Experimental studies on the structure of convection that occurs in a two-layered 'peripheral' magma chamber

摘要

Experimental studies were conducted to unravel the morphology and internal structure of convective flows of magma melts in the model of a two-layered "peripheral" magma chamber. Two systems of convective flows were found within the peripheral chamber: radial convective roll flows of magma melt in the lower layer of the peripheral chamber and cellular vertical convective flows of a "melt-solution" with lower density in the upper layer. The reason is shown that the volatile-rich melt in the "mantle" chamber separates into two unmixing layers, viz., a lower layer of magma melt and an upper layer that is a less dense melt-solution resulting from the escape of volatiles that were contained in the parent magma melt. The separation and accumulation of volatiles under the top of the peripheral chamber are due to decreasing pressure and temperature as the volatile-rich mantle melt rises owing to an ascending flow of melt within the central part of the "feeding" conduit of the peripheral chamber and a descending volatile-depleted circular flow that descends along the walls of the feeding conduit toward the mantle chamber.