Edough Massif Research Articles

Three-dimensional magnetotelluric imaging of the Edough massif and its overlying formations (Northeast Algeria)

The Edough massif (NE Algeria) is the easternmost coastal crystalline massif of the Maghrebide belt, whose current structural position remains poorly known. Magnetotelluric (MT) data from 15 stations were collected along three profiles across the Edough massif and its neighboring formations in the period range of 0.001–1000 s to assess the deep electrical resistivity structure. A phase tensor dimensionality analysis indicates that the measured data are dominated by 3-D effect of underlying geological structure, thus revealing a complex subsurface structure. A 3-D inversion model was obtained using the full impedance tensor and the vertical magnetic field transfer function including bathymetry and topography. Our preferred 3-D geo-electrical model shows heterogeneous electrical structures and are related to the known geological features of the region. We mainly observe a clear resistivity contrast characterizing the upper/middle crust. The Edough massif appears generally as a homogenous resistive structure. The shallow conductive structures are associated with the Mio-Plio-Quaternary deposits and Flysch units. Most of conductive bodies are likely related to the iron/magnetic anomaly. These may likely correspond to the suture zone. Under the Neogene basin, the high resistivities with a north dipping strong angle may correspond to the African basement.

Checklist of the springtails (Hexapoda: Collembola) of the Edough massif, northeastern Algeria.

Based on 225 samples taken from different biotopes in the Edough Massif (northeastern Algeria) from 1998 to 2018, we compiled a list of 91 collembolan species names from the literature, of which 72 can be considered valid records. Fourteen of them are only known from this massif in Algeria, and eight are endemic of northeastern Algeria. These 72 species are spread over 14 families and 49 genera. The family Neanuridae is the most diverse with 18 species, including six species of the genus Friesea. The monotypic genus Edoughnura (Neanurinae) is endemic to the Edough and Collo massifs. Several of the listed species do not fully match the diagnosis of the species to which they have been assigned and may represent undescribed taxa. Entomobryidae as well as several habitats (epigean, deep soil, littoral) remain unsampled or undersampled in Edough, and are likely to host many more species than those listed in this paper.

Vestiges of a fore-arc oceanic crust in the Western Mediterranean: Geochemical constraints from North-East Algeria

The present day architecture of the Western Mediterranean mainly results from the interplay of different lithospheric plates and the Cenozoic consumption of various branches of the Alpine Tethys and Neo-Tethys Oceans. Identifying relics of these oceanic domains in the peri-Mediterranean belts enables pinpointing the earliest stages of this evolutionary framework. In NE Algeria, the Kef Lakhal Complex (Edough Massif) is composed of amphibolites and meta-gabbros metamorphosed under amphibolite facies conditions and thrust onto the northern African margin during earliest Miocene. Geochemical analyses reveal that amphibolites and metagabbros have major and trace element signatures characteristic of tholeiitic basalts and gabbros and display N-MORB (La/SmN = 0.7–0.9) to E-MORB (La/SmN = 1.1–1.2) affinities. Enrichments in U and alkalis (Cs, Rb) and high 87Sr/86Sri ratios on bulk rocks and minerals (up to 0.70856) are typical of seawater alteration and indicate that the Kef Lakhal Complex represents a piece of altered oceanic crust. Parental magmas were derived from a Depleted Mantle source (WR εNdi = 8.2–9.9 and εHfi = 10.4–14.4) that preserved some canonical MORB ratios (Ti/Eu = 5700–7600 and Y/Ho = 27.4–29.0), but which was contaminated by a component akin to recycled oceanic crust and associated sediments (Ce/Pb = 10.5–22.2; 206Pb/204Pbi = 18.41–18.74; 207Pb/204Pbi = 15.49–15.59; 208Pb/204Pbi = 37.73–38.37). The sedimentary component is consistent with a volcaniclastic origin and substantiates an intra-oceanic setting. The geochemical characteristics of the Kef Lakhal rocks are comparable to present day (Mariana, W Pacific Ocean) or fossil (Xigaze, SE Tibet) fore-arc oceanic crust. An overview of the Western Mediterranean geodynamic indicates that the most likely period for initiating formation of a fore-arc corresponds either to the Early/Late Cretaceous or to the Middle Eocene. 40Ar/39Ar dating on amphibole further indicate that after thrusting onto the African margin, the Kef Lakhal Complex cooled down to c.550 °C at 18.14 ± 0.27 Ma (2σ).

Provenance analyses of the heavy-mineral beach sands of the Annaba coast, northeast Algeria, and their consequences for the evaluation of fossil placer deposit

The paper presents the first study of heavy-mineral sand beaches from the Mediterranean coast of Annaba/Algeria. The studied beaches run along the basement outcrops of the Edough massif, which are mainly composed by micaschists, tourmaline-rich quartzo-feldspathic veins, gneisses, skarns and marbles. Sand samples were taken from three localities (Ain Achir, Plage-Militaire and El Nasr). The heavy-mineral fraction comprises between 74 and 91 vol%. The garnets of the beaches are almandine rich and tourmalines vary with respect to their location from schorl to dravite. Tourmaline at Ain Achir and the Plage-Militaire is schorlits, while at El Nasr beach dravite is ubiquitous. The World Shale Average normalised REE of the sands and the basement outcrops reveal: (i) Ain Achir beach: REE pattern of sand and the coastal rocks from the studied beaches reflects a multiple sources; (ii) Plage-Militaire: the sand and the coastal outcrops show similar LREE and a strong enrichment in HREE, suggesting the presence HREE-rich phases found as inclusions in staurolite; (iii) El Nasr: two types of sand patterns are found: one with flat REE pattern similar to the proximal rocks and other one enriched in HREE suggesting a mixed source.

Age of UHP metamorphism in the Western Mediterranean: Insight from rutile and minute zircon inclusions in a diamond-bearing garnet megacryst (Edough Massif, NE Algeria)

Diamond-bearing UHP metamorphic rocks witness for subduction of lithospheric slabs into the mantle and their return to shallow levels. In this study we present U–Pb and trace elements analyses of zircon and rutile inclusions from a diamond-bearing garnet megacryst collected in a mélange unit exposed on the northern margin of Africa (Edough Massif, NE Algeria). Large rutile crystals (up to 300 μm in size) analyzed in situ provide a U–Pb age of 32.4±3.3 Ma interpreted as dating the prograde to peak subduction stage of the mafic protolith. Trace element analyses of minute zircons (≤30 μm) indicate that they formed in equilibrium with the garnet megacryst at a temperature of 740–810 °C, most likely during HP retrograde metamorphism. U–Pb analyses provide a significantly younger age of 20.7±2.3 Ma attributed to exhumation of the UHP units. This study allows bracketing the age of UHP metamorphism in the Western Mediterranean Orogen to the Oligocene/early Miocene, thus unambiguously relating UHP metamorphism to the Alpine history. Exhumation of these UHP units is coeval with the counterclockwise rotation of the Corsica–Sardinia block and most likely resulted from subduction rollback that was driven by slab pull.

Reworking of intra-oceanic rocks in a deep sea basin: example from the Bou-Maiza complex (Edough massif, eastern Algeria)

ABSTRACTMetagabbros and amphibolites exposed in the Bou-Maïza area of the Edough massif (northeast Algeria) are described in detail. Field and petro-structural observations point to the syn-