Due to the rare occurrences of early Archaean deep mantle-sourced magmas, it is unclear whether compositional heterogeneity existed in the early Archaean deep mantle, and if it did, how and when this compositional heterogeneity formed. We discovered the oldest mantle plume-related ferropicrite (iron- and magnesium-rich lavas with enriched trace element patterns) on the Earth and associated ultramafic cumulates in Eastern Hebei of the North China Craton (Wang et al., 2019). In situ zircon U-Pb geochronological study on the ultramafic cumulates shows that the ferropicrites were formed in the Palaeoarchaean (3.45 Ga). The detailed geochemical study suggests that the ferropicrites have trace element patterns similar to present-day ocean island basalts (OIB), but are more enriched in iron relative to typical mantle plume-related picrites. The Palaeoarchaean ferropicrites were produced by mantle plume activities from the deep mantle. Their deep mantle source was enriched in iron and incompatible elements, suggesting that deep mantle heterogeneity was present in the Palaeoarchaean with a partial enrichment of iron and incompatible elements. This research reports the third case of confirmed oldest mantle plume activities with the other two cases of 3.5–3.46 Ga komatiites in South Africa and Australia and the oldest enriched plume remnants, and proves that deep mantle compositional heterogeneity existed in the Palaeoarchaean, most probably introduced by recycled crustal material.

Reference(s)

Wang, C, Song, S, Wei, C, Su, L., Allen, MB, Niu, Y, Li, X.-H. and Dong, J 2019, Palaeoarchaean deep mantle heterogeneity recorded by enriched plume remnants: Nature Geoscience, 12(8): 672-678.