40Ar/39Ar dating of shear zones in the Variscan basement of Greater Kabylia (Algeria).: Evidence of an Eo-Alpine event at 128 Ma (Hauterivian-Barremian boundary):: geodynamic consequences

A ductile shearing event is recognized in gneisses and barite veins of the crystalline internal massifs of the Alpine Maghrebides in Algeria. Dating of shearing movement is carried out by 40Ar/39Ar laser-probe experiments performed on synchronous neoformed micas. The proposed age at 128 Ma is constrained by a two-component mixing model for the saddle-shaped age spectra on phengites and by a plateau age at 128.3 +/- 0.3 Ma on muscovite. This Hauterivian-Barremian boundary age records a strong reworking of the Alboran plate (input of detritals in the flysch basin) and surrounding areas. It can be correlated with the J magnetic anomaly in the Atlantic and with the distensive events in the Pyrenees and external Alps. Therefore, isotopic ages (80-130 Ma) obtained on the Alpine-Mediterranean basement could reflect interferences between this event at 128 Ma and late-Alpine stages. (C) 1999 Elsevier Science B.V. All rights reserved.