New Constraints on the Origin of the EM‐1 Component Revealed by the Measurement of the La‐Ce Isotope Systematics in Gough Island Lavas. (29th May 2019)

• Record Type: Journal Article
• Authors: Boyet, M.; Doucelance, R.; Israel, C.; Bonnand, P.; Auclair, D.; Suchorski, K.; Bosq, C.
• Is Part Of: Geochemistry, geophysics, geosystems. Volume 20:Number 5(2019)
• Page Start: 2484
• Page End: 2498
• Publication Date: 2019-05-29
• Subjects: Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 550.5
• DOI: 10.1029/2019GC008228
• Languages: English
• ISSNs: 1525-2027

Abstract

Abstract: Hot spot lavas show a large diversity of isotope compositions resulting from the recycling of surface material into the convective mantle. Amongst the mantle end‐members, EM‐1 (enriched mantle) is widely debated and scenarios involving either old pelagic sediments subducted into the deep mantle or subcontinental lithospheric material incorporated at shallow depths are commonly evoked. We selected 12 lavas from Gough Island (south Atlantic Ocean) for the measurement of 138 La‐ 138 Ce, 147 Sm‐ 143 Nd, and 176 Lu‐ 177 Hf isotope systems. Results show limited ranges for ε 143 Nd, ε 138 Ce, and ε 176 Hf values, and Ce/Ce* do not correlate with measured isotope ratios. Cerium isotope compositions allow us to exclude the contribution of old sedimentary material carrying a negative, elemental cerium anomaly in the mantle source. Pelagic sediments are indeed characterized by strongly negative, elemental cerium anomalies and also high La/Ce ratios. Modeling a primitive mantle source contaminated by 0.4% to 2.2% of different 2.5 Ga‐old pelagic components is able to reproduce the lowest Ce/Ce* values. However, the cerium isotope measurements show ε 138 Ce values between −0.39 and 0.15, too low to give support to the incorporation of recycled pelagic sediments in the mantle source of the lavas. Our results suggest that the incorporation of subcontinental lithospheric material at shallow depths during the plume ascent is a more suitable model to explain the formation of the EM‐1 component. Hafnium and Nd isotopes also support this scenario. Subcontinental lithosphere sampled via kimberlites and lamproites has isotopic compositions that plot generally below the mantle array, a signature that is also seen in Gough lavas. Key Points: Ce isotopes suggest that the enriched mantle EM‐1 sampled by the Gough Island lavas did not incorporate old subducted pelagic sediments Ce‐Nd‐Hf isotopes are more consistent with the contribution of subcontinental lithospheric material in the genesis of the EM‐1 component Low Ce/Ce* values measured in Gough Island lavas are not explained by the incorporation of pelagic sediments in the mantle source