Cathodoluminescence Characterization of “Ballen Quartz” In Impactites from Terrestrial IMPACT Structures

"Ballen quartz" from impactites is characterized by bubble-wall texture under a petrological microscope. It has been known to be formed as a reversion product from lechatelierite or diaplectic quartz glass at a shock pressure from ~30 to ~55 GPa [1,2]. However, its formation mechanism has not been understood well. In this study, we investigate ballen quartz by means of cathodoluminescence (CL) microscopy and spectroscopy. The samples were selected from ballen quartz found in terrestrial impact craters; Dellen, Mien (both Sweden), Lappajärvi (Finland), Terny (Ukraine), and Ries (Germany). Most of all samples exhibit a broad band peak at around 650 nm, which might be assigned to a nonbridging oxygen hole center (NBOHC) recognized in amorphous and crystalline SiO2 [3]. The CL spectral profiles are almost same among the samples suggesting the resemblance of the crystal field around luminescence centers inferred from similar formation mechanism of ballen quartz. The sample from Lappajärvi crater has an another band peak at around 450 nm, presumably attributed to a radiative recombination of the self-trapped exciton (STE) or an oxygen deficient center (ODC) [4]. Micro-XRD analysis shows that this part is composed of cristobalite and α-quartz. This indicates that ballen quartz might be formed in the quenching process from relatively high temperature.

Consequently, the facts obtained from CL result imply that the local post-shock superheating effect could play a key role in the formation of ballen quartz texture.

References: [1] Carstens H. 1975. Contributions to Mineralogy and Petrology 50: 145–155. [2] Bischoff A. and Stöffler D. 1984. Journal of Geophysical Research 89: B645-B656. [3] Stevens Kalceff M. A. and Phillips M. R. 1995. Physical Review B 52: 3122–3134. [4] Stevens Kalceff M. A. 1998. Physical Review B57: 5674–5683.