Excursions

The first day of the fieldtrip (May 5) will be dedicated to the Cenozoic High Atlas range, a typical symmetric intra-continental apline belt with a flower-type structure. It results from a lower Jurassic rifting event and tectonic inversion during Eocene with a strong thermal uplift during Mio-Pliocene. Several stops are scheduled from external to internal zones:

- The Aït Ourir Syncline made of Cretaceous to Middle Eocene deposists (marls, limestones) topped by uncomformable Upper Miocene to Pliocene conglomerate in the core of the syncline.

- The Trias-Lias syn-rift plateau basalts belonging to the Camp (Central Atlantic Magmatic Province).

- The Triassic pre-rift red sandstones (locally named Oukamaïden sandstones).

- The angular unconformity between Triassic red sandostones and Cambro-Ordivician shales and silstones.

- A view on the South Atlasic fault, a lithosphere-scale tectonic structure delineating the southern terminatin of the High Atlas.

- The Cambro-Ordovicien folded sediments forming the topographic peaks in the High Atlas.

 Suggested readings:

  • Frizon de Lamotte, D., Leturmy, P., Missenard, Y., Khomsi, S., Ruiz, G., Saddiqi, O., Guillocheau, F., Michard, A., 2009. Mesozoic and Cenozoic vertical movements in the Atlas system (Algeria, Morocco, Tunisia): An overview. Tectonophysics 475, 9-28.
  • Frizon de Lamotte, D., Saint Bezar, B.A., Bracene, R., Mercier, E., 2000. The two main steps of the Atlas building and geodynamics of the western Mediterranean. Tectonics 19, 740-761.
  • Missenard, Y., Saddiqi, O., Barbarand, J., Leturmy, P., Ruiz, G., El Haimer, F.Z., Frizon de Lamotte, D., 2008. Cenozoic denudation in the Marrakech High Atlas, Morocco: insight from apatite fission-track thermochronology. Terra Nova 20, 221-228.
  • Missenard, Y., Zeyen, H., Frizon de Lamotte, D., Leturmy, P., Petit, C., Sebrier, M., Saddiqi, O., 2006. Crustal versus asthenospheric origin of relief of the Atlas Mountains of Morocco. Journal of Geophysical Research-Solid Earth 111.

The second day of the fieltrip (May 6) will concern Neoproterozoic accreted arc and ophiolitic units from the Anti-Atlas belt, with a stop at the nearby Mio-Pliocene strato-volcano. Stops are scheduled in:


- The Tachakoucht meta-andesitic porphyroclastic gneisses, representing upper crustal igneous units rom a oceanic arc dated at 740 Ma. It was subject to partial melting in response to intrusion of hornblendite plugs around 650 Ma.

- The Iriri igneous suite dated at 650 Ma and composed of hornblendite, hornblende gabbros and micro-gabbros intruding the middle crust of the arc crust. This magmatic event generated tonalitic melts after partial melting of the host andesitic gneisses.

- The 760 Ma Khazma ophiolite, probably representing the remants of a back-arc oceanic crust, thrusting the Iriri-Tachakoucht complex southwards.

- The Siroua stratovolcano (11-2 Ma), with peculiar attetion to pumice-rich pyroclastic flows and massive trachytic lava flows.

Suggested readings:

  • Triantafyllou, A., Berger, J., Baele, J.-M., Diot, H., Ennih, N., Plissart, G., Monnier, C., Watlet, A., Bruguier, O., Spagna, P., Vandycke, S., The Tachakoucht–Iriri–Tourtit arc complex (Moroccan Anti-Atlas): Neoproterozoic records of polyphased subduction-accretion dynamics during the Pan-African orogeny. Journal of Geodynamics, in press.
  • Hefferan, K., Soulaimani, A., Samson, S.D., Admou, H., Inglis, J., Saquaque, A., Latifa, C., Heywood, N., 2014. A reconsideration of Pan African orogenic cycle in the Anti-Atlas Mountains, Morocco. Journal of African Earth Sciences 98, 34-46.
  • Thomas, R.J., Chevallier, L.P., Gresse, P.G., Harmer, R.E., Eglington, B.M., Armstrong, R.A., de Beer, C.H., Martini, J.E.J., de Kock, G.S., Macey, P.H., Ingram, B.A., 2002. Precambrian evolution of the Sirwa Window, Anti-Atlas Orogen, Morocco. Precambrian Research 118, 1-57.
  • Berrahma, M.h., Hernandez, J., 1985. Nouvelles donnees sur le volcanisme trachytique hyperalcalin du volcan du Siroua (Anti-Atlas, Maroc). Comptes Rendus de l'Academie des Sciences, Serie 2, Mecanique, Physique, Chimie, Sciences de l'Univers, Sciences de la Terre 300, 863-868.

The last day of the fieldtrip (May 7) will be the opportunity to visit the 2.0 Ga cratonic basement of the West African craton and the ~800 Ma passive margin sequence of the Anti-Atlas belt. We will visit:

- The Taznakht granite-orthogneiss (2.0 Ga)

- The Taghdout dolomitic sandstones, hosting marvellous sedimentary structures (cross bedding, ripple marks, rain-pitting, mudcracks...)

- A touristic stop at the Ksar of Aït Benhaddou (Unesco World Heritage Site).

 

Suggested readings:

  • Thomas, R.J., Chevallier, L.P., Gresse, P.G., Harmer, R.E., Eglington, B.M., Armstrong, R.A., de Beer, C.H., Martini, J.E.J., de Kock, G.S., Macey, P.H., Ingram, B.A., 2002. Precambrian evolution of the Sirwa Window, Anti-Atlas Orogen, Morocco. Precambrian Research 118, 1-57.
  • http://whc.unesco.org/en/list/444
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