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Journal of Geodynamics 77 (2014) 4–21

Contents lists available at ScienceDirect

Journal of Geodynamics

jou rn al hom epage: ht tp : / /www.e lsev ier .com/ locate / jog

ceanic units in the core of the External Rif (Morocco): Intramarginiatus or South-Tethyan remnants?

ohamed Benzaggagha, Abdelkader Mokhtari a, Philippe Rossib,c, André Michardd,∗,bdelkhader El Maza, Ahmed Chalouane, Omar Saddiqi f, Ech-Cherki Rjimatig

Université Moulay Ismail, Faculté des Sciences, Département de Géologie, BP 11201 Beni M’Hamed, Meknès, MoroccoBRGM, BP 36009 Orléans Cedex 02, FranceCCGM, 77 rue Claude-Bernard, 75005 Paris, France10, rue des Jeûneurs, 75002 Paris, FranceUniversité Mohammed V-Agdal, Faculté des Sciences, Département des Sciences de la Terre, Avenue Ibn Batouta, BP 1014 Rabat, MoroccoLaboratoire Géosciences, Université Hassan II-Casablanca, BP 5366 Maârif, Casablanca, MoroccoMinistère de l’Energie et des Mines, Direction du Développement Minier, Division du Patrimoine, BP 6208 Rabat Instituts, Morocco

r t i c l e i n f o

rticle history:eceived 10 March 2013eceived in revised form 1 October 2013ccepted 14 October 2013vailable online 25 October 2013

n memory of our professor and friendichel Durand-Delga who encouraged our

esearch in the area over several years.

eywords:est Mediterranean

lpine beltsaghrebidesorocco

uturealeomarginphiolite

a b s t r a c t

The aim of this paper is to describe the mafic rocks that crop out in the central-western Mesorif Zone(External Rif Belt), and discuss their geodynamic signification. Basalt flows, olistoliths and breccias occurin Oxfordian–Berriasian deposits of Mesorif units ascribed to the distal part of the African paleomargin.The climax of volcanic activity is observed at the northern border of a Kimmeridgian carbonate platformprogressively dismembered during the Tithonian–Berriasian. In spite of the alteration of the basalts, theirpetrological and geochemical characters point to E-MORB affinities. The studied gabbro massifs (Bou Adel,Kef el Rhar west and north) occur as restricted slivers or klippes within the Senhadja nappe or mélangeof the internal Mesorif, which overlies the basalt-bearing units and other, more external Mesorif units.The compositions range from troctolitic olivine gabbro to ferrogabbro with frequent ortho- to heteradcu-mulate textures; they display typical tholeiitic affinity. The gabbro massifs are crosscut by trondjhemitedykes and overlain by metabasalts, fault-scarp breccias, ophicalcites, marbles and radiolarites. Composi-tion featuring initial near liquid composition, display multi elements patterns close to those of E-MORB,with a weak Eu negative anomaly and evidence of slight crustal contamination. These gabbro massifs wereregarded as Jurassic–Cretaceous intrusions, locally dated (K–Ar) at 166 ± 3 Ma. Conversely, we assumethey represent discrete samples of a Jurassic–Cretaceous oceanic basement (ophiolites), emplaced tec-tonically in the Senhadja nappe (mélange) of the central Mesorif. The correlation of both these types of

hrust tectonicsranscurrent tectonics

mafic rock associations (paleomargin basalts and ophiolite klippes) with the serpentinites of the easternMesorif (Beni Malek) and Oran mountains (Algeria) is then briefly discussed. We conclude that the previ-ous hypothesis of an intramargin “Mesorif suture zone” must be reconsidered, being challenged by thatof a major, syn-collisional “Oran-Mesorif Strike-Slip Fault”. In the latter hypothesis, the newly describedMesorif oceanic klippes would represent allochthonous remnants of the Ligurian–Maghrebian (Tethyan)oceanic domain.

. Introduction

The External Zones of any collisional belts are by definition out-ide the suture zone (i.e. in the foreland side of the orogen) and,ccordingly, they are expected to be devoid of ophiolitic units,

xcept in the form of tectonic klippes as in the Prealps (e.g. Schmidt al., 1996). In the Rif Belt, as in the whole Maghrebides (Fig. 1),he External Zones lie on the northern margin of the African plate,

∗ Corresponding author. Tel.: +33 142360483.E-mail address: andremichard@orange.fr (A. Michard).

264-3707/$ – see front matter © 2013 Elsevier Ltd. All rights reserved.ttp://dx.doi.org/10.1016/j.jog.2013.10.003

© 2013 Elsevier Ltd. All rights reserved.

from which they derive (Durand-Delga and Fontboté, 1980; Wildi,1983; Favre et al., 1991). They are separated from the dismem-bered Internal Zones (Alboran Domain, Kabylias, Peloritan-Calabriaunits with European/Alpine affinities) by the Maghrebian Flyschssuture zone (Bouillin et al., 1986; Guerrera et al., 2005). This sutureis currently regarded as the result of the SE- to SW-ward retreatof the subducting Ligurian–Maghrebian slab of western Neotethys(Frizon de Lamotte et al., 1991; Lonergan and White, 1997; Jolivet

and Faccenna, 2000; Spakman and Wortel, 2004; Carminati et al.,2012, and references therein). However, if this suture zone is richin ophiolite remnants in the east (Ligurian nappes of Calabria,Sicily) as expectable, such remnants become rare in the west, with

M. Benzaggagh et al. / Journal of Geodynamics 77 (2014) 4–21 5

Fig. 1. Location of the study area in the Maghrebide Belt of North-Africa (A) and paleogeographic sketches showing the Eocene extension of the Ligurian Tethys (B) and theM and ((

tLmtptA

we(imcstewbp2ep

oBsBocc

iddle Miocene collisional setting of the West Mediterranean Alpine belts (C). (B)see text for references).

he last serpentinite-gabbro-basalt assemblage seen beneath theesser Kabylia Massif (Bouillin et al., 1997). In the Rif Belt, the onlyafic rocks associated with the Maghrebian Flyschs are a few olis-

oliths and slivers of E-MORB pillow basalts found in the easternart of the suture zone (Durand-Delga et al., 2000). Then a ques-ion arises: where are the south Tethyan (Ligurian) ophiolites in thelboran transect?

Curiously, a serpentinite massif associated with metabasitesas mapped since years within the External Zones of the east-

rn Rif, next to Beni Malek village west of the Temsamane massifSuter, 1980a,b; Choubert et al., 1984). The Beni Malek massif wasnterpreted subsequently as a mantle sliver detached from an intra-

argin hiatus distinct of the Ligurian Tethys itself, although beingoeval to it (Michard et al., 1992). The significant extension of thisliver at depth was calibrated through magnetic anomaly interpre-ation (Elazzab et al., 1997). More recently, Michard et al. (2007)mphasized that the alleged intramargin suture continues east-ard over 200 km or so, up to the Oran region at least (Algeria),

eing associated with low-grade, intermediate pressure metamor-hism as in the northern Temsamane units (Negro et al., 2007,008). However, the westward continuation of this unexpectedxternal suture remained unknown, and its tectonic interpretationoorly ascertained.

The aim of the present paper is firstly to describe the variousccurrences of Jurassic–Cretaceous mafic assemblages west of theeni Malek massif, based on new field campaigns and stratigraphictudies. Some have been already described (Ben Yaïch et al., 1989;

enzaggagh, 2011), and consists of basalt flows and clasts in pale-margin units. Others are described here for the first time, andorrespond to small gabbro massifs associated with oceanic-typeover sequences. We present the first petrological–geochemical

C) refer to the most common interpretation of the West Mediterranean evolution

description of both these mafic units. Finally we briefly discuss thetectonic interpretation of these contrasting, paleomargin-type andoceanic-type mafic units within the Rif External Zone.

2. Geological setting

In the Rif Mountains (Fig. 2), the Internal Zones constitutetwo pieces of a dismembered, Miocene metamorphic core com-plex (García-Duenas et al., 1992; Michard et al., 2006), namely theNorthern Rif and the Bokkoya massifs. The famous Beni Bouseramantle peridotites and granulites lay within the lower plate of thecomplex, i.e. its lowest and more metamorphic units (Sebtides).The upper plate (Ghomarides) corresponds to several slivers oflow-grade Paleozoic rocks interleaved with their Triassic–Cenozoiccover rocks. The Mesozoic–Cenozoic “Dorsale Calcaire” units thatfringe the south-west front of the Northern Rif and constitute mostof the Bokkoya are remnants southern or south-western paleomar-gin of the Alboran Domain north of the Maghrebian Ocean (Wildi,1979, 1983; Durand-Delga, 1980; El Hatimi et al., 1991; Blidi andHervouët, 1991; El Kadiri et al., 1992; Chalouan and Michard, 2004;Guerrera et al., 2005; Durand-Delga, 2006).

