A drastic lower Miocene regolith evolution triggered by post obduction slab break-off and uplift in New Caledonia

Abstract

A lower Miocene coarse conglomerate that crops out in the Népoui Peninsula does not represent the base of the marine transgression that followed obduction in New Caledonia. Instead, the conglomeratic alluvial fan that contains peridotite cobbles and reworked weathering products records a short-lived episode of terrestrial erosion intercalated between two intervals of subsidence marked by marine carbonate deposition. Considering the Miocene sea level evolution reported in the literature, it is concluded that neither lower Miocene transgression nor erosion were driven by sea level variation. In contrast, a southeastward propagating slab tear that initiated at the latitude of the high pressure/low temperature metamorphic complex of northern New Caledonia likely generated east to west tilting of New Caledonia, subsidence along the West Coast and hence fringing reef development together with moderate erosion of older regolith. Coincidence between conglomerate deposition and hence prominent erosion that closely followed emplacement of postobduction granitoids influenced by a slab window suggests a genetic link. Therefore, it is concluded that short-lived lower Miocene erosion was due to slab breakoff and subsequent uplift that occurred at~22 Ma. Lower Miocene erosion profoundly dissected the Peridotite Nappe and in the northern half of New Caledonia only left isolated klippes along the West Coast.

Southwest Pacific Absolute Plate Kinematic Reconstruction Reveals Major Cenozoic Tonga‐Kermadec Slab Dragging

“…After the end of subduction at the New Caledonia Trench, all plate convergence must have been accommodated at the Tonga‐Kermadec Trench. Schellart () and Schellart et al () suggested a 30‐Ma age for subduction cessation at New Caledonia and a 25‐Ma age for final slab detachment (Sevin et al, ). This suggests that subduction at the Tonga‐Kermadec Trench started at earliest between 30 and 45 Ma.…”

“…Subduction along the New Caledonia Trench ended with final obduction of the New Caledonia ophiolite at around 30–25 Ma (Paquette & Cluzel, ). Slab break‐off is thought to have occurred around 25 Ma in the New Caledonia, Three Kings Ridge and Northland regions (Schellart, ; Schellart et al, ; Sevin et al, ). A 30‐Ma age for the end of New Caledonia subduction is incorporated in our model.…”

Deepwater Fold‐and‐Thrust Belt Along New Caledonia's Western Margin: Relation to Post‐obduction Vertical Motions

“…Onshore, these dips are interpreted to be the result of postobduction epeirogenic uplift motions (Chardon & Chevillotte, ; Chevillotte et al, ). Based on the altitude of the allochthonous sole and the geometry of the planation surfaces, the central part of New Caledonia is interpreted to be the place that underwent maximum postobduction uplift in New Caledonia (Chardon & Chevillotte, ; Sevin et al, ). We suggest that the dip of reflectors within PONC‐1 along the margin is a consequence of postobduction vertical motions.…”

“…Moreover, the juxtaposition of erosion and deposition of such dense eroded material on land and in the nearby basin led to an inversion of vertical motions over a short distance, with uplift on land and subsidence in the basin that resulted in progressive steepening of the margin (Moretti & Turcotte, ); see Figure , Step B. Tilting of the margin is illustrated as a short‐wavelength flexure in Figure , but a normal fault is an alternative interpretation. A late Miocene slab‐breakoff beneath the eastern margin of New Caledonia has also been suggested as being responsible for a short‐lived east to west tilting of Grande Terre (Cluzel et al, ; Sevin et al, ). This tilting could have partly contributed to slope steepening of the western margin of NC, but this model, notably the amplitude, lateral extent, and wavelength of deformation, remains poorly documented.…”

Morphology and distribution of dolines on ultramafic rocks from airborne LiDAR data: the case of southern Grande Terre in New Caledonia (SW Pacific)

“…Geology and geomorphology of the study area From a structural point of view, fracturing and related serpentinization of the Peridotite Nappe span a long period (c. 100 Ma) and correspond to general low temperature hydration and cooling of the mantle protolith. The following geodynamic events are involved in the fracturing of the Peridotite Nappe: (i) Late Cretaceous oceanic seafloor spreading of the South Loyalty Basin (SLB) (Cluzel et al, 2001); (ii) Palaeocene-Early Eocene convergence and subsequent Eocene subduction (Cluzel et al, 2006;Maurizot, 2011Maurizot, , 2013Maurizot and Cluzel, 2014); (iii) high-pressure/ low-temperature exhumation of the Norfolk Ridge and obduction of the SLB oceanic lithosphere over the Norfolk Ridge during the Late Eocene (Cluzel et al, 2001;Baldwin et al, 2007); (iv) post-obduction unroofing of the obducted ultramafic terrane related to isostatic re-equilibrium (Lagabrielle et al, 2005;Sevin et al, 2014); (v) arrival of the New Caledonia block in Vanuatu's east-dipping active subduction zone and its forebulge (Dubois et al, 1974).…”