The Vicencia meteorite fall: A new unshocked (S1) weakly metamorphosed (3.2) LL chondrite

Autor: Klaus Keil, Maria E. Zucolotto, Alexander N. Krot, Patricia M. Doyle, Myriam Telus, Tatiana V. Krot, Richard C. Greenwood, Ian A. Franchi, John T. Wasson, Kees C. Welten, Marc W. Caffee, Derek W. G. Sears, My Riebe, Rainer Wieler, Edivaldo dos Santos, Rosa B. Scorzelli, Jerome Gattacceca, France Lagroix, Matthias Laubenstein, Julio C. Mendes, Philippe Schmitt-Kopplin, Mourad Harir, Andre L. R. Moutinho
Přispěvatelé: Centre européen de recherche et d'enseignement des géosciences de l'environnement (CEREGE), Institut de Recherche pour le Développement (IRD)-Institut National de la Recherche Agronomique (INRA)-Aix Marseille Université (AMU)-Collège de France (CdF (institution))-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Institut de Physique du Globe de Paris (IPGP), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS)
Rok vydání: 2015
Předmět:
Zdroj: Meteoritics and Planetary Science
Meteoritics & Planetary Science
Meteoritics & Planetary Science, 2015, 50, pp.1089-1111. ⟨10.1111/maps.12456⟩
Popis: The Vicencia meteorite, a stone of 1.547 kg, fell on September 21, 2013, at the village Borracha, near the city of Vicencia, Pernambuco, Brazil. It was recovered immediately after the fall, and our consortium study showed it to be an unshocked (S1) LL3.2 ordinary chondrite. The LL group classification is based on the bulk density ($3.13\; g\; cm^{-3}$); the chondrule mean apparent diameter (0.9 mm); the bulk oxygen isotopic composition ($\delta^{17}O=3.768\pm0.042{}^\text{o}\mkern-5mu/\mkern-3mu_\text{oo}$, $\delta^{18}O=5.359\pm0.042{}^\text{o}\mkern-5mu/\mkern-3mu_\text{oo}$, $\Delta^{17}O = 0.981\pm 0.020{}^\text{o}\mkern-5mu/\mkern-3mu_\text{oo}$); the content of metallic Fe,Ni (1.8 vol%); the Co content of kamacite (1.73 wt%); the bulk contents of the siderophile elements Ir and Co versus Au; and the ratios of metallic $Fe^{0}$/total iron (0.105) versus total Fe/Mg (1.164), and of Ni/Mg (0.057) versus total Fe/Mg. The petrologic type 3.2 classification is indicated by the beautifully developed chondritic texture, the standard deviation (~0.09) versus mean $Cr_{2}O_{3}$ content (~0.14 wt%) of ferroan olivine, the TL sensitivity and the peak temperature and peak width at half maximum, the cathodoluminescence properties of chondrules, the content of trapped $^{132}Xe_{tr}$(0.317 × $10^{-8}cm^{3}STP\; g^{-1}$), and the Raman spectra for organic material in the matrix. The cosmic ray exposure age is ~72 Ma, which is at the upper end of the age distribution of LL group chondrites. The meteorite is unusual in that it contains relatively large, up to nearly 100 μm in size, secondary fayalite grains, defined as olivine with $Fa_{{\textgreater}75}$, large enough to allow in situ measurement of oxygen and Mn-Cr isotope systematics with SIMS. Its oxygen isotopes plot along a mass-dependent fractionation line with a slope of ~0.5 and ${\Delta}17O$ of $4.0 \pm 0.3{}^\text{o}\mkern-5mu/\mkern-3mu_\text{oo}$, and are similar to those of secondary fayalite and magnetite in the unequilibrated chondrites EET 90161, MET 96503, and Ngawi. These data suggest that secondary fayalite in Vicencia was in equilibrium with a fluid with a $\Delta^{17}O$ of ~$4{}^\text{o}\mkern-5mu/\mkern-3mu_\text{oo}$, consistent with the composition of the fluid in equilibrium with secondary magnetite and fayalite in other unequilibrated ordinary chondrites. Secondary fayalite and the chondrule olivine phenocrysts in Vicencia are not in isotopic equilibrium, consistent with low-temperature formation of fayalite during aqueous alteration on the LL parent body. That alteration, as dated by the $^{53}Mn-^{53}Cr$ chronology age of secondary fayalite, took place $4.0^{+1.4}_{-1.1}$Ma after formation of CV CAIs when anchored to the quenched angrite D'Orbigny.
Databáze: OpenAIRE
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