The Maghrebian Flysch nappes are formed by three main thrustsheets (Mauretanian, Massylian, Numidian nappes) originatingfrom the sedimentary infill of the Ligurian–Maghrebian Ocean.The Mauretanian and Massylian Jurassic-Early Cretaceous beds areassociated with E-MORB pillow basalts (Durand-Delga et al., 2000)south of the eastern Bokkoya Massif (Fig. 2). These nappes root

beneath the Internal Zones and overlie the External Zones, exceptfor some back-thrust units (e.g. northernmost Rif and Kabylias).Thus, the fault thrust contact between the Alboran Domain and theFlysch Nappes represents the main suture zone of the Maghrebide

6 M. Benzaggagh et al. / Journal of Geodynamics 77 (2014) 4–21

F ), witS

Oouz

pI2ttowead(smwtuoTEbto(“

owm

ig. 2. Structural map of the Rif Belt after Suter (1980b) and Chalouan et al. (2008uture in the eastern Rif (Michard et al., 2007).

rogen. The Flysch Nappes are in turn obducted and diverticulatednto the uppermost units of the External Zones (Tangier and Habtnits) in the western Rif, and onto slightly deeper units of the sameones (Ketama, Aknoul) in the central and eastern Rif.

The Maghrebide External Zones derive from the North-Africanaleomargin inverted during the Early Miocene collision of the

nternal Zones (Wildi, 1983; Favre et al., 1991; Guerrera et al.,005; Crespo-Blanc and Frizon de Lamotte, 2006). In the Rif Belt,hey are divided, from NE to SW and from top to bottom, intohe Intrarif, Mesorif and Prerif Zones (Suter, 1980a,b). Within eachf these zones, deep rooted, para-autochthonous units contrastith diverticulated, gravity-driven nappes thrust over the more

xternal domains. The Intrarif zone includes the Ketama unit (Tri-ssic to Albo-Cenomanian), the Tangier and Loukos units, partlyetached from the Ketama unit, and the Habt and Aknoul nappesLate Cretaceous-Cenozoic), entirely detached. The Mesorif Zonehows allochthonous units including Triassic to Paleogene for-ations thrust over allegedly autochthonous tectonic windowshose series end with Middle-Upper Miocene turbidites and olis-

ostomes. The Prerif Zone as a whole consists of Jurassic–Miocenenits detached on the underlying Triassic evaporites and thrustver the Upper Miocene foredeep deposits (Gharb Basin, Saiss).he particular, Internal Prerif Zone corresponds to slices of Jurassic-arly Cretaceous limestones that form a string of steep hills (“sofs”)etween the Mesorif and External Prerif Zones. The early (Tor-onian) fold and thrust contacts are sealed by the transgressionf Upper Tortonian–Messinian conglomerates and sandy marlsmolasses), that have been subsequently folded (e.g. Taounatepost-nappe” syncline; Samaka et al., 1997).

The tectonic structures observed in the Rif External units andverlying Maghrebian Flysch outliers show an overall southwest-ard displacement (Frizon de Lamotte et al., 1991, 2004). Twoajor NE-trending left-lateral faults, namely the Jebha and Nekor

h location of Figs. 3 and 4 (framed), and of the Beni Malek-Tres Forcas or Mesorif

Faults (Fig. 2), give additional evidence of the obliquity of the col-lision of the Alboran Domain against Africa (Leblanc and Olivier,1984; Frizon de Lamotte, 1985). This is accounted for by the currentmodels of slab roll-back of the Ligurian–Maghrebian subductionbeneath the European lithosphere (Spakman and Wortel, 2004;Jolivet et al., 2008).

3. Basalt-bearing paleomargin units

In this section we present the volcanic and volcano-sedimentaryformations that occur mostly in the Kimmeridgian–Berriasian car-bonate formations of the Mesorif Zone. The studied outcrops arelocated in two areas of the External Rif (Fig. 2), i.e. the Ouezzanearea of Western Rif (Fig. 3A), and the Taounate-Taineste area ofCentral Rif (Fig. 3B). In the western Mesorif Zone, the volcanic eventhas been ascribed to the Bathonian–Callovian (Ben Yaïch et al.,1989; Ben Yaïch, 1991), whereas it was regarded as Barremianin the central Mesorif Zone (Vidal, 1979, 1983a,b). New accuratedatings based on planktonic assemblages have been published byBenzaggagh (2000), Benzaggagh and Habibi (2006) and Benzaggagh(2011).

The carbonate formations occur everywhere on top of a thick(1000–1500 m) Callovian–Oxfordian turbidite formation known asthe “Ferrysch” that seals the Lower-Middle Jurassic tilted-blockand hemigraben structures of the paleomargin (Wildi, 1981; Favre,1992). The Ferrysch deposits are broadly identical all over the Inter-nal Prerif, Mesorif and Intrarif Zones, but thickens from the Prerif tothe Mesorif. From the Kimmeridgian up to the Berriasian, carbon-ate facies develop everywhere above the Ferrysch turbidites. In the

Internal Prerif, they consist basically of pelagic facies (ammonite-bearing thin-bedded limestones and ammonitico rosso facies). Incontrast, in the Mesorif Zone (e.g. Jebel Tahar Bou Zhaier, Fig. 4A),the carbonate sequence begins with thick layers of calcirudites or

M. Benzaggagh et al. / Journal of Geodynamics 77 (2014) 4–21 7

Fig. 3. Location of the studied outcrops in the Mesorif framework (see Fig. 2 for map location). Numbers refer to the analyzed samples of Table 2. (A) Basalt-bearing outcropsof the western Mesorif Zone (Ouezzane area). Sketch contours of the structural zones after Suter (1964a, 1980b) and Bouhdadi (1999). (B) Basalt-bearing outcrops and mafico of the

(

mK(cewiBit

flnlfflanq

cctbtflaewattM

cfuB

ceanic units of the central Mesorif Zone (Taounate-Taïneste area). Sketch contours

Bou Adel) and 9 (Kef el Rhar).

onogenic carbonate breccias, more or less siliceous (Fig. 4B), ofimmeridgian age according to their benthic foraminifer content

Benzaggagh and Atrops, 1997). The Mesorif carbonate sequenceontinues upward in the Tithonian with varied facies of breccias,ither massive layers of carbonate breccias or chaotic brecciasith rare clayey matrix (Fig. 4C). Ammonites are scarce, and dat-

ngs are based on the planktonic assemblages (Benzaggagh, 2000;enzaggagh and Habibi, 2006). The amount of clay and silt increases

n the Berriasian deposits, which also contains breccias in some ofhe studied sections (Figs. 4D and 5A, B).

Most of the elements of the breccias are shallow water, plat-orm carbonates (up to 60–80 cm in size) dated as Kimmeridgian orower Tithonian in the Upper Tithonian breccias and Upper Titho-ian in the Berriasian breccias (Benzaggagh, 2011). Likewise, the

ayered limestones frequently contain reworked algae and benthicoraminifers (Fig. 5B and C). This suggests redeposition by massows and turbidity currents related to cannibalism phenomena,nd accounts for the frequent and important variations in the thick-ess of the Upper Jurassic carbonate sequence (Fig. 5), as alreadyuoted by Suter (1965).

Besides of the dominant carbonate clasts, all of the studied out-rops (Fig. 3) show an almost constant occurrence of magmaticlasts within the chaotic breccias. They spans from a few cen-imeters to several meters in size, with most frequent blocks andoulders (Fig. 4E and F). Their lithology ranges from typical basaltso dolerites, to fine grained gabbros (see Section 5.1). Some basaltows or fragments of lava flow are preserved by place (Fig. 5A, Cnd D). The earliest magmatic event is recorded by pyroclastic lay-rs by the very end of the Oxfordian (Fig. 5E), whereas the latestould be Upper Tithonian or Berriasian in age. The occurrence of

basalt dyke in the Ferrysch formation of Sidi Kassem (Fig. 3) nexto the Kerkor volcano-sedimentary breccias (Fig. 5D) confirms thathe Upper Jurassic–Berriasian volcanic centers were located in the

esorif Zone.In addition to the carbonate and volcanic clasts, the chaotic brec-

ias also contain pebbles or cobbles of sandstone with Ferrysch-likeacies. The abundance and size of such elements seems to increasepward. Large olistoliths of typical Ferrysch facies occur in theerriasian sequence at J. Mazoura (Fig. 5C).

structural zones after Suter (1980b) and Leblanc (1983). Framed: detail maps Figs. 6

4. The exotic gabbro massifs

In this section we describe the exotic tectonic units that wedefine here for the first time in the Central Mesorif at Bou Adeland Kef El Rhar (Fig. 3B for location). They are characterized bythe occurrence of a thick gabbro basement overlain by varied, low-grade metavolcanites and metasedimentary rocks. We particularlydevelop the Bou Adel case study.

4.1. Bou Adel unit

The Bou Adel gabbro crops out on about 2 km2 (Fig. 6) in thedeeply incised Oued Azrou valley where it is exposed in steepslopes up to 150 m high (Fig. 7A). The plutonic body was regardedas a Paleozoic granite sliver included in the “Senhadja nappe” bySuter (1964b, 1965), whereas Vidal (1983a) recognized its gab-broic nature in the fresh outcrops of the concave slope of thevalley. The latter author classified the massif as a Cretaceous (Bar-remian?) intrusion. However, revision of the map contours anddetailed petrological data (see below) enable us to discard theintrusion hypothesis and define here a tectonic unit (Bou Adelunit) including a plutonic basement and its volcanic-sedimentarycover.

The tectonic units overlying the Bou Adel unit (Fig. 6) con-sist dominantly of platform carbonates classified as Lower toUpper Liassic by Suter (1964b) and Vidal (1983a,b), although somecould be Upper Jurassic (Bulundwe, 1987; Papillon, 1989). Any-way, these carbonate units overlain the Bou Adel unit through athrust contact as they are devoid of the low-grade metamorphismthat affects the Bou Adel unit, and show distinct fold structures.They would correspond to a stack of two large units separatedby slivers of Ferrysch (Callovian–Oxfordian) and surrounded byMiddle-Upper Miocene pebbly marls (Tortonian mélange matrix;Vidal, 1983a).

The plutonic part of the Bou Adel unit is composed of differ-

ent types of gabbro (Table 2). The dominant facies is a coarse tomedium grained troctolitic gabbro that displays an igneous layer-ing dipping 40 ± 10◦ to the NW (Figs. 6 and 7B), revealed by thin(less than one centimeter thick) light layers of plagioclase that can

8 M. Benzaggagh et al. / Journal of Geodynamics 77 (2014) 4–21

Fig. 4. Upper Jurassic–Berriasian succession and volcano-sedimentary breccias. (A) General view on the J. Tahar Bou Zhaier mountain slope, looking eastward (see Fig. 3B forlocation). (B) Weathered surface of a Kimmeridgian carbonate breccia (J. Alebra; see Fig. 3A for location). (C–F) Tithonian from the J. Tahar Bou Zhaier. (C) Clast-supportedc mer, ap d limeb

bow

bBrNlsFbhbhoCgva

haotic breccia (Lower Tithonian). Notice the large limestone slab beneath the hamroportion of marly matrix (Upper Tithonian) topped by Lower Berriasian marls anoulder of dolerite or fine-grained gabbro.

e followed for some meters. Pegmatitic veins or pockets can bebserved elsewhere (Fig. 7D). Typical troctolite samples (BA1, BA6)ere collected along the Oued Azrou (Fig. 6).

From the central to the southwestern part of the massif the gab-ro is reddish due to weathering. Typical samples are BA2, BA3, BA5,A7 (Fig. 6) with a composition of Ti–Fe gabbro, hereafter called fer-ogabbro (Fig. 7E). Layering shows a rather constant strike trending70E whereas dip may change from 30◦ NW to subvertical. Thin

eucocratic dykes, sometimes enriched in dark minerals on eachide and affected by shear deformation, crosscut the ferrogabbro.ield survey did not provide opportunity to observe the transitionetween troctolitic and ferrogabbroic zones because scree and soilside a large part of the oucrops. However some observations cane made on the western bank of the Oued Azrou river near theighest part of the mafic complex (N34,53529; W4,50551) wherene metric enclave of possible troctolite is included in ferrogabbro.

lose to this last oucrop a 1 m-thick, N100E-trending dyke of pla-iogranite (BA9) crosscuts sharply the gabbro at the vicinity of theolcanic-plutonic contact. Greenschist-facies secondary mineralsre widespread (e.g. epidote, Fig. 7D).

nd the occurrence of a basalt cobble (arrow). (D) Chaotic breccia with an increasedstones. (E) Close view of a basalt block in a massive carbonate breccia. (F) Massive

At both the western and eastern tips of the massif (Fig. 6),the volcanic cover sequence of the gabbro massif is preserved.It basically consists of spilitized basalts and dolerites. The west-ern outcrops are the most interesting as they include, next to themetabasalts (Fig. 7A): (i) a mass of coarse volcanic-gabbroic brecciawith chlorite-serpentinite matrix, extending over ca. 100 m × 20 mat the bottom of the slope (Fig. 7F); we interpret this outcropas a submarine fault-scarp breccia; (ii) typical ophicalcite facies(Fig. 7G) in some blocks of this coarse breccia; (iii) white marblestransgressive onto carbonate-cemented volcanic breccias (Fig. 7Hand J); (iv) banded volcaniclastic marbles closely similar to ophi-olitic sandstone layers in the sense of Lagabrielle and Lemoine(1997) (Fig. 7I). Notice that blocks of white marbles are scatteredin the adjoining fault-scarp breccia. Conversely, detrital elementsof gabbro, dolerite and basalt can be found within the marblefacies (Fig. 7J). In some case, a clear metamorphic foliation can be

observed (Fig. 7J), which has been affected by late-metamorphicfolding (Fig. 7K).

The volcanic cover of the plutonic massif shows basically adome shape. According to the layering strike and dip in the gabbro,

M. Benzaggagh et al. / Journal of Geodynamics 77 (2014) 4–21 9

F r locam ciatedf

btmIowc

4

2s(oot(oi

isbWm

ig. 5. Stratigraphic columns of some of the studied Mesorif sections (see Fig. 3 foeridgian to Upper Berriasian chaotic breccias. The earliest basalts are also asso

oraminifers).

asically ENE and to the NW, respectively, the less differentiatedroctolitic gabbro is located to the top of the sequence, whereas the

ore differentiated ferrogabbro remains situated in lower position.f one considers that the massif results mainly of a simple processf fractional crystallization it could be concluded that the complexas tilted before being overhead by its volcanic and sedimentary

over.

.2. Kef el Rhar units

Three massifs of gabbro crop out close to the Kef el Rhar village,0 km east of Bou Adel (Fig. 3). The two largest (Kef el Rhar mas-ifs properly said) are exposed about 1.5 km north of the villageFig. 8), whereas the Dar Bou Aza massif crops out some 6 km westf it. The dimensions and geological framework (Senhadja “nappe”)f these three massifs are similar to that of the Bou Adel massif, andhey were also classified as Lower Cretaceous intrusions by Vidal1983a,b). However, like the Bou Adel massif, they show remnantsf metavolcanites and metasedimentary cover formations suggest-ng an origin from a lost oceanic sea floor.

The poorly exposed Dar Bou Aza massif, 5 km west of Kef el Rhar,s surrounded by Miocene marls and conglomerates, except on its

outhern boundary, which is a tectonic contact between the gab-ro and an overlying “Flysch noir” unit, according to Vidal (1983a).e found at the northern boundary of the massif an outcrop ofarbles that overlay directly the low-grade metagabbroic rocks

tion). Notice the almost constant association of the basalt occurrences with Kim- with resedimented beds (“Ferrysch”, layered limestones with algae and benthic

and contain scattered pebble of metabasalts and metagabbros, andboudinaged cherts (Fig. 9A). These beds are closely similar to theBou Adel volcaniclastic marbles (Fig. 7H–J).

The Kef el Rhar massifs s.str. form a pair of klippes or sliverssurrounded by Miocene clastic marls (mélange matrix according toVidal, 1983a,b) and over hanged by various carbonate units (Fig. 8).A thick volcanic cover, locally associated with marbles, is associatedto the southern klippe. Remarkably, the northern klippe preservesa well-developed, low-grade metasedimentary cover made up ofpale green, pink or red radiolarites (Fig. 9B–D). These radiolaritesare followed upward by black limestones-black shales alternationswhose facies are widespread in the Lower Cretaceous External Rifsequences. The structures observed in the radiolarites (Fig. 9D) areconsistent with an upper-greenschist facies metamorphism, whichalso affect the underlying gabbro itself.

