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

Roberts, Nick M.W.; Žák, Jiří; Vacek, František; Sláma, Jiří. 2021 No more blind dates with calcite: fluid-flow vs. fault-slip along the Očkov thrust, Prague Basin. Geoscience Frontiers, 12 (4), 101143. 10.1016/j.gsf.2021.101143

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Official URL: http://dx.doi.org/10.1016/j.gsf.2021.101143

Abstract/Summary

Dating of fracture-filling calcite with 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.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	10.1016/j.gsf.2021.101143
ISSN:	16749871
NORA Subject Terms:	Earth Sciences
Date made live:	26 Jan 2021 10:23 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/529481

Item Type:

Publication - Article

Digital Object Identifier (DOI):

10.1016/j.gsf.2021.101143

ISSN:

16749871

NORA Subject Terms:

Earth Sciences

Date made live:

26 Jan 2021 10:23 +0 (UTC)

URI:

https://nora.nerc.ac.uk/id/eprint/529481