Syn-collisional detrital zircon source evolution in the northern Moroccan Variscides

Ministerio de Economía y Competitividad (MINECO) of Spain through the project PANGEATOR (CGL2015-71692) and the Pre-doctoral scholarship BES-2016-078168.U–Pb dating and Hf isotopic analyses of detrital zircon grains from Cambrian-Devonian strata in the Moroccan Mesetas were undertaken in order to constrain its Paleozoic paleogeographic evolution. In this work, we analyzed 12 LateDevonian-Late Carboniferous samples of syn-collisional detrital rocks fromtheWestern and Eastern Moroccan Mesetas. All our samples present significant Ediacaran (ca. 620 Ma) and Rhyacian (ca. 2.1 Ga) detrital zircon populations, suggesting that theWest African Craton remained themain source of sediments for northern Morocco at least until the Late Carboniferous. Locally, a Stenian-Tonian (ca. 1.0 Ga) detrital zircon population is also present, probably fed from intermittent and distant source areas located in NE Africa (e.g. Sahara Metacraton). The collisional evolution started with the approach of an Avalonian promontory to the northern Gondwana continental margin (latest Devonian - earliest Carboniferous), after the closure of the Rheic Ocean. This process entailed the former subduction of the Rheic oceanic lithosphere underneath the Avalonian continental terrane and the formation of a magmatic arc in the upper plate. In this scenario, the first syn-collisional sediments (Tournaisian; Tiflet and Debdou-Mekkam areas) are characterized by a Devonian detrital zircon population (ca. 370 Ma), presumably derived from the magmatic arc, and an increasing number of Mesoproterozoic dates, putatively also sourced from the continental crust of the Avalonian terrane. After the initial collision, only the Visean samples located in areas close to the exotic terrane (e.g. Ben Slimane area) displayed a minor Avalonian component. Finally, the Late Carboniferous samples from the Jerada area recorded an important Middle Carboniferous (ca. 330 Ma) detrital zircon population, probably sourced from Variscan granitoids emplaced in the Eastern Moroccan Meseta and attesting to crustal thickening and subsequent thermal maturation of the Gondwana continental crust in this area.Ministerio de Economía y Competitividad (MINECO) of Spain PANGEATOR (CGL2015-71692)Pre-doctoral scholarship BES-2016-07816

Systematics of detrital zircon U–Pb ages from Cambrian–Lower Devonian rocks of northern Morocco with implications for the northern Gondwanan passive margin

This study was found by the Ministerio de Economia y Competitividad (MINECO) of Spain through the project PANGEATOR (CGL2015-71692) and the Pre-Doctoral scholarship BES-2016-078168. We are indebted to Mike Hall and Brad McDonald for their assistance and technical support on sample preparation and the LA-ICPMS, respectively. The CL imaging was carried out on the Curtin University's Microscopy & Microanalysis Facility, whose instrumentation has been partially funded by the University, State and Commonwealth Governments, and the Scanning Electron Microscope (SEM) Facility at the University of Edinburgh. Analysis in the SHRIMP and GeoHistory Facilities, JdLC, Curtin University were enabled by AuScope (auscope.org.au) and the Australian Government via the National Collaborative Research Infrastructure Strategy (NCRIS) and an Australian Geophysical Observing System grant provided to AuScope Pty Ltd. by the AQ44 Australian Education Investment Fund program, respectively. The NPII multi-collector was obtained via funding from the Australian Research Council LIEF program (LE150100013). The SIMS analyses were performed at the NERC Ion Microprobe Facility of the University of Edinburgh (UK). Comments from two anonymous reviewers and editorial handling by Prof. Victoria Pease are acknowledged. Funding for open access charge: YUniversidad de Granada / CBUA.The systematic acquisition of U–Pb geochronological data from detrital zircon grains has become an essential tool in tectonic studies focused on reconstructing the pre–Variscan geography of the northern Gondwanan passive margin. New detrital zircon ages for 16 samples from the Cambrian–Lower Devonian succession of the Moroccan Mesetas (northern Morocco) are reported here. The results, combined with previously published data, reassert the strong West African Craton affinity of the Paleozoic sedimentary rocks, characterized by dominant Cadomian/Pan–African (c. 850–540 Ma) and Eburnean (c. 2.2–1.9 Ga) detrital zircon populations and a minor Leonian/Liberian (c. 2.5 Ga) population. Primary sources of these zircon grains are well established as the West African Craton located just to the south, but also in the Precambrian basement that locally crops out in the Moroccan Mesetas themselves. During the Cambrian–Early Ordovician, erosion preferentially dismantled Cadomian (c. 590–540 Ma) arc–derived rocks of the Gondwanan continental margin, while later, the slightly older Pan–African (c. 650–600 Ma) basement became the main sediment source. In the studied samples, irregularly present minor detrital zircon populations suggest additional sediment provenance from secondary sources such as: (i) remote northeastern African cratons (e.g., Saharan Metacraton and/or Arabian–Nubian Shield) that likely could have provided the c. 1.1–0.9 Ga and, possibly, the c. 1.9–1.7 Ga zircon grains, and (ii) rift–related Cambrian–Early Ordovician volcanic centers in the Moroccan Mesetas that supplied heterogeneously distributed – although locally dominant in small areas – sedimentary detritus before rift abortion and burial underneath the overlying passive margin sedimentary succession.Ministerio de Economia y Competitividad (MINECO) of Spain through the project PANGEATOR CGL2015-71692Scanning Electron Microscope (SEM) Facility at the University of EdinburghAustralian Geophysical Observing System grant by AQ44 Australian Education Investment Fund programAustralian Research Council LE150100013Universidad de Granada / CBUA BES-2016-07816

