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 points1. 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.

Detailed 40Ar/39Ar Geochronology of the Loyalty and Three Kings Ridges Clarifies the Extent and Sequential Development of Eocene to Miocene Southwest Pacific Remnant Volcanic Arcs

“…A cursory inspection of all age spectra from groundmass separates of the dredge samples collected in this study (Supporting Information S6), as well as from our previous studies of southwest Pacific submarine lavas (e.g., Mortimer et al, 1998Mortimer et al, , 2007Mortimer et al, , 2021 reveals that they tend to fall into five distinct spectral types (Figure 4).…”

“…Importantly, the 1,000-1,500 m relief of the bathymetric walls of the CFZ allowed the expedition to acquire samples at different stratigraphic depths within the Loyalty and Three Kings Ridges. A total of 43 dredges were made on the voyage, nine on the Norfolk Ridge and 34 in the Loyalty Ridge-Three-Kings Ridge-Cook Fracture Zone area (Mortimer & Patriat, 2016;Mortimer et al, 2021; this paper; Figures 2 and 3). Map after Mortimer and Scott (2020); South Fiji Basin spreading ridge geometry from Herzer et al (2011) and MacLeod et al (2017).…”

“…RR, Rennell Ridge; WTP, West Torres Plateau; SCB, Santa Cruz Basin; SRR, South Rennell Ridge; NLB, North Loyalty Basin; CFZ, Cook Fracture Zone; NP, Northland Plateau; VMFZ, Vening Meinesz Fault Zone. Offshore data from this study andPelletier and Auzende (1996),Mortimer et al (1998Mortimer et al ( , 2007Mortimer et al ( , 2010Mortimer et al ( , 2014Mortimer et al ( , 2018Mortimer et al ( , 2021Mortimer et al ( , 2022,Ballance et al (1999), Herzer et al (2011), Meffre et al (2012,Seton et al (2016), andMacLeod et al (2017). Onland data fromGill and Whelan (1989),Rodda (1994),Hayward et al (2001),Paquette and Cluzel (2007),Stratford (2009),Shane et al (2010),Rickard and Williams (2013),Buys et al (2014), andMarien et al (2022).…”

“…In contrast, in onland New Caledonia post-obduction igneous activity is restricted to just two Oligocene granitoid stocks (Paquette & Cluzel, 2007;Sevin et al, 2020). Reconnaissance dredging and drilling has sampled scattered Eocene, Oligocene, and Miocene igneous rocks from the Rennell Ridge, D'Entrecasteaux Ridge and Basin, Norfolk Ridge and Basin, Three Kings Ridge, South Fiji Basin, and Northland Plateau (Mortimer et al, 1998(Mortimer et al, , 2007(Mortimer et al, , 2010(Mortimer et al, , 2014(Mortimer et al, , 2021. Most of these earlier sampling campaigns yielded predominantly latest Oligocene to early Miocene (24-19 Ma) ages.…”

New fossil discoveries illustrate the diversity of past terrestrial ecosystems in New Caledonia

“…Present fossil evidence does not rule out the possibility that some of the characteristic deep-branched lineages endemic to New Caledonia (e.g., Amborella) are relicts of earlier ecosystems (viz. those of Zealandia) that potentially survived obduction on neighbouring now-drowned islands, as suggested by geological studies 58,59 and biogeographic analyses based on fossil and present-day taxa 2,3,[60][61][62] . Nevertheless, assembly of the modern New Caledonian biota from the Oligocene to early Miocene is most consistent with the ages inferred by molecular dating for many extant clades 6 and the idea that much of the current biota was assembled via dispersal from elsewhere.…”