Experimental Magma Mixing and Mingling in Volcanic Environments

Abstract:

Magma mixing and mingling features are commonly observed in both plutonic and volcanic environments. Major occurrences are represented by hybrid products, enclaves and crystals in disequilibrium with the melt. According to present knowledge the complete mixing of magmas in crustal reservoirs (leading to the production of hybrids) requires a low viscosity contrast between the two end-members (0.5 log unit). On another hand, recent experimental and field works have shown that (1) crystal-free magmas with viscosity difference of 3 orders of magnitude produced mingling and mixing features at higher deformation conditions (strain and strain rate) and (2) these features are found in volcanic products out of the above mentioned rheological window. In this study, we performed magma mixing experiments, to test the effects of chaotic deformation of a two component system at volcanic conditions and strain rates comparable to natural magmatic systems (volcanic conduits and lava flows): in the ChaOtic Magma Mixing Apparatus (COMMA) installed at the University of Perugia, a synthetic haplotonalite and a natural basalt from Santorini volcano were juxtaposed and chaotically mixed for several hours at ~1140°C with a moderate strain rate of ~5.10^-3. The textural and geochemical (electronic microprobe, laser ablation mass spectrometry) features developed during the experiments show the development of complex patterns with high inter-exchange between both magmas. Our results show how chaotic convection extends the mixing capacities at moderate strain rate.