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The Moroccan Hercynides

Article  in  Journal of African Earth Sciences · October 2005

DOI: 10.1016/j.jafrearsci.2005.09.002

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 Journal of African Earth Sciences 43 (2005) 144–165
www.elsevier.com/locate/jafrearsci

The Moroccan Hercynides

a,*
Christian Hoepffner , Abderahmane Soulaimani b, Alain Piqué c

a
Department of Geology, Faculty of Sciences, University Mohammed V, B.P. 1014 Rabat, Morocco
b
Department of Geology, Faculty of Sciences, University Cadi Ayad, B.P. S 20, Marrakech, Morocco
c
21 Rd Point de lÕEsplanade, 67 000, Strasbourg, France

Received 5 April 2004; accepted 18 July 2005

Available online 18 November 2005

Abstract

In Northern Africa deformed Paleozic rocks are observed, mainly in Morocco where they are present in two structural domains: (i)
the southern domain, i.e. the Anti-Atlas belt. In this northern rim of the West African craton, the Paleozoic sequences are mildly
deformed; (ii) the northern Mesetan domain, itself subdivided into several structural subzones, corresponds—with its eastern prolonga-
tion in Algeria- to the Hercynian/Variscan belt of Northern Africa.
In the Meseta, the study of the sedimentological history and the structural analysis of the various subzones allow to discuss the tec-
tonic characters of the Hercynian/Variscan orogeny in Northern Africa:

– The deformation was realized through three main events: (i) the Late Devonian, Eovariscan Phase, which developed in the eastern
zones of the Moroccan Meseta, northwestern Algeria and in the presently Alpine allochthonous domains of the Rif and Kabylias;
(ii) the Visean Phase, which was restricted at the limit between the Moroccan eastern and western Meseta. The two preceding com-
pressional events were contemporaneous with the development of Late Devonian-Early Carboniferous transtensive sedimentary
basins; (iii) the Late Carboniferous Phase, during which the regional shortening affected the entire Hercynian domain, including
the Moroccan western Meseta and Anti-Atlas.
– The Anti-Atlas differs fundamentally from the Mesetan domains by: (i) its relatively mild deformation; (ii) the vergence of its regional
structures, directed toward the West African shield, whereas the main vergence is toward the west in the Meseta domains.
– In the Anti-Atlas like in the weakly deformed zones of the Meseta, the deformation is heterogeneous, being concentrated along several
regional shear zones. Sedimentological and stratigraphic evidences point out the control exerted by these long-lived weakness zones
through the sedimentation, and the deformation.
– No direct evidence can be found to invoke the development of a Paleozoic oceanic lithosphere in the considered domains. Therefore,
the Hercynides/Variscides of North Africa are considered to be outside the inner zones of the European belt, at the northern border of
the Paleo-Gondwana, and probably related to the Appalachian belt of North America.
Ó 2005 Published by Elsevier Ltd.

Keywords: Morocco; Hercynides; Anti-Atlas; Meseta

1. Introduction Thomson crossed the High Atlas mountains in 1888. He

described eruptive rocks (the Atlasic Palaeozoic massif)
More than one century ago, some workers penetrated, as an island inside the Cretaceous sea, and the red lacus-
with strong difficulties, the Moroccan territory and they trine NÕfis sandstones, which are folded (Thomson, 1889).
began to decipher its then ignored geology. Among them, From this onwards, the reality of the Hercynian and the
subsequent Atlasic deformations was ascertained.
*
Corresponding author. During the beginning of the 20th century, Gentil per-
E-mail address: hoepffne@fsr.ac.ma (C. Hoepffner). formed an extensive field work north of the High Atlas

1464-343X/$ - see front matter Ó 2005 Published by Elsevier Ltd.

doi:10.1016/j.jafrearsci.2005.09.002
 C. Hoepffner et al. / Journal of African Earth Sciences 43 (2005) 144–165 145

mountains. ‘‘The structure of the plateaus is characterised mentary cover. The Atlasic shortening remained weak
by a folded Palaeozoic basement, unconformably covered and correlations between the Palaeozoic massifs of the
by transgressive Mesozoic deposits, which remained mostly Meseta and of the Atlas are possible.
horizontal. Due to the erosion, we see that a wide chain, – The Rif, a part of the Alpine chain of western Mediter-
developed by the end of Carboniferous times (i.e. the ranean: the shortening was important and renders
Hercynian chain) has been completely eroded. This struc- difficult, although not impossible, comparisons between
ture of western Morocco has to be compared to the Iberian the Rifean Palaeozoic series and the other Palaeozoic
Meseta’’ (Gentil, 1918; translated). Following Gentil, massifs of Morocco. The Algerian Alpine Tell belt bears
Lecointre (1926) carefully mapped northwestern Morocco Palaeozoic blocks, for instance the Kabylias, which are
while other geologists, most of them belonging to the newly very similar to those of the Moroccan Rif.
constituted Geological Survey of Morocco, spread the
knowledge of the country in Northern Morocco and south The existence of the Hercynian deformation throughout
of the High Atlas as well. A complete list of the references Morocco and adjacent Algeria lead to distinguish several
is given by Morin (1964, 1970, 1979). structural zones (Michard, 1976; Piqué and Michard,
As shown by the ancient authors, the Hercynian (=Vari- 1981, 1989; Michard et al., 1989; Piqué, 1984, 1989, 1994,
scan) chain of Northern Africa, extending from western 2001), which are described below. The definition of the
Mauritania to Northern Algeria, is best exposed in structural zones will in turn allow to present the main char-
Morocco where the extended outcrops of Palaeozoic rocks acteristics of the Hercynian orogeny in Northern Africa
allow to distinguish several structural domains (Fig. 1). and to tentatively replace the Hercynian belt of North
Africa within the tectonic frame of the Hercynian orogeny
– The Saharian domain: in southern Morocco the Anti- of western Europe.
Atlas domain presents Precambrian inliers cartographi-
cally surrounded by more or less deformed Palaeozoic 2. The palaeozoic evolution of the Hercynian structural
rocks. Hercynian folds are known also in the Algerian domains
Ougarta and in western Mauritania. In the extreme
south, the Tindouf basin is the undeformed Palaeozoic 2.1. The Saharian domain
cover of the West African craton (Reguibat Rise).
– Middle Morocco, where the existence of the Hercynian 2.1.1. The palaeozoic sedimentation (Table 1)
deformation has been first recognised (Gentil, Lecointre, Between the northern limit of the West African craton
etc.), is subdivided into two zones: (i) the Meseta, where and the Hercynian orogenic domains of central Morocco
several massifs made of deformed Palaeozoic rocks are (see below), the Anti-Atlas (Choubert, 1947, 1963) is a
inliers, cartographically separated by a thin and tabular large and open antiform, bent during the Atlasic orogeny.
Mesozoic and Cenozoic cover; (ii) the High and Middle Its structural grain trends WSW–ENE in its western
Atlas where the Palaeozoic massifs, similar to those of part, from which it prolongates toward the Zemmour belt,
the Meseta, are separated by a thick and folded sedi- E–W in its central part, and ENE–WSW in the east, where

Fig. 1. Structural subdivisions of North Africa and location of the Paleozoic terranes. 1: Rifian-Tellian belt, a: southern front of the chain; b: Paleozoic
allochtonous terranes of the internal zones. 2: Atlasic belt (HA: High Atlas, SA: Saharian Atlas, TA: Tunisian Atlas, MA: Middle Atlas). 3: Paleozoic, a:
deformed by variscan orogeny, b: undeformed. 4: West African craton (Archean and Proterozoic massifs). 5: Mauritanides allochtones.
146 C. Hoepffner et al. / Journal of African Earth Sciences 43 (2005) 144–165

Table 1
Simplified paleozoı̈c evolution of the main structural zones of the Northern (Mesetian) domain

1: panafrican basement (Anti-Atlas); 2: sandstones and quartzites; 3: shales and greywackes; 4: shales and psammites; 5: basin deposits (deltaic or deep sea
fan sequences); 6: continental redbeds (conglomerates, sandsones); 7: limestones; 8: black shales; 9: volcanoclatic deposits with calk-alkaline volcanism; 10:
alkaline to tholeitic volcanism; 11: chaotic deposits (olistostromes, debris flows, rock falls); 12: granites; 13: strong tectonic event: folding and meta-
morphism; 14: moderate tectonic event: faults, folding; 15: main uncomformities.

it connects to the Algerian Ougarta (Figs. 1 and 2). It is Thomas et al., 2002), at least partly related to crustal exten-
separated from the High Atlas by the recent Ouarzazate sion (Piqué et al., 1999; Soulaimani et al., 2003), an east-
and Souss troughs. Its main characteristics are the wide ward-directed transgression started at the very beginning
outcrops of Precambrian rocks, visible in several inliers of the Cambrian. This event can be observed all over the
(‘‘boutonnières’’), which are covered by Palaeozoic rocks. Anti-Atlas domain. The first sediments were detrital, but
The Precambrian times in Anti-Atlas have been marked open marine conditions rapidly developed, inducing during
by the development of the Eburnian orogeny, at about the Lower Cambrian, at least in the western and central
2000 Ma and the Pan-African orogeny, at about 700– Anti-Atlas, the development of a shallow platform, more
600 Ma. The oldest granitoids and metamorphic episodes subsident in the western Anti-Atlas (Choubert, 1963;
are related to the Eburnian orogeny (Charlot, 1978; Aı̈t Benziane et al., 1983). During this period, the so-called
Malek et al., 1998; Thomas et al., 2002; Walsh et al., Lower and Upper Limestones were deposited, separated
2002). The most obvious traces of the Pan-African orogeny by purple shales (Lie-de-vin series) representing a brief
are seen in the central Anti-Atlas, where an ophiolitic regressive episode. After a regression (and an emersion?)
sequence has been described (Leblanc, 1972, 1975; at the end of the Cambrian, the sea invaded again the
Saquaque et al., 1989). This ‘‘Pan-African suture’’ is traced domain for a long time at the beginning of the Ordovician.
southeasterly in Algeria, as far as the Hoggar (Black and The region was still a shallow and epicontinental platform.
Liégeois, 1993) although its actual signification is currently The Ordovician sediments were typically detrital, being
discussed (Ennih and Liégeois, 2001). composed of sands and clays, all issued from the Saharian
After the deposition of the latest Proterozoic volcanic continent (Destombes et al., 1985). At the end of the
series and redbeds (Ouarzazate series, 575–560 Ma; Ordovician a regional glaciation developed (Ouanaimi,
 C. Hoepffner et al. / Journal of African Earth Sciences 43 (2005) 144–165 147

Fig. 2. Structural map of the northern (Meseta) and southern (Anti Atlas) domains.