5. Petrography and geochemistry

5.1. Material and methods

Six basaltic rocks sampled in the Upper Jurassic–Berriasian

formations of the Izzarene Window and Bou Haddoud Nappe (pale-omargin units) have been analyzed (Table 1 and Fig. 3). In the exoticgabbro units, the 9 analyzed samples (Table 2) were all collected inthe Bou Adel massif (Fig. 6).

10 M. Benzaggagh et al. / Journal of Geodynamics 77 (2014) 4–21

F 64b)

f ke and

mGwc

TL

TLS

ig. 6. Geologic sketch map of the Bou Adel massif based on the maps by Suter (19ound amidst the slope formations beneath the J. Keil carbonate cliffs. Layering stri

Thin sections were produced and studied both at the Depart-

ent of Geology, Meknès University and the Bureau de Rechercheséologiques et Minières (BRGM, Orléans, France). The samplesere analyzed at the BRGM: major elements by X-ray fluores-

ence (XRF), transition elements by par Inductively Coupled Plasma

able 1ocation and stratigraphic age of the analyzed basalt samples (see maps Fig. 3A and B) wi

Sample # Location

2 Harrara, 100 m north of the village

4 Zendoula path above the village (lava flow)

5 Bou Haddoud Nappe, J. Tahar Bou Zhaier

6 East of Kerkor, lava flow

8 Oued Marticha, Msila area

9 East of J. Mguedrouz

able 2ocation and petrographic characters of the nine analyzed samples from the Bou Adel gample R1 (troctolite) is located very close to BA1.

Sample # Location

BA1 S of Bou Adel springs, right bank of Azrou river

BA2 E of Bou Adel springs, right bank of Azrou river

BA3 E of Bou Adel springs, right bank of Azrou river

BA4 S of Bou Adel springs, left bank of Azrou river

BA5 E of Bou Adel springs, right bank of Azrou river

BA6 SE of Bou Adel springs, along the Azrou river

BA7 E of Bou Adel springs, right bank of Azrou river

BA8 E of Bou Adel springs, right bank of Azrou river

BA9 S of Bou Adel springs, left bank of Azrou river

BA10 SE tip of the massif, left bank of Azrou river

and Vidal (1983a), modified. See Fig. 3B for location. Several metabasalt blocks are dip are visible on the western part of the gabbro massif.

Atomic Emission Spectroscopy (ICP-AES), and Rare Earth and

other elements by Inductively Coupled Plasma Mass Spectroscopy(ICP-MS) NEPTUNE and chemical mineral analyses on a CAMECASX 50 Electron Probe Micro-Analyser (EPMA) equipped withfive wavelength-dispersive spectrometers using an acceleration

th loss on ignition (L.O.I.) to estimate weathering.

Stratigraphic position L.O.I

Dyke within the Ferrysch (Callovian–Oxfordian) 7.7End of Lower Tithonian limestones 3.6Beckeri/Hybonotum zones (base of Lower Tithonian) 12.2Lower Tithonian 7.0Lower Tithonian 18.5Tithonian-Lower Berriasian 14.1

abbro massif (see map Fig. 6), with loss on ignition (L.O.I) to estimate weathering.

Petrographic type L.O.I.

Troctolite 1.5Ferrogabbro 0.6Ferrogabbro 3.3Diorite (?) dyke 2.0Ferrogabbro 0.8Troctolite 1.3Ferrogabbro 2.5Leucocratic vein 2.0Trondjhemite dyke 0.8Congelation margin (?) 3.0

M. Benzaggagh et al. / Journal of Geodynamics 77 (2014) 4–21 11

Fig. 7. Bou Adel unit outcrops and typical rock facies. (A) View of the western tip of the gabbro massif from the northern slope of the Oued Azrou valley (see Fig. 6 for location).(B) Fresh outcrops of layered gabbros along the unpaved road on the northern slope of the valley. (C) Trondjhemite dykes in the eastern part of the massif. (D) Pegmatitictrondjhemite pocket, about 500 m east of (B). (E) Fresh ferrogabbro from the same area as (C). (F) Coarse gabbro-basalt breccia (probable oceanic fault scarp breccia) at theuppermost Bou Adel spring (see photo A for location). (G) Ophicalcite (in float close to F). (H) Stratigraphic contact between volcanic breccia and white marble, just above thebreccia (F) along the path that climbs on the south slope of the valley (see photo A). (I) Limestones with volcaniclastic sandstone layers sourced from mafic rocks; this faciescrops out along the western slope of the gabbro massif, south of the Bou Adel springs. (J–K) Two fresh blocks in float in the Oued Azrou river bedwith (J) Foliated marble withthin, boudinaged volcaniclastic layers including a large dolerite/gabbro pebble, and (K) foliated, impure metamorphic limestone with minor folds.

12 M. Benzaggagh et al. / Journal of Geodynamics 77 (2014) 4–21

Fig. 8. Geological sketch map of the northern Kef el Rhar massif based on the mapb(

vp

5

5

acbipPaMapn

5

7eUtiAtaas

tm

Table 3Analyses of basalt samples from the Mesorif paleomargin units (Table 1 and Fig. 3Aand B for location and stratigraphic context).

2 4 5 6 8 9

SiO2 46.2 51.3 41.5 48.1 34.7 38.8Al2O3 16.5 14.8 15 16.2 10.2 13.4Fe2O3t 8.9 9.9 9.5 9.1 6.3 10.7MgO 13.1 9.7 4.7 11 10.1 5.6CaO 0.9 3.7 10.8 2.7 18 12.2MnO 0.04 0.14 0.05 0.1 0.07 0.11K2O 4.77 1.25 0.11 1.3 0.03 0.12Na2O 0.4 4.9 4.9 3.9 1.3 4.3TiO2 1.09 1 1.01 1.01 0.68 1.12P2O5 0.13 0.11 0.12 0.11 0.08 0.13L.O.I. 7.7 3.6 12.2 7 18.5 14.1

Total 99.73 100.4 99.89 100.52 99.96 100.58

SiO2 50.20 53.00 47.33 51.43 42.60 44.87Al2O3 17.93 15.29 17.11 17.32 12.52 15.49Fe2O3t 9.67 10.23 10.83 9.73 7.73 12.37MgO 14.23 10.02 5.36 11.76 12.40 6.48CaO 0.98 3.82 12.32 2.89 22.10 14.11MnO 0.04 0.14 0.06 0.11 0.09 0.13K2O 5.18 1.29 0.13 1.39 0.04 0.14Na2O 0.43 5.06 5.59 4.17 1.60 4.97TiO2 1.18 1.03 1.15 1.08 0.83 1.30P2O5 0.14 0.11 0.14 0.12 0.10 0.15

100.00 100.00 100.00 100.00 100.00 100.00

U 0.5 0.3 0.4 0.4 0.7 1.2Th 6.2 4.1 4.9 4.1 4.2 4.5Ta 0.5 0.4 0.4 0.4 0.4 0.4Nb 8.3 6.6 6.1 6.7 6.1 8.1Hf 2.8 2.3 1.8 2.3 1.8 1.7Zr 86 70 50 72 55 45Cr 209 165 139 298 123 206Co 36 41 33 37 26 47Ni 72 78 67 85 53 83Rb 50 29 2 14 0.9 0.9Sr 41 131 129 74 86 160Ba 239 98 42 117 9 36Y 28 19 13 16 10 17La 17 7 5.7 3.8 4 13.5Ce 38 16 14 12 9.3 30Pr 4.7 2.2 2 1.7 1.2 4.1Nd 20 10 9.2 7.6 5.5 18Sm 5 2.7 2.3 1.9 1.5 4.2Eu 1.3 0.8 0.4 0.7 0.4 0.7Gd 5.4 3.2 2.5 2.3 1.6 4.3Tb 0.9 0.5 0.4 0.4 0.3 0.6Dy 5.9 3.5 2.3 2.8 1.9 3.4Ho 1.2 0.7 0.5 0.6 0.4 0.7Er 3.1 2.1 1.5 2 1.3 1.7Tm 0.4 0.3 0.2 0.3 0.2 0.2Yb 2.3 1.9 1.1 2 1.3 1.2Lu 0.3 0.3 0.2 0.3 0.2 0.2

y Vidal (1983a), modified. Heavy black lines are shallow-dipping tectonic contactsteeth toward upper unit when recognized).

oltage of 20 kV and a beam current of 100 nA; a PaP correctionrogram was used to correct matrix effects.

