Geology, geochemistry, and geodynamic implications of Ediacaran magmatic rocks of the Zgounder inlier, Siroua window, Anti-Atlas, Morocco

Abstract

The Zgounder inlier is located in the Precambrian Siroua Massif (central Anti-Atlas Mountains, Morocco) in the transition zone between the High Atlas Mountains in the north and the Anti-Atlas Mountains in the south. The Zgounder inlier constituted at the base by metasedimentary basement rocks of the Early Ediacaran Saghro Group which were affected by two Pan-African deformational phases and contain tholeiitic mafic sills interstratified with a metasedimentary formation of Late Cryogenian to Early Ediacaran age emplaced in an intraplate rift zone (continental tholeiites). Volcanic-detrital strata of the Bou Salda Group of Early Ediacaran age overlay the sediment formation of Saghro Group and exhibit a calc-alkaline geochemical signature. The Saghro and Bou Salda groups are overlain by volcanic rocks or intruded by subvolcanic and plutonic formations of Late Ediacaran age (Ouarzazate Group). The volcanic rocks consist of the following: (1) andesite lava containing plagioclase (andesine), amphibole, and biotite, which developed in a back-arc orogenic domain; (2) calc-alkaline rhyolite dikes that intruded the Saghro and Bou Salda groups in a post-collisional setting; (3) dolerite dikes that intersect the rhyolitic lavas with an east-west trend which show a tholeiitic geochemical signature and were emplaced in an intraplate context during the opening of a basin in the Cambrian Period; and (4) the Zgounder inlier (outcrop of plutonic rocks) of more recent age that is represented by granites, granodiorites, and granophyres; these rocks consist mainly of quartz, potassium feldspar (microcline), biotite, and muscovite. They represent a per-aluminous alkaline suite in a post-collisional anorogenic setting.