Late metal–silicate separation on the IAB parent asteroid: constraints from combined W and Pt isotopes and thermal modelling

Journal article

The short-lived ¹⁸²Hf–¹⁸²W decay system is a powerful chronometer for constraining the timing of metal–silicate separation and core formation in planetesimals and planets. Neutron capture effects on W isotopes, however, significantly hamper the application of this tool. In order to correct for neutron capture effects, Pt isotopes have emerged as a reliable in-situ neutron dosimeter. This study applies this method to IAB iron meteorites, in order to constrain the timing of metal segregation on the IAB parent body.
The ε¹⁸²W values obtained for the IAB iron meteorites range from −3.61 ± 0.10 to −2.73 ± 0.09. Correlating εⁱPt with ε¹⁸²W data yields a pre-neutron capture ε¹⁸²W of −2.90 ± 0.06. This corresponds to a metal–silicate separation age of 6.0 ± 0.8 Ma after CAI for the IAB parent body, and is interpreted to represent a body-wide melting event. Later, between 10 and 14 Ma after CAI, an impact led to a catastrophic break-up and subsequent reassembly of the parent body. Thermal models of the interior evolution that are consistent with these estimates suggest that the IAB parent body underwent metal–silicate separation as a result of internal heating by short-lived radionuclides and accreted at around Ma after CAIs with a radius of greater than 60 km.

Authors: Hunt, AC; Cook, DL; Lichtenberg, T; Reger, PM; Ek, M

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Elsevier
• Journal: Earth and Planetary Science Letters
• Volume: 482
• Pages: 490-500
• Publication date: 2017-11-27
• Acceptance date: 2017-11-14
• DOI: 10.1016/j.epsl.2017.11.034
• ISSN: 0012-821X
• Language: English
• Keywords: FFR