Frizon de Lamotte, Dominique

Dominique Frizon de Lamotte

Comptes Rendus Géoscience

/caC. R. Geoscience 337 (2005) 475–476http://france.elsevier.com/direct/CRAS2APerspectiveAbout the Cenozoic inversion of the Atlas domain in North AfriDominique Frizon de LamotteDépartement des sciences de la Terre et de l’environnement, université de Cergy-Pontoise, CNRS UMR 7072,95031 Cergy cedex, FranceAvailable online 24 February 2005eathhegenof-uthiciss-nge-e at nu-tainal-inionRe-uro-tedn-ofc-ica-w-olli-nn-sig-orsci-istheeedMo-ke-asellt al.ainlasuldonalbelt.ce-lledofIn a recent paper, Khomsi et al.[6], using subsur-face data, describe very nice structures buried benthe Kairouan–Sahel Quaternary plain (Tunisia). Tpresented data are important because, after moreeral studies of the Tertiary geodynamic evolutionwestern Mediterranean[3,9,12], they confirm the existence of large inversion structures of Tertiary age soof the ‘South Atlas Front’ (SAF), a major tectonboundary, running from Agadir (Morocco) to Tun(Tunisia), which forms the southern limit of the Atlasystem s.s. (see review in[4]). Some of these structures (‘chaînes des Chotts’ in Tunisia, Ougarta rain Algeria or Anti-Atlas in Morocco) have a morphologic expression and are consequently known sinclong time. The discovery of Khomsi et al.[6] showsthat the pattern is more general and suggests thamerous other blind structures could exist at a cerdistance from the SAF. In fact, some of them areready known as the Guerguet–Melrhir oil/gas fieldeastern Algeria[1].Another aspect of the paper concerns the inversprocess that took place since Late Cretaceous untilcent in the frame of the convergence between the Epean and African plates. On the seismic line presenby Khomsi et al.[6], the occurrence of numerous uconformities indicates alternation between periodsintense tectonic activity and periods of relative teE-mail address: dfrizon@geol.u-cergy.fr(D. Frizon deLamotte).1631-0713/$ – see front matter 2005 Académie des sciences. Publisdoi:10.1016/j.crte.2005.01.006-tonic quiescence. The active periods are clearly indtive of strong coupling between the two plates. Hoever, for chronological reasons (they predate the csion of the Tell–Rif internal domain with the Africamargin), it is established that they are not collisiorelated (see review in[2,4]). So, further work is re-quired to completely understand their geodynamicnificance.The last point is more controversial. The authpermanently refer to major strike-slip faulting assoated with the building of the Atlas Mountains. Thconcept is recurrent in the French literature sinceseventies[8]. It is certain that in Early Mesozoic therwas in North Africa a transform boundary with relattranstensional basins such as the Atlas basins ofrocco, Algeria and Tunisia[7,8,13]. However, I do notshare the opinion of many colleagues for major strislip faulting associated with the building of the AtlMountains themselves. On the contrary, field as was subsurface observations[1,2,4,5,10,11,14,15], in-cluding the cross-section presented by Khomsi e[6], rather suggest that reverse faulting was the mmechanism active during the inversion of the Atbasins. It seems to me that a good compromise wobe to conceive the Atlas as a previous transtensisystem subsequently inverted as a fold-and-thrustDuring the Quaternary, some oblique-slip displaments are possible, in particular along the so-canorth–south axis of Tunisia, but the active tectonicsNorth Africa remains dominated by thrust faulting.hed by Elsevier SAS. All rights reserved.476 D. Frizon de Lamotte / C. R. Geoscience 337 (2005) 475–476surise,e-e-on,,cad.ier,of61.nsin,v-nt de004)delin:talivemesdes977)l-si,de-enense-(3)lu-isia,.),ec.te,las3–-n-aris,-rther,s.es,th.),References[1] R. Bracène, Géodynamique de l’Algérie du Nord : impactl’exploration pétrolière, thèse, université de Cergy-Pontovol. 