Earth's evolving geodynamic regime recorded by titanium isotopes.

Earth's mantle has a two-layered structure, with the upper and lower mantle domains separated by a seismic discontinuity at about 660 km (refs. 1,2). The extent of mass transfer between these mantle domains throughout Earth's history is, however, poorly understood. Continental crust extraction results in Ti-stable isotopic fractionation, producing isotopically light melting residues3-7. Mantle recycling of these components can impart Ti isotope variability that is trackable in deep time. We report ultrahigh-precision 49Ti/47Ti ratios for chondrites, ancient terrestrial mantle-derived lavas ranging from 3.8 to 2.0 billion years ago (Ga) and modern ocean island basalts (OIBs). Our new Ti bulk silicate Earth (BSE) estimate based on chondrites is 0.052 ± 0.006‰ heavier than the modern upper mantle sampled by normal mid-ocean ridge basalts (N-MORBs). The 49Ti/47Ti ratio of Earth's upper mantle was chondritic before 3.5 Ga and evolved to a N-MORB-like composition between approximately 3.5 and 2.7 Ga, establishing that more continental crust was extracted during this epoch. The +0.052 ± 0.006‰ offset between BSE and N-MORBs requires that <30% of Earth's mantle equilibrated with recycled crustal material, implying limited mass exchange between the upper and lower mantle and, therefore, preservation of a primordial lower-mantle reservoir for most of Earth's geologic history. Modern OIBs record variable 49Ti/47Ti ratios ranging from chondritic to N-MORBs compositions, indicating continuing disruption of Earth's primordial mantle. Thus, modern-style plate tectonics with high mass transfer between the upper and lower mantle only represents a recent feature of Earth's history.

Deep roots for mid-ocean-ridge volcanoes revealed by plagioclase-hosted melt inclusions.

The global mid-ocean ridge system is the most extensive magmatic system on our planet and is the site of 75 per cent of Earth's volcanism1. The vertical extent of mid-ocean-ridge magmatic systems has been considered to be restricted: even at the ultraslow-spreading Gakkel mid-ocean ridge under the Arctic Ocean, where the lithosphere is thickest, crystallization depths of magmas that feed eruptions are thought to be less than nine kilometres2. These depths were determined using the volatile-element contents of melt inclusions, which are small volumes of magma that become trapped within crystallizing minerals. In studies of basaltic magmatic systems, olivine is the mineral of choice for this approach2-6. However, pressures derived from olivine-hosted melt inclusions are at odds with pressures derived from basalt major-element barometers7 and geophysical measurements of lithospheric thickness8. Here we present a comparative study of olivine- and plagioclase-hosted melt inclusions from the Gakkel mid-ocean ridge. We show that the volatile contents of plagioclase-hosted melt inclusions correspond to much higher crystallization pressures (with a mean value of 270 megapascals) than olivine-hosted melt inclusions (with a mean value of 145 megapascals). The highest recorded pressure that we find equates to a depth 16.4 kilometres below the seafloor. Such higher depths are consistent with both the thickness of the Gakkel mid-ocean ridge lithosphere and with pressures reconstructed from glass compositions. In contrast to previous studies using olivine-hosted melt inclusions, our results demonstrate that mid-ocean-ridge volcanoes may have magmatic roots deep in the lithospheric mantle, at least at ultraslow-spreading ridges.

Correction: Precise measurement of selenium isotopes by HG-MC-ICPMS using a 76-78 double-spike.

[This corrects the article DOI: 10.1039/C9JA00331B.].

Biomolecular evidence reveals mares and long-distance imported horses sacrificed by the last pagans in temperate Europe.

Horse sacrifice and deposition are enigmatic features of funerary rituals identified across prehistoric Europe that persisted in the eastern Baltic. Genetic and isotopic analysis of horses in Balt cemeteries [1st to 13th centuries CE (Common Era)] dismantle prevailing narratives that locally procured stallions were exclusively selected. Strontium isotope analysis provides direct evidence for long-distance (~300 to 1500 kilometers) maritime transport of Fennoscandian horses to the eastern Baltic in the Late Viking Age (11th to 13th centuries CE). Genetic analysis proves that horses of both sexes were sacrificed with 34% identified as mares. Results transform the understanding of selection criteria, disprove sex-based selection, and elevate prestige value as a more crucial factor. These findings also provide evidence that the continued interaction between pagans and their newly Christianized neighbors sustained the performance of funerary horse sacrifice until the medieval transition. We also present a reference 87Sr/86Sr isoscape for the southeastern Baltic, releasing the potential of future mobility studies in the region.

