Carbon exchange between the Earth’s interior and exterior exerts an important influence on the surface climate through geologic time and is vital for planetary habitability. The cratonic lithospheric mantle is an important reservoir in the Earth’s interior which stores vast amounts of carbon, thus, it is crucial to understand the release of CO2 from the lithospheric mantle once it underwent destruction and was thinned.
Cratons commonly retain tectonic and magmatic quiescence for billions of years. However, the eastern part of the North China Craton (NCC) is a reactivated craton and was strongly destructed in the early Cretaceous, with up to ~120 km of the lithospheric keel having been removed.
Research supervisor Sheng-Ao Liu, professor of China University of Geosciences, Beijing, said: Linking the craton destruction and CO2 degassing from lithospheric mantle can get a better understanding of the drivers of the early Cretaceous greenhouse climate episode”.
In addition to the primordial carbon in the lithospheric mantle from accretion and core-mantle differentiation processes, the team found high Ca/Al and low Ti/Eu and Mg isotopic composition (d26Mg) in early Cretaceous lamprophyres and mantle xenoliths from the North China Craton. These findings indicate that the cratonic lithospheric mantle contains a large amount of carbon from recycled surface carbonates.
As a first-order estimate, the total reservoir of carbon in the cratonic lithospheric mantle beneath the eastern was 1.04 × 108 Mt at least before cratonic destruction.
Raman analysis of bubble-bearing melt inclusions shows that primary magmas of the early Cretaceous basaltic rocks in the eastern North China Craton contain extremely high CO2 content of ~1.5 wt.% on average.
The C-rich lithospheric mantle could be readily fusible and become more oxidative due to the metasomatism caused by carbonatitic melts that have much lower viscosity and density compared to silicate melts. Therefore, the extensive thinning of lithospheric mantle keel of the eastern North China Craton could lead to extensive CO2 outgassing from the deep mantle.
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Linking deep CO2 outgassing to cratonic destruction
National Science Review
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