¹Robert W. Nicklas,¹Melody Z.-A. Chen,¹Evan J. Saltman,¹Ethan F. Baxter,¹Andrew J. Lonero,¹Anthony B. Love
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14356]
¹Department of Earth and Environmental Sciences, Boston College, Chestnut Hill, Massachusetts, USA
Published by arrangement with John Wiley & Sons

Brachinites, brachinite-like achondrites (BLA), and other similar primitive achondrites offer important constraints on differentiation processes of the earliest formed planetesimals, as they quenched amidst early differentiation processes on their parent body. Geochemical data for all major mineral phases in two previously poorly characterized meteorites, El Medano (EM) 395 and Northwest Africa (NWA) 12532, show that while EM 395 is a typical brachinite, NWA 12532 is more unusual, containing a high abundance of non-equilibrated apatite (1.26%) likely formed by a late-stage metasomatic event. These new data demonstrate that metasomatism by a P-Cl-Ca-rich fluid probably occurred on the brachinite parent body. This metasomatism may have occurred either during normal cooling of the asteroid or during later impact-related heating, consistent with the late formation of apatite in the paired andesitic achondrites Graves Nunatak (GRA) 06128 and 06129. These conclusions highlight that, while magmatism on small parent bodies ceased shortly after solar system formation, subsolidus processes may have continued much longer, and that metasomatism must be considered when interpreting bulk rock geochemical signatures of primitive achondrites.

¹Mohammad Tauseef,¹Ingo Leya,²Jérôme Gattacceca,³Sönke Szidat,²Régis Braucher,⁴Pascal M. Kruttasch,⁴Anna Zappatini,²ASTER Team
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14355]
¹Physics Institute, Space Research and Planetology, University of Bern, Bern, Switzerland
²CNRS, Aix Marseille Université, IRD, INRAE, CEREGE, Aix-en-Provence, France
³Department of Chemistry, Biochemistry and Pharmaceutical Sciences & Oeschger Center for Climate Change
Research, University of Bern, Bern, Switzerland
⁴Institute of Geological Sciences, University of Bern, Bern, Switzerland
Published by arrangment with John Wiley & Sons

This study presents a refined approach to determine 14C saturation activities and 14C/10Be saturation activity ratios in chondritic meteorites with the goal to improve terrestrial age dating. By combining new model calculations for 10Be, 14C, and cosmogenic (22Ne/21Ne)cos, along with experimental data from 17 freshly fallen chondrites, we established reliable correlations for 14C production rates and 14C/10Be production rate ratios as a function of (22Ne/21Ne)cos. The experimental data agree with the model calculations, and they fully confirm that 14C production rates and 14C/10Be production rate ratios depend on shielding. Constrained correlations describe the experimental data for all shielding conditions and all ordinary chondrites mostly within the uncertainties given by the model. The new correlations therefore provide a significant improvement compared to the earlier approaches, in which average meteorite-type-dependent 14C production rates and average 14C/10Be production rate ratios were assumed. Ignoring the shielding dependence introduces a size-dependent bias into the terrestrial age database. This study enables the determination of shielding-corrected 14C saturation activities and 14C/10Be production rate ratios to calculate shielding-corrected terrestrial ages for meteorites reducing or eliminating a size bias in the database. In addition, this novel approach enables to give reliable uncertainty estimates of within 15% for the 14C and 14C-10Be terrestrial ages.