Petrogenesis of volcanic rocks from the Quaternary Eifel volcanic fields, Germany: detailed insights from combined trace-element and Sr-Nd-Hf-Pb-Os isotope data.

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 Information: The online version contains supplementary material available at 10.1007/s00410-024-02137-w.

Long-term preservation of Hadean protocrust in Earth's mantle.

SignificanceDue to active plate tectonics, there are no direct rock archives covering the first ca. 500 million y of Earth's history. Therefore, insights into Hadean geodynamics rely on indirect observations from geochemistry. We present a high-precision 182W dataset for rocks from the Kaapvaal Craton, southern Africa, revealing the presence of Hadean protocrustal remnants in Earth's mantle. This has broad implications for geochemists, geophysicists, and modelers, as it bridges contrasting 182W isotope patterns in Archean and modern mantle-derived rocks. The data reveal the origin of seismically and isotopically anomalous domains in the deep mantle and also provide firm evidence for the operation of silicate differentiation processes during the first 60 million y of Earth's history.

Redox control on the tungsten isotope composition of seawater.

Free oxygen represents an essential basis for the evolution of complex life forms on a habitable Earth. The isotope composition of redox-sensitive trace elements such as tungsten (W) can possibly trace the earliest rise of oceanic oxygen in Earth's history. However, the impact of redox changes on the W isotope composition of seawater is still unknown. Here, we report highly variable W isotope compositions in the water column of a redox-stratified basin (δ186/184W between +0.347 and +0.810 ‰) that contrast with the homogenous W isotope composition of the open ocean (refined δ186/184W of +0.543 ± 0.046 ‰). Consistent with experimental studies, the preferential scavenging of isotopically light W by Mn-oxides increases the δ186/184W of surrounding seawater, whereas the redissolution of Mn-oxides causes decreasing seawater δ186/184W. Overall, the distinctly heavy stable W isotopic signature of open ocean seawater mirrors predominantly fully oxic conditions in modern oceans. We expect, however, that the redox evolution from anoxic to hypoxic and finally oxic marine conditions in early Earth's history would have continuously increased the seawater δ186/184W. Stable W isotope compositions of chemical sediments that potentially preserve changing seawater W isotope signatures might therefore reflect global changes in marine redox conditions.

Convective isolation of Hadean mantle reservoirs through Archean time.

Although Earth has a convecting mantle, ancient mantle reservoirs that formed within the first 100 Ma of Earth's history (Hadean Eon) appear to have been preserved through geologic time. Evidence for this is based on small anomalies of isotopes such as 182W, 142Nd, and 129Xe that are decay products of short-lived nuclide systems. Studies of such short-lived isotopes have typically focused on geological units with a limited age range and therefore only provide snapshots of regional mantle heterogeneities. Here we present a dataset for short-lived 182Hf-182W (half-life 9 Ma) in a comprehensive rock suite from the Pilbara Craton, Western Australia. The samples analyzed preserve a unique geological archive covering 800 Ma of Archean history. Pristine 182W signatures that directly reflect the W isotopic composition of parental sources are only preserved in unaltered mafic samples with near canonical W/Th (0.07 to 0.26). Early Paleoarchean, mafic igneous rocks from the East Pilbara Terrane display a uniform pristine µ182W excess of 12.6 ± 1.4 ppm. From ca 3.3Ga onward, the pristine 182W signatures progressively vanish and are only preserved in younger rocks of the craton that tap stabilized ancient lithosphere. Given that the anomalous 182W signature must have formed by ca 4.5 Ga, the mantle domain that was tapped by magmatism in the Pilbara Craton must have been convectively isolated for nearly 1.2 Ga. This finding puts lower bounds on timescale estimates for localized convective homogenization in early Earth's interior and on the widespread emergence of plate tectonics that are both important input parameters in many physical models.

Ruthenium isotope vestige of Earth's pre-late-veneer mantle preserved in Archaean rocks.

The accretion of volatile-rich material from the outer Solar System represents a crucial prerequisite for Earth to develop oceans and become a habitable planet1-4. However, the timing of this accretion remains controversial5-8. It has been proposed that volatile elements were added to Earth by the late accretion of a late veneer consisting of carbonaceous-chondrite-like material after core formation had ceased6,9,10. This view could not be reconciled with the ruthenium (Ru) isotope composition of carbonaceous chondrites5,11, which is distinct from that of the modern mantle12, or of any known meteorite group5. As a possible solution, Earth's pre-late-veneer mantle could already have contained a fraction of Ru that was not fully extracted by core formation13. The presence of such pre-late-veneer Ru can only be established if its isotope composition is distinct from that of the modern mantle. Here we report the first high-precision, mass-independent Ru isotope compositions for Eoarchaean ultramafic rocks from southwest Greenland, which display a relative 100Ru excess of 22 parts per million compared with the modern mantle value. This 100Ru excess indicates that the source of the Eoarchaean rocks already contained a substantial fraction of Ru before the accretion of the late veneer. By 3.7 billion years ago, the mantle beneath southwest Greenland had not yet fully equilibrated with late accreted material. Otherwise, no Ru isotopic difference relative to the modern mantle would be observed. If constraints from other highly siderophile elements besides Ru are also considered14, the composition of the modern mantle can only be reconciled if the late veneer contained substantial amounts of carbonaceous-chondrite-like materials with their characteristic 100Ru deficits. These data therefore relax previous constraints on the late veneer and are consistent with volatile-rich material from the outer Solar System being delivered to Earth during late accretion.

