Dyriw, Nicholas J1,2, Bryan, Scott E1, Richards, Simon W3, Parianos, John M2, Arculus, Richard J,4 Gust, David A1
1School of Earth and Atmospheric Sciences, Queensland University of Technology, Brisbane, Queensland, Australia, 2Nautilus Minerals Ltd (now Deep Sea Mining Finance Ltd), Brisbane, Queensland, Australia, 3Independent research geologist, Brisbane, Queensland, Australia, 4Research School or Earth Sciences, Australian National University, Canberra, Australian Capital Territory, Australia.
Backarc basins develop through a continuum of evolutionary phases. Surface morphology, magmatism and associated volcanism are key indicators of the various stages of development. The East Manus Basin, Papua New Guinea, is a young (<1Ma) rapidly rifting system on the eastern flank of the larger Manus Basin. Like many other backarc systems of the Southwest Pacific, numerous volcanic centers in the East Manus Basin are associated with active, Cu-Au mineralized hydrothermal systems known as seafloor massive sulfide deposits. However, not all the hydrothermal systems host significant Cu-Au mineralization and the link between the location of these seafloor massive sulfide deposits and the stages of basin evolution are unclear. Here we present the first morphotectonic description and interpretation of the East Manus Basin. Multi-resolution, multibeam echosounder seafloor data and derivatives were used in combination with the Benthic Terrain Modeler for ArcGIS to investigate seafloor characteristics, including volcano morphology and structural lineaments, and define three evolutionary phases for the East Manus Basin. Phase 1 is a period of incipient extension of existing arc crust. Phase 2 evolves to incipient crustal rifting and a transition to effusive volcanism. Phase 3 progresses to nascent organized half-graben system with axial volcanism. Intersecting rift-parallel and rift-oblique structures are important extension accommodation zones and, at the transition between Phase 1 to Phase 2, host the most significant Cu-Au seafloor massive sulfide system within the East Manus Basin. This relationship suggests the accommodation structures developed during early basin evolution may be critical to focus fluid and magma for seafloor massive sulfide formation. Furthermore, the morphotectonic features and relationships associated with modern backarc basin evolution will help to improve interpreting fossilized backarc systems around the world.
Nicholas is completing his PhD at the Queensland University of Technology (QUT). His fields of research include marine geoscience and magmatic-hydrothermal ore-forming systems. Before joining QUT, Nicholas worked as an exploration geologist for for 3 years offshore in the Southwest Pacific and in the Lachlan Fold Belt, NSW