Iron formations as new geochemical archives for early Earth evolution

In a study published in the journal Nature Communication, Andrea Mundl-Petermeier and Sebastian Viehmann from the Department of Lithospheric Research at the University of Vienna demonstrated that a new geochemical archive – 182Tungsten in banded iron formations – can be used to simultaneously track the evolution of the Earth’s mantle and continents while throughout the history of the Earth. This provides new opportunities to better understand Precambrian Earth in the future.

In order to study how the Earth’s mantle developed at the beginning of the Earth period, the short-lived isotope system 182Hafnium-182Tungsten has already been given special attention: 182Tungsten indicates, among other things, at what point the Earth was exposed to intense meteor impacts near the end of its formation and how quickly the Earth’s mantle mixed and homogenized with these meteorite components throughout Earth’s history.

However, until now, magmatic rocks from different but very limited relics from ancient continents – for example, Australia or South Africa – had to be studied for these isotopes. Andrea Mundl-Petermeier and Sebastian Viehmann from the Department of Lithospheric Research at the University of Vienna and their colleagues from the University of Cologne and Jacobs University Bremen, have now discovered a new geochemical archive published in the journal Nature Communications: isotopic signatures of tungsten in banded iron formations (BIFs), which formed mainly in the Precambrian, i.e. between 3.8 billion and about 540 million years ago.

Evolution of the Earth’s mantle and continents

Using the 2.7 billion-year-old iron formation of the Temagami greenstone belt in Canada, the team was able to reconstruct that iron- and silica-rich layers deposited from seawater can simultaneously record the evolution of the Earth’s mantle and crust. Using state-of-the-art instruments from the GeoCosmoChronology group and Geoscience’s new central solid-state mass spectrometry (GeoIsotopes) facility at the Department of Lithospheric Research, the research team obtained high-precision isotopic measurements of individual layers clear quartz and black iron. .

“With the help of high-precision measurement methods, we were able to resolve small but distinct differences within 182W of individual layers,” says Andrea Mundl-Petermeier from the Lithospheric Research Department. The new approach now addresses long-standing questions about the evolution of the mantle and crust from a seawater perspective: banded iron ores are formed by chemical deposition from the ocean. “The BIFs studied in the Temagami region therefore directly represent the chemistry of seawater 2.7 billion years ago,” explains geologist Sebastian Viehmann: “We look at the Earth at this time from the point of view of the ocean.”

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Materials provided by University of Vienna. Note: Content may be edited for style and length.

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