A tale of two eras; Pliocene-Pleistocene unroofing of Cenozoic and late Archean zircons from active metamorphic core complexes, Solomon Sea, Papua New Guinea

U/Pb ion microprobe analyses of zircons from gneisses and granodiorites exposed in the D'Entrecasteaux Islands, and from conglomerate sections of the Goodenough No. 1 well in the adjacent Trobriand Basin, provide constraints on the age of magmatism, peak metamorphism, and nature of rocks unroofed during initial stages of metamorphic core complex formation in the Solomon Sea. The youngest populations of zircons from felsic gneisses and granodiorites indicate late Pliocene (super 206) Pb*/ (super 238) U ages. No inherited zircons were identified in the granodiorites, and the (super 206) Pb*/ (super 238) U ages (1.65+ or -0.18 Ma; 1.98+ or -0.08 Ma [2]) are interpreted as crystallization ages. These synkinematically emplaced granodiorites, intruded into actively extending continental crust, are some of the youngest known granitoids currently exposed at the Earth's surface. Zircon ages from felsic gneisses (2.63+ or -0.16 Ma; 2.72+ or -0.28 Ma [2]) are interpreted to date zircon growth subsequent to eclogite facies metamorphism. Felsic gneiss samples also contained zircon xenocrysts from Cretaceous-Miocene protoliths. In striking contrast, zircons from igneous and metamorphic clasts from the Goodenough No. 1 well indicate a single population with a (super 207) Pb*/ (super 206) Pb* age of 2781+ or -9 Ma (2). We speculate that they are derived from basement rocks unroofed during initial stages of development of the D'Entrecasteaux metamorphic core complexes. These results provide the first direct evidence for the existence of Archean protoliths in the basement rocks of southeastern Papua New Guinea.