Maria Schönbächler

Last Name

Schönbächler

First Name

Maria

ORCID

0000-0003-4304-214X

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03946 - Schönbächler, Maria / Schönbächler, Maria

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Publications 1 - 10 of 55

The Magnesium Isotope Composition of Samples Returned from Asteroid Ryugu
Bizzarro, Martin; Schiller, Martin; Yokoyama, Tetsuya; et al. (2023)
The Astrophysical Journal Letters
The nucleosynthetic isotope composition of planetary materials provides a record of the heterogeneous distribution of stardust within the early solar system. In 2020 December, the Japan Aerospace Exploration Agency Hayabusa2 spacecraft returned to Earth the first samples of a primitive asteroid, namely, the Cb-type asteroid Ryugu. This provides a unique opportunity to explore the kinship between primitive asteroids and carbonaceous chondrites. We report high-precision μ²⁶Mg* and μ²⁵Mg values of Ryugu samples together with those of CI, CM, CV, and ungrouped carbonaceous chondrites. The stable Mg isotope composition of Ryugu aliquots defines μ²⁵Mg values ranging from –160 ± 20 ppm to –272 ± 30 ppm, which extends to lighter compositions relative to Ivuna-type (CI) and other carbonaceous chondrite groups. We interpret the μ²⁵Mg variability as reflecting heterogeneous sampling of a carbonate phase hosting isotopically light Mg (μ²⁵Mg ∼ –1400 ppm) formed by low temperature equilibrium processes. After correcting for this effect, Ryugu samples return homogeneous μ²⁶Mg* values corresponding to a weighted mean of 7.1 ± 0.8 ppm. Thus, Ryugu defines a μ²⁶Mg* excess relative to the CI and CR chondrite reservoirs corresponding to 3.8 ± 1.1 and 11.9 ± 0.8 ppm, respectively. These variations cannot be accounted for by in situ decay of ²⁶Al given their respective ²⁷Al/²⁴Mg ratios. Instead, it requires that Ryugu and the CI and CR parent bodies formed from material with a different initial ²⁶Al/²⁷Al ratio or that they are sourced from material with distinct Mg isotope compositions. Thus, our new Mg isotope data challenge the notion that Ryugu and CI chondrites share a common nucleosynthetic heritage.
The initial abundance and distribution of 92Nb in the Solar System
Iizuka, Tsuyoshi; Lai, Yi-Jen; Akram, Waheed; et al. (2016)
Earth and Planetary Science Letters
Precambrian mantle metasomatism preserved by the Nd-Hf isotopic compositions of modern HIMU-type intraplate basalts
Sieger, Leonie; Peters, Bradley J.; Giuliani, Andrea; et al. (2025)
Geochimica et Cosmochimica Acta
The presence of HIMU (high-²³⁸U/²⁰⁴Pb) signatures in ocean island basalts has long been used to argue that ancient oceanic crust has been tectonically recycled into the mantle sources of plume-derived volcanic hotspots such as St. Helena or Mangaia. However, alternative hypotheses regarding the origins of HIMU signatures have also been put forward. This study addresses the origins of HIMU-like Pb isotopic signatures in Isla Isabel, a small (∼1 km²) intraplate volcanic island located off the western coast of México, southeast of the southern tip of Baja California. The Nd-Hf isotopic signatures of Isla Isabel are nearly identical to the classical HIMU-type hotspots St. Helena and Mangaia; however, the physical and geochemical characteristics of Isla Isabel are inconsistent with the derivation of its lavas from deeply recycled oceanic crust. We argue that Isla Isabel lavas were instead produced by mixing of local depleted mantle and continental lithospheric mantle that experienced a prior enrichment event, likely in a ≥ 600 Ma-old paleo-subduction setting. Such preservation of ancient tectonic events is remarkable, since the exposed geological record in continental México preserves only a limited record of geological events older than the Mexican Cordillera (<165 Ma). Isla Isabel, therefore, illustrates that the origins of HIMU-type intraplate lavas are not limited to ancient recycled oceanic crust. Rather, they can also preserve information about the evolution of the upper mantle through large-scale tectonic cycles, even when these events have been otherwise erased from the surficial rock record.
Presolar Grains as Probes of Supernova Nucleosynthesis
Liu, Nan; Lugaro, Maria; Leitner, Jan; et al. (2024)
Space Science Reviews
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.
A community-led calibration of the Zr isotope reference materials: NIST candidate RM 8299 and SRM 3169
Tissot, François L.H.; Ibañez-Mejia, Mauricio; Rabb, Savelas A.; et al. (2023)
Journal of Analytical Atomic Spectrometry
