Petrographic and geochemical evidence for an allochthonous, possibly impact melt, origin of pseudotachylite from the Vredefort Dome, South Africa

A centennial reappraisal of the Vredefort pseudotachylytes: shaken, not stirred by meteorite impact

“…Pseudotachylyte as allochthonous, possibly impact melts Lieger et al (2011) reviewed the composition of pseudotachylyte and its wall rocks from different parts of the Vredefort dome and confirmed previous conclusions that, in most cases, the compositions of veins and host rocks are similar. This has also recently been confirmed by a stable isotope study (Harris et al 2013).…”

“…In most subsequent studies the pseudotachylyte bodies in the Vredefort dome have likewise been considered to be injected material, regardless of whether they were labelled as veins or other terms were used, such as dykes, melt breccias or pseudotachylitic breccias (e.g. Reimold 1995Reimold , 1998Mohr-Westheide et al 2009;Lieger et al 2011). According to our observations on clean quarry faces, the pseudotachylyte is invariably located within penetrative, highly irregular, interfingering dendritic fracture systems, which occur adjacent to all pseudotachylyte zones.…”

“…The suggestion by Lieger et al (2011) requires that siliceous melts can be transported for very long distances as centimetre-thin veins, which must be considered rather unlikely because of the high viscosity of siliceous melts and the expected rapid chilling of thin propagating veins. It is also at odds with the ubiquitous and locally derived rock fragments in the pseudotachylytes.…”

Pseudotachylitic breccia from the Dhala impact structure, north-central India: Texture, mineralogy and geochemical characterization

“…It has also been proposed that pseudotachylitic melt breccias might contain an allogenic component of impact melt that had been mixed in with authigenic lithological components (Lieger et al, 2011). Clearly further work is warranted towards a better understanding of PTB formation in the context of the highly dynamic and complex processes taking place at and directly after the impact of a large extraterrestrial projectile.…”

Comment on "Pseudotachylite in the South Boundary Fault at the Cooke Shaft, Witwatersrand Basin, South Africa by P.W. Mambane Et Al., South African Journal of Geology 114.2, 109-120

“…The recent publications about PTB from Vredefort, which have again highlighted the controversy about the genesis of especially the massive occurrences of such melt breccia through different processes -even debating that the Vredefort PTB could be mixtures of impact melt breccia that had come off the main impact melt volume with local target rock (in favor, e.g., Lieger et al, 2011; against, on mainly chemical and isotope chemical grounds, Mohr-Westheide and Reimold, 2010Reimold et al, 2011) emphasize that this issue is not yet laid to rest. i,NB; Where in the following quotes from older literature are given and refer to pseudotachylite, this is done here in order to cite the original text correctly?…”