Thermochemical anomalies in the upper mantle control Gakkel Ridge accretion

John M O’Connor,Anthony A P Koppers,Mechita C Schmidt-Aursch,Daniel P Miggins,Wilfried Jokat,Peter J Michael

doi:10.1038/s41467-021-27058-1

Abstract

Despite progress in understanding seafloor accretion at ultraslow spreading ridges, the ultimate driving force is still unknown. Here we use 40Ar/39Ar isotopic dating of mid-ocean ridge basalts recovered at variable distances from the axis of the Gakkel Ridge to provide new constraints on the spatial and temporal distribution of volcanic eruptions at various sections of an ultraslow spreading ridge. Our age data show that magmatic-dominated sections of the Gakkel Ridge spread at a steady rate of ~11.1 ± 0.9 mm/yr whereas amagmatic sections have a more widely distributed melt supply yielding ambiguous spreading rate information. These variations in spreading rate and crustal accretion correlate with locations of hotter thermochemical anomalies in the asthenosphere beneath the ridge. We conclude therefore that seafloor generation in ultra-slow spreading centres broadly reflects the distribution of thermochemical anomalies in the upper mantle.

Highlights

Despite progress in understanding seafloor accretion at ultraslow spreading ridges, the ultimate driving force is still unknown
In 2001 a high-resolution mapping and rock sampling study of Gakkel Ridge was accomplished during the international AMORE ice-breaker cruise to the high Arctic and North Pole[1]
We have drawn on recent advances in high-resolution multi-collector mass spectrometry to measure 40Ar/39Ar isotopic dates for young low-potassium basalt samples dredged from the Gakkel Ridge during the AMORE cruises in 2001 (Fig. 1)

Summary

Introduction

Despite progress in understanding seafloor accretion at ultraslow spreading ridges, the ultimate driving force is still unknown. Our age data show that magmatic-dominated sections of the Gakkel Ridge spread at a steady rate of ~11.1 ± 0.9 mm/yr whereas amagmatic sections have a more widely distributed melt supply yielding ambiguous spreading rate information These variations in spreading rate and crustal accretion correlate with locations of hotter thermochemical anomalies in the asthenosphere beneath the ridge. In 2001 a high-resolution mapping and rock sampling study of Gakkel Ridge was accomplished during the international AMORE ice-breaker cruise to the high Arctic and North Pole[1] Before this expedition, it was predicted—based on extrapolations from slow- to fast-spreading ridges—that ultraslow spreading would produce sparse volcanism, thinner crust, and very little hydrothermal activity, and low extents of melting of the underlying mantle[1]. Barring any presence of these artefacts, modern global models of seafloor spreading rates such as NNR-MORVEL568 provide the best estimate of spreading rates along the Gakkel Ridge (Fig. 1)

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Conclusion