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Temporal magma source changes at Gaua volcano, Vanuatu island arc

Temporal magma source changes at Gaua volcano, Vanuatu island arc
Temporal magma source changes at Gaua volcano, Vanuatu island arc
Gaua Island (also called Santa Maria), from the central part of the Vanuatu arc, consists of a large volcano marked by a caldera that hosts the active Mount Garet summit cone. In this paper, a geochemical study including Sr, Nd, Pb and Hf isotopic compositions of 25 lavas emitted since 1.8 Ma is presented, with a focus on the volcanic products that preceded (old volcanics, main cone and pyroclastic series) and followed (Mount Garet) the caldera forming event.

All lavas show an island arc signature with enrichment in LILE and depletion in HFSE. Post-caldera lavas define a medium-K calc-alkaline trend, whereas lavas from the former main cone have high-K calc-alkaline compositions. Compared to the pre-caldera volcanic suite, the Mount Garet lavas have similar Th/Nb (~ 1.5), 143Nd/144Nd (~ 0.51295) and 176Hf/177Hf (~ 0.28316) ratios, but higher Ba/La (~ 42 vs. ~ 27) and 87Sr/86Sr (0.70417 vs. 0.70405) ratios and lower Ce/Pb (~ 2.7 vs. ~ 4.6), La/Sm (~ 2.5 vs. ~ 4.0) and 206Pb/204Pb (18.105 vs. 18.176) ratios. High Th/Nb and low Nd and Hf isotopic ratios compared to N-MORB suggest the contribution of ~ 2% of subducted sediment melt to the mantle source of Gaua magmas. Most of the observed differences between pre- and post-caldera lavas can be accounted for by the involvement of at least two portions of the mantle wedge, metasomatized by different slab-derived aqueous fluids. In addition, the lower La/Sm (at a given 143Nd/144Nd) ratios of Mount Garet lavas suggest a higher degree of partial melting (~ 10–15%) compared to the pre-caldera lavas (~ 5%). The Santa Maria Pyroclastic Series (SMPS) eruption probably triggered the caldera collapse, in response to emptying of the magmatic chamber. This event may have allowed new access to the surface for a geochemically distinct batch of magma issued from a separate magma chamber, resulting in the birth and construction of Mount Garet within the caldera. As both magmatic suites were emitted over a very short time, the storage of their parental magmas beneath the volcano is still possible.
Gaua, Vanuatu, Geochemistry, Isotopes, Subduction, Mantle source
0377-0273
30-47
Beaumais, Aurelien
065495d1-3a28-4d8b-a994-fd9b14df63e1
Bertrand, Hervé
6a0271c6-5474-404b-ad01-5a0b65f8ba7b
Chazot, Gilles
f333718a-4daf-46bf-82bd-ecc7077ba2fa
Dosso, Laure
d3cf9f59-48ab-4269-a0ba-21747e52deb7
Robin, Claude
503cb711-7fee-4008-9ba9-36ebc4db37ba
Beaumais, Aurelien
065495d1-3a28-4d8b-a994-fd9b14df63e1
Bertrand, Hervé
6a0271c6-5474-404b-ad01-5a0b65f8ba7b
Chazot, Gilles
f333718a-4daf-46bf-82bd-ecc7077ba2fa
Dosso, Laure
d3cf9f59-48ab-4269-a0ba-21747e52deb7
Robin, Claude
503cb711-7fee-4008-9ba9-36ebc4db37ba

Beaumais, Aurelien, Bertrand, Hervé, Chazot, Gilles, Dosso, Laure and Robin, Claude (2016) Temporal magma source changes at Gaua volcano, Vanuatu island arc. Journal of Volcanology and Geothermal Research, 322, 30-47. (doi:10.1016/j.jvolgeores.2016.02.026).

Record type: Article

Abstract

Gaua Island (also called Santa Maria), from the central part of the Vanuatu arc, consists of a large volcano marked by a caldera that hosts the active Mount Garet summit cone. In this paper, a geochemical study including Sr, Nd, Pb and Hf isotopic compositions of 25 lavas emitted since 1.8 Ma is presented, with a focus on the volcanic products that preceded (old volcanics, main cone and pyroclastic series) and followed (Mount Garet) the caldera forming event.

All lavas show an island arc signature with enrichment in LILE and depletion in HFSE. Post-caldera lavas define a medium-K calc-alkaline trend, whereas lavas from the former main cone have high-K calc-alkaline compositions. Compared to the pre-caldera volcanic suite, the Mount Garet lavas have similar Th/Nb (~ 1.5), 143Nd/144Nd (~ 0.51295) and 176Hf/177Hf (~ 0.28316) ratios, but higher Ba/La (~ 42 vs. ~ 27) and 87Sr/86Sr (0.70417 vs. 0.70405) ratios and lower Ce/Pb (~ 2.7 vs. ~ 4.6), La/Sm (~ 2.5 vs. ~ 4.0) and 206Pb/204Pb (18.105 vs. 18.176) ratios. High Th/Nb and low Nd and Hf isotopic ratios compared to N-MORB suggest the contribution of ~ 2% of subducted sediment melt to the mantle source of Gaua magmas. Most of the observed differences between pre- and post-caldera lavas can be accounted for by the involvement of at least two portions of the mantle wedge, metasomatized by different slab-derived aqueous fluids. In addition, the lower La/Sm (at a given 143Nd/144Nd) ratios of Mount Garet lavas suggest a higher degree of partial melting (~ 10–15%) compared to the pre-caldera lavas (~ 5%). The Santa Maria Pyroclastic Series (SMPS) eruption probably triggered the caldera collapse, in response to emptying of the magmatic chamber. This event may have allowed new access to the surface for a geochemically distinct batch of magma issued from a separate magma chamber, resulting in the birth and construction of Mount Garet within the caldera. As both magmatic suites were emitted over a very short time, the storage of their parental magmas beneath the volcano is still possible.

Full text not available from this repository.

More information

Accepted/In Press date: 23 February 2016
Published date: 15 August 2016
Keywords: Gaua, Vanuatu, Geochemistry, Isotopes, Subduction, Mantle source
Organisations: Geochemistry

Identifiers

Local EPrints ID: 403525
URI: https://eprints.soton.ac.uk/id/eprint/403525
ISSN: 0377-0273
PURE UUID: 5fc20165-6193-4249-b3e0-780209d079d8
ORCID for Aurelien Beaumais: ORCID iD orcid.org/0000-0001-8693-4872

Catalogue record

Date deposited: 02 Dec 2016 13:58
Last modified: 06 Jun 2018 12:20

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