Timescales of magma transfer in intraplate volcanic systems from diffusion modelling of lithium isotopes in zircon and olivine

• Applicant: Shuangqing Li, Ph.D.
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 498606898

The dynamic behaviour of magma in the crust as measured by timescales of magma transfer and ascent rates is a key unknown limiting development of more reliable monitoring of volcanic eruptions and related hazards. As a result of various chemical disequilibria in dynamic magmatic systems, applying the laws of diffusion in solids or melts can guide the extraction of quantitative, first-order constraints on the rates of many magmatic processes. In this proposal, the fast diffusion of Li in zircon and olivine is proposed as a powerful combination for characterizing the magmatic plumbing systems from source to vent in intraplate volcanic fields. The reliability of these quantitative methods, however, requires a thorough understanding of the distribution and kinetic behaviour of Li in both minerals. Preliminary results of an ongoing study of Li isotopes in mantle-derived zircon lend strong support to the assumption that modelling of Li-in-zircon diffusion has an exceptional potential to constrain the duration of magma from storage to eruption. Results can be further cross-checked by modelling Li-in-olivine diffusion which has been already successfully utilized to investigate short-term magmatic processes. Li abundances and isotopic ratios in zircon from crustal xenoliths and olivine from their basaltic host rocks will be investigated to determine thermally activated diffusion timescales which can be translated into magma transfer and ascent rates for reasonable assumptions regarding the depth of xenolith entrainment. Annealing durations inferred from Raman spectroscopy of zircon and the average settling rate of xenoliths in magma allow further validation of rates extracted from Li diffusion in zircon and olivine. Samples of crustal xenoliths and host basalts for the proposed study stem from three intraplate volcanic fields with distinct crustal characteristics, which are the Massif Central (France), Kula (Turkey), and Hannuoba (China). It is expected that the study provides an in-depth understanding of Li-diffusion in zircon and olivine in natural systems. Li-diffusion chronometry combined with Raman spectroscopy of zircon to constrain annealing durations is expected to provide meaningful data for inferring timescales of magma transfer and magma ascent rates at crustal levels, thereupon further developing the application of Li-isotopes as an emerging geospeedometer and petrological tracer for high temperature igneous processes.

• DFG Programme: Research Grants
• International Connection: China, United Kingdom
• Cooperation Partners: Xiaoyan Gu, Ph.D.; Daniel Joseph Morgan, Ph.D.