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Luigi Folco - One of the best experts on this subject based on the ideXlab platform.
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isotopic and textural analysis of giant unmelted Micrometeorites identification of new material from intensely altered 16o poor water rich asteroids
Earth and Planetary Science Letters, 2020Co-Authors: Luigi Folco, M D Suttle, Zelia Dionnet, I A Franchi, J M Gibson, R C Greenwood, A Rotundi, A King, S. S. RussellAbstract:Abstract Bulk oxygen isotope data has the potential to match extraterrestrial samples to parent body sources based on distinctive δ 18 O and Δ 17 O ratios. We analysed 10 giant (>500 μm) Micrometeorites using combined micro-Computer Tomography (μCT) and O-isotope analysis to pair internal textures to inferred parent body groups. We identify three ordinary chondrite particles (L and LL groups), four from CR chondrites and the first micrometeorite from the enstatite chondrite (EH4) group. In addition, two Micrometeorites are from hydrated carbonaceous chondrite parent bodies with 16O-poor isotopic compositions and plot above the terrestrial fractionation line. They experienced intense aqueous alteration, contain pseudomorphic chondrules and are petrographically similar to the CM1/CR1 chondrites. These Micrometeorites may be members of the newly established CY chondrites and/or derived from the enigmatic “Group 4” micrometeorite population, previously identified by Yada et al., 2005 [GCA, 69:5789-5804], Suavet et al., 2010 [EPSL, 293:313-320] (and others). One of our 16O-poor micrometeorite plots on the same isotopic trendline as the CO, CM and CY chondrites – “the CM mixing line” (with a slope of ∼0.7 and a δ 17 O intercept of -4.23‰), this implies a close relationship and potentially a genetic link to these hydrated chondrites. If position along the CM mixing line reflects the amount of 16O-poor (heavy) water-ice accreted onto the parent body at formation, then the CY chondrites and these 16O-poor Micrometeorites must have accreted at least as much water-ice as CM chondrites but potentially more. In addition, thermal metamorphism could have played a role in further raising the bulk O-isotope compositions through the preferential loss of isotopically light water during phyllosilicate dehydration. The study of Micrometeorites provides insights into asteroid belt diversity through the discovery of material not currently sampled by larger meteorites, perhaps as a result of atmospheric entry biases preventing the survival of large blocks of friable hydrated material.
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intense aqueous alteration on c type asteroids perspectives from giant fine grained Micrometeorites
Geochimica et Cosmochimica Acta, 2019Co-Authors: Luigi Folco, M D Suttle, Matthew J Genge, S. S. Russell, Jens Najorka, M Van GinnekenAbstract:Abstract This study explores the petrology of five giant (>400 μm) hydrated fine-grained Micrometeorites from the Transantarctic Mountain (TAM) micrometeorite collection. For the first time, the extent and mechanisms of aqueous alteration in unmelted cosmic dust are evaluated and quantified. We use a range of criteria, previously defined for use on hydrated chondrites, including phyllosilicate fraction, matrix geochemistry and micro textures. Collectively, these Micrometeorites represent ∼2.22 mm2 of intensely altered hydrated chondritic matrix (with petrologic subtypes of
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The thermal decomposition of fine-grained Micrometeorites, observations from mid-IR spectroscopy
Geochimica et Cosmochimica Acta, 2017Co-Authors: M D Suttle, Luigi Folco, Matthew J Genge, Sara S. RussellAbstract:Abstract We analysed 44 fine-grained and scoriaceous Micrometeorites. A bulk mid-IR spectrum (8–13 μm) for each grain was collected and the entire micrometeorite population classified into 5 spectral groups, based on the positions of their absorption bands. Corresponding carbonaceous Raman spectra, textural observations from SEM-BSE and bulk geochemical data via EMPA were collected to aid in the interpretation of mid-IR spectra. The 5 spectral groups identified correspond to progressive thermal decomposition. Unheated hydrated chondritic matrix, composed predominantly of phyllosilicates, exhibit smooth, asymmetric spectra with a peak at ∼10 μm. Thermal decomposition of sheet silicates evolves through dehydration, dehydroxylation, annealing and finally by the onset of partial melting. Both CI-like and CM-like Micrometeorites are shown to pass through the same decomposition stages and produce similar mid-IR spectra. Using known temperature thresholds for each decomposition stage it is possible to assign a peak temperature range to a given micrometeorite. Since the temperature thresholds for decomposition reactions are defined by the phyllosilicate species and the cation composition and that these variables are markedly different between CM and CI classes, atmospheric entry should bias the dust flux to favour the survival of CI-like grains, whilst preferentially melting most CM-like dust. However, this hypothesis is inconsistent with empirical observations and instead requires that the source ratio of CI:CM dust is heavily skewed in favour of CM material. In addition, a small population of anomalous grains are identified whose carbonaceous and petrographic characteristics suggest in-space heating and dehydroxylation have occurred. These grains may therefore represent regolith Micrometeorites derived from the surface of C-type asteroids. Since the spectroscopic signatures of dehydroxylates are distinctive, i.e. characterised by a reflectance peak at 9.0–9.5 μm, and since the surfaces of C-type asteroids are expected to be heated via impact gardening, we suggest that future spectroscopic investigations should attempt to identify dehydroxylate signatures in the reflectance spectra of young carbonaceous asteroid families.