1998), the Anti-Atlas being located not far from the ice cap the Anti-Atlas rose up and became the source of the clastics
that spread over western Africa (Deynoux, 1978). The end (Wendt, 1985; Hassenforder, 1987). As a consequence, the
of the glaciation occurred at the beginning of the Silurian Late Devonian and Carboniferous sequences deposited in
and it was the cause of a glaciogenic transgression over the Anti-Atlas are typically detrital: sandstones, clastic
Morocco. Black shales were deposited in confined marine limestones and argillites.
environments and poorly oxygenated waters. At that time
the African shield, eroded since a long time and covered 2.1.2. The Hercynian deformation
by the marine transgression, did not provide more than The Hercynian deformation was weak in the Anti-Atlas,
very fine argillaceous minerals. Furthermore, during the when compared to its effects in central and Northern
Lower Devonian, even those fine detrital sediments lack Morocco, where emplacement of granites, regional meta-
in the Anti-Atlas marine basin, and limestones, often ree- morphism and penetrative deformation occurred. However
fal, were deposited onto the carbonate platform. detailed examination leads to distinguish several structural
During the extensional regime that had characterised the zones:
first part of the Palaeozoic, the clastics were issued from the
West African craton. From the Devonian, the extensional 2.1.2.1. The western Anti-Atlas (Figs. 2 and 3). West of
regime changed to a compressive one, expressing the devel- the Bas Drâa inlier, the Cambrian rocks are involved
opment of the Hercynian orogeny. The Proterozoic axis of in NNE–SSW folds and thrusts, all of them being
148 C. Hoepffner et al. / Journal of African Earth Sciences 43 (2005) 144–165

Fig. 3. Geological sections across the north western part of the Anti Atlas domain (see location on Fig. 2).

east-vergent (Choubert, 1963; Mattauer et al., 1972; Soulai- deformation decreases laterally toward the inliers around
mani, 1998; Belfoul et al., 2001). In the westernmost part of which the unconformable Palaeozoic sedimentary cover is
the area, near the Atlantic coast, the folds are tight and only gently tilted to the centre of the plateau.
overturned. At the scale of the outcrop, their axial plane Northeast of the Kerdous inlier, the Irherm-Tata area is
is underlined by a metamorphic foliation with an E–W a large-scale open folded zone where wide synclines cored
stretching lineation, compatible with the sense of transport by Middle Cambrian are separated by narrower uplifted
(Belfoul et al., 2001). The intensity of the deformation inlier anticlines. The structural pattern of the Variscan
decreases rapidly eastward and the Cambrian strata are folds seems erratic and it would suggest successive folding
only affected by large tens of meters-scale folds with a west- episodes. However, no refolded axis or cleavage plane are
ward steeply dipping fracture cleavage, mainly visible in observed in the field. Moreover, there is a regional distribu-
pelitic levels. Further east, in the Goulmine Plain, 15 km tion of the various trends that are controlled by vertical
from the Atlantic shoreline, the Middle Cambrian strata dominant motion of reactive crustal faults like, for
are only slightly tilted. instance, the Tata fault (Hassenforder, 1987; Faik et al.,
In the Bas Drâa inlier, the crystalline basement remained 2001; Caritg et al., 2004).
practically undeformed in the course of the Variscan orog-
eny. By contrast, the base of the sedimentary cover was 2.1.2.2. Central and eastern Anti-Atlas. In the Bou Azzer
deformed due to the uplift of the rigid basement along the inlier, the crystalline basement did not suffer any noticeable
southeastern limit of the inlier (Soulaimani et al., 1997). ductile deformation in the course of the Hercynian orog-
In the Bani area (Fig. 3), disharmonic folds affecting the eny. By contrast, its sedimentary cover was folded, locally
Cambrian limestones are concentrated in some detachment affected by an incipient cleavage and, more importantly, it
levels at the base of the cover (Helg et al., 2004). Above, the was detached by a decollement from its basement. The
Cambrian-Ordovician sandstones are affected by kilome- resulting Hercynian structure is a large scale NW–SE box
tre-scale open and box-folds, slightly overturned southeast- anticline. Vertical reactivation of basement fractures is sug-
ward and associated with an incipient cleavage in their gested by the concentration of the deformation along the
hinges. The Jbel Rich tens of meters-scale wavelength folds inlier borders, which laterally decreases toward the adja-
developed in the Devonian sandstones are often asymmet- cent Cambrian syncline (Leblanc, 1975).
ric: their southern flanks are sub-vertical or in reverse posi- South of the Tinghir oasis, the Palaeozoic rocks are
tion, their axes are subhorizontal and they display a affected by several thrust faults that dip gently north-
regional en-echelon structure. wards. After Hindermeyer (1954), and Choubert (1959);
South of the Oued Drâa, the Upper Devonian shales are Michard et al. (1982) distinguished several allochthonous
the southernmost formation of the Anti-Atlas that is units overlapping a southern autochthonous sequence
affected by metre-size folds; the Jbel Ouarkziz Carbonifer- apparently undetached from the Sahgro Precambrian
ous strata is only slightly tilted toward the south, at the basement.
northern border of the Tindouf bassin. Such southward overthrusting tectonic structures extend
North of the Bas Drâa domain, the Lakhsass Plateau to the east, since several thrusts affect the Neoproterozoic
area is located between the Ifni and Kerdous inliers. There, cover along the northern side of the Ougnate inlier and
the Hercynian structures result from an E–W regional in the Tafilalt subsurface.
shortening. They are particularly developed along old reac- Generally, in the Anti-Atlas domain, the Hercynian
tivated fractures in the centre of the area, as on both limbs metamorphism is weak, from very low grade to low grade,
of the Jbel Inter anticline. The prominent fabric in the in the range of 150–300 °C (Buggisch, 1988; Soulaimani,
cover rocks is a pervasive cleavage, axial-plane to tight or 1998). It may be explained by deep sedimentary burial
isoclinal upright folds. On both sides of this zone, the beneath more than 10 km of Paleozoic overburden.
 C. Hoepffner et al. / Journal of African Earth Sciences 43 (2005) 144–165 149

2.2. The northern domains (Fig. 4 and Table 1) dence for a Caledonian imprint in Morocco, except in the
continental margin off El Jadida, where borehole data
2.2.1. The Sehoul zone show that a Cambrian granodiorite has been mylonitized
Initially defined by Piqué (1979, 1982), the Sehoul zone around 455 Ma (K–Ar method, Kreuzer et al., 1984 in
outcrops to the east of Rabat in a small area but it can be Ruellan, 1985). This suggests that a ‘‘Caledonian’’ belt
followed northward under the Gharb Cenozoic deposits. wraps around the northwest Meseta (El Attari, 2001;
Its contact with the Meseta is a faulted zone trending Fig. 4).
N80–120° E (The Rabat Tiflet Fault Zone, RTFZ). The The folded and metamorphosed Cambrian slates and
Sehoul zone is made of Cambrian pelites and greywackes, the Tiflet granite were thrust upon the Meseta prior to
with a minimum exposed thickness of several hundreds the deposition of Late Silurian strata that unconformably
metres. Sedimentological observations suggest a shallow lie upon the granite. Elsewhere, the slates are unconform-
but subsident deltaic environment (El Hassani, 1990). ably covered by fluviatile conglomerates of Lower Visean
The rocks have been subjected to a tectono-metamorphic age (Piqué, 1979; El Hassani, 1990).
episode that gave way to the development of E–W trending In the Sehoul zone s.s., the Hercynian deformation was
folds, recumbent and overturned to the south, accompa- weak and limited to its southern margin, reactivated and
nied by a cleavage contemporaneous with a low-grade also thrust onto the Meseta, it can be connected with the
regional metamorphism. Deformation and metamorphism slight thermal event which has been dated at 320 Ma (K/
increase towards the south, from anchizonal domain (illite Ar on mica) in the Sehoul region and in the El Jadida
crystallinity data, Piqué, 1979) with spaced cleavage to epi- margin.
zonal domain (chlorite and biotite) with slaty cleavage. The
metamorphism has been dated at 453 ± 8 Ma (K/Ar on 2.2.2. The coastal block
micas; El Hassani et al., 1991). The Tiflet granite emplaced This zone corresponds to the coastal Meseta, i.e. the
within the slates at 430 ± 3 Ma (Rb–Sr method; Charlot western parts of the Central, Rehamna, Jbilete and Atlasic
et al., 1973). These data indicate an orogenic episode, Ancient massifs. Subsurface data of the Palaeozoic base-
coeval with the Caledonian orogeny. This is the only evi- ment hidden by the flat and thin younger sedimentary
cover allow to draw the main structures between these mas-
sifs (Fig. 2).
The main characteristics of this zone are the following:

