¹B. J. Tkalcec,²P. Tack,²E. De Pauw,²B. Vekemans,³T. Nakamura,⁴J. Garrevoet,⁴G. Falkenberg,²L. Vincze,¹F. E. Brenker
Meteoritics & Planetary Society (in Press) Link to Article [https://doi.org/10.1111/maps.13797]
¹Department of Geosciences, Goethe University Frankfurt, Altenhoeferallee 1, Frankfurt am Main, 60438 Germany
²Department of Chemistry, XMI Research Group, Ghent University, Krijgslaan 281 S12, Ghent, 9000 Belgium
³Department of Earth Science, Tohoku University, Sendai, Miyagi, 980-8578 Japan
⁴Deutsches Elektronen-Synchrotron DESY, Notkestr. 85, Hamburg, 22607 Germany
Published by arrangement with John Wiley & Sons

Reliable identification of chondrules, calcium-aluminum-rich inclusions (CAIs), carbonate grains, and Ca-phosphate grains at depth within untouched, unprepared chondritic samples by a nondestructive analytical method, such as synchrotron X-ray fluorescence (SXRF) computed tomography (CT), is an essential first step before intrusive analytical and sample preparation methods are performed. The detection of a local Ca-enrichment could indicate the presence of such a component, all of which contain Ca as major element and/or Ca-bearing minerals, allowing it to be precisely located at depth within a sample. However, the depth limitation from which Ca-K fluorescence can travel through a chondrite sample (e.g., ∼115 µm through material of 1.5 g cm⁻³) to XRF detectors leaves many Ca-bearing components undetected at deeper depths. In comparison, Sr-K lines travel much greater distances (∼1700 µm) through the same sample density and are, thus, detected from much greater depths. Here, we demonstrate a clear, positive, and preferential correlation between Ca and Sr and conclude that Sr-detection can be used as proxy for the presence of Ca (and, thus, Ca-bearing components) throughout mm-sized samples of carbonaceous chondritic material. This has valuable implications, especially for sample return missions from carbonaceous C-type asteroids, such as Ryugu or Bennu. Reliable localization, identification, and targeted analysis by SXRF of Ca-bearing chondrules, CAIs, and carbonates at depth within untouched, unprepared samples in the initial stages of a multianalysis investigation insures the valuable information they hold of pre- and post-accretion processes in the early solar system is neither corrupted nor destroyed in subsequent processing and analyses.