2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

Paper No. 227-8
Presentation Time: 10:45 AM

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


HEFFERAN, Kevin, Geography and Geology, University of Wisconsin-Stevens Point, Stevens Point, WI 54481 and SAMSON, S.D., Department of Earth Sciences, Syracuse University, 204 Heroy Geology Laboratory, Syracuse, NY 13244

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.