The Role of Geometrically Restricted Large Low Shear Velocity Province Source Material on Hotspot Volcanism
Thursday, 18 December 2014
Source locations of mantle plumes such as Hawai’i, Kerguelen, and Louisville reside to different degrees within the Large Low Shear Velocity Province, thought to be associated with a layer of anomalously dense, viscous material along the core-mantle boundary. Therefore, these mantle plumes may entrain different quantities of this material as they rise toward the upper mantle. Entrainment of denser, more viscous material into a plume may affect its geometry, excess temperature, upwelling rate, and long-term stability, all factors that can alter surface expressions such as volcanic flux and chemistry along hotspot chains. Previous models examined plume dynamics in the presence of a dense material blanketing the source region. Here, we use numerical simulations to quantify how different geometries of denser, more viscous material alter plume dynamics and the surface expressions of hotspots (e.g., melting rate and chemistry). The simulations are run using the finite-difference, marker-in-cell code HiPStER (Highly Parallel Stokes with Exotic Rheologies). Numerically, the mantle obeys a non-Newtonian viscous rheology that is strongly temperature dependent. Initial temperatures are adiabatic through the interior of the mantle, and a thermal perturbation is introduced along the bottom of the domain to initiate a hot, upwelling plume. The effect of different geometries of dense, more viscous fluid on plume upwelling rate and surface expressions are evaluated by varying several parameters including: the plume excess temperature, and the geometry, density, and viscosity of the anomalous material. Melting and chemistry are calculated using a hydrous batch-melting model. Results are compared to geochemical and physical data from the Hawaiian, Kerguelen (Ninetyeast Ridge), and Louisville hotspot tracks.