No more blind dates with calcite: Fluid-flow vs. fault-slip along the Očkov thrust, Prague Basin

0539613 - GLÚ 2022 RIV CN eng J - Journal Article
Roberts, N. M. W. - Žák, J. - Vacek, F. - Sláma, Jiří
No more blind dates with calcite: Fluid-flow vs. fault-slip along the Očkov thrust, Prague Basin.
Geoscience Frontiers. Roč. 12, č. 4 (2021), č. článku 101143. ISSN 1674-9871. E-ISSN 1674-9871
Institutional support: RVO:67985831
Keywords : U-Pb geochronology * Calcite * Fault dating * Fluid-flow * Prague Basin * LA-ICP-MS
OECD category: Geology
Impact factor: 7.483, year: 2021
Method of publishing: Open access
https://www.sciencedirect.com/science/article/pii/S1674987121000074

Dating of fracture-filling calcitewith U-Pb geochronology is becoming a rapidly adopted technique for determining
the absolute timing of brittle deformation in the upper crust. Slickenfibre calcite is a desirable target, as it precipitates between individual fault slip displacement events, and provides additional kinematic information. Here we present a case study of slickenfibres formed on the Očkov thrust in the Lower Palaezoic Prague Basin, Bohemian Massif, utilising a combination of petrographic and in situ methods. We demonstrate that slickenfibre external textures can be preserved, whilst internally primary textures are removed by fluid infiltration and recrystallization, leading to variable U and Pb mobilisation. One slickenfibre yielded a date of ca. 250 Ma,
which we interpret as recording fault slip along the Očkov thrust. Another cross-cutting slickenfibre yielded
more scattered U-Pb data, with an imprecise apparent age around ca. 95 Ma. This slickenfibre is recrystallised,
destroying the primary textures, and exhibits element mobility. The meaning of this younger apparent age is
therefore questionable, whereas it likely reflects Cretaceous U and Pb mobility assisted by fluid-flow along the
fault plane, it may not reflect a period of fault slip. Our results demonstrate that slickenfibre-based U-Pb dates
do not unequivocally relate to fault motion, and that petrographic and elemental analyses are important requirements for interpreting calcite U-Pb data.
Permanent Link: http://hdl.handle.net/11104/0317325