Syn-collisional detrital zircon source evolution in the northern Moroccan Variscides

Ministerio de Economía y Competitividad (MINECO) of Spain through the project PANGEATOR (CGL2015-71692) and the Pre-doctoral scholarship BES-2016-078168.U–Pb dating and Hf isotopic analyses of detrital zircon grains from Cambrian-Devonian strata in the Moroccan Mesetas were undertaken in order to constrain its Paleozoic paleogeographic evolution. In this work, we analyzed 12 LateDevonian-Late Carboniferous samples of syn-collisional detrital rocks fromtheWestern and Eastern Moroccan Mesetas. All our samples present significant Ediacaran (ca. 620 Ma) and Rhyacian (ca. 2.1 Ga) detrital zircon populations, suggesting that theWest African Craton remained themain source of sediments for northern Morocco at least until the Late Carboniferous. Locally, a Stenian-Tonian (ca. 1.0 Ga) detrital zircon population is also present, probably fed from intermittent and distant source areas located in NE Africa (e.g. Sahara Metacraton). The collisional evolution started with the approach of an Avalonian promontory to the northern Gondwana continental margin (latest Devonian - earliest Carboniferous), after the closure of the Rheic Ocean. This process entailed the former subduction of the Rheic oceanic lithosphere underneath the Avalonian continental terrane and the formation of a magmatic arc in the upper plate. In this scenario, the first syn-collisional sediments (Tournaisian; Tiflet and Debdou-Mekkam areas) are characterized by a Devonian detrital zircon population (ca. 370 Ma), presumably derived from the magmatic arc, and an increasing number of Mesoproterozoic dates, putatively also sourced from the continental crust of the Avalonian terrane. After the initial collision, only the Visean samples located in areas close to the exotic terrane (e.g. Ben Slimane area) displayed a minor Avalonian component. Finally, the Late Carboniferous samples from the Jerada area recorded an important Middle Carboniferous (ca. 330 Ma) detrital zircon population, probably sourced from Variscan granitoids emplaced in the Eastern Moroccan Meseta and attesting to crustal thickening and subsequent thermal maturation of the Gondwana continental crust in this area.Ministerio de Economía y Competitividad (MINECO) of Spain PANGEATOR (CGL2015-71692)Pre-doctoral scholarship BES-2016-07816

Mixed and recycled detrital zircons in the Paleozoic rocks of the Eastern Moroccan Meseta: Paleogeographic inferences

