What is it about?
When continents rift apart to create a new ocean basin, sea-floor spreading starts to produce characteristic magnetic anomalies, which are useful for reconstructing the movements of Earth's tectonic plates. It has been less clear how this process occurs when the newly forming basin is flooded with sediments, as has been the case when salt (rocks formed by seawater evaporation) filled it, such as offshore Brazil or Gulf of Mexico. New oceanic crust is already known to exist along the centre of the Red Sea. In our new study, we find that spatial frequencies of magnetic anomalies at the centre are typical of normal oceanic spreading, but an abrupt change to lower frequencies occurs on crust about 5 million years and older. From seismic velocity and other data, we know that this is not the transition from continent to oceanic crust. We interpret it to be the point at which the spreading centre, previously buried under the salt, became exposed and began creating normal Vine-Matthews-Morley stripes.
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Why is it important?
Interpreting the continent to ocean transition is difficult at continental margins, requiring assessment of seismic velocity structure and magnetic anomalies. The interpretation is difficult to make fully objective and therefore the transitions in the literature tend to differ from each other. Our result adds another complication to interpreting magnetic anomalies.
Perspectives
The emergence of spreading centres at the so-called deeps in the Red Sea has been pondered on by researchers since the 1970s. Ron Girdler and Bob Whitmarsh, for example, envisaged the whole sea being oceanic, only recently becoming exposed as spreading has parted the salt sufficiently (figure below is from their 1974 DSDP article). We are now getting closer to understanding the continent to oceanic crustal transition (from analysing seismic velocities and magnetic anomalies together) and this transition in exposure of the spreading centres.
Dr Neil C. Mitchell
University of Manchester
Read the Original
This page is a summary of: How have thick evaporites affected early seafloor spreading magnetic anomalies in the Central Red Sea?, Geophysical Journal International, January 2022, Oxford University Press (OUP),
DOI: 10.1093/gji/ggac012.
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