.2. Basalts of the paleomargin units

.2.1. PetrographyThese rocks suffered generally strong alteration (spilitisation

nd p.p. weathering) and thin section examination did not provideritical mineral information with the exception of one key doleriticasalt sample (# 6) from the east of Kerkor. In this doleritic basalt,

nterbedded in Lower Tithonian series, examination reveals in thelagioclase lattice: augite, pigeonite and scarce olivine (Fig. 10A).igeonite was demixed into clinopyroxene and orthopyroxenerranged according to a typical herringbone texture (Fig. 10B).atrix is mainly formed by lattice of sub automorphic plagioclase

nd rare (secondary?) quartz and Ti–Fe oxydes. The presence ofigeonite was used by Kuno (1968) to define the ‘pigeonitic series’,owadays known as tholeiitic series.

.2.2. GeochemistryLoss on ignition (L.O.I) of basalts (Table 3) is comprised between

and 18.5% and reveals a strong alteration (spilitisation and weath-ring). Major element analyses were recalculated without water.nfortunately, the part of the sample # 6 that was analyzed was not

he same where the thin section was realized. In the sampling, theres no analysis corresponding to an original magmatic composition.

large part of the major elements was enriched or depleted. Amongrace elements, the sum Cr + Ni ∼ 250 ppm and the ratio Zr/Hf = 31re characteristic of a basaltic composition. Plot of analyses onto

Winchester and Floyd (1977) diagram falls frankly in the field of

ubalkaline basalt (Fig. 11).

Analyses were plotted in a multi-elements diagram normalizedo primitive mantle (Sun and McDonough, 1989) and display two

ain groups on each side of Ta (Fig. 12). The first group from Rb to

K shows normalized values comprised (for a large part) between20 and 100, but with strong variations whereas the second groupfrom Ta to Yb shows smoother variations and normalized valuesthat remain equal or under 10. Curves of analyses #2, #8 and #9that show numerous and sharp variations will not be consideredhereafter.

In the first group, Rb to K elements pattern fits with continen-tal (Rudnick and Gao, 2003) crust or volcanic arcs (Maury et al.,1998), but strong and antithetic (e.g. K), variations could be relatedto spilitisation and/or weathering. In the second group variationsare not so sharp and REE patterns (Fig. 13) are smoothed and theirshape reveals that REE were not mobile. The possible origin of these

basalts will be discussed further.

M. Benzaggagh et al. / Journal of Geodynamics 77 (2014) 4–21 13

Fig. 9. Metasediments overlying the gabbros of the Kef el Rhar region (Fig. 3B for location). (A) Intensely deformed marbles on top of the Dar Bou Aza massif. Notice theboudinaged chert nodules, the fragments of which are rotated. Coordinates N 34◦ 30′ 12′′ , W 04◦ 18′ 51′′ . (B) Low-grade metasedimentary succession on top of the main Kefel Rhar gabbro massif (detail location in Fig. 8). The radiolarites (total thickness ca. 25 m) are alternatively pale green or red. The underlying gabbro is not visible in the photo.(C) Close view of thin-bedded, pink radiolarites. (D) Close view of another radiolarite outcrop rich in slump folds (marked with white dashes) with superimposed tectonicstructures. The latter comprise (i) S/C structures associated with a penetrative cleavage (S0-1, parallel to the stratification plane S0) in the clayey matrix around the siliceoush color

5

5

tgbosi

gccReaic

5b

inges, and (ii) conjugate extensional faults. (For interpretation of the references to

.3. Bou Adel gabbro massif

.3.1. PetrographyIn thin section (Fig. 10D), the troctolite displays an ortho-

o heteradcumulate texture. Grains of olivine are oftenrouped as clusters of about ten crystals and are surroundedy automorphic, weakly zoned plagioclase (labrador). Bothlivine and plagioclase are embedded in large poikilitic diop-ide clinopyroxene. Opaque mineral are mainly composed oflmenite.

Chemical analyses (EPMA) of olivine, clinopyroxene and pla-ioclase are given in Table 4. In the troctolite BA1, plagioclase isomposed of a large core (An 64) and smaller rim (An 60). Olivineomposition varies from: Fo 70 ± 0.3 to Fo 63 ± 0.8 and, in sample1, from Fo 72 ± 0.6 to Fo 68 ± 0.1. The composition of clinopyrox-ne is rather constant (Wo 45.6, En 42.9 Fs 11.4) in the diopside field,nd Cr2O3 content can reach 1%. Ti-rich biotite (0.64 < XMg < 0.70)s scarce, its composition plots toward the phlogopite

orner.

Ferrogabbro displays orthocumulate texture. Olivine (BA5: Fo3.2 ± 0.2; BA2: Fo 53.2 ± 0.24) is the earliest mineral surroundedy automorphic plagioclase composed of a large unzoned core and

in this figure legend, the reader is referred to the web version of the article.)

a thinner rim (e.g. BA5, core: An 59–56 – rim An51 or BA2: coreAn 50 – rim An47). The clinopyroxene is not poikilitic and is inautomorphic crystals (Wo 44, En 40, Fs 16). It is in some placepartly transformed in amphibole of edenite composition (Leakeet al., 1997). Ilmenite (dominant on magnetite) is dispersed in thematrix. Ti-rich biotite (0.56 < XMg < 0.60) surrounds most frequentlyilmenite.

In spite of lack of textural evidence because of post soliduslow-temperature alteration, the three following samples will befurther tested as candidates to look for a possible initial liquidof the mafic complex: (i) BA4 from a dyke on the western bankof the Oued Azrou, (ii) BA8 from a dyke in the center of themassif, and (iii) BA10 sampled at the top of the gabbro at thebasis of the volcanic cover, which could be a congelation cumu-late.

To summarize, when magmatic texture is preserved, onecan observe the crystallization of every type of gabbro ischaracterized by an early appearance of a medium An con-

tent plagioclase at liquidus, more or less in the same timeas Fo rich olivine, which is a typical tholeiitic sequence ofcrystallization according to Kuno’s (1968) original defini-tion. Experimental data in the system forsterite-fayalite show

14 M. Benzaggagh et al. / Journal of Geodynamics 77 (2014) 4–21

Fig. 10. Thin sections (A) Basalt from the Kerkor lava flow with large crystal of demixed pigeonite; sample BA6, Table 2. (B) Close view of the exsolution lamellae. (C)Trondjhemite from a Bou Adel dyke; sample BA9. (D) Troctolite with cumulative plagioclase, olivine grains and poikilic clinopyroxene.

Fwg(

ig. 11. Plot of the compositions of Upper Jurassic volcanic rocks from the Izzareneindow and Bou Haddoud nappe (circles) onto Winchester and Floyd (1977) dia-

ram. Possible initial liquid of the Bou Adel complex (sample BA 10) is also plotsquare).

Fig. 12. Multi-elements diagram of Upper Jurassic basalts from the Izzarene windowand Bou Haddoud nappe (see Table 1 for location). E-MORB composition (dottedblack line) values and normalization to primitive mantle using values from Sun andMcDonough (1989), continental crust composition (dotted red line) after Rudnickand Gao (2003). (For interpretation of the references to color in this figure legend,the reader is referred to the web version of the article.)

M. Benzaggagh et al. / Journal of Geodynamics 77 (2014) 4–21 15

Table 4Chemical analyses (EPMA) of olivine (4A), clinopyroxene (4B) and plagioclase (4C) from Bou Adel gabbro samples (S.D.: standard deviation).

Sample BA1 R1 BA5 BA2

Med. 3 anal. S.D. Med. 8 anal. S.D. Med. 7 anal. S.D. Med. 3 anal. S.D. Med. 4 anal. S.D. Med. 3 anal. S.D.

a: OlivinesSiO2 38.28 0.11 37.22 0.17 38.59 0.20 37.65 0.24 35.61 0.49 35.31 0.25FeO 27.00 0.29 32.00 0.64 25.41 0.60 28.16 0.04 40.01 1.16 39.25 0.09MnO 0.41 0.03 0.49 0.06 0.38 0.08 0.41 0.02 0.67 0.02 0.60 0.05MgO 35.94 0.16 31.47 0.49 37.08 0.44 34.76 0.09 24.78 1.23 25.40 0.31Total 101.62 0.17 101.18 101.46 100.98 101.062 100.56

Si 1.000 1.002 1.002 0.997 1.000 0.924Fe2+ 0.590 0.721 0.552 0.624 0.940 0.924Mn 0.090 0.010 0.008 0.009 0.016 0.014Mg 1.400 1.263 1.436 1.373 1.037 1.066

Fo 70.04 0.27 63.33 0.76 71.93 0.68 68.44 0.07 52.04 0.13 53.19 0.24

Sample BA1 BA2 BA5

Med. 3 anal. S.D. Med. 4 anal. S.D. Med. 3 anal. S.D.

