Effects of chaotic advection on the timescales of cooling and crystallization of magma bodies at mid crustal levels

Abstract

We numerically define the thermochemical evolution of a subduction‐related crystal‐bearing magmatic mass at mid crustal levels (0.7 GPa, 20–25 km). Two main dynamic mechanisms are considered: (1) a pure buoyancy‐driven system where the convective flow is induced by density changes during magma cooling; (2) a buoyancy‐driven convective system governed by chaotic advection. The non‐Newtonian rheology of natural magmas is taken into account linking the Herschel‐Bulkley formulation with the results of fractional crystallization experiments of magmas with the same composition and at the same conditions of temperature and pressure of the studied system. The latent heat of crystallization is also considered in order to address the thermal release in the system induced by the crystallization. Results indicate that the development of chaotic advection generates a complex thermochemical evolution of the system speeding up the crystallization process and the timing required to reach the jamming condition relative to the pure buoyancy‐driven convective system (nearly 2 times faster). Our results have important implications for both the rheological history of the magmatic body and the refilling of shallower magmatic systems. In particular, (1) a time‐dependent composition ranging from basalt to andesite can be extracted from an initial basaltic magmatic batch; (2) at the attainment of the maximum packing fraction (i.e., just before the jamming condition), homogeneous andesitic melts can be potentially extracted from the system; and (3) the development of chaotic advection within the system allows for the extraction of andesitic melt in shorter times compared to a buoyancy‐dominated system.

Timescales of water accumulation in magmas and implications for short warning times of explosive eruptions

“…8a . It consists of a two-dimensional (2D) rectangular domain initially filled with a magma at the liquidus temperature 27 (Fig. 8a ).…”

“…In the numerical model, this viscosity formulation was regularized using the Papanastasiou’s method. A source-based enthalpy method 66 was used to model the liquid–solid phase change (i.e., the crystallization) 27 by ensuring that the relationship between temperature and the liquid fraction f showed in Supplementary Fig. 3 and discussed in the section entitled “Parametrization and validation of the thermal model” was satisfied.…”

“…For comparison, an open system consisting of progressive refilling by new parental magma is also modeled. Finally, we studied the effect of the development of convective motions within the system, accounting for the non-Newtonian rheology of the magma during the crystallization 27 and considering Rayleigh numbers (Ra) up to 10 9 . The numerical simulations started at the liquidus temperature (i.e., no crystals are present within the system) and continued until the attainment of a rheological behavior close to the jamming conditions 28 , i.e., when the melt extraction from the magmatic mush becomes most probable 29 .…”

On the kinematics and dynamics of crystal‐rich systems

“…See the supporting information for methods and values used to plot data fields. Calculation details in supporting information [Androvandi et al, 2011;Caricchi et al, 2008Caricchi et al, , 2014Castruccio et al, 2010;Champallier et al, 2008;Cimarelli et al, 2011;Coetzee and Els, 2009;Dufek and Bergantz, 2005;Forien et al, 2011Forien et al, , 2015Girard and Stix, 2009;Grossmann and Lohse, 2001;Jellinek and DePaolo, 2003;Le Mével et al, 2016;Okumura et al, 2016Okumura et al, , 2015Parks et al, 2012;Petrelli et al, 2016;Pistone et al, 2012Pistone et al, , 2015Rutherford, 2008;Walker et al, 1999].…”

Numerical simulations of magmatic enclave deformation

“…The detailed process of enclave formation is highly dynamic as it involves thermal exchange, crystallization, possible gas exsolution, and possible mechanical mixing between the melts and/or the host and inclusion minerals (e.g., Coombs et al, 2000;De Campos et al, 2004;Laumonier et al, 2014;Petrelli et al, 2016;Wiesmaier et al, 2015). Even when leaving aside the roles of volatiles and crystallization, the rheology of crystal-bearing magmas is generally complex because of the feedback between melt-crystal entrainment, crystal-crystal friction and collision, and intermittent lock-up of 5 crystals in contact with each other (e.g., Bergantz et al, 2017).…”