Carbon-trapping rocks demonstrate Earth鈥檚 natural ability to store carbon dioxide
Researchers have shed new light on how a unusual rock formation in Oman was created, which could reveal new details about the Earth鈥檚 ability to store carbon dioxide (CO2) for millions of years.
The study, led by Keele University, in collaboration with 51福利社 and University of Ottawa, looked at geological evidence from Oman to better understand processes that occur in subduction zones - where one of the Earth鈥檚 tectonic plates sinks beneath another due to the plates colliding together. Such zones are active around much of the Pacific 鈥淩ing of Fire鈥� today.
Subduction zones are key to the global carbon cycle because ocean sediments carried by the sinking plate contain large amounts of CO鈧�. Scientists have long debated what happens to this carbon after it sinks - some is transported deep into the Earth, while some returns to the atmosphere via volcanic eruptions.
Another possibility is that CO鈧� becomes trapped in rocks when carbon-rich fluids react with them, forming minerals known as carbonates, which lock the carbon away for millions of years. These reactions happen tens of kilometres underground, so are difficult to observe and study.
鈥淚n some parts of the world, sections of oceanic crust and upper mantle - known as ophiolites - have been pushed to the surface, allowing us to study them in detail. One of the best preserved examples is the Semail Ophiolite in Oman, which is estimated to have naturally sequestered over one billion tons of CO鈧�. Scientists have long debated exactly how these rocks formed, and more recently attention has turned toward their role as a long鈥憈erm natural reservoir for carbon.鈥�
To resolve this, the team analysed halogens - chlorine, bromine and iodine - which were present within individual mineral grains. These elements can leave a fingerprint of the fluid reactions and sources of carbon which formed the carbonate minerals.
Their results, published in , indicated that there were at least two separate events where CO鈧� reacted with the rocks. It found that most of the carbonate minerals formed from fluids that match those usually found in subduction zones.
They also calculated that over 90% of the CO鈧� in the sinking plate could have been channelled along the plate boundary fault into the shallow mantle and locked away, indicating that carbon sinks in subduction zones are not only real, but could play a significant role in the Earth鈥檚 carbon cycle, by offering a way to store huge amounts of CO鈧� for millions of years.
Lead author, Dr Elliot Carter, from the School of Life Sciences at Keel University said: 鈥淎s our climate warms there鈥檚 been increasing attention on these strange and enigmatic rocks and what they can tell us about how the Earth moves carbon around and how humans could store it in the future鈥�
鈥淶ooming into chemical differences between different microscopic crystals really gave us the key to unlock the story of these rocks鈥�
鈥淲e can now tell that rocks such as those in Oman likely form an important part of Earth鈥檚 long-term carbon cycle.鈥�
This research was published in the journal Nature Communications.
Full title: Carbonated mantle peridotites represent a hidden sink for subducted CO2
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