Multi-scale numerical modeling of carbonatite-silicate magma interaction
Valentini L., Moore, K.R.
Department of Earth and Ocean Sciences, National University of Ireland Galway, Galway, Ireland
In the last decade, an ever increasing number of carbonatite occurrences has been documented. Nonetheless, the abundance of this peculiar type of rocks is still relatively scarce with respect to the more common silicatic rocks and a single active carbonatitic volcano exists. This results in a limited knowledge about the mechanisms of carbonatite magma ascent and emplacement dynamics with respect to the silicatic counterpart. Moreover, although carbonatites and silicatic rocks often occur in spatial and temporal association, little is known about their modes of mechanical and thermodynamical interaction. In this contribution, we utilize Computational Fluid Dynamics in order to study the interaction dynamics of theoretical liquids to which the physico-chemical characteristics (viscosity, density, diffusivity etc.) of carbonatite and silicate magmas are assigned. Numerical models are performed at different scales of analysis in order to infer the kind of mechanisms resulting in the textural features that are commonly observed in natural samples.
The formation of microstructures such as micron-scale carbonatitic globules surrounded by a silicatic matrix is simulated by means of a set of advection-diffusion equations with Korteweg Stress (i.e. gradient induced stress). At a larger scale of analysis, the effect of viscosity contrasts on the extent of mechanical interaction is investigated.
Implications for processes such as mechanical intermingling, magma hybridization and immiscible separation are discussed on the basis of our numerical results. It is highlighted how textural observation should be integrated by geochemical data and considerations about the physics of the system in order to infer reliable conclusions about the mode of carbonatite-silicate interaction.
This presentation was financially supported by INTAS project 05-1000008-7938.