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The combined Hf and Nd isotope evolution of the depleted mantle requires Hadean continental formation.

ABSTRACT: The onset and rates of continental growth are first-order indicators of early Earth dynamics, and whether substantial crust existed in the Hadean or much later has long been debated. Here, we present a theoretical analysis of published Hf and Nd isotopic data representing the depleted mantle and demonstrate that continental growth must have started in the early Hadean. Whereas the traditional interpretation of depleted mantle signatures in crustal rocks assumes unrealistic instantaneous mantle mixing, our modeling incorporates the effect of a finite mixing time over which these signatures are recorded in rocks produced through mantle melting. This effect is shown to delay, by as much as 0.65 to 0.75 billion years, the appearance of the earliest depleted mantle signatures in continental crust. Our results suggest that published observations of εHf, ε¹⁴³Nd, and μ¹⁴²Nd require Hadean growth of continental crust, with a minimum of 50% of today's continental volume already existing by the end of Hadean.

SUBMITTER: Guo M

PROVIDER: S-EPMC10038339 | biostudies-literature | 2023 Mar

REPOSITORIES: biostudies-literature

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The combined Hf and Nd isotope evolution of the depleted mantle requires Hadean continental formation.

Guo Meng M Korenaga Jun J

Science advances 20230324 12

The onset and rates of continental growth are first-order indicators of early Earth dynamics, and whether substantial crust existed in the Hadean or much later has long been debated. Here, we present a theoretical analysis of published Hf and Nd isotopic data representing the depleted mantle and demonstrate that continental growth must have started in the early Hadean. Whereas the traditional interpretation of depleted mantle signatures in crustal rocks assumes unrealistic instantaneous mantle m ...[more]

PMID: 36961892

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Project description:Quaternary rocks from the East and West Eifel volcanic fields in western Germany are a key suite of intraplate volcanic rocks that can provide insights into volcanism of the Central European Volcanic Province (CEVP) and into continental intraplate volcanism in general. We present a comprehensive dataset for Eifel lavas including isotope as well as major and trace element data for 59 samples covering representative compositions of the different volcanic fields. In line with previous studies, the lavas are all SiO2-undersaturated, alkaline-rich and mainly comprise primitive basanites, melilitites, and nephelinites (Mg# ≥ 57). Geochemical compositions of samples from both volcanic subfields display distinct differences in their trace-element as well as radiogenic isotope compositions, largely confirming previous subdivisions. Coupled trace-element and radiogenic Sr-Nd-Hf-Pb-Os isotope compositions can now provide firm evidence for spatially heterogeneous mantle sources and compositionally distinct magmatic pulses. Within the West Eifel Field, Sr-Nd-Pb isotope compositions of the younger (≤80 ka), ONB-suite (olivine-nephelinite-basanite) are similar to FOZO (FOcal ZOne) or the EAR (European Asthenospheric Reservoir) and resemble compositions that have been previously reported from plume-sourced ocean island basalts (OIB). In marked difference, older (700 Ma to 80 ka) volcanic rocks from the F-suite (Foidite) in the West Eifel field and from the entire east Eifel Field tap a more enriched mantle component, as illustrated by more radiogenic Sr isotope (86Sr/87Sr up to 0.705408) and variable Pb isotope compositions (206Pb/204Pb = 18.61-19.70, 207Pb/204Pb = 15.62-15.67 and 208Pb/204Pb = 38.89-39.76). Combined trace-element compositions of ONB-suite samples are in good agreement with results from batch melting models suggesting a hybrid composition of Eifel magmas formed through mixing 10% of a FOZO-like melt with 90% of a DMM-like melt, similar to melts from the Tertiary HEVF. However, radiogenic Sr-Nd-Pb isotope compositions of F-suite and EEVF and some ONB lavas require the admixture of melts from lithospheric mantle sources. Elevated Nb/Ta and Lu/Hf ratios in combination with variable 187Os/188Os ratios can now demonstrate the presence of residual carbonated eclogite components, either in the lithosphere or in the asthenospheric mantle. Finally, by combining geochemical and temporal constraints of Tertiary and Quaternary volcanism it becomes evident that CEVP volcanism in central and western Germany has resulted from compositionally distinct magmatic pulses that tap separate mantle sources. Although the presence of a mantle plume can neither be fully confirmed nor excluded, plume-like melt pulses which partially tap carbonated eclogite domains that interact to variable extents with the lithosphere provide a viable explanation for the temporal and compositional cyclicity of CEVP volcanism.Supplementary informationThe online version contains supplementary material available at 10.1007/s00410-024-02137-w.

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The combined Hf and Nd isotope evolution of the depleted mantle requires Hadean continental formation.

Publications

The combined Hf and Nd isotope evolution of the depleted mantle requires Hadean continental formation.

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