Characterization and significance of shocked quartz from the Woodleigh mpact structure, Western Australia

Abstract

Abstract-We re-examined the buried Woodleigh structure in Western Australia, which has been inferred to be a multi-ringed, 120 km diameter impact crater, because the proposed size and possible synchronicity with one of the pre-Mesozoic mass extinction events has attracted controversy. We undertook a detailed study of the petrology and mineralogy of a number of samples of core from the Woodleigh-1 borehole that was drilled into the central uplift of the structure. Crystalline Proterozoic basement rocks comprising granites and gneisses in the Woodleigh-1 core contain minor brecciation in discrete veins and reveal clear evidence of shock metamorphism over the full extent of the core. Imaging of laboratory-etched quartz showed that a large number of grains contain shock deformation lamellae. Microstructural and crystallographic analysis of these lamellae by TEM showed that they are planar deformation features (PDFs) that have subsequently undergone annealing and water assisted recrystallization. The available geological, petrographic, and mineralogical evidence suggest that Woodleigh is an eroded impact crater that is nearer to 60 km than 120 km in diameter. Future drilling projects should better constrain the level of erosion, and may reveal any preserved impact lithologies.

Structural characterization of natural diamond shocked to 60 GPa; implications for Earth and planetary systems

“…The optical and spectroscopic properties of the DeCarli laboratory shocked sample were similar to those found among natural impact diamonds from Popigai. Some brownish fragments show "thousands" of penetrative linear to curved lines with ~micron-scale spacing (Figure 1), reminiscent of planar deformation features (PDFs) observed in shocked quartz (De Carli et al, 2002;Hough et al, 2003). Shock deformation can thus produce diamonds containing high concentrations of planar defects, as also observed by other researchers (Nemeth et al, 2014).…”

Impact-derived features of the Xiuyan meteorite crater

“…In other suggested impact craters in China, no detailed investigation of shock effects of quartz and feldspar was reported. The characteristics of PDFs in quartz from the Xiuyan meteorite crater are identical to those revealed in other known impact craters [11,[20][21][22][23][24][25] . The founding of PDFs in this crater confirms an impact-related origin.…”

Estimating average shock pressures recorded by impactite samples based on universal stage investigations of planar deformation features in quartz—Sources of error and recommendations

“…Shock barometry may also be used to investigate the size and erosion level of an impact structure (e.g., Hough et al. ) or to help understand from which part of the target bedrock (i.e., sampling horizon) rock samples were derived before being ejected and incorporated into proximal impactites or into distal ejecta (e.g., Nakano et al. ).…”

“…In the last few decades, shock barometry studies based on PDF orientations have improved the general understanding of crater formation, and in particular, the understanding of shock wave propagation and attenuation with increasing distance from the point of impact. Shock barometry may also be used to investigate the size and erosion level of an impact structure (e.g., Hough et al 2003) or to help understand from which part of the target bedrock (i.e., sampling horizon) rock samples were derived before being ejected and incorporated into proximal impactites or into distal ejecta (e.g., Nakano et al 2008).…”