1, 2001, 84 p.[2] R. Bracène, D. Frizon de Lamotte, Origin of intraplate dformation in the Atlas System of western and central Algria: from Jurassic Rifting to Cenozoic–Quaternary inversiTectonophysics 357 (1–4) (2002) 207–226.[3] M. El Azzouzi, J. Bernard-Griffiths, H. Bellon, R.C. MauryA. Piqué, S. Fourcade, J. Cotten, J. Hernandez, C. R. ASci. Paris, Ser. IIa 329 (2) (1999) 95–102.[4] D. Frizon de Lamotte, B. Saint Bezar, R. Bracène, E. MercThe two main steps of the Atlas building and geodynamicsthe western Mediterranean, Tectonics 19 (4) (2000) 740–7[5] M. Hafid, A. Ait Salem, A.W. Bally, The western terminatioof the Jebilet–High Atlas system (Offshore Essaouira BaMorocco), M. Pet. Geol. 17 (2000) 431–443.[6] S. Khomsi, M. Bédir, H. Zouari, M.G. Ben Jemia, Mise en éidence et analyse d’une structure atlasique ennoyée au frola Chaîne alpine tunisienne, C. R. Geoscience 336 (14) (21293–1300.[7] E. Laville, Multiple releasing and restraining step-over mofor the Jurassic strike-slip basin of the central High Atlas,W. Mainspeizer (Ed.), Triassic–Jurassic Rifting: ContinenBreak-up and the Origin of the Atlantic Ocean and PassMargins, Elsevier Science, New York, 1988, pp. 499–523.[8] M. Mattauer, P. Tapponnier, F. Proust, Sur les mécanisde formation des chaînes intracontinentales : l’exemplechaînes atlasiques du Maroc, Bull. Soc. géol. France 19 (1521–526.[9] R.C. Maury, S. Fourcade, C. Coulon, M. El Azzouzi, H. Belon, A. Coutelle, A. Ouabadib, B. Semroud, M. MegartJ. Cotten, O. Belanteur, A. Louni-Hacini, A. Piqué, R. Capvila, J. Hernandez, J.-P. Réhault, Post-collisional Neogmagmatism of the Mediterranean Maghreb margin: a coquence of slab breakoff, C. R. Acad. Sci. Paris, Ser. IIa 331(2000) 159–173.[10] M.A. Morgan, J. Grocott, R.T.J. Moody, The structural evotion of the Zaghouan-Ressas Structural Belt, northern Tunin: D.S. Macgreggor, R.T.J. Moody, D.D. Clark-Lowes (EdsPetroleum Geology of North Africa, Geol. Soc., London, SpPubl. No. 132, 1998, pp. 405–422.[11] F. Outtani, B. Addoum, E. Mercier, D. Frizon de LamotJ. Andrieux, Geometry and kinematics of the South AtFront, Algeria and Tunisia, Tectonophysics 249 (1995) 23248.[12] A. Piqué, L. Aït Brahim, M. El Azzouzi, R.C. Maury, H. Bellon, B. Semroud, E. Laville, Le poinçon maghrébin: cotraintes structurales et géochimiques, C. R. Acad. Sci. PSer. IIa 326 (8) (1998) 575–581.[13] A. Piqué, P. Tricart, R. Guiraud, E. Laville, S. Bouaziz, M. Amrhar, R. Aït Ouali, The Mesozoic–Cenozoic Atlas belt (NoAfrica), Geodin. Acta 15 (2002) 159–208.[14] B. Saint Bézar, D. Frizon de Lamotte, J.-L. Morel, E. MerciKinematics of large-scale tip line folds from the High Atlathrust belt (Morocco), J. Struct. Geol. 20 (1998) 999–1011[15] R. Vially, J. Letouzey, F. Bernard, N. Haddadi, G. DesforgH. Askri, A. Boudjema, A basin inversion along the NorAfrican Margin: the Saharan Atlas (Algeria), in: F. Roure (EdPeri-Tethyan Platforms, Technip, Paris, 1994, pp. 79–118.

About the Cenozoic inversion of the Atlas domain in North Africa

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About the Cenozoic inversion of the Atlas domain in North Africa

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