The Norfolk Ridge seamounts: Eocene–Miocene volcanoes near Zealandia’s rifted continental margin

Abstract

New age and geochemical data are used to investigate the origin of a ∼670 km-long line of eight seamount volcanoes along the western side of the Norfolk Ridge between New Caledonia and New Zealand. Altered lavas and limestones were dredged from three volcanoes during the 2015 Volcanic Evolution of South Pacific Arcs cruise of N/O l’Atalante, so a total of four, including the northernmost and southernmost, have now been directly sampled and analysed. Dating of lava and volcanic breccia clasts by Ar–Ar methods gives north-to-south ages from these sites of 31.3 ± 0.6, 33 ± 5, 21.5 ± 1.0 and 26.3 ± 0.1 Ma. These ages, along with supporting stratigraphic data on a fifth seamount from IODP borehole U1507, provisionally refute the hypotheses that the seamounts represent a southward-younging, age-progressive, intraplate volcanic chain on the Australian Plate or a subduction-related chain of restricted age range. Geochemically, the upper Eocene to lower Miocene lavas have alkaline and subalkaline basaltic compositions, and some could be shoshonitic. The location of the volcanoes along the western side of the Norfolk Ridge suggests an origin related to late Eocene and early Miocene melting near an intracontinental lithosphere–asthenosphere step. Involvement of a deep slab in petrogenesis is also possible.

KEY POINTS

1. Eight seamounts form a line along the Norfolk Ridge.

2. Dating and geochemistry indicate the seamount line is not a hotspot track.

3. A rift-related origin, possibly with influence by subduction, is proposed.

Keywords:

• Southwest Pacific
• Zealandia
• Norfolk Ridge
• seamounts
• guyots
• volcanoes
• geochronology
• geochemistry
• Cenozoic

Acknowledgements

We thank the captain and crew of R/V l’Atalante and our onboard VESPA colleagues Claire Bassoulet, Méderic Amann, Nina Jordan, Charline Guérin, Caroline Juan, Mathieu Mengin, Mathilde Pitel, Clément Roussel and Fanny Soetaert. Hard work by all these people led to a successful VESPA voyage. Thin-sections were made by Ben Durrant and rock powders by John Simes. Kevin Faure is thanked for pre-submission comments on the manuscript. Useful comments on DR1A quartz microtextures were provided by Dave Craw and Dave Prior. The manuscript was improved by formal reviews from Marco Brenna and John Gamble.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

Supplemental data files that support the findings of this study are openly available in the SEANOE repository at https://doi.org/10.17882/75406. General information about the VESPA cruise can be found in the SISMER repository at http://doi.org/10.17600/15001100.

Additional information

Funding

The VESPA cruise (http://doi.org/10.17600/15001100) was funded by the Commission Nationale Flotte Hauturière of the French Ministry of Research and Higher Education, with support from the governments of New Zealand and New Caledonia. We acknowledge l’Institut National des Sciences de l’Univers, LabEx Mer and the New Zealand Ministry of Business, Innovation and Employment for post-cruise financial support.