CHAOTIC ADVECTION, FRACTALS AND DIFFUSION DURING MIXING OF MAGMAS: EVIDENCE FROM LAVA FLOWS

Abstract

Structures of magma mixing from three different lava flows have been analyzed and the degree of mingling has been quantified by measuring the contact perimeter between magmas and the fractal dimension of structures. In each lava flow, the values of these parameters suggest that the magma mixing structures were produced by chaotic dynamics induced by stretching and folding processes between the interacting magmas. The mingling of magmas has been simulated using a chaotic dynamical system consisting of repeated stretching and folding processes. The simulation shows the same patterns of variation of contact perimeter and fractal dimension as those observed in natural structures and indicates that magma interaction processes acted with different intensities in the three lava flows in response to different magmatic interaction regimes. Since physical dispersion of one magma inside another through stretching and folding processes and chemical exchanges are closely related, we performed coupled numerical simulations of chaotic advection and chemical diffusion. The results show a good agreement between the computed and natural structures, in particular, the occurrence in the same system of well- and poorly mixed regions. It is shown that magma interaction processes are able to generate magmatic masses having wide spatial heterogenity at many length scales. This occurrence can account for the presence of magmatic enclaves inside host rocks showing a variable degree of hybridization in both plutonic and volcanic environments.