Sample locations, Ar-Ar ages and major element compositions for igneous rocks dredged during the VESPA scientific cruise

Date 2022
Author(s) Agranier Arnaud1, Patriat MartinORCID1, Mortimer NickORCID2, Collot JulienORCID3, Etienne SamuelORCID3, Durance Patricia4, Gans Phil5, Chazot Gilles1
Affiliation(s) 1 : Univ Brest, CNRS, Ifremer, Geo-Ocean, F-29280 Plouzané, France
2 : GNS Science, Dunedin, New Zealand
3 : Service Géologique de Nouvelle Calédonie, Nouméa, New Caledonia
4 : GNS Science, Lower Hutt, New Zealand
5 : University of California, Santa Barbara, CA, USA
DOI 10.17882/90050
Publisher SEANOE
Keyword(s) Southwest Pacific, New Zealand, New Caledonia, Igneous rocks, Geochemistry, Volcanic Arc, Subduction, Tectonics, Eocene, Oligocene, Miocene, Geochronology, Ar/Ar
Abstract

The SW Pacific region contains several ridges and basins that are inferred to represent pre-Quaternary volcanic arcs and back-arc basins. The geology of these features is less well characterized than that of the active Tonga-Kermadec and Vanuatu arcs. We report new major and trace element, and Pb, Hf, Sr and Nd isotope data for 27 lavas dredged from the Loyalty and Three Kings ridges during the 2015 VESPA cruise of R/V l’Atalante. Low-K basalts were dredged from the seabed deeper than 3300 m, and high-K to shoshonitic suites from shallower ridge crests at 2000-3300 m. The samples are mainly basalts, with lesser trachybasalts, basaltic andesites, trachyandesites andesites, dacites, and one granite (anhydrous SiO2 and K2O+Na2O range from ~47 to 64 and 1.5 to 11 wt. % respectively). Trace element patterns allow discrimination of three geochemical signatures, identified as i) depleted, ii) transitional and iii) enriched, based on their light to heavy rare earth element (REE) ratios (with La/Sm ranging from 0.4 to 8). Depleted and transitional samples are basalts, featuring REE concentrations similar to MORB, but with high field strength element and large ion lithophile element contents, typical of back-arc basin basalts. The most enriched samples are basaltic andesites, andesites, trachyandesites and trachytes with island arc magma trace element signatures. Pb isotope ranges are limited (208Pb/204Pb ~38 to 39.8, 207Pb/204Pb ~15.51 to 15.64 and 206Pb/~17.9 to 20.1), while Hf isotopes display more diverse compositions (åHf ranging from +7.7 to +14). Both Nd (åNd= 2.8-9.3) and Sr (87Sr/86Sr= 0.79026-0.7048) isotopes are correlated with Hf data. Trace element and isotopic compositions can be explained in terms of mixing between three distinct geochemical endmembers in the mantle resembling DMM, HIMU and EM-2 sources. Our study confirms voluminous subduction-related magmatism on the Loyalty and Three Kings ridges, mostly of Late Oligocene – Early Miocene age. The issue of polarity of subduction to generate these rocks remains open, but the composition-space-time distribution of the igneous rocks can be explained in the context of SW Pacific geodynamics using a west-dipping Pacific slab model.

Licence CC-BY
Data
File Size Format Processing Access
Sample locations, Ar-Ar ages and major element compositions for igneous rocks dredged during the VESPA scientific cruise 40 KB XLS, XLSX Quality controlled data Open access
Top of the page

How to cite 

Agranier Arnaud, Patriat Martin, Mortimer Nick, Collot Julien, Etienne Samuel, Durance Patricia, Gans Phil, Chazot Gilles (2022). Sample locations, Ar-Ar ages and major element compositions for igneous rocks dredged during the VESPA scientific cruise. SEANOE. https://doi.org/10.17882/90050