Maria Schönbächler’s research while affiliated with Hochschule für Technik Zürich and other places

The short‐lived radionuclide system ¹⁴⁶Sm‐¹⁴²Nd can provide direct information about geological differentiation events in the terrestrial Hadean (>4.0 Ga) mantle. The spatiotemporal formation and evolution of crustal material that formed from different mantle domains can constrain the existing geodynamic environment in which continental crust formed and plate tectonics was initiated. The coupled 146,147Sm‐142,143Nd isotope systematics of contemporaneous felsic and mafic‐ultramafic igneous rock suites emplaced in the western Dharwar Craton (India) at ∼3.6 Ga record distinct Hadean mantle differentiation events in their source. The older mantle differentiation at 4.38−0.48+0.12 ${4.38}_{-0.48}^{+0.12}$ Ga ago is recorded in the felsic rock suites. The most primitive crustal representatives alone yield a differentiation age of 4.45−0.18+0.08 ${4.45}_{-0.18}^{+0.08}$ Ga. This early Hadean event is contemporaneous with the large silicate differentiation event recorded globally by Archean rocks. In contrast, the contemporaneous mafic‐ultramafic suites from the Dharwar Craton record a later mantle differentiation event at 4.15−0.13+0.07 ${4.15}_{-0.13}^{+0.07}$ Ga. Thus, distinct Hadean mantle differentiation events are preserved in coeval Archean felsic and mafic‐ultramafic igneous rock suites from a single location. The large spread in the isotope ratios in the differentiated felsic suites of the craton is likely related to the mixing of differentiated precursor material with other reservoirs prior to the formation of the first continental crust. The juxtaposition of coeval felsic and mafic crusts, each ultimately derived from mantle domains that evolved spatially and chemically separately for up to 1.1 Ga, implies the onset of lateral movement of lithospheric plates by ∼3.6 Ga.

Industrial activities of a silk dyeing factory in Thalwil, on the shore of Lake Zurich, Switzerland, caused extreme Sn contamination of lake sediments. In this study, we determine the contamination source, spread, and age using a multiproxy approach. We used X-ray fluorescence spectroscopy (XRF) core scanning and further geochemical analyses to assess the contamination spreading and thickness in the sedimentary column. We found elevated Sn levels throughout sediments of Lake Zurich, ranging from 177 $\hbox {g} \,\hbox {kg}^{-1}$ in front of the former silk factory to 0.05 $\hbox {g} \,\hbox {kg}^{-1}$ at the southeast end (background: ca. 0.006 $\hbox {g}\, \hbox {kg}^{-1}$). The rapid concentration drop away from the shore suggests quick precipitation of a sparingly soluble inorganic Sn compound, which is confirmed by Scanning Electron Microscope Imaging in tandem with Energy-dispersive XRF spectroscopy (SEM-EDX) data. The Sn XRF profile of a varved core indicates a contamination onset in the early 1890s, a maximum around 1900, and a gradual decrease to low levels in the 1940s. High Sn concentrations in turbidite layers from the deep basin indicate that mass movements physically remobilised Sn. However, in stable conditions, in-situ porewater measurements (conc. < 0.5 \upmu \hbox {g}\, \hbox {L}^{-1}) using dialyse plates show little Sn remobilisation into the lake water (0.05 $\hbox {mg} \,\hbox {a}^{-1} \,\hbox {m}^{-2}$). The low remobilisation, reducing conditions, and high sulphide contents in the contaminated layers suggest that Sn is firmly bound to the sediments. Combined with the low toxicity of Sn, we conclude that the Sn contamination poses no threat to lake biota or drinking water production. Supplementary Information The online version contains supplementary material available at 10.1186/s00015-024-00471-6.

The origin of volatile depletion in the solar system remains a topic of intense debate. To further inform our understanding of the mechanisms involved, this study characterized the mass-dependent Zn, Cd, and Te isotope compositions and concentrations of a comprehensive suite of carbonaceous chondrites (CCs). In accord with previous studies, Zn and Te display covariations between light isotope enrichments and elemental depletions. Observed here for the first time, Cd shows a similar trend. These correlations are consistent with the interpretation that the primary volatile element budgets of CCs were established by mixing of a volatile-rich CI-like matrix and a volatile-depleted non-matrix endmember (NME) in the solar nebula. All three elements display minor isotopic variations in CI and CM chondrites, as a consequence of aqueous alteration at low temperatures. In contrast, Cd and Te isotope compositions and concentrations are highly variable in CV and CO (Cd) and CK chondrites (Te). This reflects mobilization of the elements during thermal metamorphism at distinct redox conditions. The data of this study show that the NME has Zn, Cd, and Te concentrations that are depleted to an identical level of 0.12 ± 0.03 × CI chondrites, and it is characterized by mass-dependent isotope compositions for all three elements that are fractionated to light isotope values relative to CIs by a similar extent. In conjunction with literature data, this suggests that the concentrations and isotope compositions of NME volatiles record the same depletion processes, and that the NME volatile inventory is likely hosted predominantly in chondrules.

