TY - JOUR
T1 - Rapid accretion and differentiation of iron meteorite parent bodies inferred from 182Hf-182W chronometry and thermal modeling
AU - Qin, Liping
AU - Dauphas, Nicolas
AU - Wadhwa, Meenakshi
AU - Masarik, Jozef
AU - Janney, Philip E.
N1 - Funding Information:
We thank the Field Museum and the Smithsonian Institution for providing iron meteorite samples. We are grateful to Timothy McCoy for his guidance in the selection of the Grant specimen. L. Qin acknowledges support in the form of a graduate fellowship from the Field Museum. L. Qin is grateful to Robert N. Clayton and Lawrence Grossman for their helpful reviews on her dissertation thesis related to this manuscript, and to C. Nicole Foley for generously sharing the details of her W separation protocol. We also thank Eric Gilabert for giving us access to his compilation of meteorite exposure ages. We thank H. Palme and K. Mezger for their insightful reviews of the manuscript. This work was supported by the France-Chicago Center, a Packard Fellowship and NASA grants NNG06GG75G (to N. D.) and NNG05GG22G (to M. W.).
PY - 2008/8/30
Y1 - 2008/8/30
N2 - New high-precision W isotope measurements are presented for 33 iron meteorites from 8 magmatic groups (IC, IIAB, IID, IIIAB, IIIE, IIIF, I VA and IVB), 2 non-magmatic groups (IAB-IIICD and IIE), and one ungrouped iron (Deep Springs). All magmatic irons have ε182W values that are, within errors, equal to, or less radiogenic than, the Solar System initial of - 3.47 ± 0.20. A method was developed to correct the measured ε182W values of magmatic iron meteorites for the presence of cosmogenic effects produced during space exposure to galactic cosmic rays. The corrected data provide new constraints on the timing of metal-silicate differentiation in iron meteorite parent bodies, which must have taken place within a few million years (< 2 to 6 My) of condensation of calcium-aluminum-rich inclusions (CAIs). Metal-silicate differentiation ages (from 182Hf-182W systematics) were combined with parent body sizes (from metallographic cooling rates) into a model of planetesimal heating by 26Al-decay, to constrain the accretion timescale of iron meteorite parent bodies. Accretion of iron meteorite parent bodies most likely occurred within 1.5 My of the formation of CAIs. The fast accretion times of iron meteorite parent bodies are consistent with dynamical models indicating that these objects may have originated in the terrestrial planet-forming region, where the accretion rates were high. Our W isotopic data for non-magmatic IAB-IIICD and IIE irons provide new constraints for their formation mechanisms. In particular, they support formation of IAB-IIICD iron meteorites by melting during a single collision event dated at 4-7 My after formation of the Solar System.
AB - New high-precision W isotope measurements are presented for 33 iron meteorites from 8 magmatic groups (IC, IIAB, IID, IIIAB, IIIE, IIIF, I VA and IVB), 2 non-magmatic groups (IAB-IIICD and IIE), and one ungrouped iron (Deep Springs). All magmatic irons have ε182W values that are, within errors, equal to, or less radiogenic than, the Solar System initial of - 3.47 ± 0.20. A method was developed to correct the measured ε182W values of magmatic iron meteorites for the presence of cosmogenic effects produced during space exposure to galactic cosmic rays. The corrected data provide new constraints on the timing of metal-silicate differentiation in iron meteorite parent bodies, which must have taken place within a few million years (< 2 to 6 My) of condensation of calcium-aluminum-rich inclusions (CAIs). Metal-silicate differentiation ages (from 182Hf-182W systematics) were combined with parent body sizes (from metallographic cooling rates) into a model of planetesimal heating by 26Al-decay, to constrain the accretion timescale of iron meteorite parent bodies. Accretion of iron meteorite parent bodies most likely occurred within 1.5 My of the formation of CAIs. The fast accretion times of iron meteorite parent bodies are consistent with dynamical models indicating that these objects may have originated in the terrestrial planet-forming region, where the accretion rates were high. Our W isotopic data for non-magmatic IAB-IIICD and IIE irons provide new constraints for their formation mechanisms. In particular, they support formation of IAB-IIICD iron meteorites by melting during a single collision event dated at 4-7 My after formation of the Solar System.
KW - Hf-W model age
KW - accretion timescales
KW - metal-silicate differentiation
UR - http://www.scopus.com/inward/record.url?scp=49149084170&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=49149084170&partnerID=8YFLogxK
U2 - 10.1016/j.epsl.2008.06.018
DO - 10.1016/j.epsl.2008.06.018
M3 - Article
AN - SCOPUS:49149084170
SN - 0012-821X
VL - 273
SP - 94
EP - 104
JO - Earth and Planetary Science Letters
JF - Earth and Planetary Science Letters
IS - 1-2
ER -