Lithosphere delamination with foundering of lower crust and mantle caused permanent subsidence of New Caledonia Trough and transient uplift of Lord Howe Rise during Eocene and Oligocene initiation of Tonga-Kermadec subduction, western Pacific

Abstract

We use seismic reflection and rock sample data to propose that the first‐order physiography of New Caledonia Trough and Norfolk Ridge formed in Eocene and Oligocene time and was associated with the onset of subduction and back‐arc spreading at the Australia‐Pacific plate boundary. Our tectonic model involves an initial Cretaceous rift that is strongly modified by Cenozoic subduction initiation. Hence, we are able to explain (1) complex sedimentary basins of inferred Mesozoic age; (2) a prominent unconformity and onlap surface of middle Eocene to early Miocene age at the base of flat‐lying sediments beneath the axis of New Caledonia Trough; (3) gently dipping, variable thickness, and locally deformed Late Cretaceous strata along the margins of the trough; (4) platform morphology and unconformities on either side of the trough that indicate a phase of late Eocene to early Miocene uplift to near sea level, followed by rapid Oligocene and Miocene subsidence of ∼1100–1800 m; and (5) seismic reflection facies tied to boreholes that suggest absolute tectonic subsidence at the southern end of New Caledonia Trough by 1800–2200 m since Eocene time. The Cenozoic part of the model involves delamination and subduction initiation followed by rapid foundering and rollback of the slab. This created a deep (>2 km) enclosed oceanic trough, ∼2000 km long and 200–300 km across, in Eocene and Oligocene time as the lower crust detached, with simultaneous uplift and local land development along basin flanks. Disruption of Late Cretaceous and Paleogene strata was minimal during this Cenozoic phase and involved only subtle tilting and local reverse faulting or folding. Basin formation was possible through the action of at least one detachment fault that allowed the lower crust to either be subducted into the mantle or exhumed eastward into Norfolk Basin. We suggest that delamination of the lithosphere, with possible mixing of the lower crust back into the mantle, is more widespread than previously thought and may be commonly associated with subduction initiation, such as Cenozoic events in the Mediterranean and western Pacific.

Future accreted terranes: a compilation of island arcs, oceanic plateaus, submarine ridges, seamounts, and continental fragments

“…7). Continental fragments and microcontinents are theorized to form as a result of plume interaction with passive margins (Müller et al, 2001;Gaina et al, 2003), localized thinning on the basins surrounding continental fragments (Peron-Pinvidic and Manatschal, 2010), differential thinning due to inherited structural grains from ancient sutures zones (Hitchen, 2004), or back-arc extension over a retreating slab (Schellart et al, 2006;Sutherland et al, 2010). Because continental fragments and microcontinents are formed during extensional processes, it is likely they are bound by deep crustal detachment faults and are thinned from normal faulting (Peron-Pinvidic and Reston, 2011).…”

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“…The peak of high-pressure metamorphism in northern New Caledonia was at 44 Ma, and exhumation was largely complete by 34 Ma (Baldwin et al, 2007). Seismic-stratigraphic evidence shows that the New Caledonia Trough either formed or was substantially modified during this event, though Cretaceous sedimentary basins beneath the trough escaped Cenozoic convergent deformation in most places (Collot et al, 2008;Sutherland et al, 2010). Regional deformation and emplacement of allochthons in northern New Zealand occurred later than in New Caledonia or the Norfolk Ridge system, with the onset of tectonic activity during the late Oligocene and early Miocene (~30-20 Ma) (Bache et al, 2012;Herzer, 1995;Herzer et al, 1997;Rait et al, 1991;Stagpoole and Nicol, 2008).…”

“…Ocean currents predicted by model simulations also could be substantially wrong if paleobathymetry is not depicted accurately (e.g., if parts of the Tasman Frontier were much shallower than today during the early Eocene). There are indications that large vertical movements in the Tasman Frontier occurred during the early Eocene (Baur et al, 2014;Sutherland et al, 2010).…”

“…We aimed to test the hypothesis that the proximal basin, the New Caledonia Trough, subsided >2 km during the Paleogene, even though it was only subjected to minor convergent deformation (Sutherland et al, 2010). Sites U1507 and U1509 were chosen to constrain the magnitude and timing of subsidence in relation to other events.…”

“…Ocean Drilling Program (ODP) Legs 181 and 189 further investigated the Eocene-Oligocene opening of the southern Tasman Sea gateway (Carter et al, 2004;Exon et al, 2004b). However, the significance of unconformities in the Tasman Sea has not, so far, included consideration of regional vertical tectonics or local faulting (Sutherland et al, 2010(Sutherland et al, , 2017. Records from the Tasman Sea may also offer insights into understanding Neogene paleoceanography across the Pacific and phenomena such as the late Miocene-early Pliocene biogenic bloom (Farrell et al, 1995;Grant and Dickens, 2002).…”