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Platinum isotopes are sensitive to the effects of galactic cosmic rays (GCR), which can alter isotope ratios and mask nucleosynthetic isotope variations. Platinum also features one p- process isotope, 190 Pt, which is very low abundance and therefore challenging to analyse. Platinum-190 is relevant for early solar-system chronology because of its decay to 186 Os. Here, we present new Pt isotope data for five iron meteorite groups (IAB, IIAB, IID, IIIAB and IVA), including high-precision measurements of 190 Pt for the IAB, IIAB and IIIAB irons, determined by multi-collector ICPMS. New data are in good agreement with previous studies and display correlations between different Pt isotopes. The slopes of these correlations are well-reproduced by the available GCR models. We report Pt isotope ratios for the IID meteorite Carbo that are consistently higher than the predicted effects from the GCR model. This suggests that the model predictions do not fully account for all the GCR effects on Pt isotopes, but also that the pre-atmospheric radii and exposure times calculated for Carbo may be incorrect. Despite this, the good agreement of relative effects in Pt isotopes with the predicted GCR trends confirms that Pt isotopes are a useful in-situ neutron dosimeter. Once GCR effects are accounted for, our new dataset reveals s- and r- process homogeneity between the iron meteorite groups studied here and the Earth. New 190 Pt data for the IAB, IIAB and IIIAB iron meteorites indicate the absence of GCR effects and homogeneity in the p -process isotope between these groups and the Earth. This corresponds well with results from other heavy p -process isotopes and suggests their homogenous distribution in the inner solar system, although it does not exclude that potential p -process isotope variations are too diluted to be currently detectable. [ABSTRACT FROM AUTHOR]

The short-lived 182 Hf– 182 W 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 ε 182 W values obtained for the IAB iron meteorites range from −3.61 ± 0.10 to −2.73 ± 0.09. Correlating ε i Pt with ε 182 W data yields a pre-neutron capture ε 182 W 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 1.4 ± 0.1 Ma after CAIs with a radius of greater than 60 km. [ABSTRACT FROM AUTHOR]