b: ClinopyroxenesSiO2 50.92 0.24 53.01 0.52 51.48 0.35Al2O3 3.74 0.18 1.16 0.82 2.50 0.20FeO 6.77 0.05 9.45 0.74 8.75 0.64MgO 14.69 0.05 14.12 0.35 14.03 0.02CaO 21.71 0.12 22.36 0.51 22.36 0.25Na2O 0.50 0.04 0.45 0.06 0.48 0.05MnO 0.16 0.09 0.20 0.09 0.11 0.12TiO2 1.59 0.05 0.65 0.46 1.26 0.22Cr2O3 0.88 0.01 0.04 0.06 – –Total 100.94 101.44 100.99

Si 1.871 1.956 1.906AlIV 0.129 0.044 0.094AlVI 0.033 0.006 0.015Fe2+ 0.208 0.292 0271Mg 0.804 0.777 0.775Ca 0.854 0.884 0.887Na 0.036 0.032 0.035Mn 0.005 0.006 0.003Ti 0.044 0.018 0.035Cr 0.025 0.001 –

Wo 45.63 45.15 4579En 42.97 39.69 39.98Fs 11.37 15.20 14.17

Sample BA1 R1 BA5 BA2

C: PlagioclasesSiO2 52.23 52.60 51.62 52.42 52.92 54.35 55.13 56.26 56.00Al2O3 30.38 29.35 30.62 30.36 29.36 28.97 28.46 27.50 27.91CaO 13.34 12.80 13.93 12.82 12.72 12.02 11.05 10.00 10.71K2O 0.13 0.20 0.12 0.25 0.25 0.18 0.26 0.33 0.31Na2O 4.07 4.52 3.86 4.45 4.82 4.93 5.58 5.80 5.70FeO 0.17 0.23 0.17 0.21 0.27 0.21 0.09 0.12 0.16Total 100.31 99.71 100.32 100.52 100.33 100.66 100.58 100.00 100.78

Si 2.365 2.395 2.341 2.369 2.398 2.444 2.473 2.528 2.505Al 1.621 1.575 1.637 1.617 1.568 1.535 1.504 1.457 1.471Ca 0.647 0.624 0.677 0.621 0.618 0.579 0.531 0.481 0.513K 0.007 0.012 0.007 0.014 0.014 0.010 0.015 0.019 0.017Na 0.357 0.399 0.339 0.390 0.423 0.430 0.485 0.505 0.494Fe2+ 0.006 0.009 0.007 0.008 0.010 0.008 0.003 0.005 0.006

Ab 35.29 38.56 33.18 38.06 40.12 42.18 47.06 50.24 48.21An 63.99 60.30 66.16 60.55 58.52 56.83 51.48 47.88 50.09

ttttSt(

Or 0.71 1.13 0.66 1.38

hat mineral composition is not affected by pH2O varia-ion, whereas in the system albite-anorthite water controlshe An content of the plagioclase. A plot of the Fo con-

ent of olivine against the An value of the plagioclase (aftermith et al., 1983) improves the discrimination betweenhe calc-alkaline (“wet”) and the tholeiitic (“dry”) seriesFig. 14).

1.36 0.99 1.46 1.88 1.70

5.3.2. GeochemistryPlot of the analyses of the Bou Adel samples (Table 5) onto the

Miyashiro (1974) diagram frankly discriminates Bou Adel mafics

in the tholeiitic field (Fig. 15) in accordance with petrographic andchemical mineral data.

Rare Earth element (REE) patterns (Fig. 16) were normalized vs.mantle (normalizing values after Sun and McDonough, 1989). The

16 M. Benzaggagh et al. / Journal of Geodynamics 77 (2014) 4–21

Table 5Analyses of plutonic samples from the Bou Adel gabbro massif (Table 2 and Fig. 6 for location and type).

BA 1 BA 2 BA 3 BA 4 BA 5 BA 6 BA 7 BA 8 BA 9 BA 10

SiO2 48.31 45.1 47.53 50.06 49.35 47.53 50.49 47.93 72.71 52.58Al2O3 17.96 15.22 17.03 16.84 17.15 16.66 15.92 16.28 12.68 12.9Fe2O3t 8.87 11.58 10.82 8.98 9.11 10.55 11 9.78 3.19 9.02MgO 8.78 6.11 4.97 3.01 6.27 10.71 4.9 4.91 0.03 9.6CaO 8.91 9.95 7.56 6.75 9.82 7.96 6.8 9.32 0.74 5.49MnO 0.12 0.16 0.18 0.17 0.13 0.14 0.18 0.14 0.01 0.1K2O 0.81 0.96 1.47 1.24 1.08 0.74 1.61 1.38 0.49 1.74Na2O 3.15 3.41 3.5 5.46 3.64 2.94 4.11 3.64 7.58 3.8TiO2 1.16 4.91 3.1 4.15 2.23 0.95 1.96 4.07 0.27 1.37P2O5 0.08 1.72 0.24 1.07 0.13 0.16 0.28 0.24 0.02 0.15L.O.I. 1.5 0.6 3.3 2 0.8 1.3 2.5 2 0.8 3Total 99.65 99.72 99.7 99.73 99.71 99.64 99.75 99.69 98.52 99.75

U 0.3 0.5 0.4 1.2 0.3 0.3 0.3 0.5 46.8 0.3Th 0.9 1.5 1.5 2.6 1.1 0.9 1.1 1.5 148.2 2Ta 0.6 1.3 1.1 2.1 1 0.5 0.6 1.2 51.6 0.4Nb 10.3 18.8 16.7 40.1 15.7 8.4 12.4 17.9 718.1 6.4Hf 1.6 2.2 3.4 5.1 2.9 1.4 3.3 3.2 204.4 3.1Zr 74.2 90.9 124 217.1 96.6 64 117.8 121.2 7602.4 99.9

Cr 181.3 174.5 3.4 99.2 126.6 47.9 17.1 78.7 95.8 3.4Co 42.7 41.3 32.9 21.8 33.5 49.3 26 30.2 0.6 37.7Ni 135 <20 39 39 52 174 49 35 <20 89Rb 7.7 8.4 18.7 13.9 10 7.4 17.7 15.9 4.2 20.7Sr 552.6 495.1 693.9 498.8 515.3 472.3 446.6 493 89.3 110.8Ba 89 109 173 135 110 78 171 160 8 153Y 9.5 23.9 15.7 46.4 14.4 9.5 22.9 15.7 517.7 17.7

La 6.7 15.7 11.3 34.5 8.4 6.6 10.4 10 528.6 6.7Ce 11.9 34.4 21.8 70.3 16.6 13.4 21.5 20.5 893.5 15.2Pr 1.51 4.71 2.89 8.66 2.18 1.65 2.86 2.57 90.01 2.08Nd 7.2 23.8 14.1 37.8 11.2 6.8 11.7 11.6 303.5 8.4Sm 1.5 6.15 3.44 9.8 2.57 1.75 3.7 3.23 62.08 2.33Eu 1.07 1.9 1.42 2.35 1.29 0.92 1.45 1.18 0.53 0.34Gd 2.07 6.59 3.64 10.58 3.02 1.97 4.67 3.18 67.59 2.57Tb 0.33 0.93 0.6 1.62 0.48 0.33 0.76 0.55 13.15 0.49Dy 1.92 5.06 3.6 8.49 2.94 1.87 4.14 2.9 87.19 3.08Ho 0.35 0.93 0.64 1.72 0.55 0.36 0.87 0.63 19.43 0.72Er 1.1 2.31 1.69 4.31 1.66 0.97 2.33 1.8 59.63 2.19

0.221.4

0.22

dtaae

FHv

Tm 0.15 0.29 0.2 0.61

Yb 0.99 1.67 1.7 3.84

Lu 0.16 0.26 0.24 0.51

ifferent rocks from the Bou Adel mafic complex are organized inhree groups according to their chemical composition, their nature

nd their position in the complex: the troctolite, the ferrogabbrond the basalt and microgabbro. Their general shape show a mod-rate HREE/LREE fractionation.

ig. 13. REE patterns of Upper Jurassic basalts from the Izzarene window and Bouaddoud nappe (see Table 1 for location). Normalization to primitive mantle usingalues from Sun and McDonough (1989).

0.11 0.33 0.26 8.71 0.331.11 2.29 1.37 51.4 2.38

0.14 0.29 0.23 6.44 0.36

The REE content of cumulates is a fonction of the degree of evo-lution of the liquid in equilibrium and of the nature of the cumulusminerals:

- Troctolite cumulates (BA1, 6) are characterized by their low con-tent in REE and a positive Eu anomaly revealing processes ofplagioclase fractionation as testified by textural evidence in thinsection.