Ministerio de Economía y Competividad (MINECO) of Spain through the project CGL2015-71692-P and the Pre-Doctoral scholarship BES-2016-078168. Zircon analyses and imaging were carried out on the SHRIMP II, LA-ICPMS and SEM facilities at the John de Laeter Centre, Curtin University, with the financial support of the Australian Research Council (LE150100013) and Auscope NCRIS (AQ44 Australian Education Investment Fund program)The paleogeographic evolution of the Moroccan Variscides has been a matter of discussion for several decades, with current theoriesmostly based on classical geological correlations. In this regard, the scarce number of studies devoted to U-Pb geochronological analyses of detrital zircon populations is particularly limiting when trying to ascribe the different domains to a single continental piece either derived from the West African Craton or to different sources, with some located in the Nubian Shield or the SaharanMetacraton. In thiswork, detrital zircon grains from 10 samples of sandstones from the Paleozoic (Ordovician to Devonian) sequence of the Eastern Meseta andMiddle Atlaswere dated in order to identify possible sediment sources and elucidate the paleogeography of this easternmost portion of the Moroccan Variscides. The main detrital zircon populations have Ediacaran-Cryogenian ages (610–670 Ma, related to the Cadomian and/or Pan-African orogeny) and middle Paleoproterozoic ages (1980–2080 Ma, related to the Eburnean orogeny), which are in agreement with previous data from the Western Meseta, suggesting similarity between both Mesetas, and strong West African Craton affinity. Such an affinity verifies themost accepted paleogeographic interpretation considering that theMoroccan Mesetas remained attached to northern Gondwana during the entire Paleozoic period. The main differences between our samples and those from the Western Meseta concern the minor detrital zircon populations, such as the Cambro-Ordovician and the Tonian-Stenian ones. In particular, Eastern Meseta and Middle Atlas samples lack a Cambro-Ordovician detrital zircon population, usually interpreted as related to the rifting that opened the Rheic Ocean. This population is locally reported in the Western Meseta and widely described in southwestern Europe, where magmatism of this age is well known. Furthermore, the most northeastern samples are also characterized by a Tonian-Stenian detrital zircon population (up to 30% of the data), which might imply northeastern African sources (Saharan Metacraton and/or Arabian-Nubian Shield)Ministerio de Economía y Competividad (MINECO) of Spain CGL2015-71692-P, BES-2016-078168Australian Research Council (LE150100013)Auscope NCRIS (AQ44 Australian Education Investment Fund program

Fission track thermochronology of the Beni Bousera peridotite massif (Internal, Rif, Marocco) and the exhumation of ultramafic rocks in the Gibraltar Arc

International audienceThe Beni Bousera peridotite massif and its metamorphic surrounding rocks have been analyzed by the fission track (FT) method. The aim was to determine the cooling and uplift history of these mantle and associated crustal rocks after the last major metamorphic event that dates back to the Lower Miocene–Upper Oligocene time (∼22–24 Ma). The zircon FT analyses give an average cooling—i.e., below 320 °C—age of ∼19.5 Ma. In addition, the apatite FT data give an average cooling—i.e., below 110 °C—age of ∼15.5 Ma. Taking into account the thermal properties of the different thermochronological systems used in this work, we have estimated a rate of cooling close to 50 °C/Ma. This cooling rate constrains a denudation rate of about ∼2 mm year−1 from 20 to 15 Ma. These results are similar to those determined in the Ronda peridotite massif of the Betic Cordilleras documenting that some ultrabasic massifs of the internal zones of the two segments of the Gibraltar Arc have a similar evolution. However, Burdigalian sediments occur along the Betic segment (Alozaina area, western Betic segment) unconformably overlying peridotite. At this site, ultramafic rock was exposed to weathering at ages ranging from 20.43 to 15.97 Ma. Since the Beni Bousera peridotite was still at depth until 15.5 Ma, we infer that no simple age projection from massif to massif is possible along the Gibraltar Arc. Moreover, the confined fission track lengths data reveal that a light warming (∼100 °C) has reheated the massif during the Late Miocene before the Pliocene–Quaternary tectonic uplift

CHARACTERIZATION OF NEOGENE MARLS FROM THE KERT BASIN (N.E. MOROCCO): SUITABILITY FOR THE CERAMIC INDUSTRY

The North-Eastern region of Morocco is filled with marine marls of Neogene age. The Neogene marls from the lower-Kert area were characterized to evaluate their suitability in the ceramic industry. To meet this objective, two cross-sections involving all the Neogene facies were performed on the both banks of the Kert River. Grey and green marls occurring between sandstone and tuffs were characterized by mineralogical (XRD) and physico-chemical analyses (grain-size, Atterberg limits, XRF, and specific surface area). The studied Neogene clays are mainly calcareous silty marls with CaCO3 content ranging from 13 to 20 wt.%. The mineralogical composition showed the occurrence of quartz, calcite, feldspars, dolomite, illite, kaolinite, chlorite, and mixed-layers (10-14 Å). Cristobalite occurred only in the uppermost level of the green marls supplied from volcanic ash during the Messinian. Siderite and rhodochrosite occurred as traces pointing out to reducing or locally oxidizing conditions during sedimentation or shortly thereafter. There, marls have medium to high plasticity that is optimum for extrusion. Raw Neogene marls are suitable for structural clay products manufacturing. More specific uses were supported by geochemical results and grain-size distribution as hollow products, roofing tiles, and masonry bricks

