Determination of SiO2 raman spectrum indicating the transformation from coesite to quartz in Gföhl migmatitic gneisses in the Moldanubian Zone, Czech Republic

Abstract

The Raman spectroscopy of more than 2000 SiO2 inclusions in zircon separates from Gföhl migmatitic gneisses in the Nové Dvory area shows that most of the SiO2 inclusions are composed of quartz with clear and intense peaks at 464, 393, 266, 207 and 125 cm-1. It also reveals that a few SiO2 inclusions have a weak but clear peak at 521 cm-1, which is the most fundamental vibration of coesite, along with typical quartz vibrations mentioned above. The Raman spectrum is composed of the intense vibrations of quartz at 464, 393 and 266 cm-1 of quartz and the weak vibration of coesite at 521 cm-1 is obtained from the quartz proximal to the relict coesite inclusion in the pyrope of ultra-high-pressure (UHP) rocks in Dora Maira Massif. A similar Raman spectrum has been obtained for quartz transformed from coesite in UHP rocks recovered from the CCSD drillhole of the Sulu belt, eastern China. Therefore, we propose that the SiO2 phase whose Raman spectrum shows a weak vibration at 521 cm-1 existed as coesite in the past.