Abstract

The McMurdo Dry Valleys magmatic system, Antarctica, forming part of the Ferrar dolerite Large Igneous Province, comprises a vertical stack of four interconnected sills linked to surface flows of the Kirkpatrick flood basalts1. The lowermost intrusion, the Basement Sill, offers unprecedented exposure through a magmatic slurry flow (congested melt-particle mixture), comprised of abundant Opx pheoncrysts (MgO up to 20%). The overall geometry of the axially confined slurry is tongue-like, with the sill margins relatively aphiric2. The 3D nature of the exposure (100%) permits petrographical and structural observations to be made in unprecedented detail. Key properties of the Opx tongue that have bearing upon emplacement and solidification include microscale matrix properties (grain size, roughness, porosity and permeability, packing density and fluctuations), and the assumed fluid properties (viscosity and density) of the intergranular melt phase. These and other structures related to transport phenomena and deformation of the slurry during flow constitute the initial conditions for sophisticated physics-based modeling of the magma emplacement process. Initial results of a 2D numerical model employing a generalised form of the Navier- Stokes equations will be presented. It is noteworthy that features long recognized in classical layered intrusions formed here on a timescale (short) governed by the local cooling rate of a c. 300 m thick sill. A distinction between structures formed during transport, where the shearing regime dominates, and post- emplacement features due to mechanical compaction of the mush, is required. Information on conditions under which the touching Opx framework may collapse to expel interstitial fluid is also under investigation.