International Geology Review ISSN: 0020-6814 (Print) 1938-2839 (Online) Journal homepage: http://www.tandfonline.com/loi/tigr20 Reworking of intra-oceanic rocks in a deep sea basin: example from the Bou-Maiza complex (Edough massif, eastern Algeria) Mehdi Mechati, Renaud Caby, Dalila Hammor, Delphine Bosch , Olivier Bruguier & Laure Fernandez To cite this article: Mehdi Mechati, Renaud Caby, Dalila Hammor, Delphine Bosch , Olivier Bruguier & Laure Fernandez (2017): Reworking of intra-oceanic rocks in a deep sea basin: example from the Bou-Maiza complex (Edough massif, eastern Algeria), International Geology Review, DOI: 10.1080/00206814.2017.1343688 To link to this article: http://dx.doi.org/10.1080/00206814.2017.1343688 View supplementary material Published online: 13 Jul 2017. Submit your article to this journal Article views: 2 View related articles View Crossmark data Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=tigr20 Download by: [92.145.81.70] Date: 15 July 2017, At: 14:00 INTERNATIONAL GEOLOGY REVIEW, 2017 https://doi.org/10.1080/00206814.2017.1343688 ARTICLE Reworking of intra-oceanic rocks in a deep sea basin: example from the Bou-Maiza complex (Edough massif, eastern Algeria) Mehdi Mechatia, Renaud Cabyb, Dalila Hammorc, Delphine Bosch b, Olivier Bruguierb and Laure Fernandezb aCentre Universitaire de Tamanrasset, Tamanrasset, Algeria; bGéosciences Montpellier, UMR-CNRS 5243, Université de Montpellier 2, Montpellier, France; cLaboratoire de Géologie, Université Badji Mokhtar BP12, Annaba, Algeria ABSTRACT ARTICLE HISTORY Metagabbros and amphibolites exposed in the Bou-Maïza area of the Edough massif (northeast Received 16 December 2016 Algeria) are described in detail. Field and petro-structural observations point to the syn-sedimen- Accepted 14 June 2017 tary emplacement of gabbros as clasts, blocks and lenses of polymictic gabbroic breccias. KEYWORDS Associated amphibolites display fine-scale parallel sedimentary bedding and represent mafic Amphibolite; metagabbro; epiclastites, litharenites and mafic greywackes. The mafic beds and lenses are intercalated with sedimentary mélange; aluminous pelitic schists of continental origin, quartzite and marble. It is concluded that all mafic Maghrebides; Northeastern rocks from this locality derive from the erosion of an oceanic plutono-volcanic complex of MORB Algeria affinity that was reworked in a block matrix mélange and emplaced as turbidites and debris flows during the Mesozoic. We propose a convergent plate margin setting for these formations connected with the subducted Calabrian branch of the Tethyan slab. 1. Introduction 1977). Since 1980 (Lemoine et al. 1987), the concept of In the peri-Mediterranean belt most metabasic rocks of mantle exhumation at ocean–continent transition of MORB affinity referred to as ‘dismembered ophiolites’ slow-spreading ridges from present-day oceans and represent parts of the Late Jurassic oceanic crust and from the Alpine belt has been proposed (Lagabrielle mantle. Their mode of emplacement within sediments 2009). In the western Alps except the Chenaillet massif of continental origin has been interpreted in different (Li et al. 2013), the ophiolitic units suffered high-pressure, ways in the Apennines that escaped Alpine metamorph- low-temperature syn-kinematic metamorphism and ism and in the western/central Alps (see review in strong boudinage. However, the same characteristics are Lagabrielle 2009). An undetached post-ophiolitic cover observed in the non-metamorphic Apennines and in has been observed in most Alpine and Apenninic massifs metamorphic parts of the Alpine belt (Lemoine et al. (Lemoine 2003 and references therein). An Oman-type 1987;Mascleet al. 1991; Lemoine 2003). Following obduction mechanism is not realistic for the massifs Manatschal et al.(2011) and Lagabrielle et al.(2015), occurring as hectometer-in size lenses and boudins within most Alpine ophiolitic breccias relate to mantle exhuma- Cretaceous sediments. The model of ‘distal-continental tion at ocean–continent transition and to edification of margin’ environment for the emplacement of the serpen- mantle core complexes. tinized mantle has been applied to the Alps as well as to In the Maghrebides are exposed few occurrences of the Appennine and Corsica since Lemoine et al.