Shock barometer using cathodoluminescence of alkali feldspar

Abstract

Color cathodoluminescence (CL) images of unshocked and experimentally shocked sanidine at pressures up to 40.1 GPa showed red‐violet emission below 20.0 GPa and blue emission above 20.0 GPa. The phases in these shock‐recovered samples were identified as crystalline feldspar for red‐violet emitting areas and as diaplectic feldspar glass for blue emitting ones by micro‐Raman spectroscopy. CL spectra of these shocked sanidine have emissions at ∼330, ∼380 and 400–420 nm of which intensities increase with an increase in shock pressure. Similar UV‐blue emissions were found in alkali feldspar and the glass in Martian meteorites and Ries crater impactite. The deconvolution of these CL spectra provides the emission component at 2.948 eV assigned to shock‐induced defect center, where this intensity correlates linearly with peak shock‐induced pressure on sanidine, with little dependence on composition and structure. The correlation gives quantitative values of the shock pressures experienced by the feldspar, resulting in estimated shock pressures of Martian meteorites and Ries crater impactite. The CL intensity of feldspar has a potential for a universal shock barometer with high spatial resolution (∼1μm) and in a wide pressure range (theoretically ∼4.5–40.1 GPa). This leads to a breakthrough in understanding the impact histories on Earth, Moon, and Mars.