HR: 0800h
AN: V21D-0757    [Abstracts]
TI: Tonga - Kermadec Arc Calderas as Sites of Hydrothermal Venting: A Review of Caldera Morphology and Structure
AU: * Wright, I C
EM: i.wright@niwa.cri.nz
AF: NIWA, P.O. Box 14-901, Kilbirnie, Wellington, 6021, New Zealand
AU: Graham, I J
EM: i.graham@gns.cri.nz
AF: GNS Science, P.O. Box 30-368, Avalon, Lower Hutt, 5010, New Zealand
AU: Stoffers, P
EM: pst@gpi.uni-kiel.de
AF: Institute of Geosciences, University of Kiel Olshausenstrasse 40, Kiel, 24118, Germany
AU: Wilson, C J
EM: cjn.wilson@auckland.ac.nz
AF: School of Geography, Geology and Environmental Science, University of Auckland, Private Bag 92019, Auckland, 1142, New Zealand
AB: Within the 870 km long sector of the Tonga – Kermadec arc (between 35°S and 21°S), submarine hydrothermal venting is dominantly hosted within calderas associated with silicic eruptives. Over 50 individual >1 km wide calderas have been identified from five multibeam mapping surveys from 2002 - 2007. Caldera distribution is mostly, though not exclusively, along the central - northern Kermadec and southern Tonga arc sectors. In contrast, metrics of caldera morphology are mostly consistent along the arc; average caldera floor water-depth is 1050 m (range 1860 - 260 m), average caldera long axis is 4.9 km (range 11.6 - 1 km), and average caldera rim water-depth is 800 m (range 1500 - 160 m). As in the onshore extension of the arc (Taupo Volcanic Zone), regional arc and backarc extension strongly controls caldera structure; caldera elongation (average length:width ratio of 1.26) is orientated predominantly orthogonal to the basement rift fabric. Various styles of caldera collapse (including trap-door and funnel structures) are recognised from both multibeam and multi-channel seismic reflection data. More than half of the calderas show evidence of repetitive and nested collapse. Caldera breaching and rim collapse are common, and can be associated with mass-gravity pyroclastic debris flows, imaged as large-scale sediment bed-forms in multibeam and multi-channel seismic data. Similarly, post-collapse volcanism (but not structural resurgence) is common with both intra-caldera dome construction, and formation of cone vents and explosion pits around the caldera rim. Such post-collapse volcanism is variable in composition, however, intra-caldera dome and rim eruptives are commonly rhyolitic and basaltic, respectively.
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 8185 Volcanic arcs
DE: 8424 Hydrothermal systems (0450, 1034, 3017, 3616, 4832, 8135)
DE: 8427 Subaqueous volcanism
DE: 8440 Calderas
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting