Geochemical and geodynamic constraints on the origin of calcalkaline cryogenian mafic rocks in the Igherm inlier (Western AntiAtlas, Morocco)

In the Igherm inlier (western AntiAtlas, Morocco) dolerilic dyke swarms with various directions and gabbroic intrusive bodies were emplaced during Neoproterosoic times, cutting across either Eburnean micaschists and granites or panafrican limestones and quartzites.The mafic rocks of the lower Cryogenian magmatism from the Igherm inlier (Moroccan western Antiatlas) have calcalkaline, tholeiitic and alkaline affinities. The calcalkaline dolerite dykes and gabbros bodies emplaced before the conglomeratic formations of the Upper Cryogenian and after the tholeiitic mafic rocks that characterize the prePanAfrican rifting, are similar to rocks from orogenic setting. They are characterized by high LILE, Th, Ce, P, Sm contents and La/Nb ratio and a low HFSE content with negative anomalies in Nb, Zr and Ti. The geodynamic environment of the sedimentary country rocks corresponds to that of a passive margin in a distensive tectonic context. The calcalkaline affinity of these magmas can be attributed to the influence of a Palæoproterozoic subduction zone that contributed to the enrichment of the subcontinental mantle. During the extensional event of the PanAfrican orogenesis, the mantle would have produced tholeiitic, alkaline and/or transitional magmas before melting (caused by adiabatic decompression) reached the enriched subcontinental mantle previously enriched during the Eburnean subduction, where it would have generated calcalkaline magmas.