(1987). It mafic and ultramafic rocks considered as fragments of is now established that the Tethyan ophiolites have been the Mesozoic Tethys seafloor (Durand Delga et al. 2000) sampled from different regions of the Tethys ocean, as well as in the Rif (Bezaggagh et al. 2014; Michard including the distal, hyper-extended passive margins et al. 2014) but lack extensive petrological and geo- and the more internal (ultra-?) slow-spreading centre chemical studies. On another hand, the young oceanic (see review in Lagabrielle 2009). The intra-oceanic nature crust dredged from the Tyrrhenian Sea shows striking of most ophiolitic breccias from the Apennines is well similarities with the successions observed from the established since several decades (Abbate et al. 1970; Apennines and the western Alps (Mascle et al. 1991). Lagabrielle 2009; references therein). Some sedimentary Correlations between the Maghrebides on one hand breccias were first interpreted as clastic formations depos- and the Apennine and the Alps through the Calabria ited in the front of nappes (e.g. Grandjacquet and Haccard ophiolite belt on the other hand are thus conjectural CONTACT Renaud Caby [email protected] Géosciences Montpellier, UMR-CNRS 5243, Université de Montpellier 2, Montpellier, Cedex 05, France The supplemental data for this article can be accessed here © 2017 Informa UK Limited, trading as Taylor & Francis Group 2 M. MECHATI ET AL. and require new data from eastern Algeria. The Bou- complex of Miocene age that is exposed below the Maïza mafic complex (Figure 1) is exposed in the south- greenschist facies Tellian nappes (Caby and Hammor western part of the Edough massif, a metamorphic core 1992; Caby et al. 2001).Thecoreofthemassifis complex of Miocene age (Caby and Hammor 1992; represented by granite-gneisses and diatexites over- Caby et al. 2001; Bosch et al. 2014a). This study is mainly lain by metasediments of unknown age. On top of the based on field occurrence and petrological characters core, the Kef Lakhal mafic complex (c. 1000 m thick) of the Bou-Maïza metagabbros and amphibolites for mainly composed of amphibolites and metagabbros which new isotopic data are presented. We tend to represents a klippe (Caby et al. 2001, 2014). The highlight the relationships between mafic rocks and amphibolites suffered syn-kinematic high-temperature metasediments and to discuss between different possi- amphibolite facies metamorphism (T ≥ 800°C, P ≥ 12 ble geodynamic scenarii to explain by which mechan- kbar, Caby et al. 2001). An hectometric-sized peridotite ism the metagabbros were inserted in terrigeneous body is inserted in the anatexites of the dome (Sidi metasediments. Do they represent a dismembered sill Mohamed peridotites), its incorporation in the anatex- complex? Do they represent a case of intra-oceanic ites having taken place at c. 18 Ma (Bruguier et al. sedimentary reworking of plutono-volcanic assem- 2009). The Kef Lakhal complex has been interpreted blages in a spreading environment, as described in as a fragment of the Tethys oceanic crust (Bosch et al. the oceans and similarly to the Alpine/Apennine ophio- 2014a) obducted onto Africa at 20.85 ± 0.34 Ma lites? Or do they represent part of a mélange linked (Fernandez et al. 2016). The occurrence of meta- with the initiation of a subduction or an accretionary morphic diamonds reported from the mélange at the complex? base of this mafic complex (Caby et al. 2014)evidence that at least part of the Edough massif has been involved in a subduction environment to ≥100 km 2. Geological background depth prior to thrusting and later arching of the The Bou-Maïza mafic complex is exposed in the south- dome. The Bou-Maïza mafic complex lies in the same western part of the Edough massif (Figure 1). The structural position than the Kef Lakhal complex above Edough massif represents a metamorphic core terrigeneous metasediments (Caby et al. 2001). 7°20' 7°30' 7°40' 0° Alpine 10°E 20°E 0 10 km 45°N EU ROPE Fr o n t Aïn Barbar A pennines N Pyrenees La Voile Noire Cap de Garde 36°58' APULIA 36°58' IBERIA LPB TS NB KL TZ Betic Fr o n t AB Be t ics SM M a g h r eb i d es Edough Massif 35°N Ri f * AFRI C A Seraïdi 200 km 36°54' ANNABA 36°54' Oued El Aneb Fig. 2 Bou-Hamra Berrahal 36°50' 36°50' Université El Hadjar Bou* Maïza Fetzara Lake B e l e l i e t a 7°20' 7°30' 7°40' Mafic & ultramafic Quaternary sediments Numidian nappe Ultramylonites Diatexites rocks Pliocene sediments Micaschists Cretaceous marls Mesozoic phyllite Rhyolite & flysch marble and jasper Paleozoic granite-gneisses Miocene granite Jurassic marbles Major extensional tectonic contact Figure 1. Simplified geological map of the Edough massif (after Caby et al. 2001, modified. KL: Kef Lakhal mafic complex; SM: Sidi Mohamed peridotite). INTERNATIONAL GEOLOGY REVIEW 3 3. Rock types and field occurrences specimen by millimetre-scale parallel laminations delineated by heavy minerals bands, and layers of Due to rather poor outcrop conditions, mafic rocks of quartzite, impure marble, calcareous schist, garnet- Koudiet Bou-Maïza (Figure 2) are most often loose stones rich layers and lenses of layered actinolite schist of olivine gabbro,