Clues to how fluids shape our planet
Fluids play a critical role in the evolution of the Earth’s crust, influencing processes such as the redistribution of elements that form valuable mineral resources and hydrocarbon deposits. Finding and responsibly exploiting such reserves depends on understanding how, when and where fluids flow from the scale of micrometres to kilometres. “Understanding the mechanisms behind the transport of material in the Earth’s continental crust is essential for our prosperity in Europe,” says FluidNET(opens in new window) initiator Jan Wijbrans from VU Amsterdam(opens in new window) in the Netherlands. “Geologists have been pointing this out for the past 20 years or so, and policymakers are now catching on.”
Fluids in understanding Earth processes
The FluidNET project, supported by the Marie Skłodowska-Curie Actions(opens in new window) programme, sought to strengthen Europe’s capabilities in this field through cutting-edge research and training. On the research side, a key objective was to promote the importance of fluids in understanding Earth processes. “Earth sciences have tended to be based on the study of solids such as rocks and minerals(opens in new window),” adds Wijbrans. “Without fluids however, the picture is not complete. Fluids for example have an impact on rock strength, and act as a catalyst for mineral reactions.” To advance this field, FluidNET brought together geoscientists who study interactions within crystals at the nano and microscale, with others who look at processes at the kilometre scale. The idea was that this combination of expertise could help address certain fundamental questions, such as whether certain fluid flows occur as a continuous trickle, or as a sudden burst.
Analysing metamorphic basement rocks
At the centre of answering such questions were 12 early-stage researchers (ESRs). Wijbrans worked closely with one ESR, who focused on veins within metamorphic basement rocks in the Pyrenees. Metamorphic basement rocks are older, crystalline rocks often found deep beneath sedimentary layers. “Much of this basement in the Pyrenees was formed towards the end of the Palaeozoic era (around 300 million years ago),” says Wijbrans. “We sampled veins from these rocks, where water collected and flowed, and analysed these in our lab.” In the lab, mineral fractions were purified at the micron scale. Fluids contained within crystals were found to contain dissolved potassium, which geologists can use to extract age data. The team was also able to ascertain that fluid flow through this rock occurred not in a continuous trickle, but in pulses. “We were able to date these pulses to occurring at 10 million-year intervals,” adds Wijbrans. “This discovery sheds new light on how certain minerals might be formed.”
Tectonic modelling and fluid pulse modelling
This particular story became even more interesting when the research was expanded to include tectonic movements. Around 80 million years ago, Iberia began to rotate away from the rest of Europe while Africa pushed north, forming the Pyrenees. This tectonic history converges with FluidNET’s fluid pulse modelling. “The timing of the fluid pulses through this rock may be the cause or the result – we are never quite sure in geology – of this convergence of Africa, Europe and Iberia,” explains Wijbrans. “For example, it could suggest that fluid flows weakened the rock at certain times, allowing tectonic motion to happen. Or conversely, tectonic stress caused by the approaching Iberian plate triggered fluid release as fault zones were reactivated.” A paper on this research is currently under review at the peer-reviewed journal ‘Tectonics’. “We really think we are onto something,” concludes Wijbrans.
