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Samenvatting
Abstract We have investigated a piece of the Netschaëvo IIE iron meteorite containing a silicate inclusion by means of electron microprobe analysis (EMPA) and transmission electron microscopy (TEM). Netschaëvo contains chondrule-bearing clasts and impact melt rock clasts were also recently found. The examined inclusion belongs to the latter and is characterized by a porphyritic texture dominated by clusters of coarse-grained olivine and pyroxene, set in a fine-grained groundmass that consists of new crystals of olivine and a hyaline matrix. This matrix material has a quasi-basaltic composition in the inner part of the inclusion, whereas the edge of the inclusion has a lower SiO2 concentration and is enriched in MgO, P2O5, CaO, and FeO. Close to the metal host, the inclusion also contains euhedral Mg-chromite crystals and small (<2 μm), Si-rich globules. A TEM foil was cut from this glassy, silico-phosphate material. It shows that the material consists of elongated olivine crystallites containing up to 14 wt% P2O5, amorphous material, and interstitial Cl-apatite crystals. The Si-rich silicate glass globules show a second population of Fe-rich silicate glass droplets, indicating they formed by silicate liquid immiscibility. Together with the presence of phosphoran olivine and quenched Cl-apatite, these textures suggest rapid cooling and quenching as a consequence of an impact event. Moreover, the enrichment of phosphorus in the silicate inclusion close to the metal host (phosphoran olivine and Cl-apatite) indicates that phosphorus re-partitioned from the metal into the silicate phase upon cooling. This probably also took place in pallasite meteorites that contain late-crystallizing phases rich in phosphorus. Accordingly, our findings suggest that oxidation of phosphorus might be a general process in core–mantle environments, bearing on our understanding of planetesimal evolution. Thus, the Netschaëvo sample serves as a natural planetesimal core–mantle boundary experiment and based on our temperature estimates, the following sequence of events takes place: (i) precipitation of olivine (1400–1360 °C), (ii) re-partitioning of phosphorus from the metal into the silicate phase, and (iii) formation of immiscible melts (1230–1115 °C).
Originele taal-2 | English |
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Pagina's (van-tot) | 378-395 |
Aantal pagina's | 18 |
Tijdschrift | Geochimica et Cosmochimica Acta |
Volume | 197 |
DOI's | |
Status | Published - 15 jan 2017 |
Vingerafdruk
Duik in de onderzoeksthema's van 'Immiscible silicate liquids and phosphoran olivine in Netschaëvo IIE silicate: Analogue for planetesimal core–mantle boundaries'. Samen vormen ze een unieke vingerafdruk.-
OZR2725: ULB-VUB Joint Research Group: Brussels Institute for Geochemical Techniques in Earth Sciences - BIGE
Claeys, P. & Mattielli, N.
5/12/14 → 2/10/28
Project: Fundamenteel
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FWOTM752: Metamorfose en smelten in proto-planeten tijdens de eerste 10 miljoen jaar evolutie van het zonnestelsel: verbinding tussen gemetamorfoseerde stenen en mantel overblijfsel
Mckibbin, S. & Claeys, P.
1/10/14 → 1/07/17
Project: Fundamenteel
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SRP2: Tracers van verleden en heden global changes
Claeys, P., Elskens, M., Huybrechts, P., Gao, Y., Kervyn De Meerendre, M., Claeys, P., Baeyens, W. & Dehairs, F.
1/11/12 → 31/10/24
Project: Fundamenteel