Magnetic stripes preserved in the continent-ocean transition zone offshore NW Australia

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Authors

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

Abstract

Magnetic stripes have long been used to define oceanic crust and the onset of submarine sea-floor spreading. Identifying magnetic stripes is crucial for plate kinematic reconstructions, and for estimating spreading rates and timing of continental break-up: the most landward magnetic stripes are assumed to mark the oldest oceanic crust. However, continental crust heavily intruded by magma during active sub-aerial rifting in Ethiopia, records magnetic reversals akin to those observed in oceanic crust, implying magnetic stripes may not be diagnostic of seafloor spreading. Recent work on South Atlantic volcanic passive margins has identified linear magnetic anomalies within the continent-ocean transition zone (COTZ), which is presently overlain by seaward dipping reflector (SDR) sequences of stacked lavas. Perhaps surprisingly, magnetic stripes have rarely been observed in COTZ crust along passive margins elsewhere. We use magnetic, 2D seismic reflection, and geochemical data to examine the lithospheric structure of the Cuvier margin, offshore Northwest Australia, which hosts well-defined, ≤220 km long magnetic stripe anomalies M10N–M5. Although interpreted previously as oceanic crust, we suggest these magnetic stripes occur on a >500 km wide, Early Cretaceous COTZ. We suggest the magnetic anomalies record magnetic reversal signatures originating from sheeted dykes and gabbroic intrusions within the sub-SDR crust. Our interpretation implies the outer limit of Australia’s COTZ may thus be up to >500 km further oceanward than previously recognised. Furthermore, this work strengthens a growing consensus that magnetic reversals at rifted margins may not be truly diagnostic of the onset of oceanic crust formation.

DOI

https://doi.org/10.31223/osf.io/s8rjh

Subjects

Earth Sciences, Geology, Geophysics and Seismology, Other Earth Sciences, Physical Sciences and Mathematics, Tectonics and Structure

Keywords

Exmouth Plateau, rifting, Geodynamics, Continental Crust, lithosphere, continental breakup, igneous crust, magnetic stripes, northwest Australia, oceanic crust, SDR, SDRs, seaward dipping reflectors, transitional crust

Dates

Published: 2019-06-22 10:14

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License

CC BY Attribution 4.0 International

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