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Modelling the deep

Demonstrating hydrothermal fluid circulation in 3D

Research

By Kelly Foss

A Memorial doctoral student has created an empirical 3D model to demonstrate how hydrothermal fluid circulates beneath the seafloor.

Chris Galley, who is under the supervision of Drs. Colin Farquharson and John Jamieson in the Department of Earth Sciences, Faculty of Science, achieved the first-time feat.

“Many numerical models have been developed to predict the shape and behaviour of hydrothermal systems,” said Mr. Galley. “However, this study is the first to resolve an entire 3D convective cell upflow zone.”

Seafloor ‘chimneys’

Hydrothermal vents form on the seafloor when cold, dense seawater sinks into the seafloor and is drawn into the crust, where it is heated by magma.

As the hot water rises back up through the crust, it strips metals from the earth, permanently demagnetizing it. These metals are carried along the current and then deposited in the area around the vent.

Active vents resemble chimneys and are known as “black smokers.” They are also unique habitats that are home to organisms that don’t depend on sunlight for sustenance.

Side and front viewpoints of the hydrothermal upflow zone below the Tumai Ridge, in the East Manus Basin off Australia’s coast.
Photo: Submitted

Researchers have been trying to understand the vents as a system – how the rock, biology and fluids interact with each other – which is an important component of determining the potential environmental impacts of mining them.

Mr. Galley’s modelling technique gives researchers the ability to evaluate the connectivity between adjacent hydrothermal vents.

This provides a method to assess the potential effects of mining activities on neighbouring deposits, which is essential information for effective environmental management for mining operations.

Mr. Galley also hopes his 3D modelling could one day be used to determine the potential value of these deposits.

A map of the region of the seafloor (a) along with the magnetic data that was being modelled (b, c, d).
Photo: Submitted

“There have been studies into the average amount of minerals, such as copper or gold, in the seafloor crust,” he said. “By mapping it in 3D you can determine the volume of these deposits and use that estimate to calculate how valuable these deposits could be.”

Geometry and connectivity

Mr. Galley used inversion software developed at Memorial University to create his geophysical model.

The software uses magnetic field data collected in an underwater location near Papua New Guinea by Nautilus Minerals, a Canadian mineral exploration company and the first to commercially explore the seafloor for massive sulfide systems.

His original plan was to model one hydrothermal vent to get an idea of the thickness of the mineralization at that site. However, the company provided so much data, he was able to create a 3D model of the seafloor that was 48 kilometres by 24 kilometres.

Chris Galley’s findings were published in Science Advances last month.
Photo: Rich Blenkinsopp

Mr. Galley says the model allows them to determine the geometry and connectivity of a convection cell that supports multiple hydrothermal vent sites.

“We were able to confirm the long-held, but unverified hypothesis that circulation penetrates the seafloor down to the depths of the magmatic heat sources that drive circulation,” he said.

“Furthermore, we show for the first time that hydrothermal upflow branches before reaching the seafloor and that multiple vent fields can share a common subseafloor hydrothermal circulation cell.”

Mr. Galley’s findings were published in the American Association for the Advancement of Science’s Science Advances, a high impact, open access journal, in late October.


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