Fig. 14. Representative composition of coexisting plagioclase and olivine of gab-bros from the Bou Adel complex; plots fall in the tholeiitic field. Trends from Smithet al. (1983): Tholeiitic field with B = Bushveld, K = Kigaplait, SD = Skaergaard. Calc-alkaline field with L.A. = Lesser Antilles, P.R. = Peninsular Ranges.

M. Benzaggagh et al. / Journal of Geodynamics 77 (2014) 4–21 17

FM

-

-

pnwd

-

Fi

ig. 15. FeO*/MgO vs. SiO2 discrimination diagram with dividing line fromiyashiro (1974).

Ferrogabbro cumulates (BA3, 5, 7) display rather similar patternswith a moderate La/Lu fractionation and a systematic Eu positiveanomaly (plagioclase fractionation) whereas BA2 with a higherREE content and weak Eu negative anomaly could be a cumulatein equilibrium with evolved liquid.

Trondjhemite BA9 display a characterisitic pattern with a strongEu negative anomaly in agreement with the large cumulationof plagioclase observed in the cumulates. Plagiogranite is con-sidered as a late-stage immiscible liquid ending differentiationprocesses (Dixon and Rutherford, 1979).

As samples BA1, 6, 3, 5, 7, 2 were recognized as cumulates or.p. cumulates, i.e. fractionates of a parental magma, they shouldot be directly used to infer the composition of the magma fromhich they formed (and consequently not plotted in geotectoniciagrams).

Composition of samples having a possible liquid composition wasplotted in a multi elements diagram. As for basalt samples, gabbropatterns display two main groups from each side of Ta (Fig. 17): a

ig. 16. REE patterns of mafics from the Bou Adel complex. Normalization to prim-tive maantle using values from Sun and McDonough (1989).

Fig. 17. Multi-elements diagram of possible basaltic liquid compositions from theBou Adel complex. Normalization to primitive mantle using values from Sun andMcDonough (1989).

first group, from Rb to K elements characteristics of a continentalcrust imprint and a second group, from Ta to Yb, more frac-tionated. The interpretation of these patterns will be discussedfurther.

6. Discussion

6.1. Two types of mafic rocks in the Mesorif Zone

As stated in the previous sections, two types of mafic rocks occurin the External Rif, each one associated with a specific geologicalsetting inside the Mesorif Zone:

- Type 1: basalts and dolerites, more rarely fine-grained gabbro-diorite. They occur dominantly as spilitized lava flows and clastsblocks or boulders within the Kimmeridgian–Berriasian carbon-ate formations of typical Mesorif units (Fig. 2; Izzarene window,Bou Haddoud nappe).

- Type 2: cumulative gabbros and plagiogranite/trondjhémitedykes topped with basalts, volcanic breccias, ophicalcites, mar-bles, ophiolitic sandstones, and locally radiolarites. They formsmall, exotic slivers or klippes within a peculiar Mesorif unitknown as the Senhadja “nappe” (Fig. 2).

In the following sub-sections, we first discuss the geochemistryof these mafic rocks and their structural setting in terms of geo-dynamic significance. Then we consider their mutual relationshipsand their potential connection with the Beni Malek serpentinites ofeastern Rif (Fig. 2), i.e. the so-called Mesorif Suture Zone (Michardet al., 2007) and/or with the Ligurian-Maghrebide (Tethyan) sutureitself (Fig. 18).

6.2. Type-1 mafic rocks: continental margin basalts

The Type-1 mafic rocks are spilitized basalts emplaced in typi-cal Mesorif units defined as distal parts of the African paleomargin(relative to the more proximal Prerif Zone) in the classical recons-tructions of the External Rif (Suter, 1965, 1980b; Favre et al., 1991;Ben Yaïch, 1991; Frizon de Lamotte et al., 2004; Chalouan et al.,2008). Volcanism appears to have been active there during the LateJurassic–Berriasian (Benzaggagh and Habibi, 2006; Benzaggagh,

2011), contrary to earlier proposals (Barremian according to Vidal,1983b; Middle Jurassic according to Ben Yaïch et al., 1991). The cli-max of the volcanic event roughly coincides with a transient periodof production and resedimentation of shallow water carbonates on

18 M. Benzaggagh et al. / Journal of Geodynamics 77 (2014) 4–21

F nic reT

tatb2coapassC

tRcii(cBsEsztmr

g

ig. 18. Two alternative working hypotheses accounting for the occurrence of ocearanscurrent tectonics (this work).

op of the Ferrysch turbidite prism in the Internal Prerif–Mesorifrea (Fig. 5). This suggests some causal relationships betweenhe volcanic event and the development of unstable and proba-ly restricted platforms (thermal/magmatic doming; Benzaggagh,011). Ben Yaïch et al. (1989) compared the western Mesorif vol-anism to that of Surtsey Island, which is correct as far as the depthf water is concerned (130 m in the case of the Surtsey eruption,ccording to Baldursson and Ingadóttir, 2007; not far from thehotic zone in the case of the Mesorif, according to the presence oflgae in the coeval limestones). However, the Mesorif geodynamicetting is certainly not that of Surtsey, but corresponds to a post-rifttage of the development of a constructional margin (Favre, 1995;halouan et al., 2008; Frizon de Lamotte et al., 2004).

The presence of pigeonite in sample #6 strongly constrains itsholeiitic affinity and rules out a possible calc-alkaline origin, andEE patterns (Fig. 13) support that samples #4, #5, and #6 can beonsidered together. Multi elements diagram (Fig. 12) cannot benterpreted as Back-Arc Basalts (BAB) because of the lack of Nb pos-tive anomaly (Gorring and Kay, 2001) nor as Oceanic Island BasaltsOIB) because of the low values of Ta, Nb (10 vs. 70) and their lowerontent level in trace element (Ta to Yb lower than 10, cf. Fig. 12).ecause they display a continental imprint (Rb to K) and a basalticignature (Ta to Yb), samples #4, #5, and #6 can be interpreted as-MORB basalts having suffered a crustal contamination and a pos-ible generation/emplacement in the ocean-continent transitionone (OCT; Jagoutz et al., 2007). Samples #2, #8, and #9 were notaken into account here because their analyses plotted in multi ele-

ents diagrams display too much erratic variations that probablyeflect the effects of alteration.

To conclude, the Mesorif submarine basalts display E-MORBeochemical characteristics, suggesting an important extension

mnants in the Mesorif Zone. (A) Intramargin hiatus, after Michard et al. (2007). (B)

event and correlative thinning of the African paleomargin litho-sphere at that time. Likewise, E-MORB volcanic clasts have alsobeen described by Zaghloul et al. (2003) in Jurassic–Cretaceous bedsat the south border of the Ketama unit north of Taounate (Fig. 2).Comparing the geochemistry of the Mesorif basalts with that of thecalc-alkaline basalts of the Subbetic Zone, which emplaced duringthe Jurassic in a broadly similar setting in the Iberian paleomargin(Portugal Ferreira et al., 1995, and references therein), we observethe source of the central Mesorif basalts is somehow deeper, and thecrustal assimilation lower in the Mesorif basalts than in the Sub-betic, suggesting for the first a more frankly extensional tectonicorigin.

6.3. Type-2 mafic rocks: exotic klippes of oceanic floor

The Type-2 mafic rocks are basically gabbros, associated withsome leucocratic veins and dykes (plagiogranite, trondjhémite) andbasalts. The structural setting of these gabbros and associated mag-matic rocks is totally different of that of the Type-1 basalts, as theyform exotic slivers or klippes included in a more internal, dismem-bered sedimentary complex.

Besides of some basalts, the stratigraphic cover topping thesegabbro klippes includes ophicalcites, fault scarp mafic breccias,marbles with basalts clasts and volcanoclastic sands, and radio-larites. This is typical of magmatic-floored oceanic domains andcompares with the successions observed on top of the ophiolitemassifs of the Western Alps, Alpine Corsica and the Apennine (e.g.

Lagabrielle and Lemoine, 1997; Padoa, 1999; Molli, 2008).

Among samples having a possible composition of initial liquid,sample BA4, from a dyke, has the richest trace element contentand probably corresponds to an evolved liquid, whereas sample

l of G

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A8 shows a Ti anomaly related with cumulation of Fe-Ti opaqueinerals. Sample BA10 is also enriched in LILE and U, Th indicating

he presence of continental crust contamination but elements froma to Yb displays a rather good fit with a composition of E-MORBFig. 17) if one considers that Zr, Hf smooth peak can be related withircon crystallization and Eu anomaly to plagioclase fractionation.ne can note that this composition plots in Winchester and Floyd

1977) diagram in the subalkaline basalt field near the joint withndesite/basalt (Fig. 11).

