Late Miocene-Pliocene eclogite facies metamorphism, D'Entrecasteaux Islands, SE Papua New Guinea

The D'Entrecasteaux Islands of south-eastern Papua New Guinea are active metamorphic core complexes that formed within a region where the plate tectonic regime has transitioned from subduction to rifting. While rapid, post 4Myr exhumation and cooling of amphibolite and greenschist facies rocks that constitute the footwall of the crustal scale detachment fault system have been previously documented on Fergusson and Goodenough Islands of the D'Entrecasteaux chain, the timing of eclogite facies metamorphism in rocks of the footwall was unknown. Recent work revealed that at least one of the eclogite bodies formed during the Pliocene. We present combined in situ ion microprobe U-Pb age analyses of zircon from five variably retrogressed eclogite samples from Fergusson and Goodenough Islands that document Late Miocene-Pliocene (8-2Ma) eclogite formation on these islands. Textural relationships and zircon-garnet rare earth element partition coefficients indicate that U-Pb ages constrain zircon crystallization under eclogite facies conditions in all samples. Results suggest westward younging of eclogite facies metamorphism from Fergusson to Goodenough Island. Present-day exposure of Late Miocene-Pliocene eclogites requires exhumation rates >2.5 cm yr^-1.