Convection and redistribution of alkalis and trace elements during the mingling of basaltic and rhyolite melts

Numerous examples of long-lasting coexistence of basaltic and rhyolitic mag mas in magma chambers indicate that it results in thermal, isotopic, and ch emical exchange between the melts. This paper presents our model experiment s, which demonstrate the effect of rapid potassium and sodium diffusion fro m the basaltic to rhyolitic melt on their density and resultant convection in each of the melts. This diffusion-induced convection leads to the rapid preferential redistribution of alkalis between the melts. Ion microprobe pr ofiles demonstrate that rapidly diffusing trace elements are transported mo re quickly than bi-, tri-, and tetravalent major components, and, at the ve ry beginning of the experiments, they were redistributed between the melt i n correspondence with respective partition coefficients typical of these co mponents when the acid and mafic melts are immiscible. Convection maintains significant chemical gradients and creates a self-sufficient mechanism for the convection, diffusion, and redistribution of trace elements and alkali s between the magmas.