As the field of zirconium (Zr) stable isotopes is rapidly expanding from the study of mass-independent to that of mass-dependent isotope effects, a variety of Zr standards have appeared in the literature. While several of these standards have been proposed as the ideal isotope reference material (iRM) against which all data should be reported, none of them have been shown to meet the compositional and/or conflict-of-interest-free distribution requirements put forth by the community. To remedy this situation, we report on a community-led effort to develop and calibrate a scale defining iRM for Zr isotopes: NIST RM 8299. Developed in partnership with the National Institute of Standards and Technology (NIST) from the widely used SRM 3169 Zirconium Standard Solution (certified for mass fraction), the candidate RM 8299 was calibrated through an inter-laboratory study involving three laboratories. Our data show that candidate RM 8299 meets all requirements of an ideal iRM. It is an isotopically homogeneous, high-purity reference material, that is free of isotope anomalies, and whose composition is identical to that of a major geological reservoir (Ocean Island Basalts). Furthermore, RM 8299 will be curated and distributed by NIST, a neutral, conflict-of-interest free organization, and was produced in sufficient quantities to last multiple decades. We recommend that all Zr isotope data be reported against RM 8299. Our results also show that SRM 3169 lots #130920 and #071226 have indistinguishable composition compared to candidate RM 8299. Therefore, using RM 8299 as the scale defining iRM will enable direct comparison of all future data with the vast majority of the existing literature data, both for mass-independent and mass-dependent isotope effects. To facilitate conversion of & delta;Zr-94/90 values reported against other Zr standards, we provide high-precision conversion factors to the RM 8299 scale obtained using the double-spike method.
Cosmic pears from the Havelland (Germany): Ribbeck, the twelfth recorded aubrite fall in history
Bischoff, Addi; Patzek, Markus; Barrat, Jean-Alix; et al. (2024)
Meteoritics & Planetary Science
In 1889 the German poet and novelist Theodor Fontane wrote the popular literary ballad “Herr von Ribbeck auf Ribbeck im Havelland.” The Squire von Ribbeck is described as a gentle and generous person, who often gives away pears from his pear trees to children passing by and continued donating pears after his death. Now, 135 years later the rock called Ribbeck is giving us insight into processes that happened 4.5 billion years ago. The meteorite Ribbeck (official find location: 52°37′15″N, 12°45′40″E) fell January 21, 2024, and has been classified as a brecciated aubrite. This meteoroid actually entered the Earth's atmosphere at 00:32:38 UTC over Brandenburg, west of Berlin, and the corresponding fireball was recorded by professional all sky and video cameras. More than 200 pieces (two proved by radionuclide analysis to belong to this fresh fall) were recovered totaling about 1.8 kg. Long-lived radionuclide and noble gas data are consistent with long cosmic ray exposure (55–62 Ma) and a preatmospheric radius of Ribbeck between 20 and 30 cm. The heavily brecciated aubrite consists of major (76 ± 3 vol%) coarse-grained FeO-free enstatite (En99.1Fs<0.04Wo0.9), with a significant abundance (15.0 ± 2.5 vol%) of albitic plagioclase (Ab95.3 An2.0Or2.7), minor forsterite (5.5 ± 1.5 vol%; Fo99.9) and 3.5 ± 1.0 vol% of opaque phases (mainly sulfides and metals) with traces of nearly FeO-free diopside (En53.2Wo46.8) and K-feldspar (Ab4.6Or95.4). The rock has a shock degree of S3 (U-S3), and terrestrial weathering has affected metals and sulfides, resulting in the brownish appearance of rock pieces and the partial destruction of certain sulfides already within days after the fall. The bulk chemical data confirm the feldspar-bearing aubritic composition. Ribbeck is closely related to the aubrite Bishopville. Ribbeck does not contain solar wind implanted gases and is a fragmental breccia. Concerning the Ti- and O-isotope compositions, the data are similar to those of other aubrites. They are also similar to E chondrites and fall close to the data point for the bulk silicate Earth (BSE). Before the Ribbeck meteoroid entered Earth's atmosphere, it was observed in space as asteroid 2024 BX1. The aphelion distance of 2024 BX1's orbit lies in the innermost region of the asteroid belt, which is populated by the Hungaria family of minor planets characterized by their E/X-type taxonomy and considered as the likely source of aubrites. The spectral comparison of an average large-scale emission spectrum of Mercury converted into reflectance and of the Ribbeck meteorite spectrum does not show any meaningful similarities.
Pre-Cordilleran mantle metasomatism preserved in alkali basalts of Isla Isabel, México
Sieger, Leonie; Peters, Bradley J.; Giuliani, Andrea; et al. (2024)
EarthArXiv
