Tasuku Okumura

Planar Deformation Features in Quartz from the Ries Impact Crater: Advanced by Micro-Raman Spectroscopy

ABSTRACT Shocked quartz grains from the Ries impact structure containing planar microstructures such as Planar Deformation Features (PDFs) were characterized by using micro-Raman spectroscopy. Raman spectrum of shocked quartz shows several bands with an intense peak at 459 cm−1. Low intensity of broad Raman bands near 495 and 800 cm−1, which indicate the presence of silica glass, were detected in the PDFs. 2D Raman mapping of the shocked quartz grain shows various distribution patterns of the integrated intensity of A1 Raman band at 459 cm−1 and thus reveal a difference of crystallinity in shocked quartz. The shift and peak broadening of Raman bands to a lower wave number (459 cm−1) may be due to the degree of disordering in tetrahedral sites affected by shock pressure. The results show distinct changes of the Raman properties of quartz with shock pressure and point to a possible use of this method for the identification and characterization of Planar Deformation Features in quartz.

Cathodoluminescence microcharacterization of ballen silica in impactites

The ballen silica shows fairly weak (faint) CL with homogeneous feature in its grain exhibiting almost same spectral pattern with two broad band peaks at around 390 and 650 nm, which might be assigned to self‐trapped excitons (STE) or an intrinsic and nonbridging oxygen hole centers (NBOHC), respectively, recognized in amorphous and crystalline silica. In addition, ballen silica from Lappajarvi crater shows bright and heterogeneous CL with a broad band centered at around 410 nm, presumably attributed to [AlO4/M+]0 centers or self‐trapped excitons (STE). Micro‐Raman and micro‐XRD analyses show that fairly homogeneous CL part is α‐quartz and heterogeneous CL part is composed of α‐cristobalite and α‐quartz. These indicate that ballen silica could be formed in the quenching process from relatively high temperature.

Non-luminescent nature of the planar deformation features in shocked quartz from the Ries impact structure, Germany: A new interpretation

Quartz grains from the Ries impact structure containing shock-induced microstructures were investigated using Scanning Electron Microscopy in cathodoluminescence (SEM-CL), secondary electron (SEM-SE) and back-scattered electron (SEM-BSE) modes as well as Mott–Seitz analysis. The purpose of this study is to evaluate the mechanism by which CL detects Planar Deformation Features (PDFs) in quartz, which is one of the most important indicators of shock metamorphism in rock-forming minerals. PDFs are micron-scale features not easily identified using optical microscopy or scanning electron microscopy. The CL spectrum of PDFs in quartz that has suffered relatively high shock pressure shows no or a relatively weak emission band at around 385 nm, whereas an emission band with a maximum near 650 nm is observed independent of shock pressure. Thus, the ~385 nm intensity in shocked quartz demonstrates a tendency to decrease with increasing shock metamorphic stage, whereas the 650 nm band remains fairly constant. The re...