The depositional age of the sedimentary units was studied by dating (LA-MC-ICPMS) detrital zircon grains, and the age of LREE mobility by dating monazite and xenotime and by whole-rock Sm-Nd modeling. The maximum deposition age of the foredeep to foreland basin is 1.91-1.92 Ga based on detrital zircon data and the minimum age of the main foliation in the study area is 1.87-1.86 Ga based on the younger age limit of late-to post-tectonic xenotime and the ages of few probable metamorphic zircons. Coeval bastn?site, with xenotime in a LREE enriched sample, suggests that this was also one important stage of LREE mobility. Monazite crystallizations have occurred 1.76-1.78 Ga ago while the Rb-Sr whole rock data suggest that the closure of this isotope system took place 1732 ¡À 21 Ma ago. The Sm-Nd modeling gives ages at 0.4-1.0 Ga for LREE depletion. The Sm-Nd age of 412 ¡À 27 Ma can be considered as the age of the latest major LREE depletion event.
We propose that alkali-bearing oxidizing fluids started to form in the cratonic sequences due to diagenetic reactions maybe as early as 2.3-2.1 Ga. Alkalinity of fluids was later increased by interaction with alkaline 2.05 Ga source materials before and during the c. 1.91-1.92 Ga foredeep to foreland basin stage. Basin inversion and metamorphic crystallization occurred at 1.91-1.87 Ga. Episodes of fluid migration at 1.78-1.73 Ga and afterwards were focused along fracture zones and in microfracture networks. The 0.4 Ga stage is the most prominent of the < 1.7 Ga events and is best explained by assuming shield-scale foreland basin related to the Caledonian orogenic front, causing heat redistribution and also fluid circulation in the underlying crystalline basement. The 2.1 Ga formed marginal fault has been a very important shield-scale tectonic element and a pathway for fluid circulation for almost 2 billion years.