A new lithostratigraphic framework for the Anti-Atlas Orogen, Morocco

Abstract

-A new lithostratigraphic nomenclatural framework is proposed for the Anti-AtlasOrogen of Morocco, to replace the previous chronostratigraphic scheme. All Continued prolonged convergence gave rise to a sinistral transpressional regime in which late syn-to post-tectonic continental volcanic and clastic sequences of the Ouarzazate Supergroup were deposited. The first rocks of this new tectonic regime were deposited in narrow, tectonically active, strike-slip pull-apart rift basins (Bou Salda, Mgouna, Tafrawt and Anzi Groups), associated with intrusion of high-K calc-alkaline granitoid batholiths (e.g. Assarag, Bardouz Suites) and the juxtaposition of ophiolitic remnants in major strike-slip shear belts. These were followed by the deposition of the much more areally extensive continental volcano-sedimentary molasse, the volcanic components of which were erupted from several interfingering volcanic centres, often associated with caldera complexes and sub-volcanic alkaline granites 2 (Toufhgrane, Tanghourt and Guellaba Suites). The proposed lithostratigraphic scheme encompasses all the major rock units identified in the literature from the orogen and is flexible so that new, lower-ranking, units can be placed at the appropriate stratigraphic level in future. This framework is supported by new high-precision U-Pb zircon dates that have recently become available.

Detrital zircon ages of Neoproterozoic sequences of the Moroccan Anti-Atlas belt

“…In the Sirwa inlier, the Saghro Group was subdivided by Thomas et aL (2002) into six formations which are from bottom to top: the Tittalt, Agchtim, Tizoula, Imghi, Azarwas and Tafiat Formations. The two upper formations correspond to coarse-grained clastic rocks, while the lowermost succession is a volcanic turbidite and flysch-like sequence (Thomas et al, 2002(Thomas et al, , 2004. The following lithological descriptions of the Imghi and Azarwas Formations, where the samples AA3, AA5 and AA6 were collected, are in part after De Kock et al (2000) and Thomas et al (2002Thomas et al ( , 2004.…”

“…2 Ga) (Fig. 2b); (2) Neoproterozoic sequences with lowermost units involved in the Pan-African orogeny and (3) unconformably overlying Paleozoic rocks (Tata and Taroudant Groups; Thomas et aL, 2004 ).…”

“…The nomenclature and descriptions used in this section are taken mainly from Thomas et al (2002Thomas et al ( , 2004. The break-up and rifting of the northern margin of the WAC led to the formation of a passive margin sequence (Taghdout and Lkest Groups) which consists essentially of stromatolite-bearing carbonates at the bot- tom and quartzites at the top.…”

“…In tectono-stratigraphic reconstructions of the Anti-Atlas belt, the deformation affecting the Saghro Group was classically attributed to the Pan-African collision, and according to this view, the age of this group should be older than 660-700 Ma (Thomas et al, 2004 ). However, recent U-Pb zircon dating of the turbidites from the Saghro inlier place this group in the 630-610Ma age range (Gasquet et al,200S ).…”

Geochemical and Geodynamic Implications of Mafic Dykes of the Iguerda Inlier (Central Anti-Atlas, Morocco)

“…The bottom part The northeastern domain has been interpreted as a multiof the AASG (limestones and quartzites) consists of deformed Neoproterozoic Pan-African orogenic segment epicontinental platform sediments whereas the upper However, the Neoproterozoic magmatism of this domain divided into 2 supergroups; the Cryogenian Anti-Atlas Supergroup (OSG) (Thomas et al, 2004). The lower (Walsh et al, 2002) and a microgranite from the characteristic of an ocean basin environment.…”