Preliminary airborne geophysical surveys over the Bou Azzer-El Graara inlier (Central Anti-Atlas, Morocco): implications for geodynamic model of the Anti-Atlas Pan-African belt

Abstract

<p>The Anti-Atlas orogenic belt, located at the northwestern edge of West African Craton, hosts several Proterozoic antiformal inliers (Boutonnières) which crops out under a thick Paleozoic Cover. In its central part, along the Anti-Atlas Major Fault, the Siroua and Bou Azzer-El Graara inliers exhibit Neoproterozoic ophiolitic suture which subduction settings is still under debate. In the last two decades, huge scientific publications were done in this area, mainly focused on the structural, petrological and geochronological issues. Three broad tectonothermal events were recognized in the Pan-African cycle. The Tonian–Cryogenian period ends with the obduction of supra-subduction ophiolite and oceanic arc material at ca. 640 Ma. The Early Ediacaran period was marked by the development and subsequent closure of a wide marginal basin next to a likely Andean-type arc (Saghro Group). The Late Ediacaran period is recorded by subaerial molasse deposits associated with post-collisional high-K calc-alkaline to shoshonitic magmatism (Ouarzazate Group).This project aims to use the magnetic and electromagnetic data of the Bou Azzer-El Graara inlier, and to integrate their interpretations in the geodynamic model of the Anti-Atlas Pan-African belt. The preliminary interpretations of the available aeromagnetic data show high-level magnetic signature at the western part of the Bou Azzer inlier, while it is missing in the east of the CAMP Foum Zguid dyke. From the Bou Ofroukh at the western tip of the inlier to the Ait Abdellah village, the strength of the magnetic signal is related to the wide exposure of the ultramafic rocks along the Anti-Atlas Major Fault. A weakness of the magnetic signal is observed in the area situated between Bou Azzer and Aghbar mines. This weakness was interpreted as being due to the deeply buried serpentinites under the Ediacaran volcano-sedimentary sequence. However, filed maps and magnetic signature indicate the absence of magnetic signal and the ultramafic rocks at the eastern domain of the Bou Azzer-El Graara inlier from the Foum Zguid dyke eastward. Several pending questions should be emphasized on the structural framework and continuity of the Anti-Atlas Major Fault and the role played by this inherited NE-SW Fracture infilled by Lower Liassic dolerite during the Pangea breakup.</p>