Genetic tracing of impactors on the HED parent body using Mo and Ru isotopes
Abstract
Siderophile elements and volatiles in the Earth's mantle were likely delivered during the later stages of accretion [e.g., 1]. The relationship between late impactors and the major building blocks of the terrestrial planets is ambiguous, however, as is whether those materials varied with time or location. These issues can be investigated using impact melt rocks. Siderophile elements are strongly depleted in the crusts of differentiated planetary bodies, but have comparatively high concentrations in chondrites and iron meteorites. Impact melts rocks, thus, are often enriched in siderophile elements inherited from the impactor. Osmium isotopes and relative abundances of siderophile elements in lunar and HED impact melt rocks indicate that impactors to these bodies were varied, including both chondritic and evolved impactors, and were generally unlike known meteorite groups [e.g., 2-4].
To further characterize impactors in the inner solar system, we utilize genetic tracing; i.e, the parent body-specific isotope anomalies observed at the bulk meteorite scale for Mo and Ru [5-6]. Due to their siderophile behaviors, the isotopic compositions of Mo and Ru in impact melt rocks likely reflect those of the impactor. Molybdenum and Ru isotope data from impact melts extracted from the polymict eucrite breccia, NWA 1644 will be presented. Impact melts were identified by their dark-colored, glassy appearance in the eucrite basalt matrix, along with the presence of metal grains. Powdered splits of three large impact melt inclusions were used for Mo and Ru analyses using a Thermo Scientific Neptune Plus MC-ICP-MS at Münster. Preliminary Mo and Ru isotope data indicate that the impactor component in the eucrite impact melt belongs to the non-carbonaceous suite of the meteorite isotope dichotomy [7]. It is most similar to enstatite chondrites, near the terrestrial isotopic composition. This implies that the HED parent body and the Earth may have received a similar type of impactor that originated in the inner solar system. [1] Rubie et al. 2015. Icarus 248: 89-108. [2] Puchtel et al. 2008. GCA 72: 3022-3042. [3] Fischer-Gödde and Becker 2012. GCA 77: 135-156. [4] Shirai et al. 2016. EPSL 437: 56-65. [5] Worsham et al. 2017. GCA 467: 157-166. [6] Fischer-Gödde and Kleine 2017. Nature 541: 525-527. [7] Budde et al. 2016. EPSL 454: 293-303.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.P31G3761W
- Keywords:
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- 1027 Composition of the planets;
- GEOCHEMISTRYDE: 3672 Planetary mineralogy and petrology;
- MINERALOGY AND PETROLOGYDE: 6299 General or miscellaneous;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTSDE: 5455 Origin and evolution;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS