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.