Nature of the Cuvier Abyssal Plain crust, offshore NW Australia

Abstract

Magnetic stripes have long been assumed to be indicative of oceanic crust. However, continental crust heavily intruded by magma can also record magnetic stripes. We re-evaluate the nature of the Cuvier Abyssal Plain (CAP), offshore NW Australia, which hosts magnetic stripes and has previously been defined as oceanic crust. We show that chemical data from a basalt within the CAP, previously described as an enriched mid-ocean ridge basalt, could equally be interpreted to contain evidence of contamination by continental material. We also recognize seaward-dipping reflector sequences in seismic reflection data across the CAP. Borehole data from overlying sedimentary rocks suggests that these seaward-dipping reflectors were emplaced in a shallow water (<200 m depth) or subaerial environment. Our results indicate that the CAP may not be unambiguous oceanic crust, but may instead consist of a spectrum of heavily intruded continental crust through to fully oceanic crust. If the CAP represents such a continent–ocean transition zone, then the adjacent unambiguous oceanic crust would be located >500 km further offshore NW Australia than currently thought. This would impact plate tectonic reconstructions, as well as heat flow and basin modelling studies. Our work also supports the growing consensus that magnetic stripes cannot, by themselves, be used to determine crustal affinity.Supplementary material: Enlarged and uninterpreted versions of the magnetic data and seismic reflection lines are available at https://doi.org/10.6084/m9.figshare.c.5332172