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Mystery of heat loss from Earth’s crust solved

Sunday, Jan 3, 2016,15:48 IST By Metrovaartha A A A

London | Scientists have solved the mystery of heat loss from the Earth’s crust by discovering a new type of hydrothermal vent system, an advance that may help interpreting the evidence for past global climates accurately.

The first discovery of the new type of hydrothermal vent system in a decade helps explain the long observed disconnect between the theoretical rate at which the Earth’s crust is cooling at seafloor spreading ridge flanks and actual observations, researchers said.

The finding was made by scientists at the National Oceanography Centre (NOC) and the University of Southampton in the UK using a combination of robot-subs and remotely operated vehicles.

This will really improve our understanding of how the Earth’s interior cools, Dr Bramley Murton, who supervised this research, said.

Theory has long predicted that there must be more cooling in certain locations on the Earth’s crust than we could account for using the known mechanisms and this new class of hydrothermal vent system may account for that difference, said Murton.

What makes these hydrothermal vent systems different is that the source of heat driving them comes from hot rock pushed towards the seabed by low angle faults, called tectonic spreading centres, rather than volcanic heat from magma chambers.

We expect this new type of vent system can be found in tectonic seafloor spreading sites across the globe. However, since they are almost invisible to the traditional ways of searching for hydrothermal vents, and the process driving them was not understood, they remained unaccounted for in scientific models of how heat and chemistry is transferred from inside the Earth’s crust, said Murton, who supervised this research by Matthew Hodgkinson, a PhD student from the University of Southampton.

This new class of venting was discovered at the Von Damm Vent Field in the Caribbean during an expedition. The team used sonar on the autonomous-sub, Autosub6000, to map the vent field before sending down a remotely operated vehicle (ROV) to collect samples of hydrothermal fluids and minerals.

Multi-beam sonar on this ROV was also used to produce a map with a resolution so high it could pick out individual pebbles on the sea floor. The investigation showed that minerals and chemistry at the Von Damm Vent site are very different to those from any other known vents.

As a result of the unusual chemistry of the vent fluids, the fifty metre tall mounds and chimneys are formed largely of a magnesium-rich mineral, talc, rather than the more usual iron and copper sulphides.

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