Late Miocene coesite-eclogite exhumed in the Woodlark Rift

Abstract

Late Miocene-Pliocene eclogites were exhumed in the Woodlark Rift of eastern Papua New Guinea, an actively extending region west of the Woodlark Basin seafl oor spreading center. We report the discovery of coesite in late Miocene eclogite from the lower plate of one of the D'Entrecasteaux Islands metamorphic core complexes within the Woodlark Rift. Zircon crys- tallization temperatures (650-675 °C) and 238 U/ 206 Pb age (ca. 8 Ma), and rutile thermometry (695-743 °C) combined with garnet-pyroxene thermometry (600-760 °C) and garnet-pyroxene- phengite barometry (18-27 kbar), indicate that the coesite-eclogite was exhumed from mantle depths (≥90 km) to the Earth's surface at plate tectonic rates (cm yr -1 ). This late Miocene coesite- eclogite is the youngest exhumed ultrahigh-pressure (UHP) rock on Earth, and its preservation ahead of the westward-propagating seafl oor spreading center forces reevaluation of models for UHP exhumation, as well as the geologic and tectonic evolution of the Woodlark Rift.