Micro-X-ray diffraction assessment of shock stage in enstatite chondrites

摘要: Abstract– A new method for assessing the shock stage of enstatite chondrites has been developed, using in situ micro-X-ray diffraction (μXRD) to measure full width at half maximum (FWHMχ) peak intensity distributed along direction Debye rings, or chi angle (χ), corresponding individual lattice reflections two-dimensional XRD patterns. This μXRD technique differs from previous characterization methods: it does not require single crystals powders. In applied polished thin sections and whole-rock meteorite samples. Three frequently observed orthoenstatite were measured: (020), (610), (131); these selected as they did overlap with lines other phases. Enstatite are commonly fine grained, stained darkened by weathering, shock-induced oxidation, metal/sulfide inclusions; furthermore, most E have little olivine plagioclase. These characteristics inhibit transmitted-light petrography, nevertheless, stages assigned MacAlpine Hills (MAC) 02837 (EL3) S3, Pecora Escarpment (PCA) 91020 S5, MAC 02747 (EL4) S4, Thiel Mountains (TIL) 91714 (EL5) S2, Allan (ALHA) 81021 (EL6) Elephant Moraine (EET) 87746 (EH3) Meteorite (MET) 00783 (EH4) EET 96135 (EH4–5) Lewis Cliff (LEW) 88180 (EH5) Queen Alexandra Range (QUE) 94204 (EH7) LaPaz Icefield (LAP) 02225 (EH impact melt) S1; six published stages, there is agreement classification. FWHMχ plotted against petrographic demonstrates positive linear correlation. ranges follows: S1   3.5°, S6—not measured. Slabs Abee impact-melt breccia), Northwest Africa (NWA) 2212 examined alone; values place both S2 range, consistent literature values. Micro-XRD analysis may be applicable shocked orthopyroxene-bearing rocks.