Timing of Eocene compressional plate failure during subduction initiation, northern Zealandia, southwestern Pacific

Abstract

SUMMARY Rapid onset of subduction tectonics across the western Pacific convergent margins in the early Eocene was followed by a slower phase of margin growth of the proto Tonga-Kermadec subduction system north of Zealandia during a middle Eocene phase to tectonic adjustment. We present new age constraints from International Ocean Discovery Program Expedition 371 borehole data on deformation events in northern Zealandian sediments that document the formation of the convergent margin boundary northwest of New Zealand. The deformation shows a shortening event that lasted up to 20 myr and acted over distances of ∼1000 km inboard of the evolving plate margin, just northwest of New Zealand. Multichannel seismic profiles tied to our new borehole sites show shortening occurred predominantly between 45 Ma and 35 Ma with some deformation related to slope failure continuing into the Oligocene. The termination of shortening is linked to opening of the backarc basins of the southwest Pacific and the migration of the Tonga-Kermadec Trench to the east which may have removed the structural evidence of the Eocene plate margin. Paleogene deformation observed inboard of the evolving proto Tonga-Kermadec subduction system indicates that the lithosphere of northern Zealandia, a region of thin continental crust, was strong enough to act as a stress guide. Compressive stresses that caused intra plate folding and faulting developed behind the initiating subduction system with the finite period of deformation indicating the time frame over which an active convergent margin lay along the northern margin of Zealandia.

The Norfolk Ridge: A Proximal Record of the Tonga‐Kermadec Subduction Initiation

“…Direct and compelling evidence for contractional deformation of unit NR1 (or equivalents to the north or south) is restricted to the northern (folds on Figures 7 and 8, this paper) and southern (Bache et al, 2012;Stratford et al, 2022) terminations of the main north-south section of Norfolk Ridge. This is consistent with Eocene deformation in New Caledonia (Bordenave et al, 2021;Maurizot, Bordenave, et al, 2020;Maurizot, Cluzel, Patriat, et al, 2020), and regional observations of TECTA deformation farther west, which are mostly south of the main section of Norfolk Ridge (Stratford et al, 2022;Sutherland et al, 2017), and in Reinga Basin (Orr et al, 2020). Convergent plate motion during the interval 45-25 Ma was substantial (>1,000 km) in the vicinity of Norfolk Ridge (Bache et al, 2012;Gurnis et al, 2004).…”

“…Late Cretaceous syn‐rift clastic deposits contain coal (e.g., Rakopi Formation) and post‐rift Cretaceous and Paleocene marine sediments (e.g., Kapuni Group) similar to those found in New Caledonia (King & Thrasher, 1996). Late Eocene (45–35 Ma) convergence resulted in folding of the northern Reinga Basin and an earlier phase (56–43 Ma) accompanied by adjacent subsidence in the NCT is recognized adjacent to the West Norfolk and Wanganella ridges (Bache et al., 2012; Herzer et al., 1997; Orr et al., 2020; Skinner & Sutherland, 2022; Stratford et al., 2022). Similar to New Caledonia, this Eocene convergence is thought to have resulted in local uplift and development of Eocene to Oligocene shelfal to shallow‐marine sandstones and limestones (e.g., Tekuiti Group) that rest unconformably on basement rocks (Barrett, 1967; Edbrooke et al., 1998).…”

“…The inference of rapid late Eocene to early Oligocene subduction initiation along the Norfolk Ridge is backed up by the timing of the succession of events at the scale of northern Zealandia. Indeed, the compressional events in the area south of Norfolk Ridge (e.g., Reinga Basin, southern NCT) are dated between 40 and 30 Ma (Bache et al, 2012;Etienne et al, 2018;Orr et al, 2020;Stratford et al, 2022;Sutherland et al, 2017) which overlaps with timing of compressional events in New Caledonia that are dated 45-35 Ma (Bordenave et al, 2021;Collot et al, 2008;Dallanave et al, 2020;Maurizot, Bordenave, et al, 2020). In contrast, the earliest signs of subduction initiation in New Caledonia are dated around 55 Ma (Cluzel et al, 2006(Cluzel et al, , 2012(Cluzel et al, , 2016 and it was not until 24-20 Ma that subduction initiated beneath the northern tip of New Zealand (Herzer, 1995;Rait, 2000;Rait et al, 1991).…”

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

“…Despite our efforts on the VESPA voyage to sample the lower part of fault scarps, dredge‐based sampling will always be biased to the youngest eruptive episodes, particularly given low erosion rates in submarine settings. The c. 40 Ma start of arc volcanism over the >3,000 km length of the western volcanic belt can be correlated with regional Eocene deformation which has been interpreted to record southwest‐dipping Pacific subduction initiation (Sutherland et al., 2017, 2020; Stratford et al., 2022; see also van de Lagemaat et al., 2022). The <40 Ma arc footprint of the western volcanic belt postdates 56–40 Ma events in New Caledonia including ophiolite sole amphibolite formation, dikes with arc chemistry and blueschist facies metamorphism (Maurizot, Cluzel, et al., 2020).…”

Absolute Paleolatitude of Northern Zealandia From the Middle Eocene to the Early Miocene

“…Sedimentary record from Exp. 371 gives important information about the tectonic and paleoenvironmental evolution for the Tasman area (Alegret et al., 2021; Stratford et al., 2022; Sutherland et al., 2022), and here we also use it to constrain the absolute paleoposition of northern Zealandia during the Cenozoic. Accurate paleogeography is essential for understanding past climate dynamics (e.g., Donnadieu et al., 2006), the paleogeographic distribution of fossils (e.g., Lam et al., 2018, 2021; Middlemiss, 1979), and the absolute positions of land and ocean to constrain paleoclimate models (Herold et al., 2008; Hollis et al., 2019; Lunt et al., 2017).…”