Publications by authors named "Maria Schönbächler"

10 Publications

  • Page 1 of 1

Galactic cosmic ray effects on iron and nickel isotopes in iron meteorites.

Meteorit Planet Sci 2020 Dec 11;55(12):2758-2771. Epub 2020 Feb 11.

Institute for Geochemistry and Petrology ETH Zürich Clausiusstrasse 25 8092 Zürich Switzerland.

We present model calculations for cosmogenic production rates in order to quantify the potential effects of spallation and neutron capture reactions on Fe and Ni isotopes in iron meteorites. We aim to determine whether the magnitude of any cosmogenic effects on the isotopic ratios of Fe and/or Ni may hinder the search for nucleosynthetic variations in these elements or in the application of the Fe-Ni chronometer. The model shows that neutron capture reactions are the dominant source of shifts in Fe and Ni isotopic ratios and that spallation reactions are mostly negligible. The effects on Ni are sensitive to the Co/Ni ratio in the metal. The total galactic cosmic ray (GCR) effects on Ni and Ni can be minimized through the choice of normalizing isotopes (Ni/Ni versus Ni/Ni). In nearly all cases, the GCR effects (neutron capture and/or spallation) on Fe and Ni isotopic ratios are smaller than the current analytical resolution of the isotopic measurements. The model predictions are compared to the Fe and Ni isotopic compositions measured in a suite of six group IAB irons with a range of cosmic ray exposure histories. The experimental data are in good agreement with the model results. The minimal effects of GCRs on Fe and Ni isotopes should not hamper the search for nucleosynthetic variations in these two elements or the application of the Fe-Ni chronometer in iron meteorites or chondrites.
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http://dx.doi.org/10.1111/maps.13446DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7891426PMC
December 2020

Precise initial abundance of Niobium-92 in the Solar System and implications for -process nucleosynthesis.

Proc Natl Acad Sci U S A 2021 Feb;118(8)

Institute of Geochemistry and Petrology, ETH Zürich, 8092 Zürich, Switzerland.

The niobium-92-zirconium-92 (Nb-Zr) decay system with a half-life of 37 Ma has great potential to date the evolution of planetary materials in the early Solar System. Moreover, the initial abundance of the -process isotope Nb in the Solar System is important for quantifying the contribution of -process nucleosynthesis in astrophysical models. Current estimates of the initial Nb/Nb ratios have large uncertainties compromising the use of the Nb-Zr cosmochronometer and leaving nucleosynthetic models poorly constrained. Here, the initial Nb abundance is determined to high precision by combining the Nb-Zr systematics of cogenetic rutiles and zircons from mesosiderites with U-Pb dating of the same zircons. The mineral pair indicates that the Nb/Nb ratio of the Solar System started with (1.66 ± 0.10) × 10, and their Zr/Zr ratios can be explained by a three-stage Nb-Zr evolution on the mesosiderite parent body. Because of the improvement by a factor of 6 of the precision of the initial Solar System Nb/Nb, we can show that the presence of Nb in the early Solar System provides further evidence that both type Ia supernovae and core-collapse supernovae contributed to the light -process nuclei.
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http://dx.doi.org/10.1073/pnas.2017750118DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7923630PMC
February 2021

Bifurcation of planetary building blocks during Solar System formation.

Science 2021 01;371(6527):365-370

Institute for Computational Science, University of Zurich, Zurich, Switzerland.

Geochemical and astronomical evidence demonstrates that planet formation occurred in two spatially and temporally separated reservoirs. The origin of this dichotomy is unknown. We use numerical models to investigate how the evolution of the solar protoplanetary disk influenced the timing of protoplanet formation and their internal evolution. Migration of the water snow line can generate two distinct bursts of planetesimal formation that sample different source regions. These reservoirs evolve in divergent geophysical modes and develop distinct volatile contents, consistent with constraints from accretion chronology, thermochemistry, and the mass divergence of inner and outer Solar System. Our simulations suggest that the compositional fractionation and isotopic dichotomy of the Solar System was initiated by the interplay between disk dynamics, heterogeneous accretion, and internal evolution of forming protoplanets.
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http://dx.doi.org/10.1126/science.abb3091DOI Listing
January 2021

More than Five Percent Ionization Efficiency by Cavity Source Thermal Ionization Mass Spectrometry for Uranium Subnanogram Amounts.

