PROBABLE CAMBRIAN AGE OF METASOMATIC ALBI TITES OF TIZI-NTEST FAULT (TAGHWACHT, TAROUDANT, WESTERN HIGH-ATLAS, MOROCCO)

At the southern edge of the western High Atlas (Morocco), several albi tic masses outcrop along the Tizi-n'Test strike-slip fault zone. The a lbitite host rock is exclusively found within the volcanic and volcani clastic layers, associated to carbonates, Lower Cambrian in age, as ev idenced by occurrences of Archeocyathus. The structure of albitite ref lects an imbricated tectonic history, including Hercynian ductile phas es, post Hercynian brittle deformations and Alpine overthrusting and f aulting. it is thus demonstrated that the albitization took place befo re the Hercynian deformations. Albitite, characterized by the albite chlorite + phengite paragenesis, resulted from the metasomatic replac ement of former volcanic and hypovolcanic Cambrian rocks whose primary texture is still conspicuous. It is shown that the sodic metasomatism is older than the Tichka granite intrusion of late Hercynian age, and the Hercynian deformation (D-2 phase). Albitization is tentatively re lated to an hydrothermal event at the end of the Cambrian volcanic act ivity.