Nucleosynthetic isotope variations are powerful tracers to determine genetic relationships between meteorites and planetary bodies. They can help to link material collected by space missions to known meteorite groups. The Hayabusa 2 mission returned samples from the Cb‐type asteroid (162173) Ryugu. The mineralogical, chemical, and isotopic characteristics of these samples show strong similarities to carbonaceous chondrites and in particular CI chondrites. The nucleosynthetic isotope compositions of Ryugu overlap with CI chondrites for several elements (e.g., Cr, Ti, Fe, and Zn). In contrast to these isotopes, which are of predominately supernovae origin, s ‐process variations in Mo isotope data are similar to those of carbonaceous chondrites, but even more s‐ process depleted. To further constrain the origin of this depletion and test whether this signature is also present for other s ‐process elements, we report Zr isotope compositions for three bulk Ryugu samples (A0106, A0106‐A0107, C0108) collected from the Hayabusa 2 mission. The data are complemented with that of terrestrial rock reference materials, eucrites, and carbonaceous chondrites. The Ryugu samples are characterized by distinct ⁹⁶ Zr enrichment relative to Earth, indicative of a s ‐process depletion. Such depletion is also observed for carbonaceous chondrites and eucrites, in line with previous Zr isotope work, but it is more extreme in Ryugu, as observed for Mo isotopes. Since s ‐process Zr and Mo are coupled in mainstream SiC grains, these distinct s‐ process variations might be due to SiC grain depletion in the analyzed materials, potentially caused by incomplete sample digestion, because the Ryugu samples were dissolved on a hotplate only to avoid high blank levels for other elements (e.g., Cr). However, local depletion of SiC grains cannot be excluded. An alternative, equally possible scenario is that aqueous alteration redistributed anomalous, s ‐process‐depleted, Zr on a local scale, for example, into Ca‐phosphates or phyllosilicates.

This study presents a new procedure for high-precision Sm isotope analysis by thermal ionisation mass spectrometry (TIMS) for geological samples. A four-step chemical separation scheme results in sharp separation of Sm and Nd from the same sample aliquot. The first step utilises anion exchange resin to remove Fe from the sample solution. Two different liquid–liquid extraction resins are then used to isolate rare-earth elements (TRU-Spec) and purify Sm from Nd (DGA). Fractionation occurs on the DGA resin due to the nuclear field shift effect, but this is negligible if yields greater than 70% are achieved. Different analytical setups were tested to ascertain their ionisation efficiencies on TIMS. The effect of activators composed of Pt and Ta was tested on single Re filaments but the conventional double Re filament assembly provided efficient ionisation and more stable ion beams. The determination of nucleosynthetic isotope variations requires high precision for all Sm isotope ratios. We aimed to improve the precision on the scarce ¹⁴⁴Sm isotope (3% of all Sm). Static, multistatic and dynamic methods were tested. Isotope ratios were normalised to both ¹⁴⁷Sm/¹⁵²Sm and ¹⁵²Sm/¹⁴⁸Sm for comparison. The dynamic methods failed to provide better precision on ratios involving ¹⁴⁴Sm, whereas the multistatic method yielded improved precisions between 13 and 22 ppm (twice the standard deviation, 2 SD) on the ¹⁴⁴Sm/¹⁵²Sm ratio. Synthetic standards have variable Sm isotope compositions, thus requiring systematic and precise characterisation against terrestrial samples. Analyses conducted using this new procedure yielded high-precision values which were consistent with literature data for an array of terrestrial rock standards and the meteorite Allende.

We provide an overview of the isotopic signatures of presolar supernova grains, specifically focusing on ⁴⁴Ti-containing grains with robustly inferred supernova origins and their implications for nucleosynthesis and mixing mechanisms in supernovae. Recent technique advancements have enabled the differentiation between radiogenic (from ⁴⁴Ti decay) and nonradiogenic ⁴⁴Ca excesses in presolar grains, made possible by enhanced spatial resolution of Ca-Ti isotope analyses with the Cameca NanoSIMS (Nano-scale Secondary Ion Mass Spectrometer) instrument. Within the context of presolar supernova grain data, we discuss (i) the production of ⁴⁴Ti in supernovae and the impact of interstellar medium heterogeneities on the galactic chemical evolution of ⁴⁴Ca/⁴⁰Ca, (ii) the nucleosynthesis processes of neutron bursts and explosive H-burning in Type II supernovae, and (iii) challenges in identifying the progenitor supernovae for ⁵⁴Cr-rich presolar nanospinel grains. Drawing on constraints and insights derived from presolar supernova grain data, we also provide an overview of our current understanding of the roles played by various supernova types – including Type II, Type Ia, and electron capture supernovae – in accounting for the diverse array of nucleosynthetic isotopic variations identified in bulk meteorites and meteoritic components. We briefly overview the potential mechanisms that have been proposed to explain these nucleosynthetic variations by describing the transport and distribution of presolar dust carriers in the protoplanetary disk. We highlight existing controversies in the interpretation of presolar grain data and meteoritic nucleosynthetic isotopic variations, while also outlining potential directions for future research.

