Abstract
The compositional zoning styles of natural crystals produced during magma intrusion can be used to investigate the structure of magmatic plumbing systems and its relation to expressions of volcanic unrest (seismic, deformation, volatiles). However, magma intrusion is a progressive, dynamic process and yields non-monotonic heterogeneities in physio-chemical variables such as complex spatial variations in temperature and liquid composition with time. Such changes in variables are difficult to incorporate in models of crystal zoning in natural systems. Here we take another approach by integrating the results of a numerical multiphase simulation of melt arrival in an olivine-rich reservoir with models of chemical re-equilibration of olivine. We evaluate the diversity of chemical zoning styles and the inferred time scales using Fe–Mg diffusion in olivine for a limited range of system geometries and time-composition-temperature values. Although our models are still a large simplification of the processes that may occur in natural systems we find several time-dependent and systematic relations between variables that can be used to better interpret natural data. The proportions of zoned and unzoned crystals, the zoning length scales, and the calculated diffusion times from the crystals, vary with time and the initial position of the crystal in the reservoir. These relationships can be used, for example, to better constrain the plumbing structure and dynamics of mafic eruptions from monogenetic volcanoes by detailed studies of changes in the zoning of the crystal cargo with eruptive sequence. Moreover, we also find that the time scales obtained from modeling of crystals at a single temperature and boundary condition tend to be shorter (> about 25%) than the residence time, which could also be tested in natural studies by combining crystal time scale records with monitoring datasets.
Highlights
Modeling the zoning patterns of crystals can provide insights into the processes time scales and processes that occur below volcanoes (e.g. Costa et al 2008, 2020; Morgan and Blake 2006; Turner and Costa 2007; Costa and Morgan 2011)
To link the simulations and diffusion modeling to applications for natural crystals, we calculate the forward and inverse times from the crystal zoning, and we evaluate their different times using two different temperature proxies and zoning styles
Implications for comparison of crystal time scales with time series of monitoring and observational dataset
Summary
Modeling the zoning patterns of crystals can provide insights into the processes time scales and processes that occur below volcanoes (e.g. Costa et al 2008, 2020; Morgan and Blake 2006; Turner and Costa 2007; Costa and Morgan 2011). Costa et al 2008, 2020; Morgan and Blake 2006; Turner and Costa 2007; Costa and Morgan 2011) This crystal-scale information can be used to unravel the architecture and processes of volcano plumbing system, and can be combined with time series of volcano monitoring (seismic, deformation, gas) or other observational data (e.g., ash emissions) to illuminate causative relations that allow to better anticipate eruptions (Albert et al 2015, 2019; Kahl et al 2017; Morgan et al 2006; Rasmussen et al 2018; Ruth et al 2018; Saunders et al 2012; Kilgour et al 2014; Rae et al 2016; Tomiya et al 2013). Linking the results of such fluid-dynamic simulations with the processes of chemical re-equilibration within the crystal allow us to test the effects of changing boundary and temperature conditions into the time scales that are obtained from natural crystals (Schleicher and Bergantz et al 2017)
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