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The weathering of Micrometeorites from the Transantarctic Mountains
Geochimica et Cosmochimica Acta, 2016Co-Authors: Matthias Van Ginneken, Luigi Folco, Matthew J Genge, Ralph P. HarveyAbstract:Abstract Micrometeorites are cosmic dust particles recovered from the Earth’s surface that dominate the influx of extraterrestrial material accreting to our planet. This paper provides the first in-depth study of the weathering of Micrometeorites within the Antarctic environment that will allow primary and secondary features to be distinguished. It is based on the analysis of 366 particles from Larkman Nunatak and 25 from the Transantarctic Mountain collection. Several important morphological categories of weathering effects were identified: (1) irregular and faceted cavities, (2) surface etch pits, (3) infilled cavities, (4) replaced silicate phases, and (5) hydrated and replaced metal. These features indicate that congruent dissolution of silicate phases, in particular olivine, is important in generating new pore space within particles. Comparison of the preservation of glass and olivine also indicates preferential dissolution of olivine by acidic solutions during low temperature aqueous alteration. Precipitation of new hydrous phases within cavities, in particular ferrihydrite and jarosite, results in pseudomorph textures within heavily altered particles. Glass, in contrast, is altered to palagonite gels and shows a sequential replacement indicative of varying water to rock ratios. Metal is variably replaced by Fe-oxyhydroxides and results in decreases in Ni/Fe ratio. In contrast, sulphides within metal are largely preserved. Magnetite, an essential component of Micrometeorites formed during atmospheric entry, is least altered by interaction with the terrestrial environment. The extent of weathering in the studied Micrometeorites is sensitive to differences in their primary mineralogy and varies significantly with particle type. Despite these differences, we propose a weathering scale for Micrometeorites based on both their degree of terrestrial alteration and the level of encrustation by secondary phases. The compositions and textures of weathering products, however, suggest open system behaviour and variable water to rock ratios that imply climatic variation over the lifetime of the micrometeorite deposits.
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Chondritic Micrometeorites from the Transantarctic Mountains
Meteoritics & Planetary Science, 2012Co-Authors: Matthias Van Ginneken, Luigi Folco, Carole Cordier, Pierre RochetteAbstract:Abstract– On the basis of morphological and petrographic characteristics, eight “giant” unmelted Micrometeorites in the 300–1100 μm size range were selected from the Transantarctic Mountain micrometeorite collection, Victoria Land, Antarctica. Mineralogical and geochemical data obtained by means of scanning electron microscopy, electron probe microanalyses, and synchrotron X-ray diffraction allow their classification as chondritic Micrometeorites. The large size of the Micrometeorites increases considerably the amount of mineralogical and geochemical information compared to Micrometeorites in smaller size fractions, therefore allowing a better definition of their parent material. A large variety of material is observed: five Micrometeorites are related to unequilibrated and equilibrated ordinary chondrite, one to CV chondrite, one to CM chondrite, and one to CI chondrite parent materials. Besides reporting the first occurrence of a CV-like micrometeorite, our study shows that the abundance of chondritic material supports observations from recent studies on cosmic spherules that a large part of the micrometeorite flux in this size range is of asteroidal origin.
M D Suttle - One of the best experts on this subject based on the ideXlab platform.
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isotopic and textural analysis of giant unmelted Micrometeorites identification of new material from intensely altered 16o poor water rich asteroids
Earth and Planetary Science Letters, 2020Co-Authors: Luigi Folco, M D Suttle, Zelia Dionnet, I A Franchi, J M Gibson, R C Greenwood, A Rotundi, A King, S. S. RussellAbstract:Abstract Bulk oxygen isotope data has the potential to match extraterrestrial samples to parent body sources based on distinctive δ 18 O and Δ 17 O ratios. We analysed 10 giant (>500 μm) Micrometeorites using combined micro-Computer Tomography (μCT) and O-isotope analysis to pair internal textures to inferred parent body groups. We identify three ordinary chondrite particles (L and LL groups), four from CR chondrites and the first micrometeorite from the enstatite chondrite (EH4) group. In addition, two Micrometeorites are from hydrated carbonaceous chondrite parent bodies with 16O-poor isotopic compositions and plot above the terrestrial fractionation line. They experienced intense aqueous alteration, contain pseudomorphic chondrules and are petrographically similar to the CM1/CR1 chondrites. These Micrometeorites may be members of the newly established CY chondrites and/or derived from the enigmatic “Group 4” micrometeorite population, previously identified by Yada et al., 2005 [GCA, 69:5789-5804], Suavet et al., 2010 [EPSL, 293:313-320] (and others). One of our 16O-poor micrometeorite plots on the same isotopic trendline as the CO, CM and CY chondrites – “the CM mixing line” (with a slope of ∼0.7 and a δ 17 O intercept of -4.23‰), this implies a close relationship and potentially a genetic link to these hydrated chondrites. If position along the CM mixing line reflects the amount of 16O-poor (heavy) water-ice accreted onto the parent body at formation, then the CY chondrites and these 16O-poor Micrometeorites must have accreted at least as much water-ice as CM chondrites but potentially more. In addition, thermal metamorphism could have played a role in further raising the bulk O-isotope compositions through the preferential loss of isotopically light water during phyllosilicate dehydration. The study of Micrometeorites provides insights into asteroid belt diversity through the discovery of material not currently sampled by larger meteorites, perhaps as a result of atmospheric entry biases preventing the survival of large blocks of friable hydrated material.
