Origin of eclogite‐bearing, domed, layered metamorphic complexes (“core complexes”) in the D'entrecasteaux Islands, Papua New Guinea

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Abstract
Compositionally layered metamorphic rocks of the D'Entrecasteaux Islands, Papua New Guinea, are folded into domes and antiforms bounded by faults parallel to metamorphic layering and foliation. The structures are broadly similar to the metamorphic “core complexes” of western North America. Lenses of ultramafic rock lie on the bounding faults, and the same faults have served as loci for Quaternary andesitic volcanic activity. Metamorphic grade in the northern islands (Goodenough and Fergusson) is amphibolite facies, with pockets of eclogite (Fergusson Island only) and granulite, and is greenschist facies in the southern island (Normanby). In all three islands there is a characteristic tectonostratigraphic sequence (FMU sequence) from felsic metamorphic rocks at base, or internally, through mafic metamorphic rocks to ultramafic rocks at top, or externally. The association of metamorphic and ultramafic rocks apparently developed in a north dipping Paleogene subduction system and was exhumed to upper crustal level in the Oligocene‐‐Early Miocene, possibly by reversal of movement on faults in the former subduction system. Vigorous uplift and development of domes and antiforms in the Pliocene was triggered by westward propagation of the Woodlark Basin spreading ridge and was accompanied by rifting, rift‐related magmatism, rapid erosion, and deposition of coarse sediment in the adjacent Trobriand Basin.