Anal Chem 2019 May 22;91(9):6190-6199. Epub 2019 Apr 22.

ETH Zürich, Institute of Geochemistry and Petrology , Clausiusstrasse 25 , CH-8092 Zürich , Switzerland.

Numerous applications require the precise analysis of U isotope relative enrichment in sample amounts in the subnanogram to picogram range; among those are nuclear forensics, nuclear safeguards, environmental survey, and geosciences. However, conventional thermal ionization mass spectrometry (TIMS) yields U combined ionization and transmission efficiencies (i.e., ratio of ions detected to sample atoms loaded) of less than 0.1% or 2% depending on the loading protocol, motivating the development of sources capable of enhancing ionization. The new prototype cavity source TIMS at ETH Zürich offers improvements from 4 to 15 times in combined ionization and transmission efficiency compared to conventional TIMS, yielding up to 5.6% combined efficiency. Uranium isotope ratios have been determined on reference standards in the 100 pg range bound to ion-exchange or extraction resin beads. For natural U standards, n(U)/ n(U) ratios are measured to relative external precisions of 0.5-1.0% (2RSD, 2 < n < 11, conventional source) or 2.0% (2RSD, n = 6, cavity source) and accuracies of 0.2-0.7% (conventional source) or 0.4-0.9% (cavity source). Meanwhile, n(U)/ n(U) ratios are determined to relative external precisions of 1.7-3.6% (2RSD, 2 < n < 11, conventional source) or 5.6% (2RSD, n = 6, cavity source) and accuracies of 0.1-2.5% (conventional source) or 0.5-8.3% (cavity source), which would benefit further from in-run organic interference and peak tailing corrections.
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http://dx.doi.org/10.1021/acs.analchem.9b00849DOI Listing
May 2019

Excess W in IIAB iron meteorites: Identification of cosmogenic, radiogenic, and nucleosynthetic components.

Earth Planet Sci Lett 2018 Dec 28;503:29-36. Epub 2018 Sep 28.

Institut für Geochemie und Petrologie, ETH Zürich, Clausiusstrasse 25, 8092 Zürich, Switzerland.

The origin of W excesses in iron meteorites has been a recently debated topic. Here, a suite of IIAB iron meteorites was studied in order to accurately determine the contribution from galactic cosmic rays (GCR) and from potential decay of Os to measured excesses in the minor isotope W. In addition to W isotopes, trace element concentrations (Re, Os, Ir, Pt, W) were determined on the same samples, as well as their cosmic ray exposure ages, using Cl-Ar systematics. These data were used in combination with an improved model of GCR effects on W isotopes to correct effects resulting from neutron capture and spallation reactions. After these corrections, the residual W excesses correlate with Os/W ratios and indicate a clear contribution from Os decay. A newly derived decay constant is equivalent to a half-life for Os of (3.38 ± 2.13) × 10 a. Furthermore, when the data are plotted on an Os-W isochron diagram, the intercept (W = 0.63 ± 0.35) reveals that the IIAB parent body was characterized by a small initial nucleosynthetic excess in W upon which radiogenic and GCR effects were superimposed. This is the first cogent evidence for -process variability in W isotopes in early Solar System material.
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http://dx.doi.org/10.1016/j.epsl.2018.09.021DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6398611PMC
December 2018

Evidence for extremely rapid magma ocean crystallization and crust formation on Mars.

Nature 2018 06 27;558(7711):586-589. Epub 2018 Jun 27.

Centre for Star and Planet Formation and Natural History Museum of Denmark, University of Copenhagen, Copenhagen, Denmark.

The formation of a primordial crust is a critical step in the evolution of terrestrial planets but the timing of this process is poorly understood. The mineral zircon is a powerful tool for constraining crust formation because it can be accurately dated with the uranium-to-lead (U-Pb) isotopic decay system and is resistant to subsequent alteration. Moreover, given the high concentration of hafnium in zircon, the lutetium-to-hafnium (Lu-Hf) isotopic decay system can be used to determine the nature and formation timescale of its source reservoir. Ancient igneous zircons with crystallization ages of around 4,430 million years (Myr) have been reported in Martian meteorites that are believed to represent regolith breccias from the southern highlands of Mars. These zircons are present in evolved lithologies interpreted to reflect re-melted primary Martian crust , thereby potentially providing insight into early crustal evolution on Mars. Here, we report concomitant high-precision U-Pb ages and Hf-isotope compositions of ancient zircons from the NWA 7034 Martian regolith breccia. Seven zircons with mostly concordant U-Pb ages define Pb/Pb dates ranging from 4,476.3 ± 0.9 Myr ago to 4,429.7 ± 1.0 Myr ago, including the oldest directly dated material from Mars. All zircons record unradiogenic initial Hf-isotope compositions inherited from an enriched, andesitic-like crust extracted from a primitive mantle no later than 4,547 Myr ago. Thus, a primordial crust existed on Mars by this time and survived for around 100 Myr before it was reworked, possibly by impacts, to produce magmas from which the zircons crystallized. Given that formation of a stable primordial crust is the end product of planetary differentiation, our data require that the accretion, core formation and magma ocean crystallization on Mars were completed less than 20 Myr after the formation of the Solar System. These timescales support models that suggest extremely rapid magma ocean crystallization leading to a gravitationally unstable stratified mantle, which subsequently overturns, resulting in decompression melting of rising cumulates and production of a primordial basaltic to andesitic crust.
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http://dx.doi.org/10.1038/s41586-018-0222-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6107064PMC
June 2018

Separation of Platinum from Palladium and Iridium in Iron Meteorites and Accurate High-Precision Determination of Platinum Isotopes by Multi-Collector ICP-MS.

Geostand Geoanal Res 2017 12 29;41(4):633-647. Epub 2017 Jul 29.

Institute of Geochemistry and Petrology ETH Zürich Clausiusstrasse 25 Zürich 8092 Switzerland.

This study presents a new measurement procedure for the isolation of Pt from iron meteorite samples. The method also allows for the separation of Pd from the same sample aliquot. The separation entails a two-stage anion-exchange procedure. In the first stage, Pt and Pd are separated from each other and from major matrix constituents including Fe and Ni. In the second stage, Ir is reduced with ascorbic acid and eluted from the column before Pt collection. Platinum yields for the total procedure were typically 50-70%. After purification, high-precision Pt isotope determinations were performed by multi-collector ICP-MS. The precision of the new method was assessed using the IIAB iron meteorite North Chile. Replicate analyses of multiple digestions of this material yielded an intermediate precision for the measurement results of 0.73 for εPt, 0.15 for εPt and 0.09 for εPt (2 standard deviations). The NIST SRM 3140 Pt solution reference material was passed through the measurement procedure and yielded an isotopic composition that is identical to the unprocessed Pt reference material. This indicates that the new technique is unbiased within the limit of the estimated uncertainties. Data for three iron meteorites support that Pt isotope variations in these samples are due to exposure to galactic cosmic rays in space.
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http://dx.doi.org/10.1111/ggr.12176DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5784402PMC
December 2017

A new methodology for precise cadmium isotope analyses of seawater.

Anal Bioanal Chem 2012 Jan 28;402(2):883-93. Epub 2011 Oct 28.

Department of Earth Science and Engineering, Imperial College London, London, UK.

Previous studies have revealed considerable Cd isotope fractionations in seawater, which can be used to study the marine cycling of this micronutrient element. The low Cd concentrations that are commonly encountered in nutrient-depleted surface seawater, however, pose a particular challenge for precise Cd stable isotope analyses. In this study, we have developed a new procedure for Cd isotope analyses of seawater, which is suitable for samples as large as 20 L and Cd concentrations as low as 1 pmol/L. The procedure involves the use of a (111)Cd-(113)Cd double spike, co-precipitation of Cd from seawater using Al(OH)(3), and subsequent Cd purification by column chromatography. To save time, seawater samples with higher Cd contents can be processed without co-precipitation. The Cd isotope analyses are carried out by multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS). The performance of this technique was verified by analyzing multiple aliquots of a large seawater sample that was collected from the English Channel, the SAFe D1 seawater reference material, and several samples from the GEOTRACES Atlantic intercalibration exercise. The overall Cd yield of the procedure is consistently better than 85% and the methodology can routinely provide ε (114/110)Cd data with a precision of about ±0.5 ε (2sd, standard deviation) when at least 20-30 ng of natural Cd is available for analysis. However, even seawater samples with Cd contents of only 1-3 ng can be analyzed with a reproducibility of about ±3 to ±5 ε. A number of experiments were furthermore conducted to verify that the isotopic results are accurate to within the quoted uncertainty.
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http://dx.doi.org/10.1007/s00216-011-5487-0DOI Listing
January 2012

Measurement of zinc stable isotope ratios in biogeochemical matrices by double-spike MC-ICPMS and determination of the isotope ratio pool available for plants from soil.

Anal Bioanal Chem 2010 Dec 4;398(7-8):3115-25. Epub 2010 Oct 4.

Imperial College London, Department of Earth Science and Engineering, London SW7 2AZ, UK.

Analysis of naturally occurring isotopic variations is a promising tool for investigating Zn transport and cycling in geological and biological settings. Here, we present the recently installed double-spike (DS) technique at the MAGIC laboratories at Imperial College London. The procedure improves on previous published DS methods in terms of ease of measurement and precisions obtained. The analytical method involves addition of a (64)Zn-(67)Zn double-spike to the samples prior to digestion, separation of Zn from the sample matrix by ion exchange chromatography, and isotopic analysis by multiple-collector inductively coupled plasma mass spectrometry. The accuracy and reproducibility of the method were validated by analyses of several in-house and international elemental reference materials. Multiple analyses of pure Zn standard solutions consistently yielded a reproducibility of about ±0.05‰ (2 SD) for δ(66)Zn, and comparable precisions were obtained for analyses of geological and biological materials. Highly fractionated Zn standards analyzed by DS and standard sample bracketing yield slightly varying results, which probably originate from repetitive fractionation events during manufacture of the standards. However, the δ(66)Zn values (all reported relative to JMC Lyon Zn) for two less fractionated in-house Zn standard solutions, Imperial Zn (0.10 ± 0.08‰: 2 SD) and London Zn (0.08 ± 0.04‰), are within uncertainties to data reported with different mass spectrometric techniques and instruments. Two standard reference materials, blend ore BCR 027 and ryegrass BCR 281, were also measured, and the δ(66)Zn were found to be 0.25 ± 0.06‰ (2 SD) and 0.40 ± 0.09‰, respectively. Taken together, these standard measurements ascertain that the double-spike methodology is suitable for accurate and precise Zn isotope analyses of a wide range of natural samples. The newly installed technique was consequently applied to soil samples and soil leachates to investigate the isotopic signature of plant available Zn. We find that the isotopic composition is heavier than the residual, indicating the presence of loosely bound Zn deposited by atmospheric pollution, which is readily available to plants.
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http://dx.doi.org/10.1007/s00216-010-4231-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2990013PMC
December 2010

Niobium-zirconium chronometry and early solar system development.

Science 2002 Mar;295(5560):1705-8

Institute of Isotope Geology and Mineral Resources, ETH Zürich, 8092 Zürich, Switzerland.

Niobium-92 (92Nb) decays to zirconium-92 (92Zr) with a half-life of 36 million years and can be used to place constraints on the site of p-process nucleosynthesis and the timing of early solar system processes. Recent results have suggested that the initial 92Nb/93Nb of the solar system was high (>10(-3)). We report Nb-Zr internal isochrons for the ordinary chondrite Estacado (H6) and a clast of the mesosiderite Vaca Muerta, both of which define an initial 92Nb/93Nb ratio of approximately 10(-5). Therefore, the solar system appears to have started with a ratio of <3 x 10(-5), which implies that Earth's initial differentiation need not have been as protracted as recently suggested.
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http://dx.doi.org/10.1126/science.1067400DOI Listing
March 2002