New interpretation of the geological structure of the Beni Bou Ifrour Massif (Eastern Rif, Morocco)

Workshop Alboran domain and Gibraltar Arc: geological research and natural hazards, Barcelona (Spain), 16-18 October, 201

Sedimentology and sequence stratigraphy of the late-Messinian - Early pliocene continental to marine deposits of the Boudinar basin (North Morocco)

International audienceDuring the Messinian Salinity Crisis (MSC), between 5.97 and 5.33 Ma, the marine connections between the Atlantic Ocean and the Mediterranean Sea were temporarily restricted. The post-MSC reflooding of the Mediterranean Sea by the Atlantic waters and its sedimentary record are debated. The Boudinar basin (North-Morocco) provides an exceptional record of this period between ca 5.32–5.27 and 4.37 Ma at youngest (Zanclean - Zone PL1). The sedimentary succession of this basin comprises seven facies associations corresponding to depositional settings ranging from continental to open marine environments.We provide a new sequence stratigraphic framework, based on twelve stratigraphic sections. Two orders of depositional sequences (4th, 3rd order), related to base-level changes during the Late-Messinian Early-Pliocene time interval, are correlated at the basin scale. According to our reconstruction, the post-MSC base level rise and the Zanclean reflooding lasted from a minimum of several tens up to hundreds thousands years, suggesting a gradual, not catastrophic event indicative of a progressive transgression

Déformation polyphasée néogène liée à l’évolution du bassin d’Alboran : nouvelles données sur le massif de Beni Bousera (Rif interne, Maroc)

International audienceLocated in the Internal domain of the Rif belt, the Beni Bousera massif is characterized by astack of peridotites and crustal metamorphic units. The massif is intruded by granitic dykes and affected byseveral normal ductile shear zones. Structural, petrological and40Ar–39Ar dating analyses performed onthese two elements highlight that (1) the granitic dykes are emplaced within major N70°to N140°trendingnormal faults and shear zones, resulted from an NNE-SSW extension (2) the Aaraben fault in its NE part ischaracterized by N70°to N150°trending ductile normal shear zones, resulted from a nearly N-S extensionand (3) the age of this extensional event is comprised between 22 and 20 Ma. Available paleomagnetic dataallow a restoration of the initial orientation of extension, which was nearly E-W contemporary with theAlboran Basin opening in back-arc context, during the Early Miocene. At the onset of the extension, theperidotites were somehow lying upon a partially melted continental crust, and exhumed during this event bythe Aaraben Normal Shear Zone. Afterward, the Alboran Domain suffered several compressional events.Dans le Rif interne (domaine d’Alboran), le massif de Beni Bousera expose un empilement de péridotites et d’unités métamorphiques crustales. Ce massif est recoupé par des filons granitiques et affecté par plusieurs zones de cisaillement ductiles normales. Des analyses structurales, pétrologiques et des datations 40Ar–39Ar réalisées sur ces deux types d’objets montrent que, (1) les filons granitiques se sont mis en place dans des zones de failles et des zones de cisaillement normales, orientées en majorité entre N70° à N140° résultant d’une extension NNE-SSW, (2) la faille d’Aaraben dans sa partie NE est caractérisée par des zones de cisaillement ductiles normales, orientées N70° à N150° résultant d’une extension N-S et (3) l’âge de cet évènement extensif est compris entre 22 et 20 Ma. Les données paléomagnétiques disponibles, permettent de restaurer l’orientation initiale de cette extension, qui était approximativement E-O contemporaine de l’ouverture du bassin d’Alboran en position d’arrière-arc, au cours du Miocène inférieur. Au début de l’extension, les péridotites reposaient sur une croûte continentale partiellement fondue, et exhumées pendant cet évènement par la zone de cisaillement normale d’Aaraben. Le domaine d’Alboran a ensuite été affecté par plusieurs événements compressifs