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intense aqueous alteration on c type asteroids perspectives from giant fine grained Micrometeorites
Geochimica et Cosmochimica Acta, 2019Co-Authors: Luigi Folco, M D Suttle, Matthew J Genge, S. S. Russell, Jens Najorka, M Van GinnekenAbstract:Abstract This study explores the petrology of five giant (>400 μm) hydrated fine-grained Micrometeorites from the Transantarctic Mountain (TAM) micrometeorite collection. For the first time, the extent and mechanisms of aqueous alteration in unmelted cosmic dust are evaluated and quantified. We use a range of criteria, previously defined for use on hydrated chondrites, including phyllosilicate fraction, matrix geochemistry and micro textures. Collectively, these Micrometeorites represent ∼2.22 mm2 of intensely altered hydrated chondritic matrix (with petrologic subtypes of
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diagenetically altered fossil Micrometeorites suggest cosmic dust is common in the geological record
Earth and Planetary Science Letters, 2017Co-Authors: M D Suttle, Matthew J GengeAbstract:Abstract We report the discovery of fossil Micrometeorites from Late Cretaceous chalk. Seventy-six cosmic spherules were recovered from Coniacian ( 87 ± 1 Ma ) sediments of the White Chalk Supergroup. Particles vary from pristine silicate and iron-type spherules to pseudomorphic spherules consisting of either single-phase recrystallized magnetite or Fe-silicide. Pristine spherules are readily identified as Micrometeorites on the basis of their characteristic mineralogies, textures and compositions. Both magnetite and silicide spherules contain dendritic crystals and spherical morphologies, testifying to rapid crystallisation of high temperature iron-rich metallic and oxide liquids. These particles also contain spherical cavities, representing weathering and removal of metal beads and irregular cavities, representing vesicles formed by trapped gas during crystallization; both features commonly found among modern Antarctic Iron-type (I-type) cosmic spherules. On the basis of textural analysis, the magnetite and Fe-silicide spherules are shown to be I-type cosmic spherules that have experienced complete secondary replacement during diagenesis (fossilization). Our results demonstrate that Micrometeorites, preserved in sedimentary rocks, are affected by a suite of complex diagenetic processes, which can result in disparate replacement minerals, even within the same sequence of sedimentary beds. As a result, the identification of fossil Micrometeorites requires careful observation of particle textures and comparisons with modern Antarctic collections. Replaced Micrometeorites imply that geochemical signatures the extraterrestrial dust are subject to diagenetic remobilisation that limits their stratigraphic resolution. However, this study demonstrates that fossil, pseudomorphic Micrometeorites can be recognised and are likely common within the geological record.
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Shock Fabrics in Fine-Grained Micrometeorites
Meteoritics & Planetary Science, 2017Co-Authors: M D Suttle, Matthew J Genge, Sara S. RussellAbstract:The orientations of dehydration cracks and fracture networks in fine-grained, unmelted Micrometeorites were analyzed using rose diagrams and entropy calculations. As cracks exploit pre-existing anisotropies, analysis of their orientation provides a mechanism with which to study the subtle petrofabrics preserved within fine-grained and amorphous materials. Both uniaxial and biaxial fabrics are discovered, often with a relatively wide spread in orientations (40°–60°). Brittle deformation cataclasis and rotated olivine grains are reported from a single micrometeorite. This paper provides the first evidence for impact-induced shock deformation in fine-grained Micrometeorites. The presence of pervasive, low-grade shock features in CM chondrites and CM-like dust, anomalously low-density measurements for C-type asteroids, and impact experiments which suggest CM chondrites are highly prone to disruption all imply that CM parent bodies are unlikely to have remained intact and instead exist as a collection of loosely aggregated rubble-pile asteroids, composed of primitive shocked clasts.
