| 2 | Nomore blind dates with calcite: Fluid-flow vs. fault-slip along the Očkov thrust, Prague Basin显示文摘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. | Nick M.W.Roberts JiříŽák František Vacek JiříSláma | 2021 | Geoscience Frontiers2021，12，4： | 1 |
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