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A Late Cretaceous-Eocene Geomagnetic Polarity Time Scale (MQSD20) that steadies spreading rates on multiple mid-ocean ridge flanks
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  • Alberto Malinverno,
  • Keegan W. Quigley,
  • Alice Staro,
  • Jérôme Dyment
Alberto Malinverno
Lamont-Doherty Earth Observatory of Columbia University

Corresponding Author:alberto@ldeo.columbia.edu

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Keegan W. Quigley
Brown University
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Alice Staro
Università Statale di Milano
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Jérôme Dyment
Institut de Physique du Globe de Paris & CNRS, Sorbonne Paris Cité
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Abstract

Magnetic anomalies over mid-ocean ridge flanks record the history of geomagnetic field reversals, and the width of magnetized crustal blocks can be combined with absolute dates to generate a Geomagnetic Polarity Time Scale (GPTS). We update here the current GPTS for the Late Cretaceous-Eocene (chrons C33-C13, ~84-33 Ma) by extending to several spreading centers the analysis that originally assumed smoothly varying spreading rates in the South Atlantic. We assembled magnetic anomaly tracks from the southern Pacific (23 ship tracks), the northern Pacific (35), the southern Atlantic (33), and the Indian Ocean (55). Tracks were projected onto plate tectonic flow line, and distances to magnetic polarity block boundaries were estimated by fitting measured magnetic anomalies with a Monte Carlo algorithm that iteratively changed block model distances and anomaly skewness angles. Distance data from each track were then assembled in summary sets of block model distances over 13 ridge flank regions. We obtained a final MQSD20 GPTS with another Monte Carlo algorithm that iteratively perturbs ages of polarity chron boundaries to minimize the variability of spreading rates over all ridge flanks and fit an up-to-date set of radioisotopic dates. The MQSD20 GPTS highlights a major plate motion change at ~47 Ma, when spreading rates decreased in the Indian Ocean as India collided with Eurasia while spreading rates increased in the South Atlantic and Northern Pacific and the Hawaii-Emperor seamount chain changed its orientation.
Aug 2020Published in Journal of Geophysical Research: Solid Earth volume 125 issue 8. 10.1029/2020JB020034