Tomography reconstruction was performed using the GENeralized Fourier Iterative REconstruction (GENFIRE) algorithm (41). Before reconstruction, elemental tilt series of C, O, Mg, Al, Si, S, Cr, Fe, and Ni were extracted from the EDS spectra using Python’s HyperSpy package (42) for multidimensional data analysis. HAADF and EDS projections were aligned to a common tilt axis using the center of mass and common line methods (19). The background was subtracted from each projection by removing the average value in an empty region of the sample, and the process was optimized by minimizing the differences between common lines. Next, projections were normalized to have the same total sum, as the integrated 3D density of the sample should be constant. Each GENFIRE reconstruction ran for 100 iterations, using an oversampling ratio of 2 and a 0.7-pixel interpolation distance, and with positivity and support constraints enforced.

Elemental abundances in the meteorite grain were estimated from the zero-degree EDS image using HyperSpy. The spectral data were a 3D array, where x and y axes corresponded to probe positions and the z axis corresponded to the energy of detected x-rays. Non-negative matrix factorization was used to decompose data dimensionality and segment regions based on spectral similarities. Net x-ray intensities were obtained in HyperSpy by sampling and integrating the background-subtracted spectrum peaks at the elements of interest. To obtain quantitative elemental compositions at subregions of the grain, mass fractions were quantified using the Cliff-Lorimer equation (43), I1I2=k12*C1C2, where Ii and Ci are the integrated peak intensities and mass fractions of the ith element, respectively, and k12* is the thickness-corrected Cliff-Lorimer sensitivity factor (“k-factor”) between elements 1 and 2. For more than two species, the formula becomes ∑i=1,2,3, …Ci = 1. The default k-factors were provided by EDS system manufacturer Bruker software and account for detector sensitivity to different elements’ dispersed x-rays. Thickness correction was applied to the vendor-supplied k-factors to obtain k12* (44), which accounts for non-negligible absorption and fluorescence effects in the thick sample, and was calculated using the average grain thicknesses estimated from EDS tomography results.

Local chemical information in the meteorite was provided by STXM-XAS analysis using the MANTiS software (45). A series of STXM transmission images recorded at different incident x-ray energies spanning different atomic resonances were first converted to optical densities using fully transmitting regions in the specimen. Hot pixels were replaced by the average value in the surrounding pixels, and the background was subtracted. The image stack was then aligned iteratively using the center of mass and common line alignment methods. Next, spectra in the 3D image stack were decomposed using principal components analysis (PCA) and k-means clustering to group spectra with similar spectral signatures. Last, singular value decomposition without reference spectra was used to produce chemical maps and their corresponding absorption spectra.

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