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Southampton Marine and Maritime Institute

From the Mantle to Mountains – Just add Water

Published: 25 June 2021
Highly serpentinised mantle rocks
Highly serpentinised mantle rocks that form the uppermost heights of the Troodos mountains in Cyprus

The Troodos Mountains of Cyprus are iconic to geologists. It was here in the 50’s and 60’s that the great British geologist Ian Gass recognised that the particular suite of “ophiolite” rocks preserved in the Troodos mountains formed at an ocean spreading ridge and preserve on-land an ancient slice of ocean crust and upper mantle. These were key observations in the development of plate tectonic theory. Subsequently generations of Earth Science students, particularly from the UK, have inspected the rocks and sediments exposed in Cyprus as an essential pilgrimage during their geological training. However, to date, there has been no quantitative mechanistic explanation of why the deepest mantle rocks crop out at the top of the Troodos mountains, almost 2000m above sea level, while shallower forming rocks are exposed at progressively lower altitudes.

University of Southampton researchers have shown that the simple reaction between water and mantle rocks, known as serpentinization, can generate enough expansion and uplift to form high elevation mountains.  These water-mantle reactions alter the physical properties and chemistry of mantle minerals through the addition of water to their mineral structures. This results in a significant reduction in density and also an expansion of volume by up to 40%.  In response, gravitational equilibrium is restored by progressively uplifting the Earth’s surface - consequently forming high altitude mountains composed of partially to completely serpentinized mantle rocks.

Although such serpentinization-induced uplift has been qualitatively described, Southampton-led research has quantitatively modelled how these reaction between mantle rocks and water are capable of exclusively forming mountains of significant altitude.

University of Southampton SPITFIRE PhD student Aled Evans, who led this study said: “The importance of the Troodos ophiolite to our current understanding of ocean crust and processes that govern the architecture of 2/3 of the planet’s surface cannot be understated. Despite its great significance, the unique geometry that results in a ‘bulls-eye’ geological outcrop pattern with the deep mantle rocks at the top has to date remained poorly explained”.

Aled continued: “Our calculations show that the required amount of uplift to form the towering Mount Olympus may be generated solely from the reaction between mantle rocks and water. This also explains how serpentinization has caused differential uplift between the mantle rocks and the Troodos ocean crustal rocks, consequently producing the unique ‘bulls-eye’ geometry of the Troodos ophiolite.”

The team, including scientists from the University of Otago and the National Oceanography Centre, then applied their model to other settings both in the oceans and on land.

Aled said: “These calculations highlight that in each setting, serpentinization-induced uplift may be a significant contributor to the overall elevation. In some cases, the required uplift may be generated solely through serpentinization and in other cases it may be a minor contribution that in combination with tectonic uplift produces prominent exposures of mantle rocks across the planet’s surface.”

The Geological Survey Department of Cyprus are gratefully thanked for their support and assistance during this work. Funding for this research, which has been published in a special section of the Journal of Geophysical Research: Solid Earth was provided by a UKRI Natural Environmental Research Council (NERC) SPITFIRE-CASE PhD studentship award (CASE Partner – Natural History Museum).

Read the publication here.

Full reference:  Evans, A. D., Teagle, D. A. H., Craw, D., Henstock, T. J., & Falcon-Suarez, I. H. (2021). Uplift and exposure of serpentinized massifs: Modeling differential serpentinite diapirism and exhumation of the Troodos mantle sequence, Cyprus. Journal of Geophysical Research: Solid Earth, 126, e2020JB021079. https://doi. org/10.1029/2020JB021079

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