Mafic Dikes at Kahel Tabelbala (Daoura, Ougarta Range, South
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C. R. Geoscience 349 (2017) 202–211 Contents lists available at ScienceDirect Comptes Rendus Geoscience w ww.sciencedirect.com Petrology, Geochemistry Mafic dikes at Kahel Tabelbala (Daoura, Ougarta Range, south-western Algeria): New insights into the petrology, geochemistry and mantle source characteristics a,b a, Abderrahmane Mekkaoui , Nace´ra Remaci-Be´naouda *, c Khadidja Graı¨ne-Tazerout a De´partement des sciences de la Terre, Laboratoire « Ge´oressources, environnement et risques naturels », FSTU, Universite´ d’Oran 2, Mohamed Ben Ahmed, Oran, Algeria b De´partement de l’hydraulique, Universite´ de Be´char, Be´char, Algeria c Laboratoire de me´talloge´nie, USTHB, Alger, Algeria A R T I C L E I N F O A B S T R A C T Article history: New petrological, geochemical and Sr–Nd isotopic data of the Late Triassic and Early Received 21 April 2017 Jurassic Kahel Tabelbala (KT) mafic dikes (south-western Algeria) offer a unique Accepted after revision 27 June 2017 opportunity to examine the nature of their mantle sources and their geodynamic Available online 25 August 2017 significance. An alkaline potassic Group 1 of basaltic dikes displaying relatively high MgO, 87 86 TiO2, Cr and Ni, La/YbN 15, coupled with low Sr/ Sri 0.7037 and relatively high eNd(t) Handled by Marc Chaussidon +3, indicates minor olivine and clinopyroxene fractionation and the existence of a depleted mantle OIB source. Their parental magma was generated from partial melting in Keywords: the garnet–lherzolite stability field. A tholeiitic Group 2 of doleritic dikes displaying low Kahal Tabelbala MgO, Cr and Ni contents, La/YbN 5, positive Ba, Sr and Pb anomalies, the absence of a Ougarta Range 87 86 Algeria negative Nb anomaly coupled with moderate Sr/ Sri 0.7044 and low eNd(t) 0 (BSE- Mafic dikes like), indicates a contamination of a mantle-derived magma that experienced crystal Petrology-Geochemistry fractionation of plagioclase and clinopyroxene. This second group, similar to the low-Ti Sr–Nd isotopes tholeiitic basalts of the Central Atlantic Magmatic Province (CAMP), was derived from Mantle plume partial melting in the peridotite source within the spinel stability field. Lower Mesozoic continental rifting could have been initiated by a heterogeneous mantle plume that supplied source components beneath Daoura, in the Ougarta Range. C 2017 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved. 1. Introduction can thus provide important information for understanding not only the mantle source of the magmas, but also the Mafic dike swarms are a common expression of mantle- tectonic evolution of the orogenic belt (Gorring and Kay, derived magma generation in continental setting charac- 2001; Yang et al., 2007). terized by extensional tectonic regimes in post-collisional Mafic dikes, distributed in southwestern Algeria, or intraplate extensional settings (Rock, 1991). They outcrop in the Ougarta Range, the Tindouf basin, the resulted from a considerable extension of the continental Eglab, the Reggane and Abadla regions. These occurrences lithosphere (Halls, 1982; Tarney and Weaver, 1987). They have been widely investigated, especially in Morocco (Bensalah et al., 2011; Bertrand and Westphal, 1977, Choubert and Faure-Muret, 1974; El Aouli et al., 2001; El Maidani et al., 2013; Hafid et al., 1998; Hollard, 1973; * Corresponding author. E-mail address: [email protected] (N. Remaci-Be´naouda). Leblanc, 1973; Mahmoudi and Bertrand, 2007; Verati et al., http://dx.doi.org/10.1016/j.crte.2017.06.003 C 1631-0713/ 2017 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved. A. Mekkaoui et al. / C. R. Geoscience 349 (2017) 202–211 203 2007). In contrast with Morocco, a few studies have been 2. Geological setting carried out in southern and southwestern Algeria (Bois- sie`re, 1971; Chabou et al., 2007; Chabou et al., 2010; The Ougarta Range corresponds to an imposing series of Conrad, 1972; Djellit et al., 2006; Fabre, 1976; Mekkaoui, reliefs arising within the Saharan platform (Fig. 1a). These 2015; Mekkaoui and Remaci-Be´naouda, 2014; Menchikoff, reliefs are confined to the Saoura and Daoura basins 1930; Sebai et al., 1991). (Menchikoff, 1930). The KT, which is a major orogenic This paper presents a new study of the petrology and entity within the Daoura, is aligned along a Ougartian geochemistry of these Mesozoic mafic dikes in the direction from N1308 to N1408. It is bounded to the north Ougarta Range, southwestern Algeria. New major and by the ‘‘Hamada of Mande’’, to the east by Erg er Raoui, and trace elements analyses as well as Sr–Nd isotopic data of to the south by the Erg Chech, and to the west, by the Iguidi mafic-dike rocks were collected from representative and El Aaˆtchane ergs (Fig. 1a and b). The Ougarta Range sections in Kahel Tabelbala (KT). These data allow us to belonging to the northern boundary of the West African identify the magma types, investigate their mantle Craton (Fig. 1c) is involved in the Late Pan-African history sources and petrogenesis, and understand the evolution (Ennih and Lie´geois, 2001; Kurek and Preidl, 1987). The of the Mesozoic lithospheric mantle beneath KT, Ougarta continental collision between Gondwana and Laurasia in Range. the Late Carboniferous was originally a major uprising and Fig. 1. Map of the studied area, showing (A) the location of Ougarta Range (Michard, 1976), a simplified geological map of the studied area, Kahel Tabelbala (B), a WAC sketch map placing the Ougarta range into its regional context (C) (modified after Fabre, 1976; Ennih and Lie´geois, 2001). 204 A. Mekkaoui et al. / C. R. Geoscience 349 (2017) 202–211 overlaps in the northwestern part of the North African 15 nA, with a beam diameter of 1 mm. The counting time platform by folding and inversion in associated intraplate was 10 s. areas. The Ougarta Range was originated in a subsiding A suite of 11 fresh samples were selected for major and area that developed during the Cambrian along an old trace element analysis, using X-ray fluorescence (XFR oceanic suture bordering the West African Craton. The spectrometer Phillips PW 1404) at the University of Lyon. Central Atlantic Oceanic Opening during the Trias–Lias, The precision was 1–2% for major elements and 10–15% for and the simultaneous separation of the Apulian terrane of trace elements. Seven of these samples were analyzed for northeastern Africa, followed a major extension accompa- rare-earth elements (REE) using inductively coupled plasma nied by volcanic emissions throughout the North African mass spectrometry (ICP–MS) (Jobin Yvon JY38 P) at the platform (Bensalah et al., 2011; Bertrand, 1991; Chabou ‘‘E´ cole des mines’’, Saint-E´ tienne, France. The analyses were et al., 2007; Chabou et al., 2010; Marzoli et al., 1999; realized on solid solutions, after HF dissolution to 130 8C, Meddah et al., 2007; Mekkaoui, 2015; Mekkaoui and evaporation of the fluorides was resumed using HCl 2 N. Remaci-Be´naouda, 2014; Sebai et al., 1991; Verati et al., Sr and Nd isotopes were measured by TIMS at the 2007). A second major extensive Mesozoic stage took GET (Observatoire Midi-Pyre´ne´es, Toulouse-3 University, place during the Cretaceous, followed by the opening of France). 100 mg of whole-rock powder were weighed in a the south equatorial Atlantic Ocean, which generated the Teflon beaker and dissolved in a 2:1 HF/HNO3 mixture. Nd development of a series of aborted rift systems in the and Sr were extracted from the matrix using a combination northern and central African platform (Gomez et al., 2000; of Sr-Spec, Thru-spec and Ln-Spec resins. An equivalent of Pique´ et al., 1998). The rifting of the northern part of the 500 ng Sr and 150 ng Nd were run on a MAT261 Finnigan North Atlantic during the Cretaceous was originally a mass spectrometer. NBS987 and La Jolla isotopic standards sudden change in the movements of the European plate. were regularly run during the measurements. The stan- Intrusions of mafic dikes of Mesozoic age along the KT dard reproducibility values are 0.510855 Æ 18 (n = 50) for structure are widespread, occurring as NW–SE-trending La Jolla and 0.710250 Æ 35 (n = 70) for NBS987. Typical blanks swarms, orientations determined also in Morocco (Bensa- were 30 pg for Nd and 150 pg for Sr. lah et al., 2011; Bertrand, 1991; Mahmoudi and Bertrand, 2007; Verati et al., 2007). These rocks cut across the Neoproterozoic and Cambrian-Ordovician sedimentary 4. Results stacks (Bouima and Mekkaoui, 2003; Chikhaoui, 1974; Columb and Donzeau, 1974; Fabre, 1976, 2005; Mekkaoui, 4.1. Petrography–Mineralogy 2015; Ne´djari, 2007). Two areas are briefly described in this structure (Mekkaoui, 2015; Mekkaoui and Remaci- Distinct petrographic features were noted for two Be´naouda, 2014): (i) at Guelb Berrezouk, the volcanic Groups. The Guelb Berrezouk Group-1 volcanic rocks occurrences also show a remarkable growth, spreading as outcrop as basaltic dikes. They have a mainly porphyritic dikes and sills (Figure is listed in electronic annex as A1a). texture, and contain various amounts of olivine and They are referred to as the Jebel Guelb Berrezouk group clinopyroxene phenocrysts (Fig. 2a and b). Plagioclase (Group 1). At the foot of Jebel, a 0.5- to 1-m-thick dike, phenocrysts are generally absent. The groundmass consists visible over 150 m, punctuates the Ougartian fault of plagioclase, clinopyroxene, olivine and oxides. In separating the Neoproterozoic from the Cambrian. The contrast, the periclinal closure event (axial dikes) Group top of this Jebel is crowned by two sills, from 0.5 m to 0.8 m 2 is comprised of subvolcanic rocks. They are massive and in thickness. In the reverse side of this peak, a system of are medium-grained (in the core) to fine grained (at the dikes and sills outcrops in the Cambrian sandstones.