Subduction erosion: contributions of footwall and hanging wall to serpentinite mélange; field, geochemical and radiochronological evidence from the Eocene HP-LT belt of New Caledonia

• Published in: Australian journal of earth sciences 2021-01, Vol.68 (1), p.99-119
• Main Author: Cluzel, D.
• Format: Article
• Language: English
• Subjects: Abyssal zone; Basalt; Chert; Components; Earth Sciences; Eclogite; Eocene; Footwalls; forearc accretion; forearc basin; Forearc basins; Geochemistry; Hanging walls; High pressure; Isotopes; Lava; Limestone; Low temperature; mélange; Obduction; Oceanic crust; Passive margins; Peridotite; Sciences of the Universe; Sedimentary facies; Sedimentary rocks; Serpentinite; Slivers; Subduction; Subduction (geology); subduction erosion; Subduction zones; Tectonics; Turbidites
• ISSN: 0812-0099; 1440-0952
• DOI: 10.1080/08120099.2020.1761876

Slivers of mixed and metamorphosed ultramafic, mafic and sedimentary rocks crop out within the Eocene high pressure-low temperature metamorphic complex of northern New Caledonia. These units consist of: (1) slices of the serpentinite sole of Peridotite Nappe (upper plate), which characteristically contain fragmented supra-subduction dykes; (2) Intermediate Mélange units composed of elements of the serpentinite sole mixed with basalt and red chert clasts, and supra-subduction magmatic rocks that represent the interface of Peridotite Nappe and Poya Terrane (lower plate); and (3) the Pouébo Terrane, an eclogite-blueschist facies mélange, which crops out over 150 km along the northeast coast of the island. Intermediate Mélange units are transitional between shallowly accreted oceanic crust rocks of the Poya Terrane and the deeply subducted Pouébo Terrane. Their metamorphic grade is similar to that of the enclosing metasedimentary units of the Diahot Terrane and steeply increases northeastward. The composition of blocks in the Pouébo Mélange suggests that they come from: (1) subducted oceanic material (Poya Terrane Basalts, abyssal argillite/chert, passive margin sedimentary and magmatic components, terrigenous turbidites, limestone and dolerites) and (2) supra-subduction components (mantle wedge serpentinite, 55-52 Ma supra-subduction dykes, forearc basin), which characteristically refer to the lower plate and upper plate of the subduction/obduction system, respectively. KEY POINTS Metamorphosed serpentinite mélanges of New Caledonia contain elements from the footwall and the hanging wall of the subduction zone. Elements of the forearc crust and mantle formed immediately after subduction inception have been dragged into the subduction zone. Many blocks in the serpentinite mélange come from supra-subduction dykes that intruded the serpentinised hanging wall.