Continental Extension in the western Woodlark Basin: P-T-t-D constraints from Normanby and Misima Islands

Syracuse University, Syracuse NY

Investigators

Abstract

The Woodlark Basin of southeastern Papua New Guinea is one of the world's most rapidly extending rifts and provides a natural laboratory to study how continental lithosphere ruptures during the transition from rifting to seafloor spreading. It is here that the active metamorphic core complexes of the D'Entrecasteaux Islands were first discovered (e.g.,Hill et al.,1992). These islands preserve some of the youngest, most rapidly exhumed metamorphic and igneous rocks known on Earth (Baldwin et al.,1993).The exhumed lower plates of the D'Entrecasteaux Island metamorphic core complexes provide a record of active continental extension and magmatism synchronous with the westward propagation of the Woodlark Basin seafloor spreading system. While the seafloor spreading history (e.g.,Taylor et al.,1999) and the transition from rifting to spreading in the vicinity of the Moresby Seamount (Taylor and Huchon, in review) is known, more onshore geologic research is required to fully understand the history and mechanisms of continental rifting in the Woodlark Basin. Rupturing of continental lithosphere imparts a thermal record of events that are preserved as isotopic variations within minerals. These events can be revealed using thermochronology, and when integrated with P-T-D constraints, can be used to determine the timing and rates of exhumation associated with continental extension and magmatism. The PI's propose to further investigate the relationship between continental rifting and seafloor spreading in the western Woodlark Basin by 1) documenting the P-T-t-D histories of rocks exposed on Normanby Island, the easternmost of the D'Entrecasteaux Islands, located west of the active rift tip, 2) documenting the P-T-t-D histories of rocks exposed on Misima Island, part of the southern rifted continental margin and 3) determining the age of eclogite facies metamorphism in the exhumed lower plates of the D'Entrecasteaux Islands core complexes. Results will be compared to previous P-T-t-D studies on the D'Entrecasteaux Islands and Moresby Seamount. Longitudinal and latitudinal variations (or lack thereof) in the timing of continental extension and magmatism will be interpreted in relation to the history of seafloor spreading in the Woodlark Basin and recently proposed models for the evolution of the region.