Timescales of Magma Recharge and Reactivation of Large Silicic Systems from Ti Diffusion in Quartz

Timescales of magma chamber assembly and recharge are investigated here by applying 1D and 2D diffusion modeling techniques to high-resolution maps of titanium in quartz from a large-volume ignimbrite eruption in the Taupo Volcanic Zone, New Zealand. We compare quartz zonation patterns and associated diffusion timescales from the similar to 340 ka Whakamaru super-eruption (magma volume similar to 1000 km(3)) with the Younger Toba Tuff super-eruption, 74 ka (2000 km(3)), Sumatra, and the smaller volume similar to 50 ka Earthquake Flat eruption (10 km(3)), Okataina Caldera Complex, New Zealand. Two principal timescales are presented: that of chamber recharge and eruption triggering events, and that of magma generation (involving long-term assembly, stirring and reactivation). Synchrotron micro-X-ray fluorescence maps of core-rim quartz transects provide a high-resolution record of magma chamber conditions throughout quartz crystallization. Quartz crystals from the Whakamaru magma display complex zonation patterns indicating fluctuating pressure-temperature conditions throughout the crystallization history. Toba and Earthquake Flat, in contrast, display simple quartz-zoning patterns and record slightly longer periods of crystal residence in the chamber that fed the eruption. We apply Lattice Boltzmann 2D diffusion modeling to reconstruct the timescales of quartz crystal zonation, accounting for crystal boundary complexities. Quartz crystal orientation is also accounted for by using geometry constraints from the synchrotron data. Our calculations suggest that crystal-mush reactivation for the main Whakamaru magma reservoir occured over a period of the order of 10(3)-10(4) years. Both the Earthquake Flat and Toba eruptions experienced a significant recharge event (causing a temperature and pressure change), which occurred within similar to 100 years of eruption. In comparison, the complex Whakamaru quartz zoning patterns suggest that the magma body experienced numerous thermal and compositional fluctuations in the lead-up to eruption. The final magma recharge event, which most probably triggered the eruption, occurred within similar to 10-60 years of the eruption. Even though the volume of these systems spans two orders of magnitude, there does not appear to be a relationship between magma volume and diffusion timescale, suggesting similar histories before eruption.