Late Cenozoic volcanism and extension in eastern Papua

SUMMARY: The sea floor around eastern New Guinea is divided into a number of deep basins, separated by submarine ridges which are capped in places by islands of metamorphic, volcanic or coralline rock. The area has been subject o phases of extension since at least the Palaeocene, when the Coral Sea basin was formed. There have also been major compressive events, including the thrust emplacement of an ophiolite, the Papuan Ultramafic Belt, on to the Papuan Peninsula in the Oligocene. This peninsula, on the E of New Guinea, has been volcanically active from the Middle Miocene to the present day, and there have been eruptions on many of the surrounding islands and in the marine basins. Extension-related volcanic rocks include low-K tholeiites dredged from the floor of the Woodlark Basin and a peralkaline rhyolite association on islands near the E end of the peninsula. Volcanic rock types usually regarded as indicators of subduction, including andesites and high-K trachybasalts (shoshonites), are common. During the Neogene, two phases of extension with associated igneous activity can be interpreted; the first in the Middle and Late Miocene, and the second from the Middle Pliocene to the present day. Only in the first phase was the formation of marginal basin