No more blind dates with calcite:Fluid-flow vs.fault-slip along the O(c)kov thrust,Prague Basin

• 作者: Nick M.W.Roberts Ji(r)í (Z)ák Franti(s)ek Vacek Ji(r)í Sláma
• 来源期刊: 地学前缘（英文版）
• 年，卷（期）: 2021,（4）
• 所属期刊栏目: Research Paper
• 页码范围: 163-174
• 页数: 12页
• 语种: 英文

摘要

Dating of fracture-filling calcite with U-Pb geochronology is becoming a rapidly adopted technique for determin-ing the absolute timing of brittle deformation in the upper crust.Slickenfibre calcite is a desirable target,as it pre-cipitates between individual fault slip displacement events,and provides additional kinematic information.Here we present a case study of slickenfibres formed on the O(c)kov thrust in the Lower Palaezoic Prague Basin,Bohe-mian Massif,utilising a combination of petrographic and in situ methods.We demonstrate that slickenfibre ex-ternal 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 O(c)kov 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 require-ments for interpreting calcite U-Pb data.