Metamorphism of four desert ureilites and luminescence spectroscopy of defects in ureilitic diamonds

C. A. LORENZ1, A. A. SHIRYAEV2,3, I. I. VLASOV4, and S. E. BORISOVSKY3
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13274]
11Vernadsky Institute of Geochemistry and Analytical Chemistry RAS, Kosygin St. 19, 119999 Moscow, Russia
2A. N. Frumkin Institute of Physical Chemistry and Electrochemistry RAS, Leninsky pr. 31 korp. 4, 119071, Moscow, Russia
3Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry RAS, Staromonetnyi per, 35, 119017,Moscow, Russia
4A.M. Prokhorov General Physics Institute RAS, Vavilova St., 38, 119991, Moscow, Russia
Published by arrangement with John Wiley & Sons

Four ureilites subjected to impact metamorphism in a pressure range of ~15–100 GPa were investigated for mineralogical and petrological features and optical luminescence of their diamonds with the aim to understand how properties of ureilitic diamonds are correlated with shock and thermal histories of the host meteorite. Petrological data show that all the investigated ureilites experienced multistage metamorphic histories. Some of them were shocked at least twice or/and underwent high‐temperature thermal metamorphism and fluid metasomatism in the parent body interior. Photoluminescence spectra of individual diamond grains reveal the presence of neutral and negatively charged nitrogen‐vacancy (NV0 and NV, respectively) and H3 (two nitrogens and a vacancy) defects, indicating relatively high nitrogen contents of the diamonds and some degree of thermal annealing of the grains. The diamond grain size and morphology, a texture of graphite‐diamond aggregates, and spectroscopic properties of the diamond phase vary widely both within an individual meteorite and between the ureilites. Shock‐driven transformation of sp2‐C into diamond provides the most natural explanation of the observed spectroscopic diversity of the diamond grains if one takes into account strong dependence of the PT parameters and efficiency of the transformation on structure of the carbonaceous precursor.

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