– The Precambrian basement is scarcely present at the

outcrop. It is represented by acidic and intermediate vol-
canic and volcano-clastic formations, the El Jadida rhy-
olites (Gigout, 1951; Cornée et al., 1984, 1985). These
rocks can be compared to the Anti-Atlas Ouarzazate
formations with whom they share the same geochemical
high K calc-alkaline affinity (El Attari, 2001).
– The Lower Cambrian rocks are, like in the Anti-Atlas,
limestones and dolomites. These thin strata are dated
by Archeocyaths in the western Jbilete massif. Above,
the Middle Cambrian is represented by greywackes
and pelitic rocks. Their variable thickness (1000–
6000 m) and the distribution of the depocentres suggest
that they accumulated in a NNE–SSW trending graben
(Bernardin et al., 1988). Indeed, the intercalated volca-
nic flows and basaltic dykes (Gigout, 1956) yield the
characters of a within-plate alkaline series (El Attari,
Fig. 4. The main structural zones of the northern domain (Meseta s.l.) 2001; Ouali et al., 2000). This extensive episode took
with the most important variscan inliers. 1: Sehoul Zone (a) and its likely place within the post-rift deposition of uppermost
prolongation to the west (b) with ‘‘Caledonian’’ events. 2: Coastal Block:
Mid-Cambrian sandstones and quartzites and thin peli-
lower and middle Paleozoic, weakly deformed. 3: Central Meseta: lower to
upper Paleozoic with carboniferous pull-apart and foreland basins, tic and sandy Upper Cambrian horizons (André et al.,
strongly deformed by variscan phases. 4: Southern Zone: lower to upper 1987).
Paleozoic similar to the southern domain (Anti-Atlas), moderately folded – After a sedimentary hiatus during the Tremadocian,
by the variscan phases. 5: Eastern Zone: lower and middle Paleozoic the Ordovician strata (800–1000 m thick) were deposited
deformed by eovariscan events, small carboniferous basins with calc-
in a shallow marine platform submitted to the storm
alkaline volcanism. 6: Internal zones of the Rifian chain. Main structural
limits: RTFZ: Rabat-Tiflet Fault Zone, WMSZ: Western Meseta Shear waves (Hammoumi, 1988). They begin with Arenigian
Zone, SOFZ: Smaala-Oulmès Fault Zone, TBBFZ: Tazekka–Bsabis– micaceous shales, followed by Llandeilian and
Bekrit Fault Zone, APTZ: Atlas Paleozoic Transform Zone. Caradocian sandstones and quartzites. Ashgillian
150 C. Hoepffner et al. / Journal of African Earth Sciences 43 (2005) 144–165

microconglomeratic shales are indicative of a periglacial The timing of the tectono-metamorphic activity is not pre-
environment (Destombes and Jeannette, 1966). cisely determined. Affecting Late Devonian rocks, it should
– The Silurian sequence is thin (100–150 m) and mainly be post-Devonian. However, a recent interpretation of seis-
represented from the Llandoverian by Graptolitic black mic data in the Doukkala basin suggests that the Devonian
shales directly lying on the Ashgillian or even Carado- and Carboniferous rocks, only mildly deformed, uncon-
cian strata. Some carbonates are present in the Wenloc- formably blanket a substratum affected by NNE–SSW folds
kian and especially the Ludlowian. The beginning of the and thrusts identical to the structures known at the surface
Silurian corresponds to a marine transgression during (Echarfaoui et al., 2002). This observation suggests that at
which shallow and non oxygenated waters invaded least a part of the Hercynian structures of the Coastal block
again the considered area. Mafic lavas are intercalated have developed early.
in the Silurian rocks in the Oum er Rbia valley (Cornée
et al., 1985). They are intraplate, anorogenic, alkaline 2.2.3. The Central Meseta
basalts (El Kamel et al., 1998). This zone covers the main parts of the Central,
– The Lower Devonian (Lochkovian-Praguian) is repre- Rehamna and Jbilete Mesetian massifs, the Atlasic Ancient
sented by limestones and shales deposited in a more or massif and the Tamlelt inlier in the Atlas mountains. It is
less subsident marine shelf. A true carbonate shelf limited to the west by the Western Meseta shear zone;
with many reefal buildings developed since the late to the north by the Sehoul zone, to the south by the
Emsian and it lasted during the Mid-Devonian (Eif- Tizi nÕTest fault zone; and to the east by the Tazekka–
elian-Givetian) and the beginning of the Frasnian. Its Bsabis–Bekrit fault zone (TBBFZ). Two subzones must
central part rose up and constituted a NNE–SSW ori- be distinguished, separated by the Smaala-Oulmes fault
ented emerged ridge during the Late Devonian. Note zone (SOFZ) the Western Central Meseta and the Eastern
that such a positive trend occurred since the Silurian, Central Meseta (Figs. 2 and 4).
as indicated by the transgressive direct contact of the The Precambrian basement is, like in the Coastal block,
Lower Devonian strata upon the Caradocian rocks in represented by felsic volcano-clastic rocks. Neoproterozoic
western Jbilete (Beun et al., 1986). Anyway, west of granitoids crop out scarcely in the Eastern Central Meseta
the emerged area, a subsident zone acted during the (Zaı̈an Block; Morin, 1960, 1962, in Michard, 1976; Allary
Famennian and at least the Tournaisian as a large depo- et al., 1976; Bouabdelli, 1989; Verset, 1988; Cailleux, 1994).
centre. The latter is known from seismic and subsurface Above, the Lower and Middle Cambrian strata (600 m) are
data (Barbu, 1977; Echarfaoui et al., 2002; Echarfaoui, limestones and marbles covered by slates and greywackes
2003). with intercalated tuffs and tholeiitic basaltic flows (Ouali
et al., 2001, 2003). They are themselves covered by a thick
Broadly speaking, the Hercynian deformation was weak series (3000 m) of quartzites in which Acritarchs date from
in the Coastal block. The kilometric-scale folds, NNE–SSW the lowermost Ordovician (Cailleux, 1994). In the Western
trending, are ordinarily upright or overturned towards the Central Meseta, the Neoproterozoı̈c basement is visible as
west, rarely towards the east. From west to east, the rocks metarhyolites in the Rehamna (Corsini et al., 1988a), dated
are affected by an increasing penetrative cleavage and meta- at 593 ± 8 Ma (U/Pb on zircons, Baudin et al., 2003) and
morphic grade (Piqué and Wybrecht, 1987) (Fig. 5). The granodiorites in the High Atlas of Marrakech dated at
eastern limit of the Coastal block is therefore affected by 598 ± 5 Ma (U/Pb on zircons Eddif, 2002); and the
an important deformation, especially in the Rehamna and Cambrian is represented by thick slates in the core of the
Jbilete massifs, where folds and west-verging thrusts are anticlines. Like in the Coastal Block, the first Ordovician
associated to right-lateral wrench-faults, allowing to define rocks have an Arenigian age and their deposit succeeded
the Western Meseta shear zone (WMSZ: Piqué et al., 1980). to a hiatus during the Tremadocian. In the Western Central

Fig. 5. Simplified geological section across the northern mesetian domain (see location on the Fig. 2). P3: Neoproterozoic; Cb: Cambrian; O: Ordovician;
Si–D: Silurian to Middle Devonian; UD–LC: Upper Devonian, Lower Carboniferous; V–N: Visean–Namurian; W: Upper Westphalian; A: Autunian; c:
granitoı̈ds. S1: eovariscan cleavage, S2: main variscan cleavage. SBB: Sidi-Bettache Basin, AKB: Azrou-Khénifra Basin.
 C. Hoepffner et al. / Journal of African Earth Sciences 43 (2005) 144–165 151

