NUCLEOSYNTHETIC TUNGSTEN ISOTOPE ANOMALIES IN ACID LEACHATES OF THE MURCHISON CHONDRITE: IMPLICATIONS FOR HAFNIUM-TUNGSTEN CHRONOMETRY

Journal Article · Sun Jul 01 04:00:00 EDT 2012 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/753/1/L6· OSTI ID:22047716

Burkhardt, Christoph; Wieler, Rainer ^[1]; Kleine, Thorsten ^[2]; Dauphas, Nicolas ^[3]

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1. Institute of Geochemistry and Petrology, Clausiusstrasse 25, ETH Zurich, CH-8092 Zurich (Switzerland)
2. Institut fuer Planetologie, Westfaelische Wilhelms-Universitaet Muenster, Wilhelm-Klemm-Strasse 10, D-48149 Muenster (Germany)
3. Origins Laboratory, Department of the Geophysical Sciences and Enrico Fermi Institute, University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637 (United States)

Progressive dissolution of the Murchison carbonaceous chondrite with acids of increasing strengths reveals large internal W isotope variations that reflect a heterogeneous distribution of s- and r-process W isotopes among the components of primitive chondrites. At least two distinct carriers of nucleosynthetic W isotope anomalies must be present, which were produced in different nucleosynthetic environments. The co-variation of {sup 182}W/{sup 184}W and {sup 183}W/{sup 184}W in the leachates follows a linear trend that is consistent with a mixing line between terrestrial W and a presumed s-process-enriched component. The composition of the s-enriched component agrees reasonably well with that predicted by the stellar model of s-process nucleosynthesis. The co-variation of {sup 182}W/{sup 184}W and {sup 183}W/{sup 184}W in the leachates provides a means for correcting the measured {sup 182}W/{sup 184}W and {sup 182}W/{sup 183}W of Ca-Al-rich inclusions (CAI) for nucleosynthetic anomalies using the isotopic variations in {sup 183}W/{sup 184}W. This new correction procedure is different from that used previously, and results in a downward shift of the initial {epsilon}{sup 182}W of CAI to -3.51 {+-} 0.10 (where {epsilon}{sup 182}W is the variation in 0.01% of the {sup 182}W/{sup 183}W ratio relative to Earth's mantle). This revision leads to Hf-W model ages of core formation in iron meteorite parent bodies that are {approx}2 Myr younger than previously calculated. The revised Hf-W model ages are consistent with CAI being the oldest solids formed in the solar system, and indicate that core formation in some planetesimals occurred within {approx}2 Myr of the beginning of the solar system.

• OSTI ID: 22047716
• Journal Information: Astrophysical Journal Letters, Journal Name: Astrophysical Journal Letters Journal Issue: 1 Vol. 753; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ASTEROIDS
ASTROPHYSICS
CHONDRITES
EARTH MANTLE
HAFNIUM
HYDROFLUORIC ACID
IRON METEORITES
METEOROIDS
NUCLEOSYNTHESIS
PLANETS
R PROCESS
S PROCESS
SOLAR SYSTEM
SOLAR SYSTEM EVOLUTION
STARS
TUNGSTEN
TUNGSTEN 182
TUNGSTEN 183
TUNGSTEN 184