Abstract
Pseudotachylytes and their host rocks from the North Range of the 1.85 Ga Sudbury impact structure have been investigated using analytical scanning electron microscopy, electron microprobe analysis and XRF spectrometry. The results show that the pseudotachylytes were produced in high-speed slip zones by the frictional comminution and selective melting of wall rock lithologies. The preferential assimilation of hydrous ferromagnesian phases during frictional melting produced relatively basic melts, leaving the more mechanically resistant quartz and, to a lesser extent, plagioclase as included mineral clasts. Three distinct assemblages are identified within the pseudotachylytes: (a) pre-impact (>1.85 Ga) rock and mineral clasts derived from host lithologies; (b) a syn- to immediately post-impact (1.85 Ga), rapidly cooled, quartz + sanidine + labradorite + phlogopitic biotite matrix assemblage, formed due to crystallization from a melt at 800–900°C and (c) a post-impact (<1.85 Ga) retrograde assemblage which overprints both clasts and matrices. Field evidence indicates that most pseudotachylyte formed in large-displacement fault systems during gravitational collapse of the impact-generated transient cavity. The Sudbury pseudotachylytes, like endogenic pseudotachylytes, were generated by frictional melting on fault surfaces. The difference is primarily one of scale. Large (km) displacements occurring on impact-induced ring faults can generate immense volumes of friction melt resulting in spectacular pseudotachylyte bodies up to 0.5 km thick and more than 10 km long.
Article PDF
Similar content being viewed by others
Avoid common mistakes on your manuscript.
Author information
Authors and Affiliations
Additional information
Received: 15 March 1996 / Accepted: 15 June 1996
Rights and permissions
About this article
Cite this article
Thompson, L., Spray, J. Pseudotachylyte petrogenesis: constraints from the Sudbury impact structure. Contrib Mineral Petrol 125, 359–374 (1996). https://doi.org/10.1007/s004100050228
Issue Date:
DOI: https://doi.org/10.1007/s004100050228