3 STAGE PAN AFRICAN OROGENIC CYCLE IN MOROCCO: TRANSITION FROM ISLAND ARC TO GONDWANAN CONTINENTAL ARC SYSTEM

Since 2000, precision geochronologic dating by researchers in the Anti-Atlas Mountains of Morocco has provided critical data by which it is now appropriate to designate a Pan African orogenic cycle which culminated in the development of the Western Gondwana supercontinent. The Pan African orogenic cycle consists of three distinct orogenic events: Iriri-Tichibanine orogeny (760-700 Ma), Bou Azzer orogeny (680-640 Ma) and the WACadomian orogeny (620-555 Ma). Most workers now agree that the Iriri-Tichibanine and Bou Azzer orogenies involved northward directed subduction beneath island arc volcanic terranes. These orogenic events generated calc-alkaline magmatism and supra-subduction zone ophiolites exposed in the Bou Azzer and Siroua erosional inliers.

The WACadomian orogeny, in contrast, has been the subject of continued controversy as to whether extensive calc-alkaline to high K magmatism and clastic basin development 620-555 Ma was due to 1. Post-orogenic strike slip motion and rift tectonics or 2. Continued subduction related magmatic activity. Available data support a subduction polarity flip 620-555 Ma. Southward directed subduction beneath the amalgamated West African Craton/Cadomia terrane generated extensive continental volcanic arc magmatism during the WACadomian orogenic event. Gondwana rifting appears to have initiated after 555 Ma in northwest Africa.