Calibration of the Lithium-in-Feldspar Geospeedometer for Timing Magmatic Events

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2). “Crystal clock” techniques use element concentration profiles preserved in minerals to constrain the timescales of magmatic processes. Magma recharge, degassing, foaming, fragmentation, and other perturbations that spur mass transport and trigger eruptions can occur mere hours to seconds before final magma ascent.

Thus, only the fastest-diffusing cations, like the volatile element lithium (Li) will preserve a crystalline record of these rapid volcanic events. The goal of this project is to experimentally quantify the transport of Li isotopes in feldspar solid solutions to yield data that can be applied to natural volcanic rocks to determine the onset and duration of these magmatic events.

Laboratory experiments will be run to assess the diffusivities of both total Li and the relative diffusivities of its two isotopes in feldspar, harnessing the potential of Li isotope geochemistry to track high-temperature kinetic processes. This project will also re-assess existing Li diffusion data in plagioclase feldspars and produce the first data for Li diffusion in potassium feldspars, filling a need for crystal clocks that are suitable for application to the highly evolved, large volume magma systems that produce super eruptions.

In addition to the intellectual merits of improved understanding of eruption timescales, this project has broader impacts that include development of community standards for Li mass spectrometry and training of a PhD student at Cornell University. Project outcomes will be incorporated into an educational module on volcano science that will be delivered to incarcerated persons in upstate New York in collaboration with the Cornell Prison Education Program (CPEP).

Quantifying the drivers of volcanic eruptions is one of the most important tasks facing Earth scientists today. A Li-in-feldspar diffusion chronometer is uniquely suited to address this task because feldspar solid solutions are found across magma compositions and concentrations of total Li in feldspar are well-resolved by common analytical tools like laser ablation ICP-MS.

Recent work has found that Li diffusion occurs by complex mechanisms in a variety of crystal systems, necessitating a re-assessment of existing Li diffusion coefficients in plagioclase feldspars to accurately quantify the rates and timescales of magmatic processes. This project will also produce the first experimental measurements of Li diffusion in potassium feldspars and the first measurements of the kinetic fractionation of Li isotopes in feldspar, data which are critical for discriminating between Li concentration profiles produced by growth zoning and those produced by mass transport.

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.