Meseta, the stratigraphic succession (Llanvirnian and are indicative of a shelf, inner or outer, and a slope where
Llandeilian pelitic rocks followed by Caradocian quartz- evidences of sedimentary gliding and resedimentation
ites) is similar to that of the Coastal block facies, indicating increase during the Upper Devonian. The allochthonous
a similar shallow marine platform. Further to the east, facies correspond to sediments which were deposited
however, in the Eastern Central Meseta, the sedimentary further to the east: the Praguian and Emsian rocks are
facies are more distal and deeper; the Caradocian and thick turbiditic sequences; the Middle and Upper Devonian
the Ashgillian facies are argillaceous and turbidites are are slope deposits similar to those of the autochthonous
present in the autochthonous series of the Eastern Jbilete series.
(Hammoumi, 1988). North of the Meseta, in a narrow At the end of Devonian times, rapid changes, known as
stripe in tectonic contact with the Sehoul zone (The Rabat the ‘‘Famennian revolution’’ (Piqué, 1975) occurred in the
Tiflet zone, Table 1), the Ordovician is only represented by Western Central Meseta. In the Central Massif, where they
Arenigian-Llanvirnian pelitic rocks. Its main characteristic have been extensively studied, coarse clastic rocks: con-
is to yield evidences of a mafic magmatic activity, basaltic glomerates, rock fall deposits, debris flows, olistostromes
flows and doleritic dikes (Piqué, 1979). and proximal turbidites were deposited during the Famen-
The Silurian rocks are similar to those of the Coastal nian and the Tournaisian upon Devonian limestones.
Block, with Llandoverian black shales and phtanites. To These Devonian limestones are often involved as olistho-
the west, the first levels are detrital. Above, the limestones liths in the chaotic sedimentation. Laterally, these deposits
beds increase in importance up to the Ludlowian and grade to more distal argillites and sandstones (Piqué, 1979;
Pridolian. South of the Sehoul zone, the upper Silurian Fadli, 1990; Zahraoui, 1991; Tahiri, 1991; Tahiri and
rocks lies directly upon the Arenigian rocks, indicating an Hoepffner, 1988; El Hassani, 1990; Izart et al., 2001a).
earlier uplift of this area. Toward the west of the Central Since Piqué (1979), these chaotic facies are considered to
Meseta, the Lower Devonian is represented by clastic, con- delineate the borders of the incipient late Devonian-Car-
glomeratic and locally by fluviatile deposits, characteristic boniferous Sidi-Bettache basin (SBB). The basin limits
of the development of a tectonic instability (Cornée et al., are the western boundary of the Coastal Block, the south-
1987a,b; Cornée, 1989; Mayol and Muller, 1985; Hollard ern limit of the Sehoul zone and the Zaer-Oulmes anticlinal
et al., 1982). Toward the north of the Central Meseta, the zone (Figs. 3 and 6). Some volcanic flows are associated
Lower Devonian is not represented. The first Devonian to the peripheral zones of the SBB. Their geochemical affin-
deposits are Emsian in age. They contain conglomerates ity is transitional to alkaline (Kharbouch et al., 1985;
with granitic pebbles probably extracted from the Tiflet Kharbouch, 1994). The SBB is thought to have a southern
granite (Charrière and Regnault, 1989). Elsewhere in the prolongation in the Rehamna (Hollard et al., 1982;
Western Central Meseta, the observed Lower and Middle Destombes et al., 1982) and Jbilete (Bordonaro et al.,
Devonian facies suggest an open marine shelf. Undifferenti- 1979; Mayol and Muller, 1985) massifs. In the Eastern
ated at the beginning, its paleogeography became more Central Meseta, the Tournaisian is represented by con-
complicated through time. The limestones were predomi- glomerates, discordant upon the Middle Devonian rocks
nant since the Praguian and reefal buildings were wide- (Bouabdelli, 1989). During the Lower Visean, clastic rocks
spread from the Emsian to the Frasnian, with a maximum (1000–2000 m) were deposited in the SBB inside a shallow
extension during the Givetian (Termier, 1936; Piqué, but subsident shelf (Piqué, 1979; Izart, 1991) and in the
1979; Zahraoui, 1991; Tahiri, 1991; Chakiri, 2002). Some Eastern Central Meseta, inside another subsident area,
clastic, often turbiditic sediments indicate deeper areas named the Azrou-Khenifra basin (AKB; Bouabdelli,
within the shelf (Razin et al., 2001). In the Eastern 1989). The Upper Visean transgression deposited a wide
Central Meseta, Allary et al. (1976); and Bouabdelli range of sediments that cover all the areas of the Central
(1989), among others, distinguished autochthonous and Meseta, with variable facies and thicknesses. Several envi-
allochthonous Devonian series. The autochthonous facies ronments are distinguished: (i) marine shelves where clastic

Fig. 6. Simplified geological section across the Tamlelt inlier (from Houari and Hoepffner, 2000; location on Fig. 2). P3: Neoproterozoic, Cb: Cambrian;
O–Si: Ordovician and Silurian; Cb–O: Cambrian-Ordovician (eastern zone); M: mesozoı̈c cover (High Atlas). S1: eovariscan cleavage, S2: main variscan
cleavage.
152 C. Hoepffner et al. / Journal of African Earth Sciences 43 (2005) 144–165

sediments were deposited and reefs built. Such deposits are mechanisms responsible for the opening of the Permian
often discordant on the underlying strata from the Lower basins (Doblas et al., 1998).
and Middle Palaeozoic. They occur in the Eastern Central The Hercynian deformation started early, at the
Meseta (Zaian area) and in the Western Central Meseta end of Devonian times, and lasted during most of the
(Zaer-Oulmes area) (Table 1); (ii) basins or elon- Carboniferous.
gated NE–SW trending depocentres, where thick clastic
sequences of Upper Visean and Namurian ages accumu- – An Early Variscan phase corresponds to the opening of
lated. In Western Central Meseta, the SBB was still active, the SBB and AKB at the limit between the Famennian
from the Central Massif to the Jbilete (Bordonaro et al., and the Tournaisian-Visean period. Piqué (1979); and
1979; Beauchamp and Izart, 1987). Eastward, beyond the Bouabdelli and Piqué (1996) interpreted these basins
Smaala-Oulmes fault, the AKB is marked by an important as transtensive areas bounded by NE–SW transcurrent
tectonic activity, especially at its eastern margin. Here, the faults or faulted zones: the Western Meseta shear zone,
olistostromes that were deposited have been related (i) to the Smaala-Oulmes fault and the Tazekka–Bsabis–Bek-
the emplacement of gravity-driven nappes gliding toward rit fault (Figs. 2 and 7), which acted at that time as posi-
the AKB from its eastern uplifted margin (Huvelin, 1977; tive flower structures and determined the development
Allary et al., 1976; Bouabdelli, 1989; Jenny and Le Marrec, of sedimentary ridges. Besides, a tilted block tectonics is
1980; Jenny et al., 1989), (ii) to some extension faults often assumed (Tahiri, 1991; Zahraoui, 1991; Bouabdelli
(Beauchamp and Izart, 1987; Izart et al., 2001b; Verset, and Piqué, 1996). Compressive deformations, responsi-
1988; Berkhli et al., 2000), or (iii) to the dislocation of ble for the development of cleavage, folds (Tahiri,
shelves by extension faults at the nose of a duplex complex 1991) and limited thrusts (Cailleux, 1985), attributed
moving from east to west during the Visean–Namurian to the stacking of slices (Benabbou, 2001a,b), can be rec-
(Benabbou, 2001a,b; Benabbou et al., 2001). A mafic mag- onciled with the flower structure model along these
matism accompanied the development of these basins. faults.
Within and near the Jbilete massif intrusive rocks, tron- – The Visean deformations (330–320 Ma; K/Ar on micas,
dhjemites, gabbros and dolerites were emplaced Huon et al., 1987, 1988) are depicted in the Eastern
(Bordonaro et al., 1979; Aarab, 1995; Kharbouch, 1994; Central Meseta. At the eastern margin of the AKB,
Essaifi, 1997). Further to the north (Rehamna, Fourhal), the structure is a conspicuous cleavage, axial plane of
volcanic flows and doleritic sills and dykes (Hoepffner, N30°E folds, recumbent toward the west, followed by
1982; Kharbouch, 1994; Remmal et al., 1997; Remmal, thrusts directed towards the same direction. The eastern
2000; Benabbou, 2001a,b; Roddaz et al., 2002; Ntarmou-
chant, 2003) yield a transitional to tholeiitic affinity
(Kharbouch, 1994; Remmal, 2000), although a calc-alka-
line trend is evidenced in the northeast of the Fourhal area
(Roddaz et al., 2002).
The final filling of the Mesetan basins occurred during the
Namurian and the Lower Westphalian, when the very shal-
low marine shelf emerged and when the Meseta was sub-
jected to the last stage of the Hercynian deformation.
The Upper Westphalian is represented in Central Mor-
occo by the Sidi Kassem continental red beds (Termier,
1936). Resting unconformably upon the Hercynian folds,
they are affected by open folds and thrusts, suggesting that
the Late Westphalian was still a period of syntectonic sed-
imentation (Benabbou, 2001a,b; Hoepffner et al., 2000;
Razin et al., 2001).
The true post-tectonic strata are continental beds dated
from the Stephanian in the Atlas Palaeozoic massif
(Broutin et al., 1989) and the Jbilete and Haouz massifs
(Essamoud and Courel, 1996). Elsewhere, the first discor-
dant sequences are red conglomerates, sandstones and
argillites (El Wartiti, 1990; El Wartiti et al., 1990) that were
deposited in restricted basins during the Autunian (Lower
Permian). These sedimentary rocks are associated to ande-
Fig. 7. Opening model of the Carboniferous basins (from Bouabdelli and
sites, dacites, rhyolites and ignimbrites (Cailleux et al.,
Piqué, 1996). 1: Sidi-Bettache and Azrou-Khénifra basins. 2: Eovariscan
1986; Youbi et al., 1995). The geochemical affinity of these structures and vergence (eastern zone—EZ). 3: Suspected eovariscan
magmatic rocks evolves from calc-alkaline for the oldest to structures in the anticline zones. 4: Strike-slip along the main faults. CB:
alkaline for the youngest, according to variations in the Coastal Block; SZ: Sehoul Zone.
 C. Hoepffner et al. / Journal of African Earth Sciences 43 (2005) 144–165 153

