Timescales of magma hybridization and remobilization in the steady-state plumbing system of Popocatépetl volcano, Mexico

Abstract:

Diffusion chronometry is widely used to constrain timescales of pre-eruptive magmatic processes such as ascent rates and mixing-to-eruption timescales. Usually, diffusion models are restricted to outermost crystal rims, yielding information on relatively late-stage processes, while the magmatic record stored in crystal interiors is left untapped. Here, we unlock information stored in core-to-rim profiles of orthopyroxene crystals at Popocatépetl volcano (Mexico) by using composition-specific temperatures for individual crystal zones as input for a non-isothermal incremental step diffusion model (NIDIS; Petrone et al., 2016; 2018). We show that ≤49 % of erupted pyroxene crystals are of mafic origin and were injected into a shallow evolved reservoir, where they were stored in a heterogeneous crystal mush and hybridized for centuries to millennia prior to eruption. New mafic injections into the evolved reservoir frequently replenish and remobilize the crystal mush, which can lead to eruptions within weeks. Subsequent re-homogenization of the evolved reservoir is achieved over timescales of weeks to years. This cycle of magma recharge, remobilization and hybridization is steadily repeated over >14.1 ka and buffers whole-rock compositions at Popocatépetl. Our crystal records show that mafic injections intensify prior to larger eruptions, yielding a positive correlation between pre-eruptive magma injection frequency and VEI for Popocatépetl. Similarly, a literature review hints at a consistent global relationship between duration of magma influx (as derived by diffusion chronometry) and eruption magnitude. Our work highlights the untapped potential of crystal-scale diffusion chronometry to explore and constrain long-term magma dynamics in volcanic plumbing systems far beyond late-stage pre-eruptive timescales. Understanding such ‘deep time’ magmatic processes is crucial to improve our ability to forecast timing and size of volcanic eruptions.