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  • ddc:549  (7)
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  • 2020-2024  (7)
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  • 2020-2024  (7)
  • 1990-1994
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  • 1
    facet.materialart.
    Unknown
    Aluminum Components in Bridgmanite Coexisting With Corundum and the CF‐Phase With Temperature (2023)
    Details
    Publication Date: 2023-11-02
    Description: Abstract Phase relations in the MgSiO〈sub〉3〈/sub〉–MgAl〈sub〉2〈/sub〉O〈sub〉4〈/sub〉–Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 system are investigated at 27 GPa and 2000–2600 K using a multi‐anvil apparatus. The AlAlO〈sub〉3〈/sub〉 content in the bridgmanite increases from 8.6 to 20.0 mol% with increasing temperature from 2000 to 2600 K, while the MgAlO〈sub〉2.5〈/sub〉 content remains nearly constant, that is, 3–4 mol% at these temperatures. Therefore, the presence of an additional Al‐bearing phase suppresses the oxygen vacancy substitution for Al〈sup〉3+〈/sup〉 in bridgmanite. Conversely, significant amounts of the Al〈sub〉8/3〈/sub〉O〈sub〉4〈/sub〉 component can be dissolved into the calcium‐ferrite type MgAl〈sub〉2〈/sub〉O〈sub〉4〈/sub〉–Mg〈sub〉2〈/sub〉SiO〈sub〉4〈/sub〉–Al〈sub〉8/3〈/sub〉O〈sub〉4〈/sub〉 phase (CF‐phase), implying that the CF‐phase likely contains some amount of vacancies. Therefore, the CF‐phase could also be a candidate mineral for transporting volatiles into the lower mantle. Our results, combined with previous studies on Al‐bearing bridgmanite, indicate that, once the Al per formula unit exceeds 0.12 in bridgmanite, the MgAlO〈sub〉2.5〈/sub〉 content remains nearly constant and the AlAlO〈sub〉3〈/sub〉 component becomes dominant.
    Description: Plain Language Summary: Bridgmanite, the most abundant mineral in the Earth's mantle, can contain Al〈sup〉3+〈/sup〉 in the forms of MgAlO〈sub〉2.5〈/sub〉 and AlAlO〈sub〉3〈/sub〉. To constrain the substitution mechanism of Al〈sup〉3+〈/sup〉 in bridgmanite, we investigate the MgAlO〈sub〉2.5〈/sub〉 and AlAlO〈sub〉3〈/sub〉 contents in bridgmanite coexisting with a calcium‐ferrite type phase and corundum at different temperatures. Our results demonstrate that the MgAlO〈sub〉2.5〈/sub〉 content reaches saturation (3–4 mol%) when an additional Al‐bearing phase exists in the system.
    Description: Key Points: The MgAlO〈sub〉2.5〈/sub〉 content in bridgmanite remains constant with temperature when bridgmanite coexists with corundum and the CF‐phase. The MgAlO〈sub〉2.5〈/sub〉 content in bridgmanite reaches a solubility of 3–4 mol% when bridgmanite coexists with an additional Al‐bearing phase. A significant amount of the Al〈sub〉8/3〈/sub〉O〈sub〉4〈/sub〉 component can be dissolved into the CF‐phase.
    Description: HORIZON EUROPE European Research Council http://dx.doi.org/10.13039/100019180
    Description: Japan Society for the Promotion of Science London http://dx.doi.org/10.13039/501100000646
    Description: cooperative research program of the Earthquake Research Institute
    Description: https://doi.org/10.5281/zenodo.7512647
    Keywords: ddc:549 ; Al‐bearing bridgmanite ; Al substitute mechanism ; phase relation ; volatile
    Language: English
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  • 2
    facet.materialart.
    Unknown
    Twinned calcite as an indicator of high differential stresses and low shock pressure conditions during impact cratering (2023)
    Details
    Publication Date: 2023-11-02
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Shock‐related calcite twins are characterized in calcite‐bearing metagranite cataclasites within crystalline megablocks of the Ries impact structure, Germany, as well as in cores from the FBN1973 research drilling. The calcite likely originates from pre‐impact veins within the Variscan metagranites and gneisses, while the cataclasis is due to the Miocene impact. Quartz in the metagranite components does not contain planar deformation features, indicating low shock pressures (〈7 GPa). Calcite, however, shows a high density (>1/μm) of twins with widths 〈100 nm. Different types of twins (〈italic toggle="no"〉e〈/italic〉‐, 〈italic toggle="no"〉f‐〈/italic〉, and 〈italic toggle="no"〉r〈/italic〉‐twins) crosscutting each other can occur in one grain. Interaction of 〈italic toggle="no"〉r〈/italic〉‐ and 〈italic toggle="no"〉f〈/italic〉‐twins results in 〈italic toggle="no"〉a〈/italic〉‐type domains characterized by a misorientation relative to the host with a misorientation angle of 35°–40° and a misorientation axis parallel to an 〈italic toggle="no"〉a〈/italic〉‐axis. Such 〈italic toggle="no"〉a〈/italic〉‐type domains have not been recorded from deformed rocks in nature before. The high twin density and activation of different twin systems in one grain require high differential stresses (on the order of 1 GPa). Twinning of calcite at high differential stresses is consistent with deformation during impact cratering at relatively low shock pressure conditions. The twinned calcite microstructure can serve as a valuable low shock barometer.〈/p〉
    Description: Bavarian Natural History Collections
    Keywords: ddc:549 ; Ries impact structure ; twinned calcites ; cataclasis
    Language: English
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  • 3
    facet.materialart.
