This synthesis benefited from discussions with colleagues working in Papua New Guinea over many years. In particular, I thank Geoff Abers, Ray Binns, Hugh Davies, Geoff Francis, June Hill, Wally Johnson, Rick Rogerson, and many others at the Geological Survey of Papua New Guinea for sharing their work and insights. Support from the U.S. NSF-ODP is greatly appreciated. Reviews by Hugh Davies, Adam Klaus, and Manuel Pubellier helped to improve the manuscript. SOEST contribution #4709.