We provide an overview of the isotopic signatures of presolar supernova grains, specifically focusing on 44Ti-containing grains with robustly inferred supernova origins and their implications for nucleosynthesis and mixing mechanisms in supernovae. Recent technique advancements have enabled the differentiation between radiogenic (from 44Ti decay) and nonradiogenic 44Ca excesses in presolar grains, made possible by enhanced spatial resolution of Ca-Ti isotope analyses with the Cameca NanoSIMS (Nano-scale Secondary Ion Mass Spectrometer) instrument. Within the context of presolar supernova grain data, we discuss (i) the production of 44Ti in supernovae and the impact of interstellar medium heterogeneities on the galactic chemical evolution of 44Ca/40Ca, (ii) the nucleosynthesis processes of neutron bursts and explosive H-burning in Type II supernovae, and (iii) challenges in identifying the progenitor supernovae for 54Cr-rich presolar nanospinel grains. Drawing on constraints and insights derived from presolar supernova grain data, we also provide an overview of our current understanding of the roles played by various supernova types - including Type II, Type Ia, and electron capture supernovae - in accounting for the diverse array of nucleosynthetic isotopic variations identified in bulk meteorites and meteoritic components. We briefly overview the potential mechanisms that have been proposed to explain these nucleosynthetic variations by describing the transport and distribution of presolar dust carriers in the protoplanetary disk. We highlight existing controversies in the interpretation of presolar grain data and meteoritic nucleosynthetic isotopic variations, while also outlining potential directions for future research.

The isotopic compositions of samples returned from Cb-type asteroid Ryugu and Ivuna-type (CI) chondrites are distinct from other carbonaceous chondrites, which has led to the suggestion that Ryugu and CI chondrites formed in a different region of the accretion disk, possibly around the orbits of Uranus and Neptune. We show that, like for Fe, Ryugu and CI chondrites also have indistinguishable Ni isotope anomalies, which differ from those of other carbonaceous chondrites. We propose that this unique Fe and Ni isotopic composition reflects different accretion efficiencies of small FeNi metal grains among the carbonaceous chondrite parent bodies. The CI chondrites incorporated these grains more efficiently, possibly because they formed at the end of the disk's lifetime, when planetesimal formation was also triggered by photoevaporation of the disk. Isotopic variations among carbonaceous chondrites may thus reflect fractionation of distinct dust components from a common reservoir, implying CI chondrites and Ryugu may have formed in the same region of the accretion disk as other carbonaceous chondrites.

The unresolved question of when modern tectonic processes arose on Earth has restricted our understanding of how and how quickly Earth reached its present, habitable form. Plate tectonics, and in particular deep subduction, is central to many facets of habitability: it controls heat flow, biogeochemical cycling, and creates a variety of marine and terrestrial biomes that are crucial for biological evolution. Many petrological, geodynamical, and geochemical perspectives have offered circumstantial evidence for both an early onset of plate tectonics, in the first 10% of Earth’s history, or a late onset after the great oxidation event (2.5 Ga ago). We present geochemical evidence from the products of early subduction, which have been recycled into the deep mantle and then tapped by the modern Marquesas volcanic hotspot. These products must have been stored and protected in the deep mantle largely unchanged for more than four billion years before they were brought to the surface by the Marquesas mantle plume. The felsic composition of these subducted materials further requires that both subcrustal melting and sedimentation processes were active in some form before this time. The early development of a mature plate tectonic system on Earth implies that its pathway to complex life was protracted: the foundations for habitability potentially began billions of years before the emergence of life. Emerging planetary bodies may, therefore, need long-term sustained plate tectonic processes to become host to complex biological systems. Further, the preservation of evidence for foundational planetary events in geologically young rocks, rather than ancient rocks, reveals that Earth’s volcanic hotspots could provide a defining perspective on the early planetary-scale processes that build Earth-like planets.

The isotopic compositions of samples returned from Cb-type asteroid Ryugu and Ivuna-type (CI) chondrites are distinct from other carbonaceous chondrites, which has led to the suggestion that Ryugu/CI chondrites formed in a different region of the accretion disk, possibly around the orbits of Uranus and Neptune. We show that, like for Fe, Ryugu and CI chondrites also have indistinguishable Ni isotope anomalies, which differ from those of other carbonaceous chondrites. We propose that this unique Fe and Ni isotopic composition reflects different accretion efficiencies of small FeNi metal grains among the carbonaceous chondrite parent bodies. The CI chondrites incorporated these grains more efficiently, possibly because they formed at the end of the disk’s lifetime, when planetesimal formation was also triggered by photoevaporation of the disk. Isotopic variations among carbonaceous chondrites may thus reflect fractionation of distinct dust components from a common reservoir, implying CI chondrites/Ryugu may have formed in the same region of the accretion disk as other carbonaceous chondrites.