part of the AKB was deformed at that time. Its depocen- Carboniferous rocks of the synforms, while both grade
tre migrated toward the west, in the Fourhal basin, towards the antiforms, where a conspicuous cleavage is
which was attained during the Namurian-Westphalian observed, coeval with a low-grade metamorphic evolution.
(Bouabdelli and Piqué, 1996). Propagating folds in a The most important deformations are located in the Reha-
duplex system (Benabbou et al., 2001) may have play mna massif, where they are associated to a medium-grade
a role in this deformation migration. In the southern metamorphism (kyanite-staurotide). This culmination of
part of the Fourhal Basin, the pre-Visean (Neoprotero- the metamorphic grade and of the associated deformation
zoic to Ordovician) rocks of the ‘‘Zaian block’’ display has been related to a high thermal gradient during the
N–S folds (Fig. 2). The associated cleavage, more or less deformation that combined ductile thrusts and wrench-
developed, is flat-lying. Upper Visean sequences uncon- faulting (Hoepffner et al., 1982; Lagarde and Michard,
formably cover the pre-Visean deformed rocks (Fig. 5). 1986; Piqué and Michard, 1989; Essaifi et al., 2001). More-
The pre-Visean structures are interpreted as the result of over, the piling up of symmetamorphic nappes or slices
the deformation of the basin bottom during its initia- likely played a role in the burial of the Palaeozoic rocks
tion. East of the AKB, and in its southern prolongation (Corsini et al., 1988b; Diot, 1989). A subsequent exhuma-
(Jbilete and Ait Tamlil massifs), several nappes, respec- tion resulted from the inversion of the ductile thrusts
tively verging to the NW and the SW were emplaced (Baudin et al., 2003).
between the end of the Upper Visean and the Namu- The Late Carboniferous tectono-metamorphic events
rian-Westphalian. The mechanism of their individualiza- were accompanied by the emplacement of granitoids whose
tion is attributed to gravity slidings (Allary et al., 1976; ages are considered to be between 320 and 270 Ma (Mrini
Huvelin, 1977; Bouabdelli, 1989; Jenny and Le Marrec, et al., 1992). The granitic magmas injected in the upper
1980; Jenny et al., 1989). These allochthonous units are crust along the sinistral NNE–SSW and dextral ENE–
made of Ordovician, Silurian-Devonian and Visean WSW crustal shear zones, interfering with the regional
rocks. All of them are free of any pre- or Visean defor- deformation (Diot, 1989; Lagarde, 1989; Lagarde et al.,
mation, suggesting therefore the initial decollement of 1990). Three magmatic associations (calc-alkaline, sub-
the sedimentary sequences predated the development alkaline and peraluminous) are distinguished by Gasquet
of these deformations in their original location, i.e. the et al. (1996). They characterize a post-collisional tectonic
eastern zones. regime and the granitoids are mainly of crustal origin.
– The Late Carboniferous deformations affected the whole The most recent granites are Permian in age and they pres-
Central Meseta. Considered as the ‘‘major phase’’ by ent an alkaline (Mabkhout et al., 1988) or nearly alkaline
Michard (1976), they post-dated the Westphalian and (Gasquet et al., 1996) affinity.
they predated the Stephanian-Permian. Small neo-
formed micas developed during this deformation yielded – The last Hercynian compression affected the Stephanian
K/Ar isotopic ages between 300 and 290 Ma (Huon and Permian deposits. They are weak and consist of
et al., 1987). This deformation is complex and polyph- open folds and brittle shears in a compressive regime
ased. The general direction of the folds is NNE–SSW oriented first E–W then NW–SE to N–S (Aı̈t Brahim
to NE–SW (Fig. 2). The regional anticlines and synclines and Tahiri, 1996).
correspond, respectively to the former sedimentary
ridges and depocentres that had previously controlled
the sedimentation, even for the N70° E to N110° E folds 2.2.4. The eastern zone
along the Sehoul zone, and the N–S to N140°E folds in The eastern zone corresponds to the Eastern Meseta
the western part of the SBB. The folds and the ductile- inliers from Midelt to Oujda, further east in Western
brittle associated thrusts are verging to the west and Algeria, and to some Atlasic inliers such as the Tazekka
the NW from the High Atlas to the Rehamna massif. and north Tamlelt massifs (Figs. 2 and 4). The oldest rocks,
In the Central Massif, the structures are SE facing from attributed to the Cambrian on the basis of facies similarities
the Sidi Bettache syncline to the Fourhal syncline (Hoepffner, 1987), crop out in the Tazekka, Midelt and
(Fig. 5). This can be interpreted: (i) as the result of a north-Tamlelt massifs. They are made of slates and grey-
polyphased deformation; the SE facing structures are wackes with mafic intercalations. Among them the Midelt
more recent since they affected the Upper Westphalian amphibolites correspond to old intraplate alkaline basalts
rocks, which are discordant upon NW vergent folds (Ouali et al., 2000).
(Razin et al., 2001); (ii) as a change in the dip of the deep The Ordovician is represented by sedimentary rocks
structures that controlled the deformations (Cailleux, indicative of a shallow sea. Sandy pelitic rocks, dated from
1987); or (iii) as antithetic folds and thrusts in a glob- the Arenigian-Llanvirnian in several inliers (Hoepffner,
ally NW facing regional structure (Bensahal, 2001; 1977; Rauscher et al., 1982; Torbi, 1996), are covered by
Benabbou, 2001a,b; Benabbou et al., 2001). sandstones and quartzites attributed to the Upper
Ordovician.
The intensity of the deformation is highly variable. The Silurian sequences are thin (150 m) and they often
Generally, cleavage and metamorphism are absent in the have been squeezed by the Hercynian deformations. Their
154 C. Hoepffner et al. / Journal of African Earth Sciences 43 (2005) 144–165

base is made from Llandoverian phtanites. Then the Wen- Hoepffner, 2000). The metamorphism, generally low-
lockian and the Ludlowian are represented by argilites and grade, was more intense at Midelt, where biotite and
graptolitic black shales (Hoepffner, 1987). Note the lack, garnet crystallised.
here, of the limestones present in more western Upper The age of the Eo-Variscan phase is dated at 366 Ma in
Silurian strata. Midelt (Rb/Sr, Clauer et al., 1980) and at 368–372 Ma
The Devonian sequence starts with Lochkovian rocks in Debdou-Mekkam (K/Ar on micas: Huon et al.,
identical to those of the Ludlovian. Here, slumps and ball 1987).
and pillow sedimentary structures in the sandstones testify – The Visean deformations are evidenced in the Tazekka
the instability of the shelf. Above, a thick detrital sequence, massif, at the limit between the Western and Eastern
sometimes turbiditic, is made of argillites and greywackes. Central Meseta. Folds and west-vergent thrusts with
It is represented in most of the inliers, from the Tazekka to small displacements are associated to a conspicuous
western Algeria. Their age, determined by palynomorphs, cleavage and a low-grade syntectonic metamorphism
is Praguian to Givetian-Frasnian (Marhoumi et al., dated at 330 Ma (K/Ar on micas: Huon et al., 1987).
1983), suggesting the development of a turbiditic basin dur- Note that elsewhere in the Eastern Meseta, this period
ing the Devonian. The clastic character of the Devonian corresponds to the initiation of the volcano-clastic
sedimentation distinguishes the eastern zone from the basins. This is also at that time that the oldest granitoids
Western Meseta and its carbonate shelf. The only turbiditic of eastern Meseta were emplaced: in the Tazekka
Devonian sequences observed in the Western Meseta are (Huvelin, 1992), in Midelt (333–319 Ma; U–Pb on zir-
present in the allochthonous units of central Eastern cons: Oukemeni et al., 1995), and SW of Oujda (328–
Meseta, which originated in the eastern zone. Note that, 321 Ma; Rb/Sr, Mrini et al., 1992).
in spite of the volcano-clastic facies of the greywackes, no – The late Hercynian deformations affect the Carbonifer-
true volcanic rock, tuff or flow, has been observed. ous rocks and overprint their substratum. They are folds
The oldest Carboniferous rocks are conglomerates and and thrusts, NE–SW to E–W oriented (Fig. 2). Their
bioclastic limestones, unconformable upon older rocks vergence is often to the north like at Jerada (Erraji,
deformed by the Eo-Variscan Phase (Hoepffner, 1987). 1997). The associated metamorphism remained weak.
They are dated from the Upper Visean (Médioni, 1980; These deformations post-dated the Westphalian, as con-
Huvelin and Mamet, 1989; Berkhli et al., 1999). Above firmed by isotopic ages at 300 Ma (K/Ar on micas;
them, a thick volcano-clastic sequences is made of pyro- Huon et al., 1987). Following Mrini et al. (1992), granite
clastites and epiclastites associated to intermediate to felsic emplacement ended afterwards, since the isotopic ages
flows: andesite, dacite, rhyolite and ignimbrite (Hoepffner, given by these authors are within the 286–247 Ma age
1981; Huvelin, 1986; Chalot-Prat, 1990). The volcanic interval.
activity lasted up to the beginning of the Namurian. A con-
temporaneous faulting is deduced from chaotic facies
developed at that time (El Ghazi and Huvelin, 1981; 2.2.5. The Rifian–Kabylian zone
Huvelin, 1986; Torbi, 1996), the faults having controlled This zone includes the inner massifs of the Alpine Rifian–
the development of the volcano-clastic basins (Chalot-Prat, Kabylian belt, which are made of Palaeozoic sequences and
1990). The magmatism is calc-alkaline, similar to that of probably older crystalline rocks. These rocks are included in
the active margins (Kharbouch, 1994). However, there is several Alpine allochthonous units, such are for instance the
no other evidence for an active subduction of the oceanic Ghomarides and Sebtides in the Rif belt. All these rocks
lithosphere during the Carboniferous and its occurrence belong to the allochthonous Alboran ‘‘terrane’’. However,
is therefore questionable, consequently, the geodynamical they present several similarities with the autochthonous
setting of this calc-alcaline magmatism remain in debate NE Moroccan and NW Algerian units.
(see Section 3.2.1). In the Ghomarides, the Ordovician and Silurian are rep-
Anyway, the sea withdrew to the East, in the Jerada resented by shelf sequences where a volcanic activity is
basin, from the Namurian to the upper Westphalian. Ini- noted, becoming important at the Silurian-Devonian
tially marine, the sedimentation became paralic since the boundary. In Kabylia, the oldest dated Palaeozoic rocks
Westphalian B (Izart, 1991; Desteucq et al., 1988; Essa- represent the Cambrian (Baudelot and Géry, 1979) or the
moud and Courel, 1998). Tremadocian (Baudelot et al., 1981). According to Bossière
In the eastern zone, the Hercynian deformation was (1980), they unconformably cover an older basement. They
polyphased. are covered by Arenigian-Llanvirnian sequences.
The Lower Paleozoic shelf was disrupted during the
– The oldest compressive events are attributed to the so- early Devonian. Bourrouilh et al. (1980); and Chalouan
called Eo-Variscan phase. They gave way to flat-lying (1986) described from north to south a carbonate and
and stretched folds, accompanied by a well developed reefal shelf, a slope and a turbiditic basin. Contemporane-
slaty cleavage. The axes are oriented NNE–SSW, N–S, ous volcano-clastic and volcanic rocks are known in the
and NW–SE (Figs. 2 and 5). Their vergence is gener- Middle Devonian of Kabylia (Gélard et al., 1978). In the
ally towards the west (Hoepffner, 1987; Houari and Rifian Ghomarides, the Upper Visean–Naurian beds
 C. Hoepffner et al. / Journal of African Earth Sciences 43 (2005) 144–165 155

