TY - JOUR
AU - Wysoczanski, R. J.
AB - The Whakamaru eruption is the largest-volume eruption known to have originated from the hyper-productive Taupo Volcanic Zone, New Zealand. Major, minor and trace element concentrations of plagioclase crystals and cathodoluminescence images, used as a proxy for Ti concentrations in quartz crystals, have been used to explore their chemical zonation. Three plagioclase populations are identified. Group 1 crystals are characterized by inherited cores of composition An4560, Ba 115650ppm and La 39ppm, rims of c. An30, Ba 450800ppm and La 710ppm and the presence of a thin overgrowth rim on several crystals cores. Group 2 crystals are oscillatory-zoned plagioclases of composition An3040, Ba 450730ppm and La 8595ppm. Group 3 plagioclase crystals have cores of An2535 and rims of An2025 and low Sr contents (280480ppm). From the chemical composition of these plagioclase crystals, four physicochemically distinct rhyolitic melts are identified: (1) an andesitic progenitor melt in which the cores of Group 1 crystals crystallized; (2) a greywacke melt or greywacke protolith melt responsible for narrow overgrowth rims on Group 1 crystal cores; (3) melt derived from the rejuvenation of a mature crystal mush body from which Group 3 plagioclase crystals crystallized; (4) a final, rhyolitic melt created by the amalgamation of varying proportions of the andesitic, greywacke-derived and rejuvenated melts with subsequent, open-system fractional crystallization of a plagioclase-dominant crystal assemblage. Cathodoluminescence imaging of quartz crystals reveals complex zonation, the result of a dynamic crystallization history from potentially polygenetic sources. Diffusion modelling of the greyscale intensity of cathodoluminescence images (as a proxy for Ti content) for a selection of bright corerim interfaces of quartz crystals suggests that renewed quartz growth at the rim zones occurred <300 years (peak likelihood 5070 years) prior to and continued towards the climactic eruption. This is consistent with timescales of <280 years determined from corerim interfaces of Group 1 plagioclase crystals, suggesting that the magma chamber was ephemeral, derived from mixing of magmas from multiple sources shortly prior to eruption. This study adds to a growing body of evidence for the ephemeral nature and geologically rapid mixing and mobilization of liquid silicic magma bodies leading to supereruptions, compared with the timescales of hundreds of thousands of years required to accumulate the precursor magma and crystals.
TI - The Magmatic Evolution of the Whakamaru Supereruption, New Zealand, Constrained by a Microanalytical Study of Plagioclase and Quartz
JF - Journal of Petrology
DO - 10.1093/petrology/egq064
DA - 2010-12-23
UR - https://www.deepdyve.com/lp/oxford-university-press/the-magmatic-evolution-of-the-whakamaru-supereruption-new-zealand-AV0jNKpy3L
SP - 2465
EP - 2488
VL - 51
IS - 12
DP - DeepDyve
ER -