Tectonic and metamorphic evolution of the Temsamane units, External Rif (northern Morocco): implications for the evolution of the Rif and the Betic-Rif arc

Journal of the Geological Society, Jul 2007 by Negro, F, Agard, P, Goff�, B, Saddiqi, O

The External Zones in the eastern Rif

Regional geology of the eastern Rif. The Temsamane units (Mesorif) crop out in the eastern part of the Rif, between Al Hoceima and Melilla (Fig. Ia). This massif is elongated NE-SW, and is bounded to the west by the Nekor sinistral strike-slip fault, and to the south by the Rif foreland units and the External Rif nappes (Fig. 2a). The Ketama unit is composed of Triassic-Liassic to Upper Cretaceous low-grade metamorphic sediments (Frizon de Lamotte & Leikine 1985). The Aknoul nappe, of Intrarif origin, represents the cover of the Ketama unit (Frizon de Lamotte 1985) and is composed of Upper Cretaceous to Oligocene non-metamorphic sediments. The Senhadja and Bou Haddoud nappes, of Mesorifan origin, comprise probable Palaeozoic to Middle Miocene sediments (Wildi 1983). All these units are unconformably overlain by Messinian to Pliocene sediments (Fig. 2a).

Lithostratigraphy and structure of the units. The stratigraphy and structure of the Temsamane units presented here is based on the work of Frizon de Lamotte (1985) (Fig. 2a and b). The Temsamane units are composed of Mesozoic to Cenozoic sedimentary units with rare mafic intercalations (Fig. 3). The massif can be divided into seven distinct tectonic units (Fig. 2a and b), each with its own stratigraphie succession (Fig. 3). The units are bounded by north-dipping thrusts, which strike parallel to the length of the massif (Fig. 2a and b). We also assign the Tres Forcas (VIII) and Khebaba units (IX) to the Temsamane group on the basis of metamorphic characteristics. The Ras Afraou, Tres Forcas and Khebaba units were interpreted as allochthonous units belonging to the Alboran Domain (Fig. 2a; Suter 1980). However, the Ras Afraou unit was assigned to the Temsamane units by Frizon de Lamotte (1985). Furthermore, the Khebaba unit is interpreted as an allochthon on top of the Aknoul nappes (Hervouet 1981), or as part of the Senhadja-Bou Haddoud group located below the Aknoul nappe (Frizon de Lamotte 1985; Darraz & Leblanc 1989). We consider that the Khebaba unit does indeed underlie the Aknoul nappe, and will discuss its origin after presenting new petrological data.

Constraints on the tectonometamorphic evolution of the Temsamane units. Only qualitative constraints were available on the tectonometamorphic evolution of the Temsamane units, based on an XRD study by Frizon de Lamotte & Leikine (1985). The North Temsamane units were considered to have experienced only low-grade metamorphism with chlorite-muscovite-paragonite-quartz assemblages, with increasing metamorphic grade towards the north. The South Temsamane units are affected by only very low-grade, anchizonal metamorphism postdating the Mid-Miocene (Frizon de Lamotte 1985). Few geochronological data are available to constrain the age of metamorphism and exhumation of the Temsamane units, with ages ranging between 28 and 8 Ma (Moni� et al. 1984). Unpublished preliminary ^sup 40^Ar-^sup 39^Ar data (Negro 2005) also give ages ranging between 23 and 8 Ma.