Argon/Argon, micropaleontological and Uranium/Lead geochronological data for igneous and sedimentary rocks dredged during the VESPA scientific cruise
|Author(s)||Gans Phil B1, Mortimer Nick2, Patriat Martin3, Turnbull Rose E2, Crundwell Martin4, Agranier Arnaud3, Calvert Andrew5, Seward Gareth1, Etienne Samuel6, Durance Patricia Mj4, Campbell Hugh J4, Collot Julien6|
|Affiliation(s)||1 : University of California, Santa Barbara, CA, USA
2 : GNS Science, Dunedin, New Zealand
3 : Univ Brest, CNRS, Ifremer, Geo-Ocean, F-29280 Plouzané, France
4 : GNS Science, Lower Hutt, New Zealand
5 : U.S. Geological Survey, Menlo Park, CA, USA
6 : Service Géologique de Nouvelle Calédonie, Nouméa, New Caledonia
|Keyword(s)||Southwest Pacific, New Zealand, New Caledonia, Igneous rocks, Sedimentary rocks, Ar/Ar geochronology, U/Pb geochronology, Micropaleontology, Geochemistry, Volcanic arc, Subduction, Tectonics, Cretaceous, Eocene, Oligocene, Miocene|
Abstract: The 2015 VESPA voyage (Volcanic Evolution of South Pacific Arcs) was a seismic and rock dredging expedition to the Loyalty and Three Kings ridges and South Fiji Basin. In this paper we present 33 Ar/Ar, 23 micropaleontological and two U/Pb ages for igneous and sedimentary rocks from 33 dredge sites at 25-28°S in this previously little-studied part of the southwest Pacific Ocean. Igneous rocks include basalts, dolerites, basaltic andesites, trachyandesites and a granite. Successful Ar/Ar dating of altered and/or low-K basalts was achieved through careful sample selection and processing, detailed petrographic and element mapping of groundmass, and incremental heating experiments on both phenocryst and groundmass separates to interpret the complex spectra produced by samples having multiple K reservoirs. The Ar/Ar ages of most of the sampled lavas, irrespective of composition, are latest Oligocene to earliest Miocene (25-22 Ma), but two are Eocene (39-36 Ma). The granite has a U/Pb zircon age of 23.6±0.3 Ma. Ar/Ar lava ages based on dating are corroborated by microfossil ages and by detrital U/Pb zircon dating of a sandstone. In a southwest Pacific regional context, the VESPA lavas are part of a >4000 km long disrupted western belt of Eocene to Miocene subduction-related volcanic rocks. The belt includes arc rocks in Northland New Zealand, Northland Plateau, Three Kings Ridge, and Loyalty Ridge and, more speculatively, D’Entrecasteaux Ridge, West Torres Plateau and Rennell Ridge. This western belt is the product of superimposed Eocene and Oligocene-Miocene remnant volcanic arcs that were stranded along the edge of Zealandia as still-active arcs migrated east with the Pacific trench. The eastern belt of Eocene-Miocene volcanic arcs is more tectonically disrupted and less well-sampled than the western belt. Overall Eocene-Miocene SW Pacific arc development is explained in terms of west-dipping subduction and southward propagating tectonics.
Plain word summary: Samples of lava from the seabed between New Zealand and New Caledonia have been dated using atomic clocks and fossils. Most lavas erupted in a big pulse of volcanic activity between 25 and 22 million years ago. They are part of a >4000 km long belt of now-extinct undersea volcanoes that lie between New Zealand and the Solomon Islands, and which were related to early subduction of the Pacific Plate under the Australian Plate.