Properties of Carbonatite Magma and Processes in Carbonatite Magma Chambers

Abstract

The physical and thermal properties of carbonatite magmas are estimated by analogy with alkali carbonate melts, which are ionic liquids, composed of discrete, unpolymerized ions. Carbonatite magmas are estimated to have low viscosity (on the order of 5 × 10-2 poise), low heat of fusion (175 J/gm), and large thermal diffusivity (4 × 10-3 J/cm-sec-K) compared to silicate melts. Dissolved water will reduce viscosity; dissolved orthosilicate will have little effect on viscosity because silicate tetrahedra will remain as unpolymerized, discrete anions. Solution of polymerized silicate compounds will increase melt viscosity as long-chain or network silicate polymers form; exsolution of polymerized silicate melt will limit the concentration of long-chain or network silicate polymers in the carbonate melt and provide an upper limit on viscosity. Given estimates of the physical and themal properties of carbonatite magma, it is possible to evaluate the importance of possible physical processes in carbonatite magma ...