The “Eovariscan Synmetamorphic Phase” of the Moroccan Meseta Domain Revisited; A Hint for Late Devonian Extensional Geodynamics Prior to the Variscan Orogenic Evolution

Abstract

In eastern parts of the Meseta Variscan domain of Morocco, Eo-variscan (Late Devonian) syn-metamorphic folding is described in the literature. In contrast, Late Devonian extension is clearly established in western parts of the Meseta domain and in its southern foreland (Anti-Atlas). We revisited three classical outcrops of the eastern Moroccan Central Massif (Zaian Mountains) where Eo-variscan folding has been described beneath the unconformable Tournaisian-Visean conglomerates and limestones. In fact, only one slaty cleavage occurs in the Ordovician and overlying Lower Carboniferous formations when their lithology is appropriate, and then results from the Variscan compression. The Lower Carboniferous unconformity can be ascribed to block tilting, likely coeval with the widely observed Late Devonian extension. The reality of a Late Devonian syn-metamorphic folding in easternmost Meseta (Midelt-Mekam zone) is poorly documented, either. At 330–320 Ma the Variscan Meseta orogen would include an eastern volcanic arc overlying early Variscan folds and a western forearc basin above the subducting Rheic lithosphere.