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The thermal decomposition of fine-grained Micrometeorites, observations from mid-IR spectroscopy
Geochimica et Cosmochimica Acta, 2017Co-Authors: M D Suttle, Luigi Folco, Matthew J Genge, Sara S. RussellAbstract:Abstract We analysed 44 fine-grained and scoriaceous Micrometeorites. A bulk mid-IR spectrum (8–13 μm) for each grain was collected and the entire micrometeorite population classified into 5 spectral groups, based on the positions of their absorption bands. Corresponding carbonaceous Raman spectra, textural observations from SEM-BSE and bulk geochemical data via EMPA were collected to aid in the interpretation of mid-IR spectra. The 5 spectral groups identified correspond to progressive thermal decomposition. Unheated hydrated chondritic matrix, composed predominantly of phyllosilicates, exhibit smooth, asymmetric spectra with a peak at ∼10 μm. Thermal decomposition of sheet silicates evolves through dehydration, dehydroxylation, annealing and finally by the onset of partial melting. Both CI-like and CM-like Micrometeorites are shown to pass through the same decomposition stages and produce similar mid-IR spectra. Using known temperature thresholds for each decomposition stage it is possible to assign a peak temperature range to a given micrometeorite. Since the temperature thresholds for decomposition reactions are defined by the phyllosilicate species and the cation composition and that these variables are markedly different between CM and CI classes, atmospheric entry should bias the dust flux to favour the survival of CI-like grains, whilst preferentially melting most CM-like dust. However, this hypothesis is inconsistent with empirical observations and instead requires that the source ratio of CI:CM dust is heavily skewed in favour of CM material. In addition, a small population of anomalous grains are identified whose carbonaceous and petrographic characteristics suggest in-space heating and dehydroxylation have occurred. These grains may therefore represent regolith Micrometeorites derived from the surface of C-type asteroids. Since the spectroscopic signatures of dehydroxylates are distinctive, i.e. characterised by a reflectance peak at 9.0–9.5 μm, and since the surfaces of C-type asteroids are expected to be heated via impact gardening, we suggest that future spectroscopic investigations should attempt to identify dehydroxylate signatures in the reflectance spectra of young carbonaceous asteroid families.
Matthew J Genge - One of the best experts on this subject based on the ideXlab platform.
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intense aqueous alteration on c type asteroids perspectives from giant fine grained Micrometeorites
Geochimica et Cosmochimica Acta, 2019Co-Authors: Luigi Folco, M D Suttle, Matthew J Genge, S. S. Russell, Jens Najorka, M Van GinnekenAbstract:Abstract This study explores the petrology of five giant (>400 μm) hydrated fine-grained Micrometeorites from the Transantarctic Mountain (TAM) micrometeorite collection. For the first time, the extent and mechanisms of aqueous alteration in unmelted cosmic dust are evaluated and quantified. We use a range of criteria, previously defined for use on hydrated chondrites, including phyllosilicate fraction, matrix geochemistry and micro textures. Collectively, these Micrometeorites represent ∼2.22 mm2 of intensely altered hydrated chondritic matrix (with petrologic subtypes of
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diagenetically altered fossil Micrometeorites suggest cosmic dust is common in the geological record
Earth and Planetary Science Letters, 2017Co-Authors: M D Suttle, Matthew J GengeAbstract:Abstract We report the discovery of fossil Micrometeorites from Late Cretaceous chalk. Seventy-six cosmic spherules were recovered from Coniacian ( 87 ± 1 Ma ) sediments of the White Chalk Supergroup. Particles vary from pristine silicate and iron-type spherules to pseudomorphic spherules consisting of either single-phase recrystallized magnetite or Fe-silicide. Pristine spherules are readily identified as Micrometeorites on the basis of their characteristic mineralogies, textures and compositions. Both magnetite and silicide spherules contain dendritic crystals and spherical morphologies, testifying to rapid crystallisation of high temperature iron-rich metallic and oxide liquids. These particles also contain spherical cavities, representing weathering and removal of metal beads and irregular cavities, representing vesicles formed by trapped gas during crystallization; both features commonly found among modern Antarctic Iron-type (I-type) cosmic spherules. On the basis of textural analysis, the magnetite and Fe-silicide spherules are shown to be I-type cosmic spherules that have experienced complete secondary replacement during diagenesis (fossilization). Our results demonstrate that Micrometeorites, preserved in sedimentary rocks, are affected by a suite of complex diagenetic processes, which can result in disparate replacement minerals, even within the same sequence of sedimentary beds. As a result, the identification of fossil Micrometeorites requires careful observation of particle textures and comparisons with modern Antarctic collections. Replaced Micrometeorites imply that geochemical signatures the extraterrestrial dust are subject to diagenetic remobilisation that limits their stratigraphic resolution. However, this study demonstrates that fossil, pseudomorphic Micrometeorites can be recognised and are likely common within the geological record.
