Browsing by Author "Berry, A"

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    Havre 2012 pink pumice is evidence of a short-lived, deep-sea, magnetite nanolite-driven explosive eruption
    (Goldschmidt, 2022-07-16) Knafelc, J; Byran, SE; Jones, MWM; Gust, D; Mallmann, G; Cathey, H; Berry, A; Ferré, EC; Howard, DL
    The Havre 2012 deep-sea eruption produced a massive pumice raft (~1.2 km3) at the sea surface from a volcano that sits 900 mbsl (~9.6 MPa) in the Kermadec Arc. Lava flows/domes and a field of sunken seafloor pumice were also emplaced across the summit during the eruption. Havre raft and seafloor pumice are considered to have erupted contemporaneously and as part of an effusive eruption due their similarity in appearance and bulk chemistry. A distinctive feature of the raft is the common occurrence of pink pumice. Pink pumice has been reported from subaerial explosive eruptions, and results from high-temperature atmospheric iron-oxidation (> 700 °C). The pink raft pumice therefore poses problems given the deep water setting that is assumed to prevent eruption explosivity and the effusive eruption model for the 2012 eruption. Here, pink pumice is experimentally produced by heating white Havre raft pumice for several minutes in air at temperatures between 675-900°C (Fig. 1). The degree of reddening in experimental pumices increases with increased temperatures and times, resulting in a similar spectrum of colouration observed in natural pink raft pumice. The origin of the pink colouration was then investigated using several microanalytical techniques including X-ray Fluorescence Microscopy (XFM), Fe X-ray Absorption Near Edge structures (Fe-XANES), EPMA, rock magnetics, and TEM imaging. We found that white and pink raft pumice contain abundant magnetite nanolites/microlites and higher amounts of hematite in the pink pumice. In contrast, no magnetite nanolites or hematite occurs in the seafloor pumice. Magnetite nanolites line vesicle walls of pink raft pumice where the colour is microscopically localized. This provides evidence the magnetite nanolites are oxidizing to hematite and also acted as nucleation sites for enhanced volatile exsolution. Our results demonstrate a short-lived but powerful explosive eruption phase occurred during the 2012 eruption that penetrated the water column allowing hot pyroclasts to oxidize in air (Fig. 2). In light of these results the known depth limits for explosive eruptions (~10 MPa) in the marine realm need to be reassessed and we suggest pink pumice can be an indicator of magnetite nanolite-driven explosive eruptions.
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    Recent enhancements and performance gains from upgrades to ANSTO's thermal neutron instrument TAIPAN and the triple-axis and Be-filter spectrometers
    (Australian Nuclear Science and Technology Organisation, 2017-11-28) Rule, KC; Ogrin, A; Berry, A; Stampfl, APJ; Bartlett, D; Franceschini, F; Darmann, FA; Olsen, SR; Danilkin, SA; Pangelis, S; Oste, T; Ersez, T
    TAIPAN is the thermal-neutron spectrometer located at the reactor face of Australia's OPAL reactor (ANSTO). TAIPAN hosts two interchangeable secondary instruments; the triple-axis spectrometer (TAS) and the beryllium filter spectrometer. The TAS option has been operating since 2010 whilst the Be-filter only began operating in 2015. TAIPAN is renowned for its versatility and high neutron flux which has allowed the TAS to measure a broad range of samples including single crystals, powders, thin films, and co-aligned multi-crystal arrays. While the TAS option is used mostly to study structural and magnetic excitations in materials, the Be-filter option is used to measure vibrational density of states from powder samples. TAIPAN has recently undergone some upgrades to improve the accessible momentum and energy range of both the TAS and the Be-filter spectrometers. Four key features have been modified to improve performance: the accessible momentum transfer has been increased by re-designing the enclosure; a sapphire-filter translation-stage mechanism has been installed to allow epithermal neutrons to pass to the monochromators; a new Cu-200 double-focussing monochromator has been installed to allow monochromatic scattering of neutrons up to 180 meV; and finally a new tertiary shutter and snout have been designed to improve the signal-to-noise ratio and reduced background outside the instrument enclosure. Extensive testing and alignment of all new motion stages were undertaken with reproducibility within ±0.05degrees or ±0.25mm obtained for both the monochromator rotation angle & sapphire-filter alignment. © The Authors.
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    Recent upgrades to ANSTO’s thermal neutron spectrometer, TAIPAN
    (Australian Institute of Physics, 2018-01-30) Rule, KC; Darmann, FA; Oste, T; Olsen, SR; Bartlett, D; Franceschini, F; Berry, A; McGregor, A; Ogrin, A; Ersez, T; Kafes, A; Pangelis, S; Danilkin, SA; Stampfl, APJ