date, most experiments on the diffusivity of Fe and Mg in olivine were done at atmospheric pressure and in dry conditions. These conditions don't apply to the geological settings where olivine diffusion chronometry is used. To address this, the team proposes two projects where they will study the effect of water on the diffusivity of Fe and Mg in olivine. They will vary the activity of water while keeping the pressure, temperature, oxygen fugacity, and composition constant. Then, the team will measure Mg (isotopic) or Fe-Mg diffusion profiles and use infrared spectroscopy to understand how water affects diffusion in this system. Finally, the researchers will be able to provide a road map for applying the data to natural samples, which will be made directly available to the community. This may be the last major hurdle in improving the accuracy of Fe-Mg in olivine diffusion chronometry. This study will provide results that will be extremely important for applications in diffusion chronometry and adding to our understanding of the timescales of volcanic eruptions. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.