Cathodoluminescence of high‐pressure feldspar minerals as a shock barometer

Abstract

AbstractCathodoluminescence (CL) analyses were carried out on maskelynite and lingunite in L6 chondrites of Tenham and Yamato‐790729. Under CL microscopy, bright blue emission was observed in Na‐lingunite in the shock veins. Dull blue‐emitting maskelynite is adjacent to the shock veins, and aqua blue luminescent plagioclase lies farther away. CL spectroscopy of the Na‐lingunite showed emission bands centered at ~330, 360–380, and ~590 nm. CL spectra of maskelynite consisted of emission bands at ~330 and ~380 nm. Only an emission band at 420 nm was recognized in crystalline plagioclase. Deconvolution of CL spectra from maskelynite successfully separated the UV–blue emission bands into Gaussian components at 3.88, 3.26, and 2.95 eV. For comparison, we prepared K‐lingunite and experimentally shock‐recovered feldspars at the known shock pressures of 11.1–41.2 GPa to measure CL spectra. Synthetic K‐lingunite has similar UV–blue and characteristic yellow bands at ~550, ~660, ~720, ~750, and ~770 nm. The UV–blue emissions of shock‐recovered feldspars and the diaplectic feldspar glasses show a good correlation between intensity and shock pressure after deconvolution. They may be assigned to pressure‐induced defects in Si and Al octahedra and tetrahedra. The components at 3.88 and 3.26 eV were detectable in the lingunite, both of which may be caused by the defects in Si and Al octahedra, the same as maskelynite. CL of maskelynite and lingunite may be applicable to estimate shock pressure for feldspar‐bearing meteorites, impactites, and samples returned by spacecraft mission, although we need to develop more as a reliable shock barometer.