unconformably overlie deformed older Palaeozoic rocks. The Hercynian structures are E–W folds and overlaps
The succession of the environment was the same as in the directed towards the craton. At Tamelelt (Fig. 6), the
Devonian, leading again from proximal turbidites and deformation resulted from a combination of thrusting
olistostroms to the north to distal turbidites in the south, and strike-slip faulting. The folds are overturned to the
indicating therefore the southward deepening of the basin SSE and associated to E–W dextral shears, parallel to the
(Chalouan, 1986). contact with the eastern zone (Houari and Hoepffner,
The Hercynian deformation was polyphased. The Eo- 2000, 2003). The cleavage is rough or slaty, the metamor-
Variscan phase, pre-Upper Visean in age, is described in phic grade is weak (sericite-chlorite). At Tineghir, the folds
the Kabylia (Bouillin and Perret, 1982) and analyzed in and thrusts, southward-directed, are typical of a foreland
the Rif (Chalouan, 1986). It developed folds facing to west deformation (Michard et al., 1982). At Skoura the struc-
and northwest, and a low-grade regional metamorphism. tures are also E–W. Beyond, the Southern Zone links west-
The Upper Carboniferous phase was mild. The folds are ward with the N80° E Tizi nÕTest fault zone, through the
NW–SE and E–W and their vergence is variable. In Kaby- N120° E Skoura fault (Ouanaimi and Petit, 1992). These
lia, late Hercynian granitoids were emplaced around 270– faults underline the direct contact between the northern
280 Ma (U–Pb on zircons, Peucat et al., 1996). Mesetan domain and the Anti-Atlas domain. These defor-
The similarities between the Rifian–Kabylian Palaeozoic mations are attributed to the Late Carboniferous phase
zones and the eastern Morocco and northwestern Algeria known in the other zones.
have been emphasised by Chalouan (1986); Hoepffner
(1987); and Piqué et al. (1993). The correlations are based 3. The North African Hercynides: Geological and tectonic
mainly on the existence of a Devonian turbiditic basin and characters
the development of the Eo-Variscan phase. They suggest
that the Rif and Kabylia were the prolongation of NE 3.1. The development of the Hercynian orogeny
Morocco and NW Algeria during the Palaeozoic, at the
northwestern margin of the Paleo-Gondwana. Note, how- 3.1.1. The deformation
ever, that the crustal extension revealed by the mafic volca- 3.1.1.1. Ages. Within the Hercynian belt of Morocco
nic activity was probably more important in the Rif and and adjacent areas, stratigraphic and structural argu-
the Kabylia. On the other hand, the Carboniferous calc- ments issued from field observations and isotopic datings
alkaline magmatism was less important there than in NE lead to distinguish four major tectono-stratigraphic events
Morocco and NW Algeria. (Piqué and Michard, 1989; Piqué, 2001): (1) a first event,
coeval with the Caledonian deformation of Europe, is
2.2.6. The southern zone dated at 450–430 Ma. It is known in the Sehoul zone, in
This zone includes the centre and the south of the the northernmost part of the Moroccan Meseta. Besides,
Tamelelt inlier, the region of Tineghir and the Skoura inlier some disturbances occurred at that time in the Coastal
(Figs. 2 and 4). It marks the transition with the Anti-Atlas Block and the Northern Moroccan Meseta. The docking
domain. It is situated in the High Atlas and its southern of the Sehoul zone with the Moroccan Meseta by thrusts
border. Its limit with the Central Meseta zone and the and/or transcurrent faulting occurred prior to the Late
Oriental Zone is not observable except in the north of the Silurian; (2) the Eo-Variscan deformation, 372–366 Ma
Tamelelt inlier (Fig. 6). The Precambrian is represented in age, is well developed in the Eastern Meseta of
by Neoproterozoic flows and volcanoclastic rocks. During Morocco, in western Algeria and in the Rifian–Kabylian
the Lower Palaeozoic, from Cambrian to Devonian, the blocks; (3) the Intra-Visean deformation developed at
considered area received detrital and carbonate sediments 330 Ma in the Tazekka and the Eastern Central
that were deposited on a platform showing more analogies Meseta of Morocco; (4) the Late Carboniferous event,
with the Anti-Atlas than with northern domains (Destom- between 300 and 290 Ma, corresponds to the second fold-
bes et al., 1985; Wendt, 1985; Houari, 2003) with the nota- ing phase in the eastern zones of Morocco and in the wes-
ble absence of any of magmatic activity. Carboniferous tern Algeria, and to the main folding in the Western
rocks are absent in the Tamelelt, Tineghir and Skoura Moroccan Meseta.
areas. However, during the Carboniferous detrital sedi- This suggests that the deformation became younger
ments were deposited on the subsident northern margin from east to west, since the Late Devonian to the Late Car-
of the Saharan shield. From the Tournaisian to the boniferous. Exceptions to this general rule are the
Namurian-Westphalian, deltaic deposits grade northward Pre-Upper Visean deformations in the Central Moroccan
into olistostromes and turbidites (Michard et al., 1982; Meseta basins, which probably initiated the development
Izart et al., 1989; Soualhine et al., 2003). A communication of sedimentary ridges bordering the depocentres. Such a
probably existed north of Skoura with the Ait Tamlil turbi- deformation is also suspected in the subsurface of Western
ditic basin, and therefore with the Central Meseta zone. Morocco. Actually, the isotopic ages suggest a continuum
The absence of the Carboniferous magmatism is another of the regional shortening, moving westward rather than
distinctive feature of this zone which is a thus rather part discontinuities between distinct tectonic events separated
of the sub-cratonic domain. by episodes of stress relaxation.
156 C. Hoepffner et al. / Journal of African Earth Sciences 43 (2005) 144–165

In the Anti-Atlas, the age of the Hercynian deformation Eastern part of the Anti-Atlas are characterized by a very
is not accurately determined. The regional contrast weak and heterogeneous deformation, concentrated along
between the Bani and Rich folded strata and the Ouarkziz restricted faulted zones that separate undeformed or only
unfolded sequences is not an unconformity but a progres- tilted wide areas. Values of 5–10% for the Hercynian short-
sive transition from the weakly deformed domain of the ening are given by Leblanc (1975); and Hassenforder
southern Anti-Atlas to the undeformed Carboniferous (1987).
sequences at the northern border of the Tindouf platform Globally, the amount of deformation decreases progres-
(Soulaimani et al., 1997). The Hercynian deformation sively towards the south and the southeast and it vanishes
could be contemporaneous with a thermal event depicted within the undeformed and stable Tindouf platform, a part
at around 290 Ma (Bonhomme and Hassenforder, 1985). of the West African craton.

