Apatite fission-track analyses on basement granites from south-western Meseta, Morocco: Paleogeographic implications and interpretation of AFT age discrepancies

Tectonophysics 475 (2009) 29–37

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Apatite fission-track analyses on basement granites from south-western Meseta, Morocco: Paleogeographic implications and interpretation of AFT age discrepancies O. Saddiqi a,⁎, F.-Z. El Haimer a, A. Michard b, J. Barbarand c, G.M.H. Ruiz d, E.M. Mansour a, P. Leturmy e, D. Frizon de Lamotte e a

Laboratoire Géosciences, Faculté des Sciences, Université Hassan II Aïn Chock, BP. 5366 Maârif, Casablanca, Maroc, Morocco 10 rue des Jeûneurs, 75002 Paris, France Univ Paris Sud, UMR CNRS 8148 IDES, Bâtiment 504, Orsay cedex, F-91405, France d Institut de Géologie, Université de Neuchâtel, 11 rue Emile-Argand, 2009 Neuchâtel, Suisse, France e Département des Sciences de la Terre et de l'Environnement (CNRS, UMR 7072), Université de Cergy-Pontoise, 5 mail Gay Lussac, Neuville/Oise 95 031 Cergy-Pontoise cedex, France b c

a r t i c l e

i n f o

Article history: Received 11 April 2008 Received in revised form 15 December 2008 Accepted 2 January 2009 Available online 14 January 2009 Keywords: Apatite fission-tracks Thermochronology Vertical movements Morocco Meseta Atlas

a b s t r a c t This work is based on apatite fission-track analysis of samples (mostly granites) from the basement of the Cretaceous–Tertiary Phosphate and Ganntour Plateaus, exposed in the Jebilet and Rehamna massifs (Western Meseta, Morocco). This basement belongs to the Carboniferous–Early Permian Variscan Belt, and the earlier marine onlap is Late Triassic in age. However, the AFT ages are post-Triassic and different in the Jebilet (186– 203 Ma) and Rehamna (148–153 Ma). Track length modelling support the occurrence of moderate heating events during the Jurassic and the Eocene, respectively, with cooling during the Permian and Cretaceous intervals. These results are partly accounted for by considering a moderate subsidence during the Late Triassic– Liassic, which is a noticeable change in the regional paleogeographic concept of “West Moroccan Arch”. However, the discrepancies between the AFT results from the studied massifs make necessary to explore further explanation. We interpret the observed discrepancies by the difference in age and depth of crystallization of the sampled granites in the Variscan Orogen, i.e. 330 Ma, 5–6 km in the Jebilet versus ~ 300 Ma, 8–10 km in the Rehamna. The importance of the Late Jurassic–Early Cretaceous uplift and erosion of the entire Meseta and that of its Late Eocene burial are emphasized. © 2009 Elsevier B.V. All rights reserved.

1. Introduction Thermochronology on apatite have been used recently in Morocco to discuss the vertical movements of the basement of the High Atlas (Barbero et al., 2007) and Anti-Atlas mountain belts (Malusà et al., 2007). In this work, we present an apatite fission track (AFT) study in a domain that is defined, according to the classical geological criteria (Choubert and Faure-Muret, 1962) as a tabular domain, namely the Moroccan (or Western) Meseta. In fact, this domain forms a relatively stable area bounded by Cenozoic mountain belts to the south, east and north (the High Atlas, Middle Atlas, and Rif belt, respectively), and by the Atlantic Ocean to the west (Fig. 1a). The Western Meseta region includes Paleozoic massifs characterized by Variscan deformation and metamorphism, varied granite intrusions, and late orogenic (Early Permian) continental basins. The Paleozoic basement is directly overlain either by Triassic–Liassic series (Tabular Middle Atlas) or by Cretaceous–Tertiary plateaus (“Plateau des Phosphates” and Ganntour), and surrounded by Neogene basins (Bahira-Tadla, Haouz, ⁎ Corresponding author. E-mail address: [email protected] (O. Saddiqi). 0040-1951/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.tecto.2009.01.007

Doukkala, External Rif foredeep). The Cretaceous–Tertiary plateaus have been intensely studied for phosphate exploitation (three quarters of the phosphate reserves of the world), oil and deep water resources. Ultimately, Ghorbal et al. (2008) have presented AFT data from the northern (Zaer) and central (Rehamna) parts of Western Meseta, respectively. Our independent study is mainly based on sampling in the southernmost Meseta massif, i.e. the Jebilet Massif, and on additional sampling in the Rehamna Massif. The Jebilet Massif culminates at 1050 m above sea level (a.s.l.), being bounded to the north by a major Neogene (Atlasic) reverse fault (Hafid, 2006; Hafid et al., 2006; Frizon de Lamotte et al., 2008). The Rehamna Massif, which culminates at ca. 600 m a.s.l., belongs to the most “stable” part of the Meseta, barely affected by the Atlas orogeny. The striking hiatus of Triassic–Liassic deposits over most of Western Meseta is classically interpreted as related to the occurrence, during the Triassic–Liassic, of an emergent land between the Atlantic margin and the Atlas basins. Choubert and Faure-Muret (1960–62) coined the name of “Terre des Almohades” for this allegedly emergent domain, which is currently referred to as the West Moroccan Arch (WMA; Hafid, 2006; El Arabi, 2007). Our AFT data allow us to discuss

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O. Saddiqi et al. / Tectonophysics 475 (2009) 29–37

Fig. 1. Location maps. (a) Structural provinces of northern Morocco. PR: Prerif Ridges; SB: Selloum Basin; TMA: Tabular Middle Atlas. — (b) Schematic map of the studied basement massifs and surrounding areas, after Hollard et al. (1985) and Hoepffner et al. (2006). Dashed lines (DK 25, etc.): Seismic profiles (Hafid, 2006; Hafid et al., 2008); Kh: Khouribga; WMSZ: Western Meseta Shear Zone, Y: Youssoufia.

this classical description, and to suggest that, in fact, the WMA subsided before being eroded during the Late Jurassic–Early Cretaceous. On the other hand, we recognized puzzling discrepancies between the AFT ages from two different groups of granite intrusions,

belonging to the Jebilet and Rehamna massifs, respectively. Discussing these discrepancies represents one of the most significant topics of the present study. Our study points to the importance of considering not only the evolution of the subsidence/uplift history of a tabular area, but also the structure and evolution of its basement, as the depth and

Fig. 2. (a) Topographic model of the Moroccan Meseta (GETOPO data) and surrounding areas, with location of the studied granites. Bold line: approximate trace of cross-section (b). Asterisk: location of the photos Fig. 5. (b) Geological cross-section of the Moroccan Meseta south of the Central Massif, located on (a) and more exactly in Fig. 1b. Notice the strong vertical exaggeration. The shape of the granite intrusions is diagrammatic.

