Conference proceeding
Uranium-series disequilibria in Vanuatu arc volcanic rocks; constraints on pre-eruptive processes in contrasting volcanic systems
American Geophysical Union Fall Meeting, Vol.2011
American Geophysical Union 2011 fall meeting
12/2011
Abstract
Recent and present volcanism in the Vanuatu arc (South West Pacific Ocean) occurs at a variety of volcano types that exhibit a wide range of eruptive behaviour: from post-caldera lava-lake activity and lava flows at shield volcanoes (Ambrym), moderately explosive sub-plinian events and associated pyroclastic-flows and lava flows at stratovolcanoes (Lopevi), to persistent strombolian and vulcanian-style eruptions at scoria cones (Yasur). This precludes a generic model of magmatic and eruptive behaviour for the Vantuatu arc volcanoes and necessitates a detailed study of each system. Uranium-series disequilibria in volcanic rocks offer unique insights into pre-eruptive magmatic systems over process-relevant timescales e.g., (super 238) U- (super 230) Th (380 Ka), (super 230) Th- (super 226) Ra (8 Ka) and (super 226) Ra- (super 210) Pb (100 a). The short half-life of (super 210) Pb (t (sub 1/2) = 22.6 years) and the volatile nature of the intermediate isotope, (super 222) Rn, (intermediate between the (super 226) Ra parent and (super 210) Pb daughter) provide valuable information on magma transport, evolution and degassing over a timescale more pertinent to the processes leading up to volcanic eruptions. We present new Uranium-series isotope data (U-Th-Ra- (super 210) Pb) for young (< 100 years old) volcanic samples from Ambrym, Lopevi and Yasur volcanoes to investigate the timescales of magmatic evolution and degassing in the contrasting volcanic systems. (super 210) Pb deficits (( (super 210) Pb/ (super 226) Ra) (sub 0) < 1) in Ambrym and Yasur volcanic rocks suggest effective open-system magmatic degassing of (super 222) Rn, consistent with the persistent lava-lakes/exposed magma and significant gas emissions observed at both volcanoes. Lopevi, on the other hand, largely displays excess (super 210) Pb (( (super 210) Pb/ (super 226) Ra) (sub 0) > 1) suggesting that (super 222) Rn gas accumulation and fluxing preceding and/or during eruption (on a decadal timescale) is responsible for the more explosive-style of eruption witnessed at this volcano. Significant accumulation of recently crystallised plagioclase phenocrysts can also create (super 210) Pb excesses in volcanic rocks, however, this process is not supported by the petrographic and geochemical data. In summary (super 210) Pb- (super 226) Ra disequilibria in Vanuatu volcanic rocks reveal a strong link between pre-eruptive magma degassing systematics and the resultant style of volcanic activity.
Details
- Title: Subtitle
- Uranium-series disequilibria in Vanuatu arc volcanic rocks; constraints on pre-eruptive processes in contrasting volcanic systems
- Creators
- Heather K Handley - Macquarie UniversitySimon TurnerMark K ReaganGuillaume GirardS. J CroninChris Firth
- Resource Type
- Conference proceeding
- Publication Details
- American Geophysical Union Fall Meeting, Vol.2011
- Conference
- American Geophysical Union 2011 fall meeting
- Publisher
- American Geophysical Union
- Alternative title
- AGU 2011 fall meeting
- Language
- English
- Date published
- 12/2011
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9984240886102771
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