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Ignimbrites sample large magma reservoirs in the Earth’s upper crust, sometimes digging deep enough to link the volcanic realm with the plutonic world. Integrating textural, petrological, geochemical, and geochronological information on such deposits with geophysical signals suggest incremental growth and evolution of subvolcanic magma bodies that are dominated by high crystallinity mush zones, but sometimes remain sufficiently liquid to erupt. The eruptible upper portions are either extracted melt from the mush and constitute only a small volumetric fraction of the vertically extensive mushy batholithic magma body. The high-flux, ignimbrite flare-up phases are typically preceded by waxing magmatism that prime the crust to hold large, upper crustal silicic reservoirs where melt rich magma accumulates. Gas exsolution within such mushy reservoirs, and accumulation of the low density bubbles in the most melt-rich parts of the system, will also enhance eruptibility, emphasizing some of the observed chemical differences between evolved plutonic and volcanic rocks.
Geological Engineering | Mining Engineering
Deering, Chad, "Ignimbrites to batholiths" (2016). TechTalks. 20.