SIMPLY COMPLICATED: PERSPECTIVES ON SUPERERUPTIVE SYSTEMS FROM MULTIPLE AND VARIED DATASETS
We are exploring such questions in multiple large-volume silicic systems from a variety of tectonic settings: 767 ka Bishop Tuff, CA, USA; 18.8 Ma Peach Spring Tuff (PST), SW, USA; 25.4 ka Oruanui, 240 ka and Ohakuri-Mamaku (Oh-Ma), TVZ, New Zealand. We are using a plethora of methods, including: field observations; crystal and melt inclusion textures; whole-rock, glass, and mineral geochemistry; and phase-equilibria modeling. Such a broad dataset provides us with a nuanced perspective on individual systems and reveals both striking similarities and notable distinctions in the pre- and syn-eruptive timescales, crustal storage conditions, and geometry of these magmas more generally:
- Crystal size distributions (CSD), melt inclusion faceting, and Ti diffusion chronometry in quartz crystals indicate that the final pre-eruptive accumulation of melt-rich HSR magmas occurs over impressively short centennial-millennial timescales.
- CSDs and diffusion chronometry of quartz rims suggest that eruptive decompression is a short-lived event (days-a year). In some cases (Oruanui), we cannot resolve such groundmass or rim crystallization; this may indicate that ascent and eruption can occur even more quickly.
- Crystal textures and compositions suggest that late-stage thermal events may be important in the final destabilization of giant systems (PST); however, these indicators are not ubiquitous, intimating that such events are either not always recorded or are not required for the triggering of an eruption.
- Geobarometry indicates that HSR magmas are restricted to shallow upper-crustal depths. Yet, in combination with field relations, whole-rock, glass, and mineral geochemistry and textures, phase-equilibria geobarometry also suggests multiple potential models for the geometry of large-volume HSR systems in the crust, from a single zoned magma body (PST) to multiple simultaneously erupted batches (Bishop, Oh-Ma).