New petrographic and U–Pb geochronology data from the Mazagan Escarpment, offshore Morocco: Support for an African origin

Abstract

Two samples of a granodiorite and a hypersthene granodiorite provided a unique opportunity to investigate the nature of the basement of the Mazagan Escarpment, the northwestern margin of continental Africa (Morocco) on a steep part of the lower continental slope in offshore Morocco. We conducted U–Pb LA-ICPMS geochronology on zircon from the granodiorite, which was acquired from a deep sea drilling program core DSDP544, and on zircon and monazite from a hypersthene granodiorite collected previously during the Cyamaz submersible campaign, to determine the ages of the rocks of the Mazagan Escarpment and interpret their origins. Zircon from the granodiorite yielded a 556 ± 10 Ma crystallization age, abundant inherited zircon cores up to 620 Ma and three ~2.68, ~1.76 and ~1.20 Ga cores. The hypersthene granodiorite yielded ~1950–1750 Ma zircon and ~1820–1640 Ma monazite ages. Some rocks of the closest onshore continental platform have recently been interpreted as belonging to an exotic Avalonian terrane, and correlated with the Mazagan Escarpment. Our data do not provide evidence that the Mazagan Escarpment is part of an exotic terrane. It is more likely that the hypersthene granodiorite formed in an extensional setting after the 2.25–2.07 Ga Eburnean orogeny, at a time of otherwise predominantly mafic magmatism that may have caused magmatic underplating and heating from below. The granodiorite formed during the late Ediacaran, which is characterized by widespread magmatism in Northwest Africa. Therefore, it is likely that the rocks of the Mazagan Escarpment have a Northwest African origin, which implies that the Pangean suture zone lies west of it.