New study suggests Earth's mantle is more chemically uniform than previously thought

New study suggests Earth's mantle is more chemically uniform than previously thought
by Clarence Oxford
Los Angeles CA (SPX) Sep 20, 2024

Lavas from volcanic hotspots around the world, such as Hawaii, Samoa, and Iceland, likely come from a chemically uniform reservoir in Earth's mantle, according to new research published in 'Nature Geoscience'. The study challenges the long-standing belief that the mantle contains chemically distinct reservoirs.

The research suggests that Earth's mantle is more homogeneous than scientists had previously assumed. The differences in lava composition observed at the surface are likely due to interactions that occur as magma rises to the surface, rather than differences in the mantle itself.

"The discovery literally turns our view of hotspot lavas and the mantle upside down," said Dr. Matthijs Smit, associate professor and Canada Research Chair at the University of British Columbia's Department of Earth, Ocean and Atmospheric Sciences. "In a way, Earth's lavas are much like humankind itself - a beautifully diverse population with a common ancestor, which developed differently wherever it went."

Studying the mantle is challenging, as it cannot be directly sampled. Scientists must rely on geochemical analysis of lava that originates from the mantle and erupts at oceanic volcanoes. Until now, the variation in lava composition, along with assumptions about isotope consistency from source to surface, has led to the belief that the mantle consists of distinct chemical reservoirs. However, the observations made by Dr. Smit and co-author Dr. Kooijman of the Swedish Museum of Natural History suggest otherwise.

"By looking at a specific set of elements, we were able discern the chemical effects of various processes that act on magma melts on their way to the surface to discover that all hotspot lavas actually share the same starting composition," said Dr. Smit. "The lavas only come out differently because the magmas interact with different types of rocks as they ascend."

Earth's mantle, which accounts for 84% of the planet's volume, lies between the iron core and the surface crust. When magma from the mantle reaches the surface, it becomes lava. Understanding the mantle's composition is crucial for understanding Earth's formation, its tectonic activity, and the global cycle of elements.

The analysis also revealed a surprising link between oceanic hotspot lavas and basaltic lavas found on continents, including those containing diamond-bearing kimberlites. While these melts are geochemically distinct, they appear to have the same "ancestor" magma.

"The discovery is a game-changer when it comes to models for Earth's chemical evolution and how we look at global element cycles," added Dr. Smit. "Not only is the mantle much more homogeneous than previously thought, it likely also no longer contains 'primordial reservoirs' - entities that were once needed to explain the data, but could never really be reconciled with the concept of mantle convection."

"This model explains the observations in a simple way and permits a myriad of new hypotheses for global geochemical research going forward," added Dr. Kooijman.

Research Report:A common precursor for global hotspot lavas