    Unknown
    Mid‐Infrared Spectroscopy of Feldspars From the Bühl Basalt (Northern Hesse, Germany) Formed Under Reducing Conditions as Terrestrial Analogue of Mercury for MERTIS (2023)
    Details
    Publication Date: 2023-12-19
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉The MErcury Radiometer and Thermal Infrared Spectrometer instrument onboard the BepiColombo spacecraft is designed to investigate Mercury’s surface in the mid‐infrared (mid‐IR). Based on MESSENGER data and modeling, Mercury is thought to be evolved under highly reducing conditions (e.g., McCubbin et al., 2017, 〈ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1002/2017JE005367"〉https://doi.org/10.1002/2017JE005367〈/ext-link〉; Namur & Charlier, 2017, 〈ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1038/ngeo2860"〉https://doi.org/10.1038/ngeo2860〈/ext-link〉). The modeling also indicates that Mercury's surface is rich in feldspar. However, it is unknown if reducing conditions during the emplacement of volcanic melts have an influence on the IR properties of feldspars. Therefore, we investigated basaltic samples from the Bühl quarry in northern Hesse, Germany, that evolved under reducing conditions in the mid‐IR and compared the spectra with samples that experienced more oxidizing conditions during their formation. The Bühl samples are feldspar‐rich and contain metallic iron in some areas. Our investigations show that there are no differences between feldspars that formed under different oxidizing conditions. All spectral properties could be explained by well‐known factors that affect mid‐IR spectra of silicates.〈/p〉
    Description: Plain Language Summary: ESA's and Japan Aerospace Exploration Agency’s spacecraft BepiColombo is equipped, beside other instruments, with a thermal infrared (IR) radiometer and spectrometer called MErcury Radiometer and Thermal Infrared Spectrometer (MERTIS). For the accurate interpretation of the data from the MERTIS instrument, laboratory analog material is necessary. This analog material must fulfill different characteristics, such as different chemical and mineralogical compositions. Another not yet studied property is the availability of oxygen during the formation of the minerals. Depending on how much oxygen is available, different minerals form. However, this is an important feature, because Mercury is thought to have evolved under highly reducing conditions, as opposed to Earth where nearly all material formed significant more oxidizing conditions. One phase that is strongly associated with reducing magma formation conditions is metallic iron. There are only few natural outcrops on Earth, were stronger reducing conditions were present so that metallic iron could be formed. One of these outcrops is the Bühl quarry in northern Hesse, Germany. From there we used different samples to analyze the effect of oxygen availability on mid‐IR spectra of plagioclase feldspars.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉We present infrared spectra of basaltic samples from the Bühl, Hesse, Germany in preparation of the MERTIS experiment〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Comparison of feldspars formed at different oxygen fugacities showed no spectral differences〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉This is an important result for MERTIS, which will investigate Mercury that formed under reducing conditions〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: DLR
    Description: http://bc-mertis-pi.uni-muenster.de/
    Keywords: ddc:549 ; infrared reflectance spectroscopy ; feldspars ; Bühl basalt ; reducing conditions ; Mercury ; MERTIS
    Language: English
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  • 4
    facet.materialart.
