Temporal source evolution and crustal contamination at Lopevi Volcano, Vanuatu Island Arc

Type Article
Date 2013-08
Language English
Author(s) Beaumais Aurelien1, Chazot Gilles1, Dosso Laure2, Bertrand Herve3
Affiliation(s) 1 : Univ Brest UBO, UMR Domaines Ocean 6538, Inst Univ Europeen Mer, F-29280 Plouzane, France.
2 : CNRS, IFREMER, UMR6538, Dept Geosci Marines, F-29280 Plouzane, France.
3 : Univ Lyon 1, Ecole Normale Super Lyon, Lab Geol Lyon, UMR CNRS 5570, F-69364 Lyon, France.
Source Journal Of Volcanology And Geothermal Research (0377-0273) (Elsevier Science Bv), 2013-08 , Vol. 264 , P. 72-84
DOI 10.1016/j.jvolgeores.2013.07.005
WOS© Times Cited 8
Keyword(s) Lopevi, Vanuatu, Geochemistry, Isotopes, Subduction, Mantle source
Abstract Here we present a new geochemical study of Lopevi volcano, one the most active volcanoes in the Vanuatu island arc. We focus on the temporally well-defined sequence of lava flows emitted since 1960, and for the first time, on pre-1960 volcanic products, including high-MgO basalts and felsic andesites, the most evolved lavas sampled so far on this island. This work reports the first Pb and Hf isotopic study of lavas from Lopevi island. These lavas display correlations between differentiation indexes such as SiO2 content and isotopic ratios. The felsic andesites extend the known correlations with both the least (Sr-Pb) and the most (Nd-Hf) radiogenic isotopic compositions on the island. Our results confirm that the rising magma interacted with the sub-arc crust. Assimilation-Fractional Crystallization (AFC) quantitative modeling of trace element ratios and isotopic compositions requires 1% and 10% of assimilated partial melts of a mafic oceanic crust to account for the pre- and post-1960 lavas, respectively. The post-1960 lavas differ from the former lavas emitted similar to 20 years earlier by enrichments in fluid mobile elements (K, Ba, Rb ... ), Th, and Light Rare Earth Elements (LREE). We ascribe these features to slight variations in the metasomatic agent added to the sub-arc mantle and ultimately derived from the subducted lithosphere. However, the contrasting time scales involved in subducted lithosphere dehydration and magma genesis, relative to the time elapsed between eruptions of the two lava series, suggest that two different portions of mantle which have undergone slightly different metasomatism, gave birth to the Lopevi lavas. These distinct magmas are still present beneath the volcano.
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