3.1.1.2. Amount of the shortening. At the scale of Morocco, 3.1.1.3. Vergence and virgations of the structures. During
the southern domain, where the shortening is relatively the Eo-Variscan phase in Northern and Eastern Morocco
weak, differs from the northern zones, more intensively and in Western Algeria, the structures, foliations and
deformed. thrusts, delineate a regional virgation (Figs. 2 and 7). This
In the relatively strongly deformed northern domain, we virgation seems to have controlled later the Intra-Visean
distinguish: (1) the pre-Upper Visean phases during which deformation, with a west-directed vergence in the north-
the deformation was homogeneous and accompanied by a ern part and a south-directed vergence in its southern
generalised metamorphism. West-verging recumbent folds part. In the Western Central Moroccan Meseta, the trend
were interpreted as the result of a crustal thickening of the regional structures is NNE–SSW to NE–SW.
(Hoepffner, 1987; Piqué and Michard, 1989). However, The variations, locally observed like in the Sidi Bettache
the Midelt granitoids have been considered to have basin area (Fig. 2) result from an en-échelon setting
emplaced during a Visean crustal thinning (Diot and between ductile NNE–SSW shear zones, as well as the role
Bouchez, 1989) that have been thought to moreover con- play by some rigid buttresses like the Sehoul zone (Fadli,
trol the main deformations (Filali et al., 1999); (2) the Late 1990).
Carboniferous deformation was heterogeneous, especially In the western Anti-Atlas, the folds and thrusts are typ-
in the Central Meseta and the Coastal Block. It was con- ically east- to south-east verging. In the Central and East-
centrated along relatively narrow and elongated domains ern Anti-Atlas, like in the Tinerhir area, the folds and
generally corresponding to the former sedimentary ridges. thrusts are south-facing (Fig. 2). Roughly, the structural
There, the main structures are narrow folds, incipient to vergence of the Anti-Atlas Hercynian structures is directed
well developed cleavage, and ductile shear zones, which towards the West African craton. From the Zemmour to
indicate a transpressive regime. The most noticeable shear the Ougarta, the craton acted as an apron, along which
zones are the WMSZ dextral and west-vergent thrust, the the Hercynian folds are moulded.
SOFZ wrench- and thrust fault, and the ATPZ dextral
and south-vergent all along the southern limit of the High 3.1.1.4. Control of the Hercynian deformation by the
Atlas (Fig. 4). The resulting pattern is a contrasted oro- basement structures. In the Central Moroccan Meseta, the
genic domain, constituted by poorly deformed to unde- regional shear zones are located at the limits of the late
formed wide areas separated by regional shear zones, Devonian-Carboniferous basins such as the SBB (Piqué,
themselves characterised by a relatively intense deforma- 1979). In other words, the wrench/thrust ductile shear
tion and an important metamorphic grade. At depth, these zones are reactivations of synsedimentary faults. The mag-
structures are probably accommodated by ductile thrusts, matic activity recorded along the basin limits suggests that
one of which is exposed in the Rehamna metamorphic they correspond to deep-seated faults. Similar observations
zones (Michard et al., 1989; Piqué and Michard, 1989; are made for the Smaala-Oulmes fault.
Aghzer and Arenas, 1995). Eastward, the Tazekka–Bsabis–Tazekka faulted zone
In the Anti-Atlas, the Hercynian shortening was at the corresponds to the eastern limit of the AKB, intensively
origin of the reactivation of Precambrian blocks and of dis- deformed (Bouabdelli, 1989). From the Tazekka massif
harmonic folds within the Palaeozoic strata. It was also to Oujda, NE–SW to ENE–WSW faults controlled the
accommodated by many detachment and decollement lev- trend of the compressive structures. There also, the associ-
els. It differs clearly from west to east. (1) In the Western ated magmatism (Kharbouch, 1994) indicates the crustal
Anti-Atlas, the southeasterly verging shortening was rela- character of these faults (Hoepffner, 1987; Torbi, 1996).
tively important, as evidenced by the stacking of metamor- In the Anti-Atlas, the trend of the Hercynian structures
phic slices and the ductile deformation affecting the base of was inherited from Proterozoic fractures by the rigid reac-
the cover, especially beyond the reactiv basement fractures. tivation during the uplift of the basement blocks. This con-
An amount of about 15–20% for the horizontal shortening trol was strict at the regional scale, allowing therefore
is deduced from the restoration of the Western folded Bani partial decoupling of the basement from its cover, where
(Helg et al., 2004). (2) On the contrary, the Central and local decollement occurred (Fig. 3).
 C. Hoepffner et al. / Journal of African Earth Sciences 43 (2005) 144–165 157

3.1.2. ‘‘Inner’’, ‘‘outer’’ zones and pericratonic domains; the The actual relation between Anti-Atlas and the Moroc-
kinematics of the Hercynian deformation can Meseta is not yet deciphered. However, the boundary
By many aspects, the Palaeozoic evolution of the North- is probably the Atlas Palaeozoic transform zone (APTZ:
ern and Southern domains of Morocco presents important Piqué and Michard, 1989), which is a very important and
differences: long-lived shear-zone. This zone separated these two
domains since the Lower Palaeozoic, as a part of a transfer
– To the South, the Palaeozoic sediments were deposited fault joining the southern and the northern branch of the
on a relatively stable shelf, at the northern margin of Late Precambrian–Cambrian rift (Piqué and Jeannette,
the Reguibat shield. This cratonic platform, dislocated 1981). The Hercynian shortening, larger to the north than
during the Late Proterozoic-Lower Cambrian rifting, to the south of the fault, was accommodated by a sinistral
became relatively stable during the Palaeozoic. The het- motion along this fault during the Eo-Variscan and intra-
erogeneous Hercynian deformation, globally weak Visean deformations. Later, during the late Carboniferous
except in the Western Anti-Atlas and the Zemmour, phase, the collision of the two domains occurred through
occurred during the development of a very low-grade the reactivation of the APTZ as a right-lateral and south-
metamorphism, without any magmatic activity. verging thrust. During this deformation, recorded in the
– To the North, the marine platform was instable during Southern Mesetan zones, the Anti-Atlas acted as the
the Cambrian, with the initiation of a graben in the Hercynian southern foreland.
Western Moroccan Meseta. Since the Famennian ‘‘revo-
lution’’, it was broken and disintegrated by the develop- 3.2. The tectonic development of the Hercynian orogeny
ment of the late Devonian-Carboniferous subsident
basins. The deformation was largely controlled by the 3.2.1. The North African Hercynides: An intracontinental
basement architecture. It developed differently in the belt
Eastern and the Western parts of the Moroccan Meseta. The Hercynian belt results from the continental collision
The Eo-Variscan phase, which is the main Hercynian between the Paleo-Gondwana to the south, and the
deformation event in the eastern zone of Morocco and Laurentia-Baltica to the north (in present coordinates)
western Algeria, testifies for the initiation of regional after the disappearance of oceans (Matte, 1986, 2001). Sev-
stresses in these areas. It is suggested that the same stress eral microcontinents, or microplates, such as Armorica,
field was also responsible for the initiation of the pull- Avalonia, etc. participated to the general scheme (Fig. 9).
apart SBB and AKB in more western zones, which A fundamental question concerning the position of the
opened through transcurrent motions along NNE– Moroccan and Western Algerian orogenic segment in the
SSW trending crustal faults (Fig. 7 and Hoepffner, Hercynian belt is the presence or not, of remnants of
1987; Bouabdelli and Piqué, 1996). The end of the trans- the oceans. From palaeomagnetic studies in Cambrian
current motion along the Tazekka–Bsabis–Bekrit fault and Ordovician flows in the Western Meseta and the com-
was the result of its activation as a west-vergent thrust parison of data given by stable Africa and the Anti-Atlas,
during the Middle Carboniferous. Then, the deforma- Feinberg et al. (1990) suggested that an ocean, several
tion moved westward, reaching the Fourhal and Sidi- thousands kilometres wide, separated the Moroccan Mes-
Bettache foreland basins during the Namurian and the eta from the Anti-Atlas during the Lower Palaeozoic. It
Westphalian. would have been progressively resorbed during the Silurian
and the Devonian and the subduction-collision process
By its earlier deformation and the general vergence of would have been achieved during the Carboniferous. Sub-
the structures toward the Carboniferous foreland basins, sequent palaeomagnetic studies proved the inaccuracy of
the Eastern Moroccan Meseta (and northwest Algeria) is this model (e.g. Khattach et al., 1995). Moreover, the total
therefore considered as the ‘‘inner’’ zone of the Hercynian lack of volcanic activity during the Devonian testifies for
belt in North Africa, while the Central and Western the absence of any subduction of an oceanic lithosphere
Morocccan Meseta represent the ‘‘outer’’ zones of this belt. under the Meseta domain during the Middle Palaeozoic.
Such a distinction is useful but we must note that the term The study of the Carboniferous flows in the Moroccan
‘‘inner zone’’ does not imply here the existence of a high- Meseta and their relationships with the Hercynian struc-
pressure metamorphism and of remnants of a continental tures afford the most accurate tools to give valuable
collision. arguments allowing geodynamical models. The Visean–
Even if the deformation is noticeable in its Western part, Namurian volcanic rocks are typically calc-alkaline and
it is globally weak and no Hercynian granitoids are known associated to early deformations in the Eastern Moroccan
in the Anti-Atlas, which can be regarded as a pericratonic Meseta and Western Algeria, while they are transitional-
domain. It is noticeable that in the Anti-Atlas, the defor- alkaline or tholeiitic and associated to the initiation of
mation is stronger to the west, which is the opposite of sedimentary basins in the Central Moroccan Meseta
what is observed in the Meseta, where the more deformed (Kharbouch, 1994). From this, two models have been pro-
zones are located to the east. posed (Fig. 8):
158 C. Hoepffner et al. / Journal of African Earth Sciences 43 (2005) 144–165

