Geochronological constraints on Late Precambrian intrusion, metamorphism, and tectonism in the anti-atlas mountains

The Bou Azzer inlier, Anti-Atlas Morocco, is a critical element for understanding Gondwanan geology because it exposes rocks formed during the paleosuturing of the Gondwanan margin with peri-Gondwanan arc terranes. Numerous intrusions within the inlier allow specific tectonic events associated with the tectonic evolution of the Gondwanan margin to be bracketed. Detailed examination of plutons within the inlier reveal down temperature magmatic to solid-state fabrics and contact relationships indicative of emplacement during oblique collision between the margin and one or more arc terranes. U-Pb geochronological data for the Aït Abdulla diorite (653.8 ± 1.6 Ma) and Bou Offroh granodiorite (653.0 ± 1.3 Ma) provide a limit to the onset of collision and regional metamorphism. A precise age of 640.8 ± 1.4 Ma for the Ousdrat quartz diorite provides an indication of the lower limit of the collision in the region. Tectonothermal activity in the Anti-Atlas at ca. 650 Ma correlates with similar periods of tectonism in the peri-Gondwanan terranes of Avalonia and Cadomia and points to the emergence of continent-wide tectonism in western Gondwana as early as 650 Ma.