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A geochemical contribution to the discussion about the genesis of impact-related pseudotachylitic breccias: Studies of PTB in the Otavi and Kudu Quarries of the Vredefort Dome support the “In Situ Formation” hypothesis

2016; Geological Society of South Africa; Volume: 119; Issue: 3 Linguagem: Inglês

10.2113/gssajg.119.3.453

1996-8590

W. U. Reimold, Marie C. Hoffmann, Natalia Hauser, R-T. Schmitt, P. T. Zaag, T. Mohr-Westerheide,

Geology and Paleoclimatology Research

Research Article| September 01, 2016 A geochemical contribution to the discussion about the genesis of impact-related pseudotachylitic breccias: Studies of PTB in the Otavi and Kudu Quarries of the Vredefort Dome support the "In Situ Formation" hypothesis W.U. Reimold; W.U. Reimold Museum für Naturkunde – Leibniz-Institute for Evolution and Biodiversity Research, Invalidenstrasse 43, 10115 Berlin, Germany Humboldt Universität zu Berlin, Unter den Linden 6, 10099 Berlin, Germany Institute of Geosciences, Laboratório de Estudos Geocronológicos, Geodinâmicos e Ambientais, Universidade de Brasília, Brasília, DF, CEP 70910-900, Brasil e-mail: uwe.reimold@mfn-berlin.de Search for other works by this author on: GSW Google Scholar M. Hoffmann; M. Hoffmann Museum für Naturkunde – Leibniz-Institute for Evolution and Biodiversity Research, Invalidenstrasse 43, 10115 Berlin, Germany Institut für Erd- und Umweltwissenschaften, Universität Potsdam, Karl-Liebknecht-Str. 24-25,14476, Potsdam-Golm, Germany e-mail: marie.hoffmann@mfn-berlin.de Search for other works by this author on: GSW Google Scholar N. Hauser; N. Hauser Institute of Geosciences, Laboratório de Estudos Geocronológicos, Geodinâmicos e Ambientais, Universida de de Brasília, Brasília, DF, CEP 70910-900, Brasil e-mail: nataliah@unb.br Search for other works by this author on: GSW Google Scholar R-T. Schmitt; R-T. Schmitt Museum für Naturkunde – Leibniz-Institute for Evolution and Biodiversity Research, Invalidenstrasse 43, 10115 Berlin, Germany e-mail: ralf-thomas.schmitt@mfn-berlin.de; patrice.zaag@mfn-berlin.de; tanja.mohr-westheide@mfn-berlin.de Search for other works by this author on: GSW Google Scholar P.T. Zaag; P.T. Zaag Museum für Naturkunde – Leibniz-Institute for Evolution and Biodiversity Research, Invalidenstrasse 43, 10115 Berlin, Germany e-mail: ralf-thomas.schmitt@mfn-berlin.de; patrice.zaag@mfn-berlin.de; tanja.mohr-westheide@mfn-berlin.de Search for other works by this author on: GSW Google Scholar T. Mohr-Westerheide T. Mohr-Westerheide Museum für Naturkunde – Leibniz-Institute for Evolution and Biodiversity Research, Invalidenstrasse 43, 10115 Berlin, Germany e-mail: ralf-thomas.schmitt@mfn-berlin.de; patrice.zaag@mfn-berlin.de; tanja.mohr-westheide@mfn-berlin.de Search for other works by this author on: GSW Google Scholar Author and Article Information W.U. Reimold Museum für Naturkunde – Leibniz-Institute for Evolution and Biodiversity Research, Invalidenstrasse 43, 10115 Berlin, Germany Humboldt Universität zu Berlin, Unter den Linden 6, 10099 Berlin, Germany Institute of Geosciences, Laboratório de Estudos Geocronológicos, Geodinâmicos e Ambientais, Universidade de Brasília, Brasília, DF, CEP 70910-900, Brasil M. Hoffmann Museum für Naturkunde – Leibniz-Institute for Evolution and Biodiversity Research, Invalidenstrasse 43, 10115 Berlin, Germany Institut für Erd- und Umweltwissenschaften, Universität Potsdam, Karl-Liebknecht-Str. 24-25,14476, Potsdam-Golm, Germany N. Hauser Institute of Geosciences, Laboratório de Estudos Geocronológicos, Geodinâmicos e Ambientais, Universida de de Brasília, Brasília, DF, CEP 70910-900, Brasil R-T. Schmitt Museum für Naturkunde – Leibniz-Institute for Evolution and Biodiversity Research, Invalidenstrasse 43, 10115 Berlin, Germany P.T. Zaag Museum für Naturkunde – Leibniz-Institute for Evolution and Biodiversity Research, Invalidenstrasse 43, 10115 Berlin, Germany T. Mohr-Westerheide Museum für Naturkunde – Leibniz-Institute for Evolution and Biodiversity Research, Invalidenstrasse 43, 10115 Berlin, Germany e-mail: uwe.reimold@mfn-berlin.de e-mail: marie.hoffmann@mfn-berlin.de e-mail: nataliah@unb.br e-mail: ralf-thomas.schmitt@mfn-berlin.de; patrice.zaag@mfn-berlin.de; tanja.mohr-westheide@mfn-berlin.de Publisher: Geological Society of South Africa First Online: 20 Nov 2017 Online Issn: 1996-8590 Print Issn: 1012-0750 © 2016 September Geological Society of South AfricaGeological Society of South Africa South African Journal of Geology (2016) 119 (3): 453–472. https://doi.org/10.2113/gssajg.119.3.453 Article history First Online: 20 Nov 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation W.U. Reimold, M. Hoffmann, N. Hauser, R-T. Schmitt, P.T. Zaag, T. Mohr-Westerheide; A geochemical contribution to the discussion about the genesis of impact-related pseudotachylitic breccias: Studies of PTB in the Otavi and Kudu Quarries of the Vredefort Dome support the "In Situ Formation" hypothesis. South African Journal of Geology 2016;; 119 (3): 453–472. doi: https://doi.org/10.2113/gssajg.119.3.453 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySouth African Journal of Geology Search Advanced Search Abstract This work is aimed at contributing to the understanding of the formation of massive pseudotachylitic breccias (PTB) in impact structures. In the past this has been debated as being due to either melting of locally available country rocks or a combination of injection of impact melt from a higher level of the impact structure plus assimilation of other, including locally derived, material. Two occurrences of massive PTB in the Otavi and Kudu quarries of the outer crystalline core of the Vredefort Dome (South Africa) have been investigated petrographically and chemically. As shown in many previous studies of PTB, lithic and mineral clast populations only support derivation of PTB from local precursor material (granitic gneiss and amphibolite in the case of Kudu Quarry and various granitoids and a dolerite/amphibolite component in Otavi Quarry). The new major and trace element chemical systematics of melt rock and possible local precursors are fully consistent with this petrographic finding: in both cases PTB chemistry is readily explained by derivation from directly adjacent country rock, or mixtures of locally occurring granitoids and amphibolite. Harmonic least-squares mixing (HMX) calculations also do not indicate that additional components, such as a Vredefort Granophyre-like impact melt intrusive phase, contributed to the formation of these PTB. Absence of evidence (such as significant displacements along PTB developments) for the origin of PTB by friction melting along significant faults/shear zones is also recorded. As melting immediately after shock wave propagation (end of early compression stage of cratering), which is widely considered as the genetic process for shock vein formation in impact-affected rocks, including meteorites, does not apply to formation of such voluminous PTB, only local melting due to rapid decompression upon central uplift formation, followed by melt pooling in dilation sites, can be called upon to satisfactorily address PTB formation. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.