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Fig. 3. Sampling maps and AFT results (mean ages). (a) Central Jebilet; geologic contours after Huvelin (1977). (b) Central Rehamna; geologic contours after Michard (1982). See Fig. 1b for location.

Atlantic (Favre et al., 1991; Medina, 1995; Hafid, 2006) and Atlas (Tethyan) Gulf (Zizi, 2002; El Arabi et al., 2006a,b), respectively. Rifting occurred during the Late Permian–Late Triassic, ending temporarily at 200 Ma with the emplacement of the basalts of the Central Atlantic Magmatic Province (CAMP: Knight et al., 2004; Verati et al., 2007). During the Liassic–early Dogger, rifting resumed in the Middle Atlas (Charrière, 1990) and High Atlas Basins (Studer, 1987; Warme, 1988), resulting in the accumulation of 3 to 8 km-thick deposits, respectively. In contrast, the Western Meseta exhibits large exposure of basement units, from north to south, the Central Massif and Coastal Meseta, the Rehamna and the Jebilet (Fig. 1b). Triassic and Liassic cover sequences are preserved only at the fringe of Western Meseta, either exposed as outcrops to the northeast and north (e.g. Tabular Middle Atlas, Prerif Ridges; Fig. 1a; Hollard et al., 1985) or documented in the subsurface to the southeast (Tadla, Bahira), southwest (Essaouira

age of emplacement of a given basement granite control its distance to surface after a given erosional event. 2. Geological setting The basement of the Western (Moroccan) Meseta belongs to the southern branch of the Variscan Orogen, within which a number of granite stocks emplaced during the Visean to Early Permian interval (Hoepffner et al., 2006; Michard et al., 2008). In particular, the Jebilet granites are dated at 330 Ma (U–Pb zircon; Essaifi et al., 2003; Boummane and Olivier, 2007), and those of the Rehamna at ~300 Ma (Baudin et al., 2003). The belt collapsed and was eroded first during the Late Carboniferous–Early Permian (Hmich et al., 2006; Saber et al., 2007). Then, the rifting associated with the Pangaea break-down occurred on both sides of the future Western Meseta, i.e. in the Central Table 1 Apatite fission-track analyses of Jebilet and Rehamna samples. Sample

Lithology

n

ρs

Ns 5

× 10 t/cm

2

ρi

Ni 6

× 10 t/cm

2

ρd

Nd 5

× 10 t/cm

2

P (χ2)

FT age

%

Ma ± 1σ

N

L

Dpar

µm ± 1SD

µm

Jebilet massif JGO1 Granodiorite JOG3 Granodiorite JGO4 Granodiorite JTB2 Granophyre JTB3 Granophyre JTB4 Granophyre

26 29 26 29 24 26

7.76 6.21 5.55 6.52 1.81 2.05

5496 4029 4881 4229 2482 2702

3.76 2.91 2.72 3.28 8.47 9.42

2224 1891 2394 2126 1163 1243

5.41 5.41 5.41 5.41 5.41 5.41

16,464 16,464 16,464 16,464 16,464 16,464

99.9 99.1 100 99.3 100 99.8

193 ± 5 199 ± 6 190 ± 5 186 ± 5 199 ± 7 203 ± 7

111 – 100 80 – –

11.90 ± 2.12 – 11.07 ± 2.27 11.37 ± 2.45 – –

1.48 ± 0.12 1.43 ± 0.19 1.28 ± 0.12 1.32 ± 0.10 1.31 ± 0.10 1.27 ± 0.13

Rehamna massif RH1 Schist RH4B Schist RH8 Leucogranite RH9A Leucogranite

11 10 15 15

1.90 0.19 3.88 4.00

633 168 649 997

1.80 0.18 3.62 3.55

598 154 605 885

8.52 8.52 8.52 8.52

17,645 17,645 17,645 17,645

99.9 99.8 99.6 100

148 ± 9 153 ± 18 150 ± 9 153 ± 8

– – 100 100

– – 12.43 ± 1.96 11.91 ± 1.94

1.75 ± 0.14 1.83 ± 0.15 1.30 ± 0.09 1.49 ± 0.13

See Fig. 3 for sample location. n, Ns and Ni, respectively number of crystals dated, total number of spontaneous and induced tracks counted; s and i, respectively spontaneous and induced track density in apatite grains and their detectors (JGO-JTB: kapton; RH: muscovite); d, means induced track density in the detectors associated to NIST neutron glass monitors 962 (JGO-JTB) and CN5 (RH). P(2) is the probability of obtaining a 2 value for n-1 degrees of freedom. As all samples passed the test at a 95% confidence level with P(2) N 5%, ages were calculated using pooled statistics (Green, 1981). Zeta value of F.Z. El Haimer, analyst, 350 17 (JGO-JTB) and O. Saddiqi, analyst, 333 8 (RH) (1). Confined tracks: L and l s.d. are respectively the mean value and standard deviation, (N) is the number of tracks measured.

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Fig. 4. Modelling experiments (AFTSolve) for the Central Jebilet granite (a, b) and Central Rehamna granite and schists samples (c, d).

Basin; Hafid, 2006) and west (Doukkala, Abda; Echarfaoui et al., 2002a,b). Elsewhere, the Western Meseta basement is onlapped by younger deposits, Late Jurassic–Early Cretaceous in the Mouissat hills west of the Jebilet (Hollard et al., 1985), and Cretaceous (mainly postAptian) in the Rehamna and southern Central Massif (Gigout, 1954; Bolleli et al., 1959; Baudin et al., 2003). In addition to the map in Fig. 1b, these geological constraints are summarized in the cross-section in Fig. 2. The latter figure also makes clear that the southernmost part of the Meseta has been involved in the Atlas shortening, with the Jebilet Massif thrust over the Bahira Triassic–Neogene deposits through a southward-dipping reverse fault. In contrast, further to the north, the Meseta basement and overlying Cretaceous–Eocene tabular sequence are only affected by much weaker deformation.