Eo-Variscan phase, giving way to a continental sub-

duction (orogenic prism) during the Carbonifer-
ous, the oceanic lithosphere being ‘‘fossilized’’
under the Meseta (Kharbouch et al., 1985; Roddaz
et al., 2002). In this model, all the Meseta is charac-
terized by Carboniferous retro-arc foreland basins
where the structural vergence is opposite with
regard to the subduction plane dipping. Such a
model implies the existence of an oceanic lithosphere
to the east of Morocco. This is hardly compati-
ble with the absence of ophiolitic complexes, sub-
duction-related metamorphism and syn-collisional
granitoids.
(2) The calc-alkaline volcanism of the Eastern Meseta
and Western Algeria is related to movements
along transcurrent/thrust shears deeply seated in the
crust (Lagarde, 1989; Kharbouch, 1994; Piqué,
1994, 2001). This means that the extensive regime,
active several times in the considered domain, espe-
cially in its eastern zones during the Devonian, did
Fig. 8. Geodynamical models for the Moroccan Hercynides (Middle
Carboniferous). Subducted oceanic crust: A from Kharbouch et al. (1985);
not give way to an oceanic accretion.
B from Roddaz et al. (2002). Intracontinental shear zones, C from
Kharbouch (1994); and Piqué (2001). 1: continental crust; 2: upper mantle; In other words, in this model—which seems the more
3: oceanic crust; 4: calc-alkaline magmatism; 5: alkaline to tholeitic realistic—, the Hercynian belt of Morocco and Western
magmatism. CB: Coastal Block; SBB: Sidi Bettache Basin; AKB: Azrou Algeria is an intracontinental segment of the Hercynian
Khenifra Basin.
belt. It belonged to the margin of the Gondwana all
through the Palaezoı̈c.
(1) The calk-alkaline magmatism is related to the sub-
duction of a lithospheric plate plunging to the 3.2.2. Relations of the Moroccan Hercynides with the other
west under the Moroccan Meseta. This subduction Hercynian zones
would have been active during the Carboniferous By its location at the northwestern corner of Africa, the
(Boulin et al., 1988), or it would have ceased since the Hercynian chain of Morocco and Western Algeria appears

Fig. 9. Possible configuration of the periatlantic paleozoı̈c orogens in Permian time (from Matte, 2001; Houari and Hoepffner, 2003). 1: Gondwanan
stable blocks (West African Shield); 2: Parts of Avalonia and Armorica microplates; 3: Carboniferous foreland basins); 4: main sutures (Is: Iapetus suture;
Ts: Theic suture; Bs: Beja suture; CCsz: Coimbra-Cordoba shear zone; LRHs: Lizard Rheno-Hecynian suture;TPs: Tepla suture; GSBs: Galicia South-
Brittany suture). NAF: North Appalachian Front; NVF: North Variscan Front; Me: Meguma Zone and *: Caledonian terranes (like Sehoul Zone); CB:
Coastal Block; CM: Central Meseta; EZ: Eastern Zone; AA: Anti-Atlas; Ma: Mauritanides belt.
 C. Hoepffner et al. / Journal of African Earth Sciences 43 (2005) 144–165 159

to be close to other Palaeozoic belts of the circum-Atlantic unstable during the Cambrian Rifting in the Western
realm (Fig. 9). Meseta and it disintegrated by the development of the
To the South, the Western Anti-Atlas extends into the late Devonian-Carboniferous subsident basins. The
Zemmour and further into the Mauritanides foreland architecture resulting from these extensional episodes
(Lécorché and Sougy, 1978; Lécorché et al., 1991). is critical for the understanding of the subsequent
To the West, beyond the present Atlantic ocean, Hercy- control of the Variscan structures that individualized
nian Morocco is at the contact with the Eastern Appala- in the course of the Eo-Variscan and late Carbonifer-
chian zones. Similarities between the geological evolution ous compressive deformations.
of the Avalon and Meguma Appalachian zones have been (2) Within the Hercynian belt of Morocco and Algeria,
recognised a long time ago (Hughes, 1972). They are four major tectono-stratigraphic events are recorded:
explained by their Palaeo-Gondwanian origin and their (i) ‘‘Caledonian’’ event (450–430 Ma) known only
docking to the Appalachians when the Theic ocean was in the Sehoul zone in the northernmost part of
consumed (Piqué, 1981; Piqué et al., 1990; Piqué and the Morocco (ii) Eo-Variscan deformation (372–
Skehan, 1992). 366 Ma) developed in the Eastern Meseta, the wes-
To the Northeast, the relationship with the European tern Algeria and the Rifian–Kabylian blocks; (3)
Hercynian belt is obscured by the Alpine orogeny and Intra-Visean deformation (330 Ma) in the Tazekka
the opening of the Mediterranean sea. Moreover, from and the Eastern Central Moroccan Meseta; (4) Late
Upper Carboniferous to Permian, great dextral wrench- Carboniferous event (300 and 290 Ma), second
faults cut up the chain allowing the westward displacement folding phase in the eastern zones, and to the main
of Africa and the separation between North Gondwana folding in the Western ones and probably in the
and Western Europe (Bard, 1997). Therefore, it is difficult Anti-Atlas.
to connect the North African and European Hercynides, (3) Two episodes characterised the Major Hercynian
especially the Moroccan and Iberian Mesetas. Compari- shortening, relatively more important in the northern
sons between North Africa and Europe have however domain than in the Anti-Atlas: (i) the pre-Upper Vis-
been made early (e.g. Gentil, 1918; Lecointre, 1926). Strati- ean phases in the Eastern Morocco and Eastern Alge-
graphical and structural evidence indicate the Paleo- ria, giving way to a homogeneous deformation
Gondwanian origin of many European zones (Iberian accompanied by a generalised metamorphism and
Meseta, Central and Northern French Armorican massif, west-verging recumbent folds, (ii) the Late Carbonif-
southern Germany, etc.). Anyway, by its sedimentary erous heterogeneous deformation, in the Central
column, the age and the intensity of its main deforma- Meseta and the Coastal Block, concentrated along
tions, the Hercynian belt of Morocco and Western Algeria relatively narrow and elongated domains marked by
is to be compared (even for its eastern zones) to the isoclinal folds, incipient to well developed cleavage,
External zones of the Hercynian belt, devoid of any oce- ductile shears zones (WMSZ, APTZ, . . .) and west-
anic signature (Piqué and Michard, 1989). Finally, accord- vergent thrusts (SOFZ).
ing to the similarities between Eastern Moroccan Meseta, (4) In the Anti-Atlas, the Hercynian deformation is lar-
Palaezoic Rifian–Kabylia massifs, Western Mediterranean gely governed by the reactivation of Precambrian
palaezoic blocks and Alpine external massifs, the Morroc- blocks uplift that induced regionally variable dishar-
can Hercynides belong to the southern limit of the monic folds trend within the Palaeozoic strata. The
Hercynian belt, near the Gondwana (Piqué et al., 1993; east-southeast verging fold-and-thrust in its western-
Bard, 1997). most side contrasts with the folded cover that wraps
Precambrian NE–SW linear inliers in the rest of the
4. Conclusion chain. The southeasterly verging Hercynian deforma-
tion decreases progressively toward the southeast and
The present review of the sedimentological evolution vanishes within the undeformed Tindouf platform, a
and the Hercynian orogeny throughout Palaeozoic areas part of the West African craton.
of Morocco and adjacent Algeria, reported in this paper, (5) In the lack of any ophiolitic complexes of the Paleo-
lead us to define several structural zones which sedimento- Tethys ocean, subduction-related metamorphism and
logical and structural features are briefly summarized syn-collisional granitoids, the Hercynian belt of Mor-
below. occo and Western Algeria appears to be an intracon-
tinental segment of the Hercynian belt.
(1) The Palaeozoic evolution presents important differ- (6) By its location at the northwestern corner of Africa,
ences between the Northern and Southern domains the Hercynian chain of Morocco and Western Alge-
of Morocco; (i) To the South, the Palaeozoic ria is close to other Palaeozoic belts of the circum-
sediments were deposited on a cratonic platform Atlantic realm, the Mauritanides belt to the South,
(Reguibat rise), relatively stable during the Palaeo- the Eastern Appalachian zones to the West and
zoic since the Late Proterozoic-Lower Cambrian the European Hercynian belt to the Northeast. All
rifting; (ii) To the North, the marine platform was these orogenic belts define a broadly synchronous
160 C. Hoepffner et al. / Journal of African Earth Sciences 43 (2005) 144–165

circum-Atlantic Hercynian–Alleghanian belt devel- hercynienne de lÕAnti Atlas occidental, Maroc. J. Afr. Earth Sci. 32 (4),
oped during the Late Paleozoic Paleo–Gondwana– 723–739.
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Laurentia–Baltica collision. signatures tectoniques, sédimentaires et magmatiques de lÕévolution de
la chaıˆne hercynienne du Maroc Central septentrional. State Thesis,
University of Marrakech, 305p.
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signatures tectoniques, sédimentaires et magmatiques de lÕévolution de
la chaıˆne hercynienne du Maroc central septentrional. State Thesis,
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authors have been supported by French-Moroccan inter- Benabbou, M., Soula, J.C., Brusset, S., Roddaz, M., Ntarmouchant, A.,
governmental scientific cooperation programs and also by Driouch, Y., Christophoul, F., Bouabdelli, M., Majesté-Menjoula, C.,
French and Moroccan Universities. We are particularly Béziat, D., Debat, P., Déramond, J., 2001. Contrôle tectonique de la
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