LIQUID FRACTIONATION .4. SCALE MODELS FOR LIQUID FRACTIONATION OF CALC-ALKALINE MAGMAS

Liquid fractionation has been modeled experimentally using scale theor y. The results confirm that under conditions of constant viscosity a l ow-density magma can ascend as a coherent laminar layer along the vert ical walls. The results also suggest, however, that if viscosity incre ases with differentiation the fractionated liquid forms small centimet re-sized plumes not only along inclined and irregular walls and along the bottom of magma chambers, but even on vertical walls. The formatio n of plumes enhances the accumulation of rhyolitic magma, and may incr ease the efficiency of fractionation.