We report the hydrogen (H) and nitrogen (N) elemental and isotopic compositions of the recently recovered CI chondrite Oued Chebeika 002 (OC 002) and compare them with published data for other CI meteorites and CI-like samples returned from the asteroids Ryugu and Bennu. When measured using the same protocol (vacuum degassing at 120 °C for 48 hr), OC 002 exhibits similar H concentrations but lighter isotopic compositions than other CIs and Bennu samples. Nitrogen data likewise indicate that the parent body of OC 002 accreted isotopically lighter nitrogen. Compilation of available data reveals pronounced H-N isotopic heterogeneities among CI-like materials, even when analysed under comparable conditions. These observations suggest that CI chondrites are intrinsically heterogeneous and that a single representative CI isotopic composition cannot be defined. This variability likely reflects the late accretion history of CIs and the incorporation of organic grains and ammonia ice that experienced diverse thermal histories in the protosolar disk. Such intrinsic heterogeneity strongly affects mass balance estimates of CI contributions to Earth’s surface volatiles, potentially varying by more than a factor of two depending on the CI reference used.

The geochemical signatures of nearly all Earth’s volcanic hotspots converge on a common isotopic composition, which is often termed the ‘focal zone’ (FOZO) and has been associated with a shared deep mantle source. Yet, unlike other characteristic geochemical components of hotspots, the origin and nature of FOZO remain unclear. Geochemical evidence has been invoked to support both an ancient and a relatively young age for FOZO, and long lived radiogenic isotopic data support many potential geochemical relationships between geographically disparate hotspots. We examine this issue using the short lived 146Sm-142Nd isotopic system, which can identify diverse geochemical origins in the Hadean Eon, more than four billion years ago. Two hotspots with strong geochemical affinity to FOZO, the Crozet and Juan Fernandez hotspots, have statistically distinct 142Nd compositions, meaning that despite the similarity in their long lived radiogenic isotopic compositions, they must reflect different Hadean-aged geological heritages. Detailed analysis of the isotopic compositions of global hotspots using machine learning further reveals that FOZO is most likely not singular but rather represents a spectrum of discrete domains that each have histories dating back to the first 10 % of Earth’s history.

Melt inclusions in olivine phenocrysts from high 3He/4He proto-Iceland plume (PIP) basalts from Baffin Island and West Greenland have elevated Br/Cl ratios, extending to values significantly above those found in mid-ocean ridge basalt (MORB) and ocean island basalt (OIB). Chlorine isotope compositions are indistinguishable from MORB-source mantle and high Br/Cl occurs in the absence of geochemical indicators for serpentinite, altered oceanic crust or sediment. The highest Br/Cl occurs in melt inclusions from basalts with the highest 3He/4He. The high Br/Cl ratios are at the high end of the range of putative Earth-source meteorites (CI- and CM-type carbonaceous chondrites). The PIP melt inclusion compositions are consistent with the addition of a small volume of halogen-rich, high Br/Cl chondritic material to halogen-depleted, low Br/Cl mantle.

In geochemistry and cosmochemistry, chondrites provide important reference values for comparison with planetary compositions. Employing isotope dilution, we report a comprehensive high precision data set for the refractory high field strength elements (HFSEs; W-Nb-Ta-Zr-Hf) and Sm-Nd-Lu-U-Th in different types of chondrites and in refractory inclusions, mainly from CV3 chondrites. Except for U, parent body processes and terrestrial alteration appear to have negligible effects. The CI chondrite data allow calculation of canonical trace element ratios such as Nb/Ta, Zr/Nb, Zr/Hf, Hf/W or Th/U at unprecedented precision and accuracy. Enstatite chondrites exhibit resolvably lower Hf/W and Zr/Hf than carbonaceous and ordinary chondrites. Ratios of Nb/Ta are uniform between all chondrite classes and groups, except for CV chondrites, where Nb/Ta is lowered by admixture of refractory inclusions that display systematic depletions of the slightly less refractory and more siderophile Nb. Regarding parent-daughter ratios of the Lu-Hf, Sm-Nd, Hf-W, and Nb-Zr radioactive decay systems, the variations in chondrites and their refractory components must have already been established in the solar nebula by selective processing of metal and silicate components and condensation processes during CAI formation.