Earth's volatile element depletion pattern inherited from a carbonaceous chondrite-like source.

Earth's volatile element abundances (e.g., sulfur, zinc, indium and lead) provide constraints on fundamental processes such as planetary accretion, differentiation, and the delivery of volatile species, like water, which contributed to Earth becoming a habitable planet. The composition of the silicate Earth suggests chemical affinity but isotopic disparity to carbonaceous chondrites, meteorites that record the earliest element fractionations in the protoplanetary disk. However, the volatile element depletion pattern of the silicate Earth is obscured by core formation. Another key problem is the overabundance of indium, which could not be reconciled with any known chondrite group. Here we complement recently published volatile element abundances for carbonaceous chondrites with high precision sulfur, selenium, and tellurium data. We show that both Earth and carbonaceous chondrites exhibit a unique hockey stick volatile element depletion pattern where volatile elements with low condensation temperatures (750 - 500 K) are unfractionated from each other. This abundance plateau accounts for the apparent overabundance of indium in the silicate Earth without the need of exotic building materials or vaporization from precursors or during the Moon-forming impact and suggests the accretion of 10-15 % CI-like material before core formation ceased. Finally, more accurate estimates of volatile element abundances in the core and bulk Earth can now be provided.

La-Ce isotope measurements by multicollector-ICPMS.

The 138La-138Ce decay system (half-life 1.02 × 1011 years) is a potentially highly useful tool to unravel information about the timing of geological processes and about the interaction of geological reservoirs on earth, complementing information from the more popular 147Sm-143Nd and 176Lu-176Hf isotope systems. Previously published analytical protocols were limited to TIMS. Here we present for the first time an analytical protocol that employs MC-ICPMS, with an improved precision and sensitivity. To perform sufficiently accurate La-Ce measurements, an efficient ion-chromatographic procedure is required to separate Ce from the other rare earth elements (REE) and Ba quantitatively. This study presents an improved ion-chromatographic procedure that separates La and Ce from rock samples using a three-step column separation. After REE separation by cation exchange, Ce is separated employing an Ln Spec column and selective oxidation. In the last step, a cation clean-up chemistry is performed to remove all remaining interferences. Our MC-ICPMS measurement protocol includes all stable Ce isotopes (136Ce, 138Ce, 140Ce and 142Ce), by employing a 1010 ohm amplifier for the most abundant isotope 140Ce. An external reproducibility of ±0.25ε-units (2 r.s.d) has been routinely achieved for 138Ce measurements for as little as 150-600 ng Ce, depending on the sample-skimmer cone combinations being used. Because the traditionally used JMC-304 Ce reference material is not commercially available anymore, a new reference material was prepared from AMES laboratory Ce metal (Cologne-AMES). In order to compare the new material with the previously reported isotopic composition of AMES material prepared at Mainz (Mainz-AMES), Cologne-AMES and JMC-304 were measured relative to each other in the same analytical session, demonstrating isotope heterogeneity between the two AMES and different JMC-304 batches used in the literature. To enable sufficiently precise age correction of radiogenic 138Ce and to perform isochron dating, a protocol was developed where La and Ce concentrations are determined by isotope dilution (ID), using an isotope tracer enriched in 138La and 142Ce. The new protocols were applied to determine the variations of Ce isotope compositions and La-Ce concentrations of certified geochemical reference materials (CRMs): BCR-2, BCR-1, BHVO-2, JR-1, JA-2, JB-3, JG-1, JR-1, JB-1b, AGV-1 and one in-house La Palma standard.

Tracing copper derived from pig manure in calcareous soils and soil leachates by 65Cu labeling.

Copper is used as a growth promoter in animal husbandry, resulting in high Cu concentrations in animal manure. We tested whether Cu would be mobilized in soils receiving excessive loads of manure, both from recently added and from aged fractions. To discriminate between these Cu sources, manure was labeled with (65)Cu. After soil application of 0, 15, and 30 Mg manure ha(-1), leachate was collected in free-draining lysimeters (40 cm depth) under undisturbed soil over a 53 day period. Determining the total amounts of Cu and the fractions of (65)Cu in leachate and the soil profile enabled us to trace the translocation of Cu derived from labeled manure. More than 84% of the applied Cu was retained in the top 2 cm of soil. Less than 0.01% of the applied Cu was detected overall in the leachate. Of this amount, however, 38% (± 8.9 SE) was leached within 8 days after application. The total Cu concentration in leachates (32-164 µg L(-1)) frequently exceeded the Chinese groundwater quality standard of 50 µg L(-1). The added (65)Cu, however, accounted for less than 3.6% of the total Cu leaching load, suggesting that Cu from older sources and/or geological background controls contamination, regardless of current land management.

Evolution of planetary cores and the Earth-Moon system from Nb/Ta systematics.

It has been assumed that Nb and Ta are not fractionated during differentiation processes on terrestrial planets and that both elements are lithophile. High-precision measurements of Nb/Ta and Zr/Hf reveal that Nb is moderately siderophile at high pressures. Nb/Ta values in the bulk silicate Earth (14.0 +/- 0.3) and the Moon (17.0 +/- 0.8) are below the chondritic ratio of 19.9 +/- 0.6, in contrast to Mars and asteroids. The lunar Nb/Ta constrains the mass fraction of impactor material in the Moon to less than 65%. Moreover, the Moon-forming impact can be linked in time with the final core-mantle equilibration on Earth 4.533 billion years ago.