Diversity aboard a Tudor warship: investigating the origins of the Mary Rose crew using multi-isotope analysis.

The great Tudor warship, the Mary Rose, which sank tragically in the Solent in 1545 AD, presents a rare archaeological opportunity to research individuals for whom the precise timing and nature of death are known. A long-standing question surrounds the composition of the Tudor navy and whether the crew were largely British or had more diverse origins. This study takes a multi-isotope approach, combining strontium (87Sr/86Sr), oxygen (δ18O), sulfur (δ34S), carbon (δ13C) and nitrogen (δ15N) isotope analysis of dental samples to reconstruct the childhood diet and origins of eight of the Mary Rose crew. Forensic ancestry estimation was also employed on a subsample. Provenancing isotope data tentatively suggests as many as three of the crew may have originated from warmer, more southerly climates than Britain. Five have isotope values indicative of childhoods spent in western Britain, one of which had cranial morphology suggestive of African ancestry. The general trend of relatively high δ15N and low δ13C values suggests a broadly comparable diet to contemporaneous British and European communities. This multi-isotope approach and the nature of the archaeological context has allowed the reconstruction of the biographies of eight Tudor individuals to a higher resolution than is usually possible.

Global Fe-O isotope correlation reveals magmatic origin of Kiruna-type apatite-iron-oxide ores.

Kiruna-type apatite-iron-oxide ores are key iron sources for modern industry, yet their origin remains controversial. Diverse ore-forming processes have been discussed, comprising low-temperature hydrothermal processes versus a high-temperature origin from magma or magmatic fluids. We present an extensive set of new and combined iron and oxygen isotope data from magnetite of Kiruna-type ores from Sweden, Chile and Iran, and compare them with new global reference data from layered intrusions, active volcanic provinces, and established low-temperature and hydrothermal iron ores. We show that approximately 80% of the magnetite from the investigated Kiruna-type ores exhibit δ56Fe and δ18O ratios that overlap with the volcanic and plutonic reference materials (> 800 °C), whereas ~20%, mainly vein-hosted and disseminated magnetite, match the low-temperature reference samples (≤400 °C). Thus, Kiruna-type ores are dominantly magmatic in origin, but may contain late-stage hydrothermal magnetite populations that can locally overprint primary high-temperature magmatic signatures.

Isotopes and trace elements as natal origin markers of Helicoverpa armigera--an experimental model for biosecurity pests.

Protecting a nation's primary production sector and natural estate is heavily dependent on the ability to determine the risk presented by incursions of exotic insect species. Identifying the geographic origin of such biosecurity breaches can be crucial in determining this risk and directing the appropriate operational responses and eradication campaigns, as well as ascertaining incursion pathways. Reading natural abundance biogeochemical markers using mass spectrometry is a powerful tool for tracing ecological pathways as well as provenance determination of commercial products and items of forensic interest. However, application of these methods to trace insects has been underutilised to date and our understanding in this field is still in a phase of basic development. In addition, biogeochemical markers have never been considered in the atypical situation of a biosecurity incursion, where sample sizes are often small, and of unknown geographic origin and plant host. These constraints effectively confound the interpretation of the one or two isotope geo-location markers systems that are currently used, which are therefore unlikely to achieve the level of provenance resolution required in biosecurity interceptions. Here, a novel approach is taken to evaluate the potential for provenance resolution of insect samples through multiple biogeochemical markers. The international pest, Helicoverpa armigera, has been used as a model species to assess the validity of using naturally occurring δ2H, 87Sr/86Sr, 207Pb/206Pb and 208Pb/206Pb isotope ratios and trace element concentration signatures from single moth specimens for regional assignment to natal origin. None of the biogeochemical markers selected were individually able to separate moths from the different experimental regions (150-3000 km apart). Conversely, using multivariate analysis, the region of origin was correctly identified for approximately 75% of individual H. armigera samples. The geographic resolution demonstrated with this approach has considerable potential for biosecurity as well as other disciplines including forensics, ecology and pest management.