Primary Trapped Melt Inclusions in Olivine in the Olivine-Augite-Orthopyroxene Ureilite Hughes 009 (Articolo in rivista)

Type
Label
  • Primary Trapped Melt Inclusions in Olivine in the Olivine-Augite-Orthopyroxene Ureilite Hughes 009 (Articolo in rivista) (literal)
Anno
  • 2001-01-01T00:00:00+01:00 (literal)
Alternative label
  • Goodrich,C.A., Fioretti A.M., Tribaudino M., Molin G. (2001)
    Primary Trapped Melt Inclusions in Olivine in the Olivine-Augite-Orthopyroxene Ureilite Hughes 009
    in Geochimica et cosmochimica acta
    (literal)
Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#autori
  • Goodrich,C.A., Fioretti A.M., Tribaudino M., Molin G. (literal)
Pagina inizio
  • 621 (literal)
Pagina fine
  • 652 (literal)
Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#altreInformazioni
  • This paper deals with petrology of ureilites, the second largest group of primitive achondritic meteorites, most of which found in Antarctica. Ureilites are unique among achondrites because although they underwent a certain degree of magmatic differentiation, they preserve some primitive characteristics of their parent chondritic asteroid. This provides an excellent opportunity to investigate the early stages of geological evolution in our solar system. Geochimica and Cosmochimica Acta is a top journal that publishes research papers in a wide range of subjects in terrestrial geochemistry, meteoritics, and planetary geochemistry. (literal)
Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#numeroVolume
  • 65 (literal)
Rivista
Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#note
  • Impact Factor 2,614 (literal)
Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#descrizioneSinteticaDelProdotto
  • In the present paper we describe the first known occurrence of primary melt inclusions in a ureilite. The melt inclusions occur in olivine crystals. They are concentrated in the central regions of their hosts, showing elongate (mostly 20-60 µm in maximum dimension), negative olivine crystal shapes and parallel alignment. These and other features indicate that they were trapped during initial growth of their hosts from a liquid, and are likely to be representative samples of that liquid. We develop a petrologic model for the postentrapment history (crystallization, reaction and reequilibration) of the inclusions, based on which we reconstruct the composition of the primary trapped liquid. TEM investigations of microtextural features in all phases and XRD determination of Fe2+-Mg site distribution in orthopyroxene have elucidated the cooling and shock history of this ureilite. Hughes 009 experienced an extremely high cooling rate (7±5°C/hr at the closure T of 630°C) late in its evolution, and two distinguishable shock events – the first at peak pressures of 5-10 GPa,; and the second at lower pressures, resulting only in brecciation and redistribution of metal. Its late history is similar to that of most ureilites, and probably reflects impact excavation. (literal)
Note
  • ISI Web of Science (WOS) (literal)
Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#affiliazioni
  • Goodrich,C.A.a), Fioretti A.M.b), Tribaudino M.c), Molin G. d). a)Max-Planck-Institut für Chemie, Abteilung Kosmochemie PO 3060,55020 Mainz, Germany; b)C.N.R. Istituto di Geoscienze e Georisorse (Sezione di Padova), Corso Garibaldi, 37 - 35137 Padova - Italy; c)Dipartimento di Scienze Mineralogiche e Petrologiche, Via Valperga Caluso 35, 10125 Torino, Italy; d) Dipartimento di Mineralogia e Petrologia Corso Garibaldi 37 I-35137 Padova, Italy. (literal)
Titolo
  • Primary Trapped Melt Inclusions in Olivine in the Olivine-Augite-Orthopyroxene Ureilite Hughes 009 (literal)
Abstract
  • We describe the first known occurrence of primary melt inclusions in a ureilite. The ureilite is Hughes 009, one of a small number of ureilites whose primary mineralogy is olivine-augite-orthopyroxene, rather than olivine-pigeonite. Hughes 009 has a coarse-grained, equilibrated texture typical of ureilites, and homogeneous primary mineral compositions: olivine – mg 87.3; augite – mg 89.2, Wo 37.0, Al2O3 = 1.6 wt.%; orthopyroxene – mg 88.3, Wo 4.9. It shows only limited secondary reduction effects and no petrographically recognizable carbon phases, which indicates that its original carbon content was lower than in most ureilites. The melt inclusions occur in olivine crystals. They are concentrated in the central regions of their hosts, showing elongate (mostly 20-60 µm in maximum dimension), negative olivine crystal shapes and parallel alignment. These and other features indicate that they were trapped during initial growth of their hosts from a liquid, and are likely to be representative samples of that liquid. They consist of glass and single, subhedral crystals of high-Ca pyroxene, with minor Cr-rich spinel and metal-phosphide-sulfide spherules. They are surrounded by halos of olivine with rounded outlines defined by tiny bits of metal and thin arcs of glass. Pyroxenes within each inclusion show zonation patterns indicating that they nucleated at the olivine/liquid interface with compositions close to that of the primary augite, and then grew inward with dramatically increasing Al2O3 (to 10.8 wt.%), Wo (to »50), TiO2 and Cr2O3 contents. Glasses within each inclusion are relatively homogeneous. Glasses from all inclusions show well-defined trends of CaO, TiO2, Cr2O3, Na2O and SiO2 vs. Al2O3, (16-23 wt.%) that can be modelled as resulting principally from crystallization of various amounts of the pyroxene. The halos, which represent olivine that grew from the trapped melts, are zoned in Cr and Ca with concentrations decreasing inward, reflecting cocrystallization of pyroxene; they have homogeneous Fe/Mg identical to that of the primary olivine, indicating reequilibration with the host. We develop a petrologic model for the postentrapment history (crystallization, reaction and reequilibration) of the inclusions, based on which we reconstruct the composition of the primary trapped liquid (PTL). The PTL was saturated only with olivine. This result implies that Hughes 009 is a cumulate (consistent with the high Mn/Mg ratio of its olivine and a low abundance of graphite) and that the composition of the PTL is close to that of its parent magma. The low-pressure equilibrium crystallization sequence predicted by MAGPOX calculations for the PTL (olivine ® augite ® plagioclase ® pigeonite) is not, however, consistent with the primary mineralogy of Hughes 009. If the conditions of these calculations are, indeed, appropriate, then complex processes such as magma mixing must have been involved in the petrogenesis of this ureilite. This conclusion is consistent with other evidence that the olivine-augite-orthopyroxene ureilites record a more complex magmatic evolution than is evident in the olivine-pigeonite ureilites. TEM investigations of microtextural features in all phases and XRD determination of Fe2+-Mg site distribution in orthopyroxene have elucidated the cooling and shock history of this ureilite. Hughes 009 experienced an extremely high cooling rate (7±5°C/hr at the closure T of 630°C) late in its evolution, and two distinguishable shock events – the first at peak pressures of 5-10 GPa, resulting in mechanical polysynthetic twinning in augite and orthopyroxene and mild undulatory extinction in olivine; and the second at lower pressures, resulting only in brecciation and redistribution of metal. Its late history is similar to that of most ureilites, and probably reflects impact excavation. (literal)
Prodotto di
Insieme di parole chiave

Incoming links:


Prodotto
Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#rivistaDi
Insieme di parole chiave di
data.CNR.it