Specific structure of convection currents in the system layered intrusion–feeding conduit–parental magma chamber

Abstract

The structure of convection currents was experimentally studied in the model system layered intrusion–feeding conduit–parental magma chamber. Persistent hydrodynamical and thermophysical interaction between interrelated melts of the parental magma and intrusive body occurs through the feeding conduit. Being associated, they control the structure of convection currents and mechanisms of heat and mass transfer in the intrusive, conduit, and magma chamber. The existence of two convection countercurrents in the conduit has experimentally been established: inner central lifting jet and outer annular downward current along the conduit walls. At the top of the conduit, the downward current has the lowest temperature and appears to be quite in equilibrium with the earlier precipitated crystals. Moving downward along the conduit wall, the annular descending current interacts with the lifting jet and, as a result, becomes hotter and undersaturated relative to the crystals that formed before. Thus, there is no possibility for heterogeneous crystallization to occur on the walls of conduit. The experimentally simulated mechanism of melt interaction in a whole natural system rules out the possibility of formation of a zone of immobile melt with stable steady-state temperature stratification anywhere in the chamber’s volume.

Numerical simulations of convection in crystal‐bearing magmas: A case study of the magmatic system at Erebus, Antarctica

“…The convective interaction of the annular current with the magma chamber, leaking down from the lake through the conduit and returning from the chamber as a central ascending flow, was also observed in experiments with a similar geometry (two reservoirs connected by a duct) [ Bazarov et al , 2007]. This similarity explains why the structure of our convection currents is in good agreement with those described by Bazarov et al [2007] for the overall magmatic system, except for the open‐system simulation, which has a more complicated convective pattern.…”

“…Characterizing the dynamics of convection currents in magmatic plumbing systems is a challenging task, which has long been approached through experimental [e.g., Jaupart and Brandeis , 1986; Weinstein et al , 1988; Bazarov et al , 2007; Huppert and Hallworth , 2007] and theoretical [e.g., Sparks et al , 1984; Jaupart and Brandeis , 1986; Jellinek and Kerr , 2001] studies that have considered magma as a perfectly homogeneous mixture of melt, crystals and bubbles. More recently, studies based on multiphase theory have been addressing the differential motion of these three phases, taking them in pairs [e.g., Dartevelle , 2004; Dartevelle et al , 2004; Dufek and Bergantz , 2005; Dartevelle and Valentine , 2007; Ruprecht et al , 2008; Dufek and Bachmann , 2010].…”