schists from the Central Rehamna. All samples were collected at 500– 600 m of elevation. Apatite grains were separated using conventional heavy liquids/ magnetic separation procedures. Samples were dated with the external detector technique using kapton foils (Jebilet samples) or muscovite (Rehamna samples). Tracks were etched in apatite with 1 M HNO3 solution at 20 °C for 45 s, in kapton using a boiling solution of potassium hypochlorite for 8 min, and in muscovite in 40% HF for 45 min. For each sample, a single age population is observed. Dpar has been measured for each sample (five measurements per grain). Horizontal confined track length (TINTS) measurements have been performed on five samples using a digitising tablet (Table 1). 4. Results

3. Sampling and experimental procedure Eight samples out of ten (Fig. 3; Table 1) have been collected from granites, among which three from the east Central Jebilet (Ouled Ouaslam granite laccolith; Boummane and Olivier, 2007), three from the west Central Jebilet (Tabouchent granophyric granite; Huvelin, 1977; Essaifi et al., 2001, 2003), and two from the Central Rehamna (Ras-El-Abiod leucogranite; Hoepffner et al., 1982; Baudin et al., 2003). Additionally, two samples were collected in the Paleozoic

Our AFT analyses on the Jebilet granites show AFT ages grouped between 202.6 ± 7.1 and 185.7 ± 5.1 Ma (Table 1). The Mean Track Length (MTL) varies from 11.90 to 11.07 m with standard deviations in the range 2.4–2.1 m. These results are consistent with those obtained by Mansour (1991) using the population method, with AFT ages ranging from 218 ± 23 Ma to 170 ± 15 Ma (mean age 186 Ma). In the Rehamna samples the AFT ages of the granite and countryrock schists are grouped between 148.4 ± 9.3 and 157.8 ± 8.4 Ma

Fig. 5. The Cretaceous transgression at the northern border of the Rehamna massif, as seen in the Oum-er-Rbia valley (see Fig. 2a for location). (a) Overview of the Lower Cretaceous (LC) — Cenomanian–Turonian (C–T) escarpment (about 100 m high) above the Paleozoic basement (Cb: Middle Cambrian). (b) The major unconformity at the bottom of the Lower Cretaceous red beds is marked by coarse conglomerates with poorly sorted, barely rounded pebbles of Ordovician quartzites likely sourced in the Central Rehamna (3 m high roadcut). S1: Variscan cleavage. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

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recorded in the adjoining Atlas Basins, Eastern Meseta Platform and Prerif domain (Charrière, 1990; Zizi, 2002). (3) A renewed exhumation bringing the Rehamna granites and schists as well as the Jebilet granite up to the surface before the transgression of the Cenomanian–Turonian, and probably as early as the Barremian–Aptian, i.e. at 120–100 Ma (Gigout, 1954; Bolleli et al., 1959; Baudin et al., 2003; Frizon de Lamotte et al., 2008).

Fig. 6. Estimated P–T conditions of crystallization of the Jebilet and Rehamna schists and granites plotted on the petrogenetic grid, based on the mineral associations described by Essaifi et al. (2001) and Hoepffner et al. (1982), respectively. Dashed: high-temperature P–T–t paths of the studied samples. Horizontally ruled: andalusite–sillimanite transition (Pattison, 1992). Vertically ruled: cordierite–garnet transition (Holdaway and Lee (1977). Staurolite–cordierite experimental curve after Richardson (1968). Peraluminous granite melt after Willye (1977). And: andalusite; As: aluminium silicate; Chl: chlorite; Cld: chloritoid; Crd: cordierite; Fe–Ctd: iron-rich chloritoid; Grt: garnet; Kfs: K-felspar; Ky: kyanite; Ms: muscovite; Qtz: quartz; Sil: sillimanite; St: staurolite.

A moderate burial during the Late Cretaceous–Eocene until 35– 40 Ma, which corresponds to the last marine sedimentation in the Atlantic gulf where the phosphate series deposited over the Meseta and Atlas domains (Boujo, 1976; Charrière, 1990; Herbig and Trappe, 1994; Zouhri et al., 2008). The T–t paths show two humps of the acceptable fit domain, whatever the sampled granite will be, whereas good fits correspond to slightly higher T in the Rehamna with respect to the Jebilet. The thermal amplitude defined by the good fit is small, as maximum temperature remains always within the APAZ domain, with T b 100 °C during the earliest heating episode (at 180–170 Ma), and T b 80 °C during the latest (around 40 Ma). 5. Discussion 5.1. Regional implications

(Table 1), which is identical to the ages obtained by Ghorbal et al. (2008) within the error bar. The MTL in the granite samples are in the range 12.43–11.91 m (less by ~ 1 m than the MTL given by Ghorbal et al.) with standard deviation 1.96–1.94 m. Dpar values are homogeneous within samples and are between 1.27 and 1.83. There is no significant variation between the Dpar values for the two studied massifs. Data have been modelled using the Ketcham et al. (1999) annealing model and AFTSolve (Ketcham, 2005). Geological constrains used in this modelling are: (1) The presence of both massifs close to the temperature of total annealing at 280 Ma as i) the studied granites are dated at 330 Ma in the Jebilet (Essaifi et al., 2003; Boummane and Olivier, 2007) and ~300 Ma in the Rehamna (Baudin et al., 2003) and ii) the lack of granite pebbles in the Autunian deposits occurring at the rim of both massifs (Fig. 1b) testifies that the granites were still below the surface at 280 Ma. Then 280 Ma represents a reasonable proxy for the initiation of the low temperature cooling history. (2) The presence of the samples at lower temperature during Triassic times as Upper Triassic deposits are recovered on top of the Ouled Ouaslam granite and to the West of the Jebilet (Huvelin, 1977; Hollard et al., 1985), in the Bahira boreholes north of the Jebilet Fault, and in the outcrops west and north of the Rehamna Massif (Figs. 1b and 2b). (3) The presence of the samples close to the surface at the end of the Lower Cretaceous prior to the overall Cenomanian– Turonian transgression which extends across North Africa (Guiraud et al., 2005; Frizon de Lamotte et al., 2008). Results of the modelling show (Fig. 4): (1) A rapid exhumation during Permian times which brings the samples towards the surface. This exhumation is coeval with the collapse and erosion of the Variscan chain. Distance to the surface appears however different for the two massifs: the Jebilet granite was at least partly at the surface (cf. onlap of Triassic sediments) whereas the Rehamna massif was still at depth. (2) A phase of heating until the Toarcian–Bajocian (180–170 Ma). This episode is coeval with the accumulation of sediments

The Moroccan Meseta is currently regarded as a former, Triassic– Liassic subaerial land, raised between the Atlantic and Atlas rift basins: this is the classical “Terre des Almohades” (Choubert and Faure-Muret, 1962), now referred to as the West Moroccan Arch (WMA: Hafid, 2006; El Arabi, 2007). Contrastingly, we might infer from the heating which affected the Jebilet and Rehamna granites up to 80 b T b 100 °C (Fig. 4) before their Late Jurassic–Early Cretaceous cooling that the southern Meseta basement subsided significantly during the Triassic– Middle Jurassic, a conclusion also reached independently by Ghorbal et al. (2008). In the case of the Jebilet granites, which were cropping out at 260–250 Ma (see above), heating would have attained 60– 80 °C. With a conservative geothermal gradient of 30 °C/km, this would correspond to 2–2.4 km-thick sedimentary burial at 180– 170 Ma, disregarding the shape of the geotherm close to the surface (Dempster and Persano, 2006). However, the geotherm was likely steeper during the 200 Ma–185 Ma interval, due to the huge CAMP magmatism (Knight et al., 2004; Verati et al., 2007). In particular, the widespread barite veins of western Jebilet yield evidence of pervasive hydrothermal activity during the Triassic–Middle Jurassic Atlantic opening (Valenza et al., 2000). Likewise, based on K–Ar analysis of the b0.2–0.4 µm micas in the Cambrian metapelites and Triassic argillites, Huon et al. (1993) documented the occurrence of a Triassic–Liassic thermal event (195 ± 4 Ma, locally 184 ± 4 Ma) in western Meseta. Therefore, assuming a geothermal gradient of 40 °C/km, burial of the WMA could have been limited to 1.5–2 km, less than the N3 km value proposed by Ghorbal et al. (2008). The 1.5–2 km burial here restored compares with the thickness of the Triassic–Liassic sequences preserved, respectively, i) west and northwest of the Jebilet Massif, beneath the Upper Jurassic–Lower Cretaceous unconformable sequences, i.e. 2–2.5 km in the Essaouira 1 well (Hafid, 2006), and 1.5–2 km in the seismic profiles from the Doukkala-Abda Basin (Echarfaoui et al., 2002a,b); ii) north and northeast of the Moroccan Meseta, i.e. 1–1.5 km in the Prerif Ridges (Sani et al., 2007), as well as in the Tabular Middle Atlas (Charrière, 1990; Gomez et al., 1996) and the Selloum Basin south of it (El Arabi et al., 2001, 2004). The contemporaneous deposits in the Atlas basins are thicker (~2–3.5 km), and subsidence continued there during the Dogger, so as the thickness of the sequences predating the Late Jurassic–Early Cretaceous regression attain ~3.5 km in the Middle Atlas (Charrière, 1990) and along the northern border of the Central

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Fig. 7. Interpretation of the AFT results obtained on the basements massifs of the southern Moroccan Meseta (diagrammatic cross-sections along the same trace as Fig. 2b). (a) At ~250 Ma (Late Permian), the early and shallow Jebilet granites are totally exhumed, whereas the deeper and younger Rehamna granites are still overlain by ~2 km of Paleozoic rocks. — (b) At the maximum of the Triassic–Liassic subsidence, i.e. at 180–170 Ma (latest Liassic–early Dogger), heating is comparable in both massifs, suggesting a southward thickening of the sedimentary burial. — (c) Late Eocene (40–35 Ma) heating event. The Late Jurassic–Early Cretaceous uplift and erosion (not shown) have completed the denudation of the Rehamna granites, whereas remnants of Triassic–Jurassic sequences are preserved southward. The Meseta basement is buried beneath the Upper Cretaceous–Eocene series, the thickness of which slightly increases south–westward. — (d) During the Atlas Orogeny, the Meseta Domain itself has been deformed, particularly close to the High Atlas (not shown, south of the Tadla and Haouz Basins). The basement massifs are exhumed and cooled below the apatite PAZ temperature. The vertical movement is related to a major reverse fault in the Jebilet, and to a very large wave-length crustal fold in the Rehamna.

High Atlas (Ellouz et al., 2003), and ~ 8 km in the axis of the CentralEastern High Atlas (Studer, 1987, Warme, 1988). In contrast, the relatively moderate Triassic–Liassic subsidence suggested by our AFT data for the southern part of the Western Meseta compares favourably with that of the High Moulouya–Missour Basin in Eastern (Oran) Meseta, which varies from 1 to 2 km (Beauchamp et al., 1996; Ellouz et al., 2003). To conclude, the Western (Moroccan) Meseta would have been a submarine high in the Triassic–Liassic paleogeography of Morocco, comparable to the Eastern (Oran) Meseta, instead of being an emergent land as postulated up to now. The partitioned Liassic high formed by the Tabular Middle Atlas and Selloum Basin (El Arabi et al., 2001) could be an image of the WMA, prior to its Late Jurassic–Early Cretaceous uplift and erosion. Another implication of the reported AFT results (Fig. 4) is the importance of the Late Jurassic–Early Cretaceous uplift which affected the Jebilet and Rehamna Massifs, and likely the entire WMA, resulting in the very active erosion (Fig. 5) of the Triassic–Jurassic cover and underlying basement. This phase of uplift (responsible for the second hump of the T–t paths) is coeval with the emersion of most of the Atlas domain, which was covered by widespread red beds of Bathonian– Barremian age, partly sourced from the rising WMA (Charrière et al., 1994, 2005; Frizon de Lamotte et al., 2008). Discussing the geodynamic meaning of this uplift event should be beyond the scope of this paper (see Frizon de Lamotte et al., 2009-this issue).

Following the Late Jurassic–Early Cretaceous uplift, thermal modelling indicates that the south-western Meseta underwent a phase of heating up to ~ 60°–80 °C, modelled from Early Cretaceous till 35–50 Ma. This would represent (assuming a gradient of 30 °C/km) a burial of 1.5–2 km, which compares with the 1 km value proposed by Ghorbal et al. (2008). In fact, in the Phosphate Plateau, the preserved Cretaceous–Eocene sequence is only 200–400 m thick as observed in industrial wells (Bolleli et al., 1959; Anonymous, 1986), whereas it attains 1000 m in the Tadla and Bahira further south (Hafid, 2006; Hafid et al., 2006). Hence, in the southern part of the WMA, the “Thersitea slab” (Lutetian) which tops presently the Cretaceous– Tertiary tabular sequence must have been covered by ~1 km thick deposits prior to the Late Eocene–Oligocene Atlas phase (Frizon de Lamotte et al., 2008). Interestingly, gypsiferous marls up to 400 m thick are preserved above the Lutetian limestones in the Timhadite syncline of Middle Atlas, i.e. in the westernmost part of the Cretaceous–Tertiary marine gulf (Charrière, 1990; Herbig and Trappe, 1994), beneath the unconformable, Oligocene (?) continental deposits (J. Hayane conglomerates: Martin, 1981; Charrière, 1990). We assume that similar deposits accumulated up to greater thickness in the central and western part of the Cretaceous–Eocene gulf. This implies that the uplift and subsequent erosion of the WMA was important during the Atlas orogeny, consistent with the last part of the T–t paths of both the Rehamna and Jebilet Massifs (Fig. 4), and although only the

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latter is bounded by a major reverse fault (Fig. 3). However, crustal shortening, which really began by the Late Eocene (Frizon de Lamotte et al., 2009-this issue), only represents a rather little part of the WMA recent uplift; the most significant part results from the regional lithosphere thinning also responsible for most of the Atlas and Anti-Atlas uplift (Teixell et al., 2005; Missenard et al., 2006; Babault et al., 2008). 5.2. General inference: role of the age and depth of emplacement of the sampled granites The Jebilet and Rehamna granites yield heterogeneous AFT ages, i.e. 186–203 Ma and 148–153 Ma, respectively, although they followed only slightly distinct T–t paths (Fig. 4). We argue in the following that this surprising AFT age discrepancy can be explained by the differences in the age and depth of emplacement of the studied granites. The Jebilet granites emplaced as shallow stocks or laccoliths at ~ 330 Ma, prior to and during the main folding event, in still weakly deformed turbidite formations of late Early Carboniferous age (Essaifi et al., 2001, 2003; Boumanne and Olivier, 2007), i.e. in the upper structural level at probably less than ~ 7 km depth. This estimation is supported by the petrology of the country-rock schists, characterized by widespread crystallization of andalusite (Fig. 6). Contrastingly, the Sebt Brikiine granite from the Rehamna Massif (Fig. 2b) yielded a Rb–Sr whole-rock age at 270 Ma (Mrini et al., 1992), and emplaced probably at 300–290 Ma, as the subsequent array of microdiorite dykes was locally dated at 285 ± 6 Ma (U/Pb zircon; Baudin et al., 2003). This late-orogenic batholith, hardly older than the Early Permian rhyolitic–dacitic volcanism, emplaced at the very bottom of the folded Paleozoic as shown by the detail mapping (Hoepffner et al., 1982; Baudin et al., 2003), i.e. at about 10 km depth (similar to the Oulmes granite in the Central Massif; Tahiri et al., 2007). The eastern part of the batholith and the adjoining apexes such as the studied Ras-el-Abiod leucogranite emplaced at similar depth in the high grade unit of the Western Meseta Shear Zone (WMSZ; Hoepffner et al.,1982; Lagarde and Michard, 1987; Michard et al., 2008). The latter unit, characterized by the widespread development of staurotide and kyanite, equilibrated first at about 15 km depth (Fig. 6) during the Early Namurian (ca. 330 Ma), which corresponds to the main Variscan folding and metamorphic event in the entire WMSZ, including the Central Jebilet (Fig. 1b). When the Sebt Brikiine granite and associated apexes emplaced (i.e. at ~ 300 Ma), the high-grade schists were already exhumed to the ~10 km depth of the granite apex due to extensional collapse (Aghzer and Arenas, 1995; Baudin et al., 2003) and erosion. Thus, exhumation of the metamorphic units during the 330–300 Ma interval can be estimated at about ~5 km in the Rehamna transect. Therefore, by the eve of the Permian (300 Ma), the “just born” Rehamna granites and their country-rocks were located at 9–10 km depth. The 330 My-aged Jebilet granites have already been exhumed (as the Rehamna schists) by several kilometres from their initial emplacement depth (~ 7 km) up to shallow depth (about 3–4 km). The Jebilet granites were probably entering the APAZ at ~ 280 Ma (Fig. 4), being prone to reach the surface during the Late Permian (~ 250 Ma), and then to be overlain by Late Triassic deposits. Assuming a similar or even slightly stronger exhumation (6–7 km?) of the Rehamna granites between 300 and 250 Ma, they were still located at about 2–3 km depth during the Late Permian, consistent with the modelled T–t path (Fig. 4). Remarkably, the Zaer granite of NW Meseta (Fig. 1), which displays the same structural characteristics and age of emplacement as the Rehamna batholith yielded also the same AFT results to Ghorbal et al. (2008). In conclusion, the discrepancy between the older AFT ages yielded by the Jebilet granites (186–202 Ma) with respect to the Rehamna granite and country-rocks (148–158 Ma) can be explained by the fact that the former emplaced 30 My earlier and 3–4 km shallower than the latter, and then crossed the APAZ earlier than the older and deeper

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Rehamna batholith (Fig. 7). One could wonder if some Permian fault could have exhumed the Jebilet granite, leaving the Rehamna granite deeper in the APAZ. This tentative hypothesis is contradicted by several observations: i) Autunian deposits are widespread all around the Rehamna and Jebilet massifs, and the associated, synsedimentary normal/wrench faults crosscut both massifs with a dominant NE trend (Saber et al., 2007); ii) the conspicuous, E-trending North-Jebilet reverse fault (NJF), similar to the other faults of the Atlas System, corresponds to a former Triassic–Early Jurassic normal fault inverted during the Tertiary orogenic evolution, with a major reverse throw dated from the Neogene (Hafid, 2006; Frizon de Lamotte et al., 2008); at that time, both massifs were located at about the same shallow depth and the reverse movement had few consequences, if any, on the AFT ages. 6. Conclusion The AFT data presented here concern a major structural zone of Morocco, i.e. the West Moroccan Arch (WMA) which constituted during the Late Permian–Middle Triassic the eastern shoulder of the Central Atlantic rift and the north-western shoulder of the Atlas (Tethyan) rift. This zone acted as a relatively stable block of Variscan crust during the Mesozoic–Paleogene, being widely covered by the tabular Cretaceous–Eocene series of the Phosphate and Ganntour Plateaus. Our AFT results are based on samples collected in two basement massifs of the southern WMA, namely the Jebilet and Rehamna Massifs. Remarkably, they yielded different ages, 203–186 Ma and 148–153 Ma, respectively. The T–t paths produced are characterized by a two-hump aspect. They demonstrate that the WMA subsided during the Triassic–Middle Jurassic before being uplifted and eroded during the Late Jurassic–Early Cretaceous. Therefore, the previous concept of a permanently subaerial Western Meseta prior to the Cenomanian–Turonian transgression must be abandoned. Our results suggest that, during the Early-Middle Jurassic, the WMA could be compared to the Eastern Meseta–Missour Basin submarine high, with less than 2 km thick sedimentary cover. Regarding the surprising discrepancies (40–50 My) between the mean AFT ages from the studied massifs, they can be explained by the difference in age and depth of emplacement of the sampled granites: the older and shallower granites crossed the APAZ earlier than the younger and deeper ones. In other words, in both massifs, the succession of cooling and heating phases was identical as far as the chronology of erosion and subsidence events is considered, but the temperature reached during the earliest phase of erosion has been different. Thus, the initial structure and evolution of the basement of any young tabular or mountainous domain has to be taken into account in order to interpret the potential differences in the AFT ages observed in the various basement rocks. Acknowledgments We are indebted to P. Van der Beek and E. Labrin (Joseph-Fourier Univ., Grenoble) and D. Seward (Univ. of Zurich) for their help in irradiation process. Thanks are due to M. Hafid (Univ. of Kenitra) for helpful discussions and to A. Charrière (Paul-Sabatier Univ., Toulouse) for enlightening comments. We acknowledge useful discussions with B. Ghorbal (Vrije Univ. Utrecht) during the MAPG-ILP congress, Marrakech 2007. This work has been supported by the FrenchMoroccan program Volubilis (Ma/05/125 and Ma/01/13). References Aghzer, A.M., Arenas, R., 1995. Evolution métamorphique des métapélites du massif hercynien des Rehamna (Maroc). J. Afr. Earth Sci. 21, 383–393.

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O. Saddiqi et al. / Tectonophysics 475 (2009) 29–37

Anonymous, 1986. Géologie des Gîtes minéraux marocains, Tome III: Phosphates, 2ème éd. Notes Mém. Serv. Géol. Maroc, vol. 276, p. 392. Babault, J., Teixel, A., Arboleya, M.L., Charroud, M., 2008. A Late Cenozoic age for long wavelength surface uplift of the Atlas Mountains of Morocco. Terra Nova 20, 102–107. Barbero, L., Teixell, A., Arboleya, M.-L., Rio, P.D., Reiners, P.W., Bougadir, B., 2007. Jurassic-to-present thermal history of the central High Atlas (Morocco) assessed by low-temperature thermochronology. Terra Nova 19, 58–64. Baudin, T., Chèvremont, P., Razin, P., Youbi, N., Andriès, D., Hoepffner, C., Thiéblemont, D., Chihani, E.M., Tegyey, M., 2003. Carte géologique du Maroc au 1/50 000, feuille de Skhour des Rehamna, Mémoire explicatif. Notes Mém. Serv. Carte géol. Maroc, 435 bis, 1-114. Beauchamp, W., Barazangi, M., Demnati, A., El Alji, M., 1996. Intracontinental rifting and inversion: Missour Basin and Atlas Mountains, Morocco. AAPG Bull. 80, 1459–1482. Bolleli, E., Choubert, G., Faure-Muret, A., Salvan, H., Suter, G., 1959. Carte géologique du Plateau des Phosphates et de la Zone synclinale du Tadla, feuilles Benahmed-El Borouj 1:200.000. Notes Mém. Serv. géol. Maroc 137. Boujo, A., 1976. Contribution à l'étude géologique du gisement de phosphates Crétacé– Eocène des Ganntour (Maroc occidental). Sci. Géol. Mém. Strasbourg, vol. 43. 227 pp. Boummane, M.H., Olivier, Ph., 2007. The Oulad Ouaslam Variscan granitic pluton (Jebilet Massif, southwestern Moroccan Meseta): a forcibly emplaced laccolithic intrusion characterized by its magnetic and magmatic fabrics. J. Afr. Earth Sci. 47, 49–61. Charrière, A., 1990. Héritage hercynien et évolution géodynamique alpine d'une chaîne intracontinentale: le Moyen Atlas au SE de Fès (Maroc), Unpubl. Doct. Etat thesis, Univ.Paul-Sabatier Toulouse, 589 pp. Charrière, A., Dépêche, F., Feist, M., Grambast-Fessard, N., Jaffrezo, M., Peybernès, B., Ramalho, M., 1994. Microfaunes, microflores et paléoenvironnements successifs dans la formation d'El Mers (Bathonien– ?Callovien) du synclinal de Skoura (Moyen Atlas, Maroc). Geobios 27, 157–174. Charrière, A., Haddoumi, H., Mojon, P.O., 2005. Découverte de Jurassique supérieur et d'un niveau marin du Barrémien dans les « couches rouges » continentales du Haut Atlas central marocain: implications paléogéographiques et structurales. C. R. Palevol. 4, 385–394. Choubert, G., Faure-Muret, A., 1962. Evolution du domaine atlasique marocain depuis les temps paléozoïques. Livre à la mémoire du Professeur Paul Fallot. Soc. Géol. Fr., Mém. h.-s. , pp. 447–527. Dempster, T.J., Persano, C., 2006. Low-temperature thermochronology: resolving geotherm shapes or denudation histories? Geology 34, 73–76. Echarfaoui, H., Hafid, M., Aït Salem, A., 2002a. Structure sismique du socle paléozoïque du bassin des Doukkala, Môle côtier, Maroc occidental. Indication en faveur de l'existence d'une phase éovarisque. C. R. Géosci. 334, 13–20. Echarfaoui, H., Hafid, M., Aït Salem, A., Aït Fora, A., 2002b. Analyse sismo-structurale du bassin d'Abda (Maroc occidental), exemple de structures inverses pendant le rifting atlantique. C. R. Geosci. 334, 371–377. El Arabi, E.H., 2007. La série permienne et triasique du rift haut-atlasique: nouvelles datations; évolution tectono-sédimentaire, Unpubl. Thesis (Thèse d'Etat) Univ. Hassan II Casablanca, 225 p. El Arabi, H., Ouhhabi, B., Charrière, A., 2001. Les séries du Toarcien-Aalénien du SW du Moyen-Atlas (Maroc): précisions stratigraphiques et signification paléogéographique. Bull. Soc. géol. Fr. 172, 723–736. El Arabi, H., Canérot, J., Ouhhabi, B., Charrière, A., Kerchaoui, S., 2004. The Selloum Basin: new element of the Middle Liassic paleogeography in the southern Middle Atlas (Morocco). J. Afr. Earth Sci. 39, 393–400. El Arabi, E.H., Diez, J.B., Broutin, J., Essamoud, R., 2006a. Première caractérisation palynologique du Trias moyen dans le Haut Atlas; implications pour l'initiation du rifting téthysien au Maroc. C. R. Géosci. 338, 641–649. El Arabi, E.H., Hafid, M., Ferrandini, J., Essamoud, R., 2006b. Interprétation de la série syn-rift haut-atlasique en termes de séquences tectonostratigraphiques, transversale de Telouet, Haut Atlas (Maroc). Notes Mém. Serv. Géol. Maroc 541, 93–101. Ellouz, N., Patriat, M., Gaulier, J.M., Bouatmani, R., Saboundji, S., 2003. From rifting to Alpine inversion: Mesozoic and Cenozoic subsidence history of some Moroccan basins. Sediment. Geol. 156, 185–212. Essaifi, A., Lagarde, J.L., Capdevila, R., 2001. Deformation and displacement from shear zone patterns in the Variscan upper crust, Jebilet, Morocco. J. Afr. Earth Sci. 32, 335–350. Essaifi, A., Potrel, A., Capdevila, R., Lagarde, J.L., 2003. Datation U–Pb: âge de mise en place du magmatisme bimodal des Jebilet centrales (chaîne varisque, Maroc); implications géodynamiques. C. R. Geosci. 335, 193–203. Favre, P., Stampfli, G., Wildi, W., 1991. Jurassic sedimentary record and tectonic evolution of the north western corner of Africa. Paleogeogr. Paleoclimatol. Paleoecol. 87, 53–73. Frizon de Lamotte, D., Zizi, M., Missenard, Y., Hafid, M., El Azzouzi, M., Maury, R.C., Charrière, A., Taki, Z., Benammi, M., Michard, A., 2008. The Atlas System. In: Michard, A., Saddiqi, O., Chalouan, A., Frizon de Lamotte, D. (Eds.), Continental Evolution: The Geology of Morocco. Lect. Notes Earth Sci., vol. 116. Springer Verl., pp. 133–202. Frizon de Lamotte, D., Leturmy, P., Missenard, Y., Khomsi, S., Ruiz, G., Saddiqi, O., Guillocheau, F., Michard, A., 2009. Mesozoic and Cenozoic vertical movements in the Atlas system (Algeria, Morocco, Tunisia): An overview. Tectonophysics 475, 9–28 (this issue). Ghorbal, B., Bertotti, G., Foeken, J., Andriessen, P., 2008. Unexpected vertical Jurassic to Neogene movements in “stable” parts of NW Africa revealed by low temperature geochronology. Terra Nova 20, 355–366. Gigout, M., 1954. Carte géologique de la Meseta entre Mechra-ben-Abbou et Safi (Abda, Doukkala et massif des Rehamna), 1/200 000. Notes Mém. Serv. Géol. Maroc 84. Gomez, F., Barazangi, M., Bensaid, M., 1996. Active tectonism in the intracontinental Middle Atlas Mountains of Morocco: synchronous crustal shortening and extension. J. Geol. Soc. (Lond.) 153, 389–402. Green, P.F., 1981. A new look at statistics in the fission track dating. Nucl. Tracks 5, 77–86. Guiraud, R., Bosworth, W., Thierry, J., Delplanque, A., 2005. Phanerozoic geological evolution of northern and central Africa: an overview. J. Afr. Earth Sci. 43, 83–143.

Hafid, M., 2006. Styles structuraux du Haut Atlas de Cap Tafelney et de la partie septentrionale du Haut Atlas occidental: tectonique salifère et relation entre l'Atlas et l'Atlantique. Notes Mém. Serv. Géol. Maroc, vol. 465. 172 pp. Hafid, M., Zizi, M., Bally, A.W., Ait Salem, A., 2006. Structural styles of the western onshore and offshore termination of the High Atlas, Morocco. C. R. Geosci. 338, 50–64. Hafid, M., Tari, G., Bouhadioui, B., El Moussaid, I., Eccharfaoui, H., Aït Salem, A., Nahim, M., Dakki, M., 2008. Atlantic Basins. In: Michard, A., Saddiqi, O., Chalouan, A., Frizon de Lamotte, D. (Eds.), Continental Evolution: The Geology of Morocco. . Lect. Notes Earth Sci., vol. 116. Springer Verl., pp. 301–329. Herbig, H.G., Trappe, J., 1994. Stratigraphy of the Subatlas Group (Maastrichtian–Middle Eocene, Morocco). Newslett. Stratigr. vol. 30, 125–165. Hmich, D., Schneider, J.W., Saber, H., Voigt, S., El Wartiti, M., 2006. New continental Carboniferous and Permian faunas of Morocco: implications for biostratigraphy, palaeobiogeography and palaeoclimate. In: Lucas, S.G., Cassinis, G., Schneider, J.W. (Eds.), Non-marine Permian Biostratigraphy and Biochronology. Spec. Publ. - Geol. Soc. Lond., vol. 265, pp. 297–324. Hoepffner, C., Jenny, P., Piqué, A., Michard, A., 1982. Le métamorphisme hercynien dans le massif des Rehamna. In: Michard, A. (Ed.), Le massif paléozoïque des Rehamna (Maroc). Stratigraphie, tectonique et pétrogenèse d'un segment de la chaîne varisque. Notes Mém. Serv. Géol. Maroc, vol. 303, pp. 130–145. Hoepffner, C., Houari, M.R., Bouabdelli, M., 2006. Tectonics of the North African Variscides (Morocco, Western Algeria), an outline. In: Frizon de Lamotte, D., Saddiqi, O., Michard, A. (Eds.), Recent Developments on the Maghreb Geodynamics. C. R. Geoscience, vol. 338, pp. 25–40. Holdaway, M.J., Lee, S.M., 1977. Fe–Mg cordierite stability in high-grade pelitic rocks based on experimental, theoretical and natural observations. Contrib. Mineral. Petrol. 63, 175–198. Hollard, H., Choubert, G., Bronner, G., Marchand, J., Sougy, J., 1985. Carte géologique du Maroc, scale 1:1,000,000.- Serv. Carte géol. Maroc, 260 (2 sheets). Huon, S., Cornée, J.J., Piqué, A., Rais, N., Clauer, N., Liewig, N., Zayane, R., 1993. Mise en évidence au Maroc d'événements thermiques d'âge triasico-liasique liés à l'ouverture de l'Atlantique. Bull. Soc. géol. Fr. 164, 165–176. Huvelin, P., 1977. Etude géologique et gîtologique du massif Hercynien des Jebilet (Maroc occidental). Notes Mém. Serv. Géol. Maroc 232, 232 bis, 1 vol. 308 p., 1 geol. map 1:100,000. Ketcham, R.A., 2005. Forward and inverse modelling of low-temperature thermochronological data. Rev. Mineral. Geochem. 58, 275–314. Ketcham, R.A., Donelick, R.A., Carlson, W.D., 1999. Variability of apatite fission-track annealing kinematics: III. Extrapolation to geological time scales. Am. Mineral. 84, 1235–1255. Knight, K.B., Nomade, S., Renne, P.R., Marzoli, A., Bertrand, H., Youbi, N., 2004. The Central Atlantic Magmatic Province at the Triassic–Jurassic boundary: paleomagnetic and 40Ar/39Ar evidence from Morocco for brief, episodic volcanism. Earth Planet. Sci. Lett. 228, 143–160. Lagarde, J.L., Michard, A., 1987. Stretching normal to the regional thrust displacement in a thrust–wrench shear zone, Rehamna Massif, Morocco. J. Struct. Geol. 8, 483–492. Malusà, M., Polino, R., Cerrina Feroni, A., Ferrero, A., Ottria, G., Baidder, L., Musumeci, G., 2007. Post-Variscan tectonics in eastern Anti-Atlas (Morocco). Terra Nova 19, 481–489. Mansour, E.M., 1991. Thermochronologie par la méthode des traces de fission dans l'apatite. Application aux massifs de l'Argentera-Mercantour (Alpes occidentales) et des Jebilet (Meseta marocaine). Thèse Univ. Joseph-Fourier, Grenoble,197 p. Martin, J., Le Moyen Atlas Central, étude géomorphologique, 1981. Notes Mém. Serv. géol. Maroc 258 bis, 445 pp. Medina, F., 1995. Syn- and postrift evolution of the El Jadida-Agadir basin (Morocco): constraints for the rifting model of the central Atlantic. Can. J. Earth Sci. 32, 1273–1291. Michard, A. (Ed.), 1982. Le massif paléozoïque des Rehamna (Maroc). Stratigraphie, tectonique et pétrogenèse d'un segment de la chaîne varisque. Notes Mém. Serv. Géol. Maroc, vol. 303, p. 180 pp. Michard, A., Hoepffner, C., Soulaimani, A., Baidder, L., 2008. The Variscan Belt. In: Michard, A., Saddiqi, O., Chalouan, A., Frizon de Lamotte, D. (Eds.), Continental evolution: The Geology of Morocco. Lect. Notes Earth Sci., vol. 116. Springer Verl., pp. 65–132. Missenard, Y., Zeyen, H., Frizon de Lamotte, D., Leturmy, P., Petit, C., Sébrier, M., Saddiqi, O., 2006. Crustal versus asthenospheric origin of the relief of the Atlas Mountains of Morocco. J. Geophys. Res. 111 (B03401). doi:10.1029/2005JB003708. Mrini, Z., Rafi, A., Duthou, J.L., Vidal, Ph., 1992. Chronologie Rb/Sr des granitoïdes hercyniens du Maroc: Conséquences. Bull. Soc. Géol. Fr. (n.s.) 3, 281–291. Pattison, D.R.M., 1992. Stability of andalusite and sillimanite and the Al2O3 triple point: constraints from the Ballachulish aureole, Scot. J. Geol. 100, 423–446. Richardson, S.W., 1968. Staurolite stability in part of the system Fe–Al–Si–O–H. J. Petrol. 9, 467–488. Saber, H., El Wartiti, M., Hmich, D., Schneider, J.W., 2007. Tectonic evolution from the Hercynian shortening to the Triassic extension in the Paleozoic sediments of the Western High Atlas (Morocco). J. Iber. Geol. 33, 31–40. Sani, F., Del Ventisette, C., Montanari, D., Bendkik, A., Chenakeb, M., 2007. Structural evolution of the Rides Prerifaines (Morocco): structural and seismic interpretation and analogue modelling. Int. J. Earth Sci. 96, 685–706. Studer, M.A., 1987. Tectonique et pétrographie des roches sédimentaires, éruptives et métamorphiques de la région de Tounfite-Tirrhist (Haut Atlas central mésozoïque, Maroc). Notes Mém. Serv. géol. Maroc 43, 321,65–197. Tahiri, A., Simancas, J.F., Azor, A., Galindo-Zaldivar, J., Lodeiro, F.G., El Hadi, H., Martinez Poyatos, D.J., Ruiz-Constán, A., 2007. Emplacement of ellipsoid-shaped (diapiric?) granite: Structural and gravimetric analysis of the Oulmes granite (Variscan Meseta, Morocco). J. Afr. Earth Sci. 48, 301–313.

O. Saddiqi et al. / Tectonophysics 475 (2009) 29–37 Teixell, A., Ayarza, P., Zeyen, H., Fernàndez, M., Arboleya, M.-L., 2005. Effects of mantle upwelling in a compressional setting: the Atlas Mountains of Morocco. Terra Nova 17, 456–461. Valenza, K., Moritz, R., Mouttaqi, A., Fontignie, D., Sharp, Z., 2000. Vein and karst barite deposits in the western Jebilet of Morocco: fluid inclusion and isotope (S, O, Sr) evidence for regional fluid mixing related to Central Atlantic rifting. Econ. Geol. 95, 587–606. Verati, C., Rapaille, C., Féraud, G., Marzoli, A., Marzoli, H., Bertrand, H., Youbi, N., 2007. Ar–Ar ages and duration of the Central Atlantic magmatic province volcanism in Morocco and Portugal and its relation to the Triassic–Jurassic boundary. Paleogeogr. Paleoclimatol. Paleoecol. 244, 308–325. Warme, J.E., 1988. Jurassic carbonate facies of the central and eastern High Atlas rift, Morocco. In: Jacobshagen, V. (Ed.), The Atlas System of Morocco. Lect. Notes Earth Sci., vol. 15, pp. 169–199.

37

Willye, P.J., 1977. Crustal anatexis: an experimental review. Tectonophysics 43, 41–71. Zizi, M., 2002. Triassic–Jurassic Extensional Systems and their Neogene Reactivation in Northern Morocco— the Rides prérifaines and Guercif basin. Notes Mém. Serv. Géol. Maroc, vol. 416. 138 pp. Zouhri, S., Kchikach, A., Saddiqi, O., El Haïmer, F.Z., Baidder, L., Michard, A., 2008. The Cretaceous–Tertiary Plateaus. In: Michard, A., Saddiqi, O., Chalouan, A., Frizon de Lamotte, D. (Eds.), Continental Evolution: The Geology of Morocco. Lect. Notes Earth Sci., vol. 116. Springer Verl., pp. 331–358.