Therefore, in view of both the stratigraphic and geochemicalbservations above, we assume that the Bou Adel and Kef el Rharnits correspond to ocean-floor (ophiolite sensu lato) klippes. Theirge is not constrained at the moment by any paleontological datarom the limestones or radiolarites, but we may hypothesize aate Jurassic age by comparison with the fossil-bearing succes-ions of the Alpine-Ligurian ophiolites quoted above. Moreover,–Ar dating of the Bou Adel gabbro yielded an age at 166 ± 3 Ma

Cantagrel, Clermont-Ferrand Laboratory, in Asebriy, 1994, p. 51).–Pb zircon dating of the ophiolitic gabbros and plagiogranites

rom the Western Alps, Liguria and Corsica (Rossi et al., 2002, 2011;i et al., 2013) suggests that the Ligurian-Piemont Ocean experi-nced a short spreading period from 169 ± 3 Ma to 152.5 ± 2.2 Ma.ccording to ICS’ stratigraphic scale (2013) this span of time isomprised between the early Bajocian and late Tithonian. Noticehat, if correct, these ophiolite s.l. remnants would be about 20 Maounger than those of the Sierra Nevada Lugros units, which belongo another Tethyan branch (Puga et al., 2011). In contrast, the Boudel gabbros are coeval with the alkaline-transitional gabbros of

he central High Atlas (Frizon de Lamotte et al., 2008, and refer-nces therein), but they differ by their tholeiitic, E-MORB affinities,onsistent with their distinct geodynamic setting.

These exotic ophiolites s. l. are included in the “Senhadjaappe” (Lacoste and Marcais, 1938; Leblanc, 1979, 1983), whichverlies the Lower-Middle Miocene sandy marls and conglomer-tes of the Mesorif windows (Fig. 2; Suter, 1965, 1980a,b). Theo-called “nappe” consists of dismembered, Mesorif-type Liassic-lbian sequences, Triassic evaporites and altered basalts, Paleozoiclivers (the largest one being the Khebaba outlier; Darraz andeblanc, 1989), and small plutonic bodies such as the Bou Adelnd Kef el Rhar massifs (Figs. 3B, 6 and 8). It was interpreted as

syntectonic Tortonian mélange by Vidal (1977, 1983a,b).

.4. Tectonic interpretation

It is clearly tempting to consider the two types of units, bothharacterized by E-MORB mafic rocks and respectively marginalnd oceanic as initially associated at the southern boundaryetween the Ligurian–Maghrebian Tethys and North Africa. On thether hand, the basalt-bearing marginal units of the Mesorif Zoneppear clearly, when looking at the External Rif structural mapsFigs. 2 and 3), in the straight continuation of the Mesorif Sutureone defined in the eastern Rif and up to the Oran Mountains byichard et al. (1992, 2007). The latter suture is marked by the

eni Malek serpentinite massif exhumed during the Late Jurassic,nd now pinched between the Temsamane Mesorif massif and theetama Intrarif unit. This location inside the External Rif domain

ed to define the corresponding suture as an intramargin sutureormed through inversion of a Jurassic–Cretaceous intramargin hia-us (Fig. 15A). Thus, the Bou Adel and Kef el Rhar ophiolitic sliversould be considered as equivalent of the Beni Malek massif, and theD tectonic scenario proposed for the eastern Mesorif suture coulde at first sight extrapolated to the central and western Mesorif

etting.

However, this scenario is open to criticism as it does notake into account the large sinistral displacements that occurredetween the south border of the Alboran Internal Zones and the

eodynamics 77 (2014) 4–21 19

north border of the African margin from the Oligocene onward(Frizon de Lamotte, 1987a, 1987b; Spakman and Wortel, 2004).As another working hypothesis (Fig. 15B), we may suggest thatthe Intrarif block originates from a western Tell location along theAfrican margin before being transported north of the Mesorif, withsome pieces of oceanic floor pinched in between, along a sinistralOran-Mesorif Strike-Slip Fault (OMSF) operating during the lat-est Oligocene–Miocene. This could account simultaneously for thelocation of the Beni Malek serpentinites and Senhadja Nappe gab-bros in the External Rif. This 3D scenario is strongly supported bythe proximal character of the Ketama stratigraphic series, rich inUpper Jurassic and Lower Cretaceous terrigenous sediments, andthen quite different of the pelagic sediments expected on top ofan intraoceanic continental block. In contrast, the Ketama–Tangier(Intrarif) Mesozoic series compare with those of western Tell(Wildi, 1983). If correct, the newly described Mesorif oceanicklippes as well as the Beni Malek massif itself would representallochthonous remnants of the Ligurian–Maghrebian (Tethyan)oceanic domain.

We feel that discriminating between the two possible scenarios,intramargin suture vs. major oblique strike-slip, needs additionalstudies in the central and eastern Mesorif regions, particularly inthe very heterogeneous Senhadja “Nappe” as well as in its putativeroot zone, i.e. the “Nekor Fault Zone” or “Nekor Triassic Breccia”(Leblanc, 1980; Frizon de Lamotte, 1981, 1985). The Nekor Zoneis currently regarded as the sinistral lateral ramp of the Intrarifthrust fault, but the heterogeneous rock bodies it contains are notyet sufficiently described.

7. Conclusion

To conclude, let us highlight first the following points:

• Flows and clasts of tholeiitic basalts with E-MORB affinities areintercalated in the Kimmeridgian–Berriasian carbonate depositsof the western to central Mesorif units; this arcuate mafic beltextends in relatively distal units from the African paleomargin.

• Ocean-floor remnants (ophiolites sensu lato), provisionally datedMiddle-Late Jurassic and described here for the first time, occur asexotic klippes in central Mesorif, i.e. in the core of the External Rif.These klippes display gabbroic basement with E-MORB affinitiesand pelagic cover sequences with fault scarp breccias, ophioliticsands, marbles and radiolarites; they are included in the Middle-Upper Miocene Senhadja “Nappe” or mélange, which is the mostinternal Mesorif unit of central-eastern Rif.

• In view of the probable origin of the Senhadja unit from the NekorFault Zone, the ocean-floor klippes can be correlated with theBeni Malek serpentinites and metabasites of the north-easternNekor Zone, which also represent remnants of a Jurassic-EarlyCretaceous oceanic-type basin floor, likely close to the OCT.

• Before their inclusion in the Senhadja “Nappe” or mélange, theophiolite (s.l.) klippes were affected by low-grade greenschist-facies metamorphism, whereas the Beni Malek unit recrystallizedin the chloritoid-bearing greenschist-facies at ca. 23 Ma. Similarmetamorphism is observed in the serpentinite-bearing units ofthe Oran Mountains (western Tell).

• Two tectonic scenarii can be proposed to account for the occur-rence of ocean-type basement units between the Mesorif andIntrarif zones, (i) a 2D scenario with a Jurassic–Cretaceous intra-margin hiatus inverted into a Mesorif suture during the Miocene,or (ii) a 3D scenario involving a major, sinistral transcurrent fault

oblique to the paleomargin, which would have carried westwardover ca. 250 km a piece of the Tellian margin, the future Intrarifblock, during the latest Oligocene–Miocene. This putative fault ishere named the Oran-Mesorif Strike-Slip Fault.

2 l of G

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Att(ao

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Thus, the new ophiolite (s.l.) klippes of the Mesorif would beomplementary to the E-MORB pillow basalts associated to theaghrebian Flyschs south of the Bokkoya Massif (Durand-Delga

t al., 2000), but likely with a distinct origin, i.e. from the southernargin (OCT) of the former ocean instead of its axis.The structure of the Rif Belt was warmly discussed in the 60–70s.

t that time, the controversy concerned particularly the origin ofhe nappes (Maghrebian Flyschs, Senhadja Nappe) and the impor-ance and age of their displacements, as summarized in Michard1976) and Durand-Delga (2006). Probably a new round of studiesnd discussions could begin today, concerning the scale and rythmf the lateral displacements in the External Rif zones.

cknowledgments

Our field campaigns have been founded by the University ofeknès, Dept of Geology (P.R.) and the Direction of Mining Devel-

pment, Ministry of Energy and Mines (A.M.). EPMA chemicalineral and ICP-MS major and trace elements analyses were real-

zed at BRGM, Orléans. We are deeply indebted to Pr. Agustinartin-Algarra for his thorough, extended and constructive review,

nd to an anonymous Reviewer for his or her detailed petrologicalomments and useful suggestions.

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