Analyses of samples returned from asteroid Ryugu have revealed chemical, mineralogical, and isotopic similarities to Ivuna-type (CI) carbonaceous chondrites. Compared to other carbonaceous chondrites, CI chondrites are characterised by heavy isotope enrichments of the moderately volatile elements, but until now no study demonstrated that this is also the case for Ryugu. Here we show that Ryugu and CI chondrites have similar elemental and mass dependent isotope systematics of the moderately volatile elements Ge, Te, and Zn, which are distinct from those of all other carbonaceous chondrites. The mass independent (nucleosynthetic) Zn isotope signatures of Ryugu are also most similar to CI chondrites, although the difference to other carbonaceous chondrites is not well resolved. Our results reinforce the notion that Ryugu and CI chondrites formed from the same precursor materials, and indicate that any processes acting on these materials before or after parent body accretion were similar. Given their similar chemical composition to the Sun, Ryugu/CI chondrites likely record the solar system’s average chemical and mass dependent isotopic composition for moderately volatile elements.

The Himalayan-Tibetan orogenic belt hosts numerous world class porphyry copper deposits (PCDs), whose metal sources are controversial. Mercury isotopes display mass independent fractionation during photoreactions, producing positive Δ199Hg in marine sediments and negative Δ199Hg in terrestrial sediments. Here, we observe non-zero Δ199Hg (−0.29 to +0.21 ‰) in PCDs from the Himalayan-Tibetan orogenic belt. These values do not support the sole contribution of Hg from juvenile lower crustal rocks, which contain terrestrially derived Hg and display negative Δ199Hg (−0.20 to +0.01 ‰). The subcontinental lithospheric mantle (SCLM) with highly variable Δ199Hg (−0.54 to +0.25 ‰) can be another Hg source for PCDs. The positive and negative Δ199Hg values observed in PCDs and the SCLM suggest the contribution of Hg from both marine and terrestrial sediments. As the Himalayan-Tibetan orogenic belt underwent Neo-Tethys oceanic subduction followed by Indian-Eurasia continental collision, dual stage fertilisation of the SCLM via oceanic subduction and continental collision likely played an essential role in the generation of metal- and volatile-rich magmas and the associated large number of PCDs. This study offers key insights into the metal source of PCDs in the Himalayan-Tibetan orogenic belt.

The fate of boron (B) and its isotopes during serpentinite dehydration is a matter of debate. To contribute to a better understanding of the B isotopic fractionation upon serpentinite dehydration, we present in situ δ11B analyses of antigorite and olivine from subducted high pressure serpentinites from the Western Alps (Zermatt-Saas and Erro-Tobbio). The different isotopic compositions of antigorite in different parts of the units (δ11B of −5 to +10 ‰ and +13 to +19 ‰ for Zermatt-Saas, and δ11B of up to +26 ‰ for Erro-Tobbio) are inherited from variable serpentinisation conditions on the sea floor. Serpentinite dehydration via the brucite-out reaction during subduction produces metamorphic olivine in oxygen (O) isotopic equilibrium with antigorite. This olivine shows near zero B isotopic fractionation with coexisting antigorite (Δ11BOl-Atg of −0.7 ± 3.4 ‰), which implies little B isotopic fractionation during serpentinite dehydration. In contrast, significant B isotopic disequilibrium (Δ11BOl-Atg of +25 ‰) is found between antigorite and olivine formed in shear bands, shear zones and veins, indicating influx of channelled external fluids, including serpentinite-derived fluids from a protolith with a different isotopic composition.