A reappraisal of the Poya Terrane (New Caledonia): Accreted Late Cretaceous-Paleocene marginal basin upper crust, passive margin sediments and Early Eocene E-MORB sill complex.

摘要

AbstractThe Poya Terrane of New Caledonia is a composite lithotectonic unit made of i) Campanian-Paleocene E-MORB and BABB-type basalts and abyssal argillite (Poya Terrane Basalts); and ii) Coniacian-Santonian sandstone, turbidites and abyssal argillite (Kone Facies) intruded by Early Eocene E-MORB sills. Remapping reveals that the Kone Facies is more extensive than previously thought. Petrography and detrital zircons provenance show that Kone Facies sediments have the same provenance as coeval autochthonous sediments, albeit with more abundant contemporaneous zircons. They accumulated on the eastern continental slope of the Norfolk Ridge, and eventually mixed with abyssal argillite. Temporally, sill emplacement is related to subduction inception at ca. 56 Ma. We postulate that either: i) E-MORB intrusion was related to transcurrent thinning of the down going plate; or, ii) the “enriched” (off axis?) partial melt zone of the ancient ridge swept the lower plate, generating E-MORBs in the upper crust, and sills in passive margin sediments before it became extinct. Sliced marginal basin upper crust, and thereafter passive margin sediments and associated dolerites were obliquely accreted to the fore-arc, and partially subducted and recrystallized into the blueschist facies. The Poya Terrane was eventually thrust onto the Norfolk Ridge and its debris fed mid- to Late Eocene syntectonic basins. Meanwhile, mafic portions of the Poya Terrane were subducted and recrystallized into the eclogite facies, mixed with serpentinite to form the Pouebo mélange, and were exhumed in the fore-arc region. Finally, Late Oligocene faulting and hydrothermal events overprinted the NE part of the terrane.