CAN A SUPERVOLCANO ERUPTION ERADICATE EXISTING ZIRCON?
A better understanding of zircon dissolution during reheating is necessary to evaluate these hypotheses. The preservation of inherited zircon in ignimbrites (e.g., preservation of Precambrian zircon with Tertiary overgrowths in Tertiary ignimbrites of the Southern Rocky Mountain volcanic field) suggest that zircon dissolution may be inefficient. Published models for zircon dissolution/crystallization during mush rejuvenation calculated under similar conditions show wide-ranging results. For example, a zircon with a radius of 100 µm is calculated to fully dissolve under magmatic conditions (750ºC, Zr-undersaturated) in a peraluminous magma anywhere between 8 ka and 180 ka depending on the model used. The disparity in these models is significant because the timescales hypothesized for magma body rejuvenation are on the order of 0.1 to 10 ka. If zircon dissolves rapidly under these conditions, it is possible that information recorded over several Ma in a growing magma body may be erased prior to eruption. However, if zircon dissolution is slow, it suggests that large ignimbrites are assembled much more quickly than plutons, requiring a different physical process for their generation. Our preliminary modeling indicates that very slow dissolution rates, consistent with the preservation of inherited cores, are correct. These preliminary results suggest that it is unlikely for incrementally assembled, intrusive suite-sized magma bodies to be rejuvenated in supervolcanic eruptions.