Are magnetic stripes on the Cuvier Abyssal Plain (offshore NW Australia) diagnostic of oceanic crust?

Matthew T. Reeve, Craig Magee , Ian Bastow, Carl McDermott, Christopher Aiden-Lee Jackson , Rebecca E. Bell, Julie Prytulak

Magnetic stripes have long been used to define the presence and age of oceanic crust. However, continental crust heavily intruded by magma can record magnetic reversals akin to those observed in oceanic crust. 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 use magnetic, 2D seismic reflection, and geochemical data to test whether the CAP structure and composition is consistent with unambiguous oceanic crust. We show chemical data from a basalt within the CAP, previously described as displaying an enriched MORB-like signature, actually contains evidence of contamination by continental material. We also recognise seaward-dipping reflector (SDR) sequences across the CAP. Borehole data from overlying sedimentary rocks suggests these SDRs were emplaced in a shallow-water (<200 m depths) or sub-aerial environment. Our results indicate the CAP may not be unambiguous oceanic crust. Instead, we suggest the CAP could comprise a spectrum heavily intruded continental crust (akin to present-day Ethiopia) through to fully oceanic crust, recording the evolution from continental rifting to progressively magma-dominated, sub-aerial to shallow-water extension. Our work supports suggestions that magnetic reversals may not be truly diagnostic of oceanic crust.