The presence of HIMU (high-238U/204Pb) signatures in ocean island basalts has long been used to argue that ancient oceanic crust has been tectonically recycled into the mantle sources of plume-derived volcanic hotspots such as St. Helena or Mangaia. However, alternative hypotheses regarding the origins of HIMU signatures have also been put forward. This paper addresses the origins of HIMU-like Pb isotopic signatures in Isla Isabel, a small (~1 km2) intraplate volcanic island located off the western coast of México, southeast of the southern tip of Baja California. The Nd-Hf isotopic signatures of Isla Isabel are nearly identical to St. Helena and Mangaia, however since there is no mantle plume underlying Isla Isabel it is unlikely that these signatures derive from recycled oceanic crust. We argue that Isla Isabel lavas were instead produced by mixing of depleted mantle-like material and continental lithospheric mantle that was metasomatized ≥600 Ma ago, an age that overlaps with the regional breakup of Rodinia. Such preservation of ancient tectonic events is remarkable, since the exposed geological record in continental México preserves a very limited record of geological events older than the Mexican Cordillera (<165 Ma). Isla Isabel therefore illustrates that the origins of HIMU-type intraplate lavas are not limited to ancient recycled oceanic crust. Rather, they can also preserve information about the evolution of the upper mantle through large-scale tectonic cycles, even when these events have been otherwise erased from the surficial rock record.
Cosmic dust may have driven the geochemical origins of life on Earth
Walton, Craig R.; Schönbächler, Maria (2024)
Nature Astronomy
Cosmic dust contains all the elements needed for life but has previously been considered too rare to have acted as a 'fertilizer' for prebiotic chemistry. Now, using a combination of astrophysical and geological models, it is revealed that cosmic dust could have gently accumulated on the surface of early Earth in sufficient quantities to promote the chemical reactions that led to first life.
Pyrrhotites in asteroid 162173 Ryugu: Records of the initial changes on their surfaces with aqueous alteration
Yui, Hiroharu; Urashima, Shu-hei; Onose, Morihiko; et al. (2024)
Geochimica et Cosmochimica Acta
The surface chemistry of pyrrhotites from intact particles directly collected from asteroid (162173) Ryugu was investigated by micro-Raman spectroscopy. The Raman peak characteristic to pyrrhotite was observed at around 115 cm−1 in Ryugu pyrrhotites, similar to freshly cleaved surfaces of terrestrial pyrrhotites. Additional Raman bands centered at around 220, 275, and 313 cm−1 with broadened features were also detected from the Ryugu pyrrhotites. The set of Raman bands at 220 and 275 cm−1 was assigned to typical Fe-S stretching vibrations of ν2 (225 cm−1) and ν1 (275 cm−1). These bands are not clearly observed in bulk crystals of pyrrhotite but appear in its nanoparticulate phase. These bands are ordinarily seen in amorphous monosulfides that formed under low oxygen fugacity (fO2) conditions in nature, indicating that the structural alteration of pyrrhotite surfaces occurred heterogeneously on the nanoscale under low fO2 conditions. Further, the Raman band at 313 cm−1 was attributed to a characteristic tetrahedral bonding of Fe(III) in the lattice of FeII1-3xFeIII1-2xS, followed by the local breakdown of the crystal lattice structures from planar bonding with Fe(II). In addition, some areas of the Ryugu pyrrhotite grains showed corroded structures with iridescence. Furthermore, assemblages of magnetite particles were also preferentially observed on small areas of the likely-dissolved pyrrhotite crystals in phyllosilicate matrices. These characteristic features in the Raman spectra and in corroded structures of Ryugu pyrrhotites record changes in the local environmental conditions via aqueous alteration. The corrosion of pyrrhotite crystals followed by the preferential formation of magnetite particles by asteroidal water is the likely product of dissolution of Fe(II) from the pyrrhotite surface and its oxidative precipitation in microchemical environments on the Ryugu parent body.
Micro-XCT chondrule classification for subsequent isotope analysis
Jäggi, Noah; Roth, Antoine S.G.; Rüfenacht, Miriam; et al. (2023)
Meteoritics & Planetary Science
Chondrules are microscopic, recrystallized melt droplets found in chondritic meteorites. High-resolution isotope analyses of minor elements require large enough element quantities which are obtained by dissolving entire chondrules. This work emphasizes the importance of X-ray computed tomography (XCT) to detect features that can significantly affect the bulk chondrule isotope composition. It thereby expands on other works by looking into chondrules from a wide range of chondrites including CR, CV, CB, CM, L, and EL samples before turning toward complex and time-consuming chemical processing. The features considered are metal and igneous rims, compound chondrules, matrix remnants, and metal contents. In addition to the identification of these features, computed tomography prevents the inclusion of non-chondrule samples (pure matrix or metal) as well as samples where two different chondrule fragments with potentially different isotope compositions are held together by matrix. Matrix surrounding chondrules is also easily detected and the affected chondrules can be omitted or reprocessed. The results strongly encourage to perform XCT before dissolution of chondrules for isotope analysis as a non-invasive method.

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Maria Schönbächler

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