Fine-scale temporal recovery, reconstruction and evolution of a post-supereruption magmatic system

Abstract

eruption of 25 rhyolitic units starting at ~12 ka. The dacites show strongly zoned minerals and wide variations in meltinclusion compositions, consistent with early magma mixing followed by periods of cooling and crystallisation at depths of >8 km, overlapping spatially with the inferred basal parts of the older Oruanui silicic mush system. The dacites reflect the first products of a new silicic system, as most of the Oruanui magmatic root zone was significantly modified in composition or effectively destroyed by influxes of hot mafic magmas following caldera collapse. The first rhyolites erupted between 12 and 10 ka formed through shallow (4-5 km depth) cooling and fractionation of melts from a source similar in composition to that generating the earlier dacites, with overlapping compositions for melt inclusions and crystal cores between the two magma types. For the successively younger rhyolite units, temporal changes in melt chemistry and mineral phase stability are observed, which reflect the development, stabilisation and maturation of a new, probably unitary, silicic mush system. This new mush system was closely linked to, and sometimes physically interacted with, underlying mafic melts of similar composition to those involved in the Oruanui supereruption. From the inferred depths of magma storage and geographical extent of vent sites, we consider that a large silicic mush system (>200 km 3 and possibly up to 1000 km 3 in volume) is now established at Taupo and is capable of feeding a new episode or cycle of volcanism at any stage in the future.

Rapid priming, accumulation, and recharge of magma driving recent eruptions at a hyperactive caldera volcano

“…Stepwise 170 changes in composition between the SG2 and SG3 rhyolites (Fig. 2) are consistent with 171 5%-10% dissolution of orthopyroxene and plagioclase, liberating compatible trace 172 elements (e.g., Sr, Eu, Zn, Mn, Ti) from the crystals to the melt phase within the crystal 173 mush (Barker et al, 2015). These signatures would only be recorded in the final SG3 174 eruptive products if heating and dissolution occurred in the mush prior to extraction of 175 the crystal-poor rhyolite melt (Fig.…”

“…The relatively large width of the diffusion profiles investigated in this study means that common problems reported in other studies of convolution and pixel size were not considered to be of significant effect (Morgan et al, 2004;Cooper, 2014 Allan et al, 2013). Average (Av) diffusion model timescales given for parameter estimates of 860 °C, 1.5 MPa and log ƒO 2 of 0.2 ∆NNO from Barker et al (2015). Maximum (Max) and minimum (Min) timescales use uncertainties ±30 ºC or ± 0.3 log units ∆NNO.…”

“…Major elements analysed by XRay Flourescence (XRF) and trace elements by solution Inductively Coupled Plasma Mass Spectrometry (ICPMS). See Barker et al (2015) for full description of analytical methods and standards. Table DR2.…”

“…Major elements measured by Electron Probe Micro-Analysis (EPMA), trace elements measured by solution-ICPMS for pure groundmass glass separates only. Temperatures are averages from Barker et al (2015) using the orthopyroxene-liquid thermometer of Putirka (2008). Viscocity (log ) of melt (in Pa s ) calculated using the model of Giordano et al (2008) (Allan et al, 2013;Cooper, 2014;Chamberlain et al, 2014), and therefore the zoning observed in BSE images is inferred to be an accurate representation of the Fe-Mg content.…”

Repeated Rhyolite Eruption From Heterogeneous Hot Zones Embedded Within a Cool, Shallow Magma Reservoir

“…Much effort on silicic magma reservoirs has focused on the products of large (10 2 –10 3 km 3 ) eruptions. However, the repeated modest‐volume (<20 km 3 ) eruptions that often precede and follow such events provide a high‐temporal‐resolution sampling of magma reservoirs that can reveal a spatial and temporal thermochemical evolution that may be obscured in voluminous ignimbrites (Bachmann et al, ; Barker et al, ; Metz & Mahood, ; Smith et al, ; Sutton et al, ). Zoned crystals record changing magmatic conditions; moreover, accessory phases with a high affinity for U and Th, such as zircon, allow for the in situ determination of the trace element composition and age within the same crystal domain (e.g., Claiborne, Miller, Flanagan, et al, ; Reid et al, ).…”