MicroRaman spectroscopy of anomalous planar microstructures in quartz from Mt. Oikeyama: Discovery of a probable impact crater in Japan

Abstract

Abstract-Planar deformation features (PDFs) and planar fractures (PFs) have been found and confirmed by optical microscope observations and microRaman spectroscopy in quartz grains from Mt. Oikeyama (Akaishi Mountains, Central Japan), for which the semicircular topographic feature of the ridge suggests a crater formed by an impact event. According to the optical microscope observations, a low shock pressure (8-10 GPa) is estimated by the occurrence of basal or x PDFs leading to lack of multiple sets of PDFs. In addition, a new type of planar microstructure was found in several quartz grains. The microRaman characteristics of PDFs in quartz from Mt. Oikeyama show the amorphous state indicating the presence of weak broad bands at 400 and 800 cm )1 peak positions. These characteristics are indicative of PDFs that are limited to shocked quartz. This indicates an impact origin for distinct planar microstructures in quartz from Mt. Oikeyama.

Impact controversies: Impact recognition criteria and related issues

“…from Mt. Oikeyama (Japan) by Sakamoto et al (2010), on a MAPS cover page. Acevedo et al (2009Acevedo et al ( , 2012 alleged the presence of an impact-crater strewn field in a volcanic province of Argentina-without presenting petrographic or geochemical evidence, but by comparison with the equally unproven Chiemgau claims.…”

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

“…In contrast to planar fractures (PFs), PDFs occur as multiple sets of more closely spaced, narrow, and parallel planar regions. [1] Raman properties of quartz amorphization by shock pressure have been reported from different impact environments such as samples from shock-recovery experiments of quartz, [2] from impact structures (Vredefort impact structure; [3] Chicxulub impactite [4] ), from a probable impact crater (Oikeyama structure, Japan [5] ), and from the impact-derived glasses including desert glasses and tektites. [6,7] In a pioneering study, Boggs et al [8] studied PDFs in shocked quartz from the Ries impact structure using a Scanning Electron This submission was presented during the CORALS-2 Meeting on Micro-Raman Spectroscopy and Luminescence Studies in the Earth and Planetary Sciences, which was held between May 19 and 21, 2011, in Madrid, Spain.…”