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Shock Fabrics in Fine-Grained Micrometeorites
Meteoritics & Planetary Science, 2017Co-Authors: M D Suttle, Matthew J Genge, Sara S. RussellAbstract:The orientations of dehydration cracks and fracture networks in fine-grained, unmelted Micrometeorites were analyzed using rose diagrams and entropy calculations. As cracks exploit pre-existing anisotropies, analysis of their orientation provides a mechanism with which to study the subtle petrofabrics preserved within fine-grained and amorphous materials. Both uniaxial and biaxial fabrics are discovered, often with a relatively wide spread in orientations (40°–60°). Brittle deformation cataclasis and rotated olivine grains are reported from a single micrometeorite. This paper provides the first evidence for impact-induced shock deformation in fine-grained Micrometeorites. The presence of pervasive, low-grade shock features in CM chondrites and CM-like dust, anomalously low-density measurements for C-type asteroids, and impact experiments which suggest CM chondrites are highly prone to disruption all imply that CM parent bodies are unlikely to have remained intact and instead exist as a collection of loosely aggregated rubble-pile asteroids, composed of primitive shocked clasts.
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The thermal decomposition of fine-grained Micrometeorites, observations from mid-IR spectroscopy
Geochimica et Cosmochimica Acta, 2017Co-Authors: M D Suttle, Luigi Folco, Matthew J Genge, Sara S. RussellAbstract:Abstract We analysed 44 fine-grained and scoriaceous Micrometeorites. A bulk mid-IR spectrum (8–13 μm) for each grain was collected and the entire micrometeorite population classified into 5 spectral groups, based on the positions of their absorption bands. Corresponding carbonaceous Raman spectra, textural observations from SEM-BSE and bulk geochemical data via EMPA were collected to aid in the interpretation of mid-IR spectra. The 5 spectral groups identified correspond to progressive thermal decomposition. Unheated hydrated chondritic matrix, composed predominantly of phyllosilicates, exhibit smooth, asymmetric spectra with a peak at ∼10 μm. Thermal decomposition of sheet silicates evolves through dehydration, dehydroxylation, annealing and finally by the onset of partial melting. Both CI-like and CM-like Micrometeorites are shown to pass through the same decomposition stages and produce similar mid-IR spectra. Using known temperature thresholds for each decomposition stage it is possible to assign a peak temperature range to a given micrometeorite. Since the temperature thresholds for decomposition reactions are defined by the phyllosilicate species and the cation composition and that these variables are markedly different between CM and CI classes, atmospheric entry should bias the dust flux to favour the survival of CI-like grains, whilst preferentially melting most CM-like dust. However, this hypothesis is inconsistent with empirical observations and instead requires that the source ratio of CI:CM dust is heavily skewed in favour of CM material. In addition, a small population of anomalous grains are identified whose carbonaceous and petrographic characteristics suggest in-space heating and dehydroxylation have occurred. These grains may therefore represent regolith Micrometeorites derived from the surface of C-type asteroids. Since the spectroscopic signatures of dehydroxylates are distinctive, i.e. characterised by a reflectance peak at 9.0–9.5 μm, and since the surfaces of C-type asteroids are expected to be heated via impact gardening, we suggest that future spectroscopic investigations should attempt to identify dehydroxylate signatures in the reflectance spectra of young carbonaceous asteroid families.
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An urban collection of modern-day large Micrometeorites: Evidence for variations in the extraterrestrial dust flux through the Quaternary
Geology, 2016Co-Authors: Matthew J Genge, M Van Ginneken, J. Larsen, M D SuttleAbstract:We report the discovery of significant numbers (500) of large Micrometeorites (>100 mm) from rooftops in urban areas. The identification of particles as Micrometeorites is achieved on the basis of their compositions, mineralogies, and textures. All particles are silicate-dominated (S type) cosmic spherules with subspherical shapes that form by melting during atmospheric entry and consist of quench crystals of magnesian olivine, relict crystals of forsterite, and iron-bearing olivine within glass. Four particles also contain Ni-rich metal-sulfide beads. Bulk compositions are chondritic apart from depletions in the volatile, moderately volatile, and siderophile elements, as observed in Micrometeorites from other sources. The reported particles are likely to have fallen on Earth in the past 6 yr and thus represent the youngest large Micrometeorites collected to date. The relative abundance ratio of barred olivine to cryptocrystalline spherule types in the urban particles of 1.45 is shown to be higher than a Quaternary average of ~0.9, suggesting variations in the extraterrestrial dust flux over the past 800 k.y. Changes in the entry velocities of dust caused by quasi-periodic gravitational perturbation during transport to Earth are suggested to be responsible. Variations in cosmic spherule abundance within the geologic column are thus unavoidable and can be a consequence of dust transport as well as major dust production events.SCOPUS: ar.jinfo:eu-repo/semantics/publishe
Pierre Rochette - One of the best experts on this subject based on the ideXlab platform.
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Chondritic Micrometeorites from the Transantarctic Mountains
Meteoritics & Planetary Science, 2012Co-Authors: Matthias Van Ginneken, Luigi Folco, Carole Cordier, Pierre RochetteAbstract:Abstract– On the basis of morphological and petrographic characteristics, eight “giant” unmelted Micrometeorites in the 300–1100 μm size range were selected from the Transantarctic Mountain micrometeorite collection, Victoria Land, Antarctica. Mineralogical and geochemical data obtained by means of scanning electron microscopy, electron probe microanalyses, and synchrotron X-ray diffraction allow their classification as chondritic Micrometeorites. The large size of the Micrometeorites increases considerably the amount of mineralogical and geochemical information compared to Micrometeorites in smaller size fractions, therefore allowing a better definition of their parent material. A large variety of material is observed: five Micrometeorites are related to unequilibrated and equilibrated ordinary chondrite, one to CV chondrite, one to CM chondrite, and one to CI chondrite parent materials. Besides reporting the first occurrence of a CV-like micrometeorite, our study shows that the abundance of chondritic material supports observations from recent studies on cosmic spherules that a large part of the micrometeorite flux in this size range is of asteroidal origin.
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Constraining the terrestrial age of Micrometeorites using their record of the Earth's magnetic field polarity
Geology, 2011Co-Authors: Clément Suavet, Pierre Rochette, Jérôme Gattacceca, Luigi FolcoAbstract:We propose a new nondestructive method that uses the paleomagnetic record of Micrometeorites in Earth9s polar regions to constrain the age of their fall. During atmospheric entry, melted Micrometeorites acquire a thermal remanent magnetization and record the polar subvertical geomagnetic field. When the fall vector can be determined, due to the location of bubbles, iron-nickel droplets, or grain-size gradients, it is possible to ascribe the fall to a normal or reverse polarity interval of the geomagnetic field. We tested this concept on a set of eight melted Micrometeorites from the Transantarctic Mountains (Antarctica). Two Micrometeorites have magnetization directions consistent with a normal polarity of the Earth9s magnetic field, whereas four others have recorded a reverse polarity, and therefore fell to Earth at least 0.78 m.y. ago. One micrometeorite has a magnetization that is seemingly unrelated to the inferred entry direction. The fall direction could not be determined with certainty for one micrometeorite. These results provide new evidence suggesting that the Transantarctic Mountains micrometeorite traps are 1–2 m.y. old, and confirm that they contain the oldest non-fossil Micrometeorites available.
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Identification of the parent bodies of Micrometeorites with high-precision oxygen isotope ratios
Earth and Planetary Science Letters, 2010Co-Authors: Clément Suavet, Luigi Folco, Jérôme Gattacceca, Anne Alexandre, Ian A. Franchi, Corinne Sonzogni, Richard C. Greenwood, Pierre RochetteAbstract:Oxygen isotopic compositions allow identification of potential parent bodies of extraterrestrial materials. We measured oxygen isotope ratios of 33 large (diameter >500 mu m) silicate melted Micrometeorites (cosmic spherules) from Antarctica, using IR-laser fluorination coupled with mass spectrometry. It is the first time that this high-precision method is used on individual Micrometeorites. The selected Micrometeorites are representative of the influx of extraterrestrial materials to the Earth. Our results show that most Micrometeorites are related to carbonaceous chondrites, which is consistent with previous studies. However, 20-50% of them seem to be related to CO/CV carbonaceous chondrites, whereas CM/CR carbonaceous chondrites were thought to be the main source for Micrometeorites. Furthermore, similar to 30% of measured samples have oxygen isotope ratios lying above the terrestrial fractionation line, which relates them to ordinary chondrites or other, as yet, unsampled parent bodies
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Magnetic properties of Micrometeorites
Journal of Geophysical Research, 2009Co-Authors: Clément Suavet, Luigi Folco, Pierre Rochette, J. Gattacceca, Natale Perchiazzi, J. Duprat, Ralph P. HarveyAbstract:Most Micrometeorites are strongly magnetic: the signal of a single micrometeorite may exceed the signal of a weakly magnetized standard sediment sample. Micrometeorites contain abundant magnetite, mostly produced by high-temperature oxidation during atmospheric entry. In this study, we carried out measurements on 520 Micrometeorites(505 melted cosmic spherules, 6 partially melted scoriaceous Micrometeorites, and 9 unmelted Micrometeorites). The natural remanent magnetization and the saturation isothermal remanent magnetization have been measured, followed by alternating field or thermal stepwise demagnetization. The natural remanent magnetization is in the range of 0.4–300 A/m for cosmic spherules; it is a stable thermal remanent magnetization acquired by quenching in the Earth’s magnetic field. The range is 3.8–16 A/m for scoriaceous Micrometeorites and 78–525 A/m for unmelted Micrometeorites, which may have preserved a preatmospheric magnetization. The magnetic susceptibility is in the range of 0.005–2.9 SI for cosmic spherules and is in the range of 0.06–0.12 SI for scoriaceous and unmelted Micrometeorites. Temperature-dependent susceptibility analyses and thermal demagnetization indicate that magnetite is cation substituted in cosmic spherules. Different populations of magnetite grains may have different degrees of cation substitution within a single micrometeorite. Anisotropy of magnetic susceptibility measurements indicates that Micrometeorites are strongly anisotropic (anisotropy degree >15%) and that most have oblate fabrics consistent with the parallel habit of magnetite in barred olivine cosmic spherules
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Statistical properties of the Transantarctic Mountains (TAM) micrometeorite collection
Polar Science, 2009Co-Authors: Clément Suavet, Luigi Folco, Pierre Rochette, Jérôme Gattacceca, Myriam Kars, Ralph P. HarveyAbstract:AbstractMicrometeorites have been recovered from traps located at the summit of nunataks in the Transantarctic Mountains (TAM), Antarctica. They constitute the TAM micrometeorite collection. Micrometeorites accumulated by direct infall for hundreds of thousands of years. This long collection duration is confirmed by the wide range of weathering by dissolution of olivine in the stony Micrometeorites from the TAM collection. A statistical study of the size distribution and frequency by type of this collection, and comparison with other Antarctic micrometeorite collections (the South Pole Water Well collection and the Walcott Névé collection), suggest that the TAM collection is essentially unbiased. Thanks to the very long exposure of the traps, large diameter (>1000μm) Micrometeorites are present in sufficiently large numbers to allow a statistically meaningful estimate of their size distribution in this size range for the first time. We found that the slope of the size distribution remains constant in the 100–1600μm size range. Therefore, the size distribution of Micrometeorites in this size range is controlled by a single process
Ralph P. Harvey - One of the best experts on this subject based on the ideXlab platform.
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The weathering of Micrometeorites from the Transantarctic Mountains
Geochimica et Cosmochimica Acta, 2016Co-Authors: Matthias Van Ginneken, Luigi Folco, Matthew J Genge, Ralph P. HarveyAbstract:Abstract Micrometeorites are cosmic dust particles recovered from the Earth’s surface that dominate the influx of extraterrestrial material accreting to our planet. This paper provides the first in-depth study of the weathering of Micrometeorites within the Antarctic environment that will allow primary and secondary features to be distinguished. It is based on the analysis of 366 particles from Larkman Nunatak and 25 from the Transantarctic Mountain collection. Several important morphological categories of weathering effects were identified: (1) irregular and faceted cavities, (2) surface etch pits, (3) infilled cavities, (4) replaced silicate phases, and (5) hydrated and replaced metal. These features indicate that congruent dissolution of silicate phases, in particular olivine, is important in generating new pore space within particles. Comparison of the preservation of glass and olivine also indicates preferential dissolution of olivine by acidic solutions during low temperature aqueous alteration. Precipitation of new hydrous phases within cavities, in particular ferrihydrite and jarosite, results in pseudomorph textures within heavily altered particles. Glass, in contrast, is altered to palagonite gels and shows a sequential replacement indicative of varying water to rock ratios. Metal is variably replaced by Fe-oxyhydroxides and results in decreases in Ni/Fe ratio. In contrast, sulphides within metal are largely preserved. Magnetite, an essential component of Micrometeorites formed during atmospheric entry, is least altered by interaction with the terrestrial environment. The extent of weathering in the studied Micrometeorites is sensitive to differences in their primary mineralogy and varies significantly with particle type. Despite these differences, we propose a weathering scale for Micrometeorites based on both their degree of terrestrial alteration and the level of encrustation by secondary phases. The compositions and textures of weathering products, however, suggest open system behaviour and variable water to rock ratios that imply climatic variation over the lifetime of the micrometeorite deposits.
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Magnetic properties of Micrometeorites
Journal of Geophysical Research, 2009Co-Authors: Clément Suavet, Luigi Folco, Pierre Rochette, J. Gattacceca, Natale Perchiazzi, J. Duprat, Ralph P. HarveyAbstract:Most Micrometeorites are strongly magnetic: the signal of a single micrometeorite may exceed the signal of a weakly magnetized standard sediment sample. Micrometeorites contain abundant magnetite, mostly produced by high-temperature oxidation during atmospheric entry. In this study, we carried out measurements on 520 Micrometeorites(505 melted cosmic spherules, 6 partially melted scoriaceous Micrometeorites, and 9 unmelted Micrometeorites). The natural remanent magnetization and the saturation isothermal remanent magnetization have been measured, followed by alternating field or thermal stepwise demagnetization. The natural remanent magnetization is in the range of 0.4–300 A/m for cosmic spherules; it is a stable thermal remanent magnetization acquired by quenching in the Earth’s magnetic field. The range is 3.8–16 A/m for scoriaceous Micrometeorites and 78–525 A/m for unmelted Micrometeorites, which may have preserved a preatmospheric magnetization. The magnetic susceptibility is in the range of 0.005–2.9 SI for cosmic spherules and is in the range of 0.06–0.12 SI for scoriaceous and unmelted Micrometeorites. Temperature-dependent susceptibility analyses and thermal demagnetization indicate that magnetite is cation substituted in cosmic spherules. Different populations of magnetite grains may have different degrees of cation substitution within a single micrometeorite. Anisotropy of magnetic susceptibility measurements indicates that Micrometeorites are strongly anisotropic (anisotropy degree >15%) and that most have oblate fabrics consistent with the parallel habit of magnetite in barred olivine cosmic spherules
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Statistical properties of the Transantarctic Mountains (TAM) micrometeorite collection
Polar Science, 2009Co-Authors: Clément Suavet, Luigi Folco, Pierre Rochette, Jérôme Gattacceca, Myriam Kars, Ralph P. HarveyAbstract:AbstractMicrometeorites have been recovered from traps located at the summit of nunataks in the Transantarctic Mountains (TAM), Antarctica. They constitute the TAM micrometeorite collection. Micrometeorites accumulated by direct infall for hundreds of thousands of years. This long collection duration is confirmed by the wide range of weathering by dissolution of olivine in the stony Micrometeorites from the TAM collection. A statistical study of the size distribution and frequency by type of this collection, and comparison with other Antarctic micrometeorite collections (the South Pole Water Well collection and the Walcott Névé collection), suggest that the TAM collection is essentially unbiased. Thanks to the very long exposure of the traps, large diameter (>1000μm) Micrometeorites are present in sufficiently large numbers to allow a statistically meaningful estimate of their size distribution in this size range for the first time. We found that the slope of the size distribution remains constant in the 100–1600μm size range. Therefore, the size distribution of Micrometeorites in this size range is controlled by a single process
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Micrometeorites from the transantarctic mountains
Proceedings of the National Academy of Sciences of the United States of America, 2008Co-Authors: Pierre Rochette, Luigi Folco, Matthias Van Ginneken, Jérôme Gattacceca, Natale Perchiazzi, C Suavet, Regis Braucher, Ralph P. HarveyAbstract:We report the discovery of large accumulations of Micrometeorites on the Myr-old, glacially eroded granitic summits of several isolated nunataks in the Victoria Land Transantarctic Mountains. The number (>3,500) of large (>400 μm and up to 2 mm in size) melted and unmelted particles is orders of magnitudes greater than other Antarctic collections. Flux estimates, bedrock exposure ages and the presence of ≈0.8-Myr-old microtektites suggest that extraterrestrial dust collection occurred over the last 1 Myr, taking up to 500 kyr to accumulate based on 2 investigated find sites. The size distribution and frequency by type of cosmic spherules in the >200-μm size fraction collected at Frontier Mountain (investigated in detail in this report) are similar to those of the most representative known micrometeorite populations (e.g., South Pole Water Well). This and the identification of unusual types in terms of composition (i.e., chondritic Micrometeorites and spherulitic aggregates similar to the ≈480-kyr-old ones recently found in Antarctic ice cores) and size suggest that the Transantarctic Mountain Micrometeorites constitute a unique and essentially unbiased collection that greatly extends the micrometeorite inventory and provides material for studies on micrometeorite fluxes over the recent (≈1 Myr) geological past.
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Micrometeorites from the Transantarctic Mountains
Proceedings of the National Academy of Sciences of the United States of America, 2008Co-Authors: Pierre Rochette, Luigi Folco, Matthias Van Ginneken, Clément Suavet, Jérôme Gattacceca, Natale Perchiazzi, Regis Braucher, Ralph P. HarveyAbstract:We report the discovery of large accumulations of Micrometeorites on the Myr-old, glacially eroded granitic summits of several isolated nunataks in the Victoria Land Transantarctic Mountains. The number (>3,500) of large (>400 mum and up to 2 mm in size) melted and unmelted particles is orders of magnitudes greater than other Antarctic collections. Flux estimates, bedrock exposure ages and the presence of approximately 0.8-Myr-old microtektites suggest that extraterrestrial dust collection occurred over the last 1 Myr, taking up to 500 kyr to accumulate based on 2 investigated find sites. The size distribution and frequency by type of cosmic spherules in the >200-mum size fraction collected at Frontier Mountain (investigated in detail in this report) are similar to those of the most representative known micrometeorite populations (e.g., South Pole Water Well). This and the identification of unusual types in terms of composition (i.e., chondritic Micrometeorites and spherulitic aggregates similar to the approximately 480-kyr-old ones recently found in Antarctic ice cores) and size suggest that the Transantarctic Mountain Micrometeorites constitute a unique and essentially unbiased collection that greatly extends the micrometeorite inventory and provides material for studies on micrometeorite fluxes over the recent ( approximately 1 Myr) geological past.