REINVIGORATING STAGNANT SILICIC MAGMA SYSTEMS: VOLCANIC AND PLUTONIC VIEWS
--Field evidence in many cases spectacularly documents modest to abundant mafic recharging within granitic plutons and in erupted rhyolites, and, more subtly, silicic recharging (Colorado River extensional corridor, Miocene, NV-CA-AZ; Iceland, Miocene to present day)
--Zircon zoning (morphology and elemental compositions) reveals major fluctuations in temperature and melt composition, with common resorption and resumed growth, in host melts (Mount St. Helens; Colorado River extensional corridor; Iceland)
--Zircon ages indicate punctuated growth episodes (resolvable on tens of k.y scale by U-Th [<350 ka: Mount St. Helens, Iceland] to 100’s of k.y. (older Icelandic and Colorado River intrusions])
--Textures – especially in erupted products –document dramatic swings in temperature (e.g. high-T zircon rims, reaction rims and resorption on other ‘evolved’ phenocrysts [quartz, sphene, sanidine]) and collection of unrelated phenocrysts (e.g. olivine-sanidine-quartz)(Colorado River)
Our experience with silicic systems spanning subduction zone, oceanic, and intracontinental settings and ranging from small, persistent eruptive centers to supereruptions suggests that thermal rejuvenation plays a vital role in the dynamic behavior of many and perhaps most silicic systems. It is further consistent with the hypothesis that such systems are long-lived but that their normal state is as melt-poor, immobile, uneruptible bodies that only sporadically spring to life. An intriguing question persists: during their stagnant stages, do systems retain some melt (remain magmatically alive), or die (fall beneath their solidi), before reinvigoration by replenishment? (Do magmatic systems emulate Snow White or Lazarus?)