Yaozhu Li’s research while affiliated with Western University and other places

Electron backscatter diffraction (EBSD) investigation of strain mainly uses polycrystalline samples to study fabric development. We extend the use of EBSD for the analysis of large single mineral grains by measuring the apparent surficial subdomain boundary density per unit area, reported here as unit segment length (USL). We apply this USL technique to examine and quantify the plastic deformation recorded by naturally shocked olivine in the low to moderately shocked ureilite meteorite Northwest Africa 2221 and the highly shocked martian dunitic cumulate meteorite Northwest Africa 2737, by assessing the types of subdomain boundaries and the increase of subdomain misorientation with increasing shock metamorphism. We further compare USL results for the shocked olivine in the meteorites with those for the terrestrial deformation of Hawaiian olivine. USL of olivine increases with shock level, and USL from shocked olivine is significantly greater than that of terrestrially deformed olivine. USL is a promising tool for the quantification of plastic deformation in large single crystals from shock as well as terrestrial deformation. The results derived from USL measurements along with local EBSD maps are complementary with quantitative 2D X-ray diffraction analysis of crystal deformation and disruption, leading to a more comprehensive understanding of characteristic shock deformation recorded by large single crystals.

As the most common ferromagnesian trioctahedral mica in kimberlites, the origin of phlogopite in association with kimberlites is still debated. There are three recognized models for the origin of kimberlite-hosted phlogopite to date, including 1) xenocrysts originating from disaggregated metasomatised mantle xenoliths (e.g., peridotites and eclogites); 2) cognate phenocrysts crystallized directly from "proto-kimberlite" melts via fractional crystallization; 3) products from previously failed kimberlite intrusions that are subsequently transported by ascending kimberlite magmas, i.e. phlogopite fragments of antecrystic origin. These conclusions are drawn based on petrographic observations, geochemical analyses and experimental modelling. Kimberlitic phlogopites frequently display signs of ductile deformation in the form of kink-banding, undulatory and mosaic (patchy) extinction. Although the deformation features are an important petrogenetic recorder of kimberlite magma evolution, they are poorly quantified from a crystallographic perspective. Here we quantify the extent of plastic deformation in a suite of deformed phlogopite grains from Drybones Bay kimberlites and their entrained mantle xenoliths using in situ micro X-ray diffraction (μXRD). All the examined phlogopites show various degrees of subdomain misorientation (or strain-related mosaic spread) indicative of non-uniform strain experienced by these samples, resulting in streaking along Debye rings or chi (χ) direction in a 2D μXRD pattern. Progressive deformation is visible in the XRD pattern, trending from discrete diffraction spots (unstrained) to streaks (non-uniform strain or bending) and sometimes showing an array of spots, or asterism (complex strain conditions), along the Debye ring dimension. This is interpreted to be proportional to increasing shear conditions. The degree of strain-related mosaic spread in phlogopite is quantified by measurement of the full width at half maximum (FWHMχ) of the X-ray streak. These results will be correlated with optical characteristics, grain size, unit cell parameters and chemical composition of kimberlite-hosted phlogopites to test whether systematic strain measurements could serve as a complementary vector to aid in discerning phlogopite paragenesis.

Ureilites are the second most abundant achondrite meteorite group, yet they are from an unknown source. They are ultramafic in composition and have undergone thermal metamorphism as well as shock deformation since their formation. In this work, olivine grains from six monomict ureilites, Northwest Africa 7059, Elephant Moraine 96042, Shişr 007 (all ˜shock level S3), Northwest Africa 2221 (S3‐S4), Larkman Nunatak 04315 (S5), and Allan Hills A81101 (˜S6) and one polymict ureilite, Elephant Moraine 87720 (S5), were examined by in situ micro‐X‐ray diffraction (XRD). It is observed in this study that with increasing shock, the samples develop more complicated 2‐D XRD patterns from diffracted spots, to streaks, to asterism, and “spotty” Debye rings, and these patterns correspond to shock metamorphic effects observed by optical microscopy from undulatory extinction to mosaicism and annealing or recrystallization textures. These 2‐D XRD patterns, representing olivine strain‐related mosaicity (SRM), as documented by given lattice planes, were each measured as the sum of the full‐width‐half‐maximum along the Debye ring or χ dimension (∑[FWHMχ]) to quantify the shock‐related deformation recorded in the olivine grains. In each meteorite, all olivine lattice planes show similar measured ∑(FWHMχ) values for the diffraction streaks. This work demonstrates an increasing trend of average ∑(FWHMχ) in degrees of arc, 4.0 ± 1.7°, 4.1 ± 1.4°, 3.7 ± 1.8° (all S3), 4.9 ± 2.1° (S3–S4), 7.0 ± 3.5° (S5), 13.4 ± 5.7° (S6), and 7.5 ± 3.3° (polymict, S5), which agrees well with petrographic observations. This quantitative method contributes to a more comprehensive shock classification system specifically for ureilites, complementing recently published shock classification systems for olivine‐bearing rocks.

Large mineral grains that have undergone shock metamorphism or tectonic stress can exhibit plastic deformation. Using in situ micro X-Ray diffraction, such deformation is revealed in a 2D detector image by distortion of diffraction spots into an angular spread or ‘streaking’ along Debye ring or chi (χ) dimension; this can provide a quantitative measurement of plastic deformation via full width at half maximum (FWHMχ) measurement of the diffraction profile along χ. Often the X-ray intensity is not a single homogeneous streak, but is partitioned into discrete orientationally-related spots along the Deybe ring, called asterism. These complex peaks require more sophisticated fitting. This study introduces a user-friendly, high efficiency data fitting program, Best Fit for Complex Peaks (BFCP), executed within Matlab®. Using XRD data as examples, we fit the integrated complex peaks by a Pseudo-Voigt function and assess the BFCP fitting ability on arbitrarily-generated complex peaks simulating XRD peaks with and without observable noise. In addition, we test BFCP with representative highly-deformed terrestrial and meteoritic samples: quartz in the Concord Granite, olivine in ureilite meteorite Larkman Nunatak 04315, and plagioclase in martian meteorite Northwest Africa 8171. We further test BFCP on Raman spectra from a plagioclase clast in martian meteorite Northwest Africa 11220. Fitting results are monitored by the Normalized Root-Mean-Squared Error (NRMSE), the sum of full width at half maximum (∑(FWHM)) and Modified-∑(FWHM). BFCP is designed for XRD data where there is contribution from both Lorentzian and Gaussian components, but it can be applied where appropriate to peak-fitting of other intensity-versus-quantity data, including spectra.