Sedimentary provenance of siliciclastic rocks from the Lalla Mouchaa Calcschists Formation (Coastal Block, Western Rehamna): Evidence of denudation of ca. 2 Ga basement in the Moroccan Meseta.

Paleoproterozoic basement rocks (ca. 2Ga) are scarce along the European and North African Paleozoic mountain chains (Fig.1a). In Morocco, ca. 2.2-2Ga granitic rocks (Gasquet et al., 2008; Kouyaté et al., 2013) have been exclusively reported in the Western Anti-Atlas at southwest of the Anti-Atlas Major Fault, (Choubert, 1963). In Eastern and Central Anti-Atlas and in the Moroccan Meseta, the existence of a Paleoproterozoic basement has only been recognized through indirect evidence (Gasquet et al., 2008; Michard et al., 2010). In the Anti- Atlas belt, ca. 2Ga detrital zircon grains are found in the Ediacaran siliciclastic rocks of the Bou Salda, Saghro and Taghdout groups (Abati et al., 2010). In the Moroccan Meseta, Paleoproterozoic (ca. 2Ga) zircon grains were extracted from gneiss and granitic xenoliths found in Triassic lamprophyre dykes, and from Carboniferous granophyric microgranite intrusions of central Jebilet (Dostal et al., 2005, Essaifi et al., 2003). Recently, a porphyritic rhyolite from the Rehamna Massif was dated at ca. 2.05Ga (Pereira et al., 2015), demonstrating for the first time, the exposure of the Eburnian basement in the Western Meseta. These Eburnian arc-related magmatic rocks, which are exposed to the south of the Permian Sebt Brikiyine granite in the core of anticlines from the Lalla Mouchaa Anticlinorium, are allegedly unconformably overlained by transgressive siliciclastic and carbonate beds (Corsini, 1988; Pereira et al., 2015). At north of the Sebt Brikiyine granite the probable Lower Cambrian sequence (Lalla Mouchaa Calcschists Formation; Guezou & Michard, 1976; Corsini, 1988) comprises a basal unit of microbreccias, arkosic sandstones and siltstones (lower member) that pass towards the top to centimeter-thick beds of calcschists interbedded with limestones and dolomites (upper member) that are conformably overlain by the “Paradoxides Shale Formation” composed of siltstone, greywacke and sandstone with Middle Cambrian fauna. In order to study the potential sources of the Lalla Mouchaa Calcschists Formation (probable Lower Cambrian), we have sampled a microbreccia at the Koudiat El Hamra region, for U-Pb geochronology on detrital zircon. This foliated microbreccia is composed of elongated Kfeldspar and quartz phenocrysts surrounded by a fine-grained matrix. Detrital zircon grains gave 206Pb/238Ub ages that in the Probability density plot curve are distributed by two main age peaks at ca. 2.05Ga and ca. 2.03Ga (Fig.1b), yielding a 206Pb/238U age-weighted mean of ca. 2.04Ga (El Houicha et al., 2018). The obtained U-Pb results point to a provenance from a Paleoproterozoic source, suggesting a possible contribution from rocks of the same age of the 2Ga porphyritic rhyolite exposed at south of the Sebt Brikiyine granite. Thus, there is a possibility that the Paleoproterozoic basement extends bellow the Paleozoic and Neoproterozoic sequences of the Rehamna massif

Zircon U-Pb geochronology and geochemistry of Cambrian magmatism in the Coastal Block (Oued Rhebar volcanic complex, Moroccan Meseta): Implications for the geodynamic evolutionary model of North-Gondwana

U-Pb dating (SHRIMP) of magmatic zircons from an intermediate-mafic agglomerate of the Oued Rhebar Volcanic Complex (Coastal Block, Western Meseta) yielded a weighted mean age of 507 ± 5 Ma. The obtained middle Cambrian age (Series 3, Stage 5) seems to be the best estimate for the crystallization of the ORVC volcanic rock, providing a maximum depositional age for the overlying Bouznika volcanosedimentary Formation. The ORVC rock is representative of middle Cambrian crust generation in North-Gondwana, but contains Ediacaran (ca. 546-542 Ma) and early Cambrian (ca. 536-526 Ma) inherited zircon which might be derived from recycling of older continental crust. This geochemistry study corroborates the existence of calcalkaline rhyolites, basaltic andesites and andesites in the ORVC rocks, but also of the existence, albeit to a lesser volume, of tholeiitic basalt. The relative higher volume of calc-alkaline compared to tholeiitic signature might reflect, in some extent, contamination of depleted mantle-derived magmas by the upper continental crust, as has been proposed for the origin of the same age rift-related igneous rocks from North-Gondwana, as the Iberian correlatives

[Pan-African overprint on Eburnian granitoids at the northern boundary of the West African Craton, Zenaga Inlier, central Anti-Atlas, Morocco]

The Zenaga Inlier shows a comprehensive record of the Eburnian and PanAfrican Orogenies. The Eburnian is characterised by high-temperature regional metamorphism and complex magmatism. The early (Azguemerzi) granodiorite has an isotopic mantle signature and was emplaced diapirically during the Eburnian Orogeny causing local thermal metamorphism. The foliation observed in this granitoid is a result of the interference between its primary syn-emplacement foliation and the regional foliation under amphibolite-facies conditions. The northern part of Zenaga has been intruded by the leucocratic granites of Tazenakht. These granites are cut by mylonites and phyllonites, corresponding to the PanAfrican shear zones and accompanied with sub-greenschist-facies metamorphism during the Pan-African Orogeny. The deformation was the result of a regional sinistral transpressive event. This study in the northern part of the West African Craton shows the superposition of the Pan-African on the Eburnian Orogeny and the presence of a major fault in the Anti-Atlas. ((C)) 2002 Elsevier Science Limited. All rights reserved

Intra-oceanic arc growth driven by magmatic and tectonic processes recorded in the Neoproterozoic Bougmane arc complex (Anti-Atlas, Morocco)

The Bougmane complex represents the lower crustal section of a Neoproterozoic oceanic arc.Successive arc magmatic pulses triggered the ‘garnetisation’ of hydrous arc mafics and the in situ formation of tonalitic melt via dehydration and dehydration-melting reactions.Moroccan oceanic arc relics reached a significant crustal thickness (>30–35 km) via a combination of intra-oceanic magmatic and tectonic processes