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The University of Southampton
Ocean and Earth Science, National Oceanography Centre SouthamptonOur research

Formation and evolution of the ocean crust

Introduction

The accretion of new crust at the mid-ocean ridges is the foundation process of the plate tectonic cycle. This is the major mechanism for the transfer of heat and mass from Earth’s interior to the external envelopes of our planet. This geologically rapid process has re-surfaced more than 60% of our planet in the past 200 million years and the chemical exchanges with the oceans are a major control on seawater chemistry and global biogeochemical cycles, and form important metal deposits.

Magma generated by the partial melting of the mantle can be erupted on to the seafloor but mostly intruded into the ocean crust and cooled by vigorous hydrothermal systems that drive black smoker vents, seafloor massive sulphide deposits, and provide unique environments for chemosynthetic ecosystems. Hydrothermal exchange between ocean floor basalts and seawater probably occurs throughout the lifetime of the ocean crust until it is subducted back into the mantle at ocean trenches. Because of the vast expanse of the ocean ridge flanks some of the low temperature reactions that occur off axis are more important for many chemical cycles, than the higher temperature exchanges that result from magma-driven exchanges at the spreading ridges.

In the past decade or so there have been two major revolutions in our understanding of mid-ocean ridge processes. One is the role of faulting and tectonic processes at slow and ultra-slow spreading ridges that leads to the exposure by detachment fault of upper mantle peridotites to seawater and the consequent hydration, oxidation and carbonation reactions that occur during the transformation of dense, strong, anhydrous magnesium silicates to serpentinite, carbonates and iron oxides. A second revelation has been the ingress of seawater into the upper mantle beneath the ocean crust, via faults associated with the bending of the downgoing plate before subduction. Serpentinization reaction also appear to occur in this Bend Fault environment but the fluid pathways and extent of reaction between mantle rocks and seawater remains poorly quantified.

Research

At Southampton we are investigating the formation and evolution of the ocean crust from multiple avenues:

  • Scientific ocean drilling including the Superfast Campaign to Hole 1256D;
  • Long term projects to drill to the Mantle in fast spreading ocean crust;
  • Investigations of tectonic windows such as Hess Deep in the Eastern Pacific Ocean;
  • Studies of Ophiolites, ancient slices of ocean crust and upper mantle now exposed on land, such as the Troodos Massif, Samail Ophiolite of Oman, Macquarie Island, the Lizard in Cornwall, or the Dun Mountain Ophiolite Belt in New Zealand;
  • Quantification of the seawater-basalt chemical exchanges on the ocean ridge flanks and impacts on global biogeochemical cycles;
  • Better understanding of slow and ultraslow spreading ridges such as the Mid-Atlantic Ridge, the south West Indian Ridge, or the Cayman Trough.

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