    Unknown
    Upper limits of water contents in olivine and orthopyroxene of equilibrated chondrites and several achondrites (2023)
    Details
    Publication Date: 2023-07-21
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Hydroxyl defects in nominally anhydrous minerals (NAMs) were potential carriers of water in the early Solar System and might have contributed to the accretion of terrestrial water. To better understand this, we have conducted a nanoscale secondary ion mass spectrometry survey of water contents in olivine and orthopyroxene from a set of equilibrated ordinary chondrites of the L and LL groups (Baszkówka, Bensour, Kheneg Ljouâd, and Tuxtuac) and several ultramafic achondrites (Zakłodzie, Dhofar 125, Northwest Africa [NWA] 4969, NWA 6693, and NWA 7317). For calibration, we used terrestrial olivine and orthopyroxene with H〈sub〉2〈/sub〉O contents determined by Fourier transform infrared. Our 99.7% (~3SD) detection limits are 3.6–5.4 ppmw H〈sub〉2〈/sub〉O for olivine and 7.7–10.9 ppmw H〈sub〉2〈/sub〉O for orthopyroxene. None of the meteoritic samples studied consistently shows water contents above the detection limits. A few exceptions slightly above the detection limits are suspected of terrestrial contamination by ferric oxyhydroxides. If the meteorite samples investigated accreted in the presence of small amounts of water ice, the upper limits of water contents provided by our survey suggest that the retention of hydrogen during thermal metamorphism and differentiation was ineffective. We suggest that loss occurred through combinations of low internal pressures, high permeability along grain boundaries, and speciation of hydrogen into reduced compounds such as H〈sub〉2〈/sub〉 and methane, which are less soluble in NAMs than in water.〈/p〉
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Europlanet 2020 RI
    Keywords: ddc:549 ; chondrites ; achondrites ; olivine ; orthopyroxene ; water contents
    Language: English
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  • 5
    facet.materialart.
    Unknown
    Silicon and iron isotopes in components of enstatite chondrites: Implications for metal–silicate–sulfide fractionation in the solar nebula (2023)
    Details
    Publication Date: 2023-07-19
    Description: Silicon and iron isotope compositions of different physically separated components of enstatite chondrites (EC) were determined in this study to understand the role of nebular and planetary scale events in fractionating Si and Fe isotopes of the terrestrial planet‐forming region. We found that the metal–sulfide nodules of EC are strongly enriched in light Si isotopes (δ〈sup〉30〈/sup〉Si ≥ −5.61 ± 0.12‰, 2SD), whereas the δ〈sup〉30〈/sup〉Si values of angular metal grains, magnetic, slightly magnetic, and non‐magnetic fractions become progressively heavier, correlating with their Mg# (Mg/(Mg+Fe)). White mineral phases, composed primarily of SiO〈sub〉2〈/sub〉 polymorphs, display the heaviest δ〈sup〉30〈/sup〉Si of up to +0.23 ± 0.10‰. The data indicate a key role of metal–silicate partitioning on the Si isotope composition of EC. The overall lighter δ〈sup〉30〈/sup〉Si of bulk EC compared to other planetary materials can be explained by the enrichment of light Si isotopes in EC metals along with the loss of isotopically heavier forsterite‐rich silicates from the EC‐forming region. In contrast to the large Si isotope heterogeneity, the average Fe isotope composition (δ〈sup〉56〈/sup〉Fe) of EC components was found to vary from −0.30 ± 0.08‰ to +0.20 ± 0.04‰. A positive correlation between δ〈sup〉56〈/sup〉Fe and Ni/S in the components suggests that the metals are enriched in heavy Fe isotopes whereas sulfides are the principal hosts of light Fe isotopes in the non‐magnetic fractions of EC. Our combined Si and Fe isotope data in different EC components reflect an inverse correlation between δ〈sup〉30〈/sup〉Si and δ〈sup〉56〈/sup〉Fe, which illustrates that partitioning of Si and Fe among metal, silicate, and sulfidic phases has significantly fractionated Si and Fe isotopes under reduced conditions. Such isotope partitioning must have occurred before the diverse components were mixed to form the EC parent body. Evaluation of diffusion coefficients of Si and Fe in the metal and non‐metallic phases suggests that the Si isotope compositions of the silicate fractions of EC largely preserve information of their nebular processing. On the other hand, the Fe isotopes might have undergone partial or complete re‐equilibration during parent body metamorphism. The relatively uniform δ〈sup〉56〈/sup〉Fe among different types of bulk chondrites and the Earth, despite Fe isotope differences among their components, demonstrates that the chondrite parent bodies were not formed by random mixing of chondritic components from different locations in the disk. Instead, the chondrite components mostly originated in the same nebular reservoir and Si and Fe isotopes were fractionated either due to gas–solid interactions and associated changes in physicochemical environment of the nebular reservoir and/or during parent body processing. The heavier Si isotope composition of the bulk silicate Earth may require accretion of chondritic and/or isotopically heavier EC silicates along with cumulation of refractory forsterite‐rich heavier silicates lost from the EC‐forming region to form the silicate reservoir of the Earth.〈/p〉
    Description: DFG, German Research Foundation
    Keywords: ddc:549 ; enstatite chondrites ; silicon istotopes ; iron isotopes ; isotopic evolution
    Language: English
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  • 6
    facet.materialart.
    Unknown
    A zircon classification scheme for sedimentary provenance analysis using radiation damage (2023)
    John Wiley & Sons, Inc. | Hoboken, USA
    Details
    Publication Date: 2023-11-17
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Detrital single‐grain zircon U–Pb geochronology is a powerful tool for provenance studies if information on the source rocks is available. This paper proposes a new source‐rock classification tool that uses the degree of annealing of radiation damage in detrital zircon; the annealing is expressed by the relationship between the width (full‐width at half‐maximum; FWHM) of the 〈italic toggle="no"〉v〈/italic〉〈sub〉3〈/sub〉[SiO〈sub〉4〈/sub〉] Raman band at ~1008 cm〈sup〉−1〈/sup〉 and the calculated α‐dose. The host rocks of the zircons are classified into three types according to their emplacement process and/or thermal history: volcanic and rapidly cooled plutonic and high‐grade metamorphic rocks (type 1); rocks with hydrothermal zircons (type 2); slowly cooled igneous and metamorphic rocks (type 3). We construct a naive Bayes prediction model by training it with a collection of zircons of known types. The unknown zircons are assigned a probability of derivation from a specific host‐rock type. This classification scheme is best used as an accessory tool in provenance studies that apply detrital zircon U–Pb geochronology.〈/p〉
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Zircons are classified into three types based on annealing state revealed by Raman analysis and calculated α‐dose. This classification can be used to distinguish zircon in provenance study.〈boxed-text position="anchor" content-type="graphic" id="gj4751-blkfxd-0001" xml:lang="en"〉 〈graphic position="anchor" id="jats-graphic-1" xlink:href="urn:x-wiley:00721050:media:gj4751:gj4751-toc-0001"〉 〈/graphic〉 〈/boxed-text〉〈/p〉
    Description: Natural Science Foundation of Hubei Province http://dx.doi.org/10.13039/501100003819
    Description: National Natural Science Foundation of China http://dx.doi.org/10.13039/501100001809
    Keywords: ddc:549 ; annealing ; Bayesian probability ; provenance analysis ; radiation damage ; zircon classification
    Language: English
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  • 7
    facet.materialart.
    Unknown
    Growth of kyanite and Fe‐Mg chloritoid in Fe2O3‐rich high‐pressure–low‐temperature metapelites and metapsammites: A case study from the Massa Unit (Alpi Apuane, Italy) (2023)
    Details
    Publication Date: 2024-01-26
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Chloritoid and kyanite coexist in metapelites from the high‐pressure/low‐temperature Massa Unit in the Alpi Apuane metamorphic complex (Northern Apennines, Italy). The composition of chloritoid is extremely variable throughout the Massa Unit. Fe‐chloritoid occurs in association with hematite‐free, graphite‐bearing schists, whereas strongly zoned Fe‐Mg chloritoid is found with hematite and kyanite. We investigated the effect of different bulk Fe〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 contents in controlling chloritoid composition through phase equilibria modelling of four selected samples, representative of the different chloritoid‐bearing parageneses found in the Massa Unit. The ferric iron content, measured through wet chemical titration, ranges from 0 (graphite‐chloritoid schist) to 73% of the total iron (hematite‐chloritoid schist). We show that Mg‐rich chloritoid compositions and stability of kyanite at greenschist to blueschist facies conditions can be reproduced in the MnO–Na〈sub〉2〈/sub〉O–K〈sub〉2〈/sub〉O–FeO–MgO–Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉–SiO〈sub〉2〈/sub〉–H〈sub〉2〈/sub〉O–TiO〈sub〉2〈/sub〉–O (MnNKFMASHTO) chemical system only considering the presence of significant amounts of ferric iron as part of the bulk composition. The stabilization of kyanite at lower grade is directly linked to the presence of Fe〈sub〉2〈/sub〉O〈sub〉3〈/sub〉, which renders the reactive bulk rock composition effectively enriched in Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 with respect to Fe and Mg. We also document that high Fe〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 contents exacerbate the effect of chloritoid fractionation, producing strongly zoned Fe‐Mg‐chloritoid grains. Finally, the P–T modelling of the Massa Units performed in this study allows, for the first time, the recognition of a two‐stage evolution at peak conditions, with an earlier pressure peak (1.2–1.3 GPa at 350–400°C), and a later thermal peak (0.7–1.1 GPa at 440–480°C), compatible with subduction, underthrusting and exhumation of the Adria continental margin during growth of the Northern Apennine orogenic wedge.〈/p〉
    Description: https://data.mendeley.com/datasets/wm3nwkrd4m/1
    Keywords: ddc:549 ; chloritoid ; ferric iron ; kyanite ; Northern Apennines ; phase equilibria modelling
    Language: English
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