Deep mantle unveils a two-faced Earth
Research led by scientists in the Earth Dynamics Research Group has uncovered how rocks sourced from the Earth’s mantle are linked to the formation and breakup of supercontinents and super oceans over the past 700 million years, and suggests that the Earth is made up of two distinct ‘faces’ or domains.
Published in the prestigious journal of Nature Geoscience, the team examined the chemical and isotopic compositions of rocks sourced from the deep mantle in order to investigate how the Earth’s mantle responded to the movement of the tecontic plates, and subsequent subduction.
The Earth’s mantle is currently divided into two main domains, the African and Pacific, but little is known about their formation and history and they are commonly assumed to have the same chemical characteristics. Lead author of the research, Dr Luc-Serge Doucet, said:
“Our team used trace metals such as lead, strontium, and neodymium, from hotspot volcanic islands including the Hawaiian islands in the Pacific Ocean and the La Reunion island in the Indian Ocean, to examine whether these two domains have the same chemical ‘make-up’.
“We found that the African domain was ‘enriched’ by subducted continental materials, which was linked to the assembly and breakup of the supercontinent Pangaea, whereas no such feature was found in the Pacific domain.”
It was found that the compostions of the two mantle domains are not as similar as previously thought. Instead, the Earth appears to have two chemically distinct hemispheric ‘faces’, with the Pacific ring of fire being the surface expression of the boundary between the two.
In work reported earlier in the year, another research group created a wonderful ‘map’ of the deep mantle that clearly shows the foundations of each domain.
Co-author, John Curtin Distinguished Professor Zheng Xiang Li, and head of the Earth Dynamics Research Group, said:
“The two chemically distinct hemispheres discovered by the team can best be explained by the distinct evolutionary histories of the two mantle domains during the Rodinia to Pangaea supercontinent cycles.
“We found that the African mantle domain contains continental materials, which were brought down by the subduction system for at least the past 600 million years. However, the Pacific mantle domain has been protected from the infiltration of such materials.
“Our research findings are significant as they showcase a dynamic relationship between plate tectonic processes that operate near the surface and the formation and evolution of Earth’s deep mantle structures.
“The work helps us to understand what drives plate tectonics and the formation and reservation of global geotectonic features such as the Pacific ring of fire. The dynamic and interactive nature of the entire Earth system has important implications on the formation of Earth resources, the evolution of Earth environment, and even the evolution of life.”
Contact person: Dr Luc Doucet, Earth Dynamics Research Group, Curtin University.
Doucet, L.S., Li, Z.X., Gamal El Dien, H., Pourteau, A., Murphy, J.B., Collins, W.J., Mattielli, N., Olierook, H.K.H., Spencer, C.J., Mitchell, R.N., 2020. Distinct formation history for deep-mantle domains reflected in geochemical differences. Nature Geoscience 13, 511–515. https://doi.org/10.1038/s41561-020-0599-9
Read an excellent Nature Geoscience News & Views article by Richard W. Carlson related to this research.
Read the Curtin University Media Release: