Journal article
Pb–Pb dating constraints on the accretion and cooling history of chondrites
Geochimica et cosmochimica acta, Vol.71(6), pp.1583-1604
2007
Handle:
https://hdl.handle.net/2376/103365
Abstract
We have analyzed the Pb isotopic compositions of whole-rocks and various components (CAIs, chondrules, and/or mineral separates) of two carbonaceous chondrites, Allende (CV3) and Murchison (CM2), and nine ordinary chondrites, Sainte Marguerite (H4), Nadiabondi and Forest City (H5), Kernouvé (H6), Bjurböle (L/LL4), Elenovka and Ausson (L5), Tuxtuac (LL5), and Saint-Séverin (LL6) by MC-ICP-MS. Three CAI fractions from Allende define an isochron with an age of 4568.1
±
9.4
Ma (MSWD
=
0.08) and plot on the same isochron as fragments of the Efremovka inclusion E60 analyzed by Amelin et al. [Amelin, Y., Krot, A. N., Hutcheon, I. D., and Ulyanov, A. A. (2002a). Lead isotopic ages of chondrules and calcium–aluminum-rich inclusions.
Science
297, 1679–1683]. When these two groups of samples are combined, the isochron yields an age of 4568.5
±
0.5 (MSWD
=
0.90), which is our best estimate of the age of the Solar System. Chondrules and pyroxene–olivine fractions from the ordinary chondrites yield ages that reflect the blocking of Pb isotope equilibration with the nebular gas. The combination of these ages with the corresponding metamorphic phosphate ages provides constraints on the thermal history of the different chondrite parent bodies. Among the H chondrites, Sainte Marguerite cooled to below ∼1100
K within a few My at 4565
Ma and to ∼800
K at 4563
Ma. Nadiabondi appears to have experienced a slightly more protracted cooling history with the corresponding interval lasting from 4559 to 4556
Ma. The data from Forest City and Kernouvé show evidence of late-stage perturbation with resulting U/Pb fractionation. Likewise, Pb isotopes in Tuxtuac (LL5) record a cooling history lasting from ∼4555 to 4544
Ma, which may indicate that the cooling history for the LL parent body was more prolonged than for the H parent body. We suggest a thermal evolution model for the growth of the planetary bodies based on the release of radiogenic heat from
26Al and
60Fe. This model incorporates the accretion rate, which determines the time at which the radiogenic heat becomes efficiently trapped, and the terminal size of the parent body, which controls its overall thermal inertia. The parent bodies of carbonaceous chondrites, which show little indication of metamorphic transformation, collect cooler nebular material at a relatively late stage. Small asteroids of ∼10–50
km radius accreting within 1–3
My could be the parent bodies of H and LL chondrites. The parent body of the L chondrites is likely to be a larger asteroid (
r
>
100
km) or possibly the product of collisions of smaller planetary bodies.
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Details
- Title
- Pb–Pb dating constraints on the accretion and cooling history of chondrites
- Creators
- Audrey Bouvier - Ecole Normale Supérieure, Laboratoire des Sciences de la Terre, 69364 Lyon Cedex 7, FranceJanne Blichert-Toft - Ecole Normale Supérieure, Laboratoire des Sciences de la Terre, 69364 Lyon Cedex 7, FranceFrédéric Moynier - Ecole Normale Supérieure, Laboratoire des Sciences de la Terre, 69364 Lyon Cedex 7, FranceJeffrey D Vervoort - Washington State University, Department of Geology, Pullman, WA 99164, USAFrancis Albarède - Ecole Normale Supérieure, Laboratoire des Sciences de la Terre, 69364 Lyon Cedex 7, France
- Publication Details
- Geochimica et cosmochimica acta, Vol.71(6), pp.1583-1604
- Academic Unit
- Environment, School of the (CAS)
- Publisher
- Elsevier Ltd
- Identifiers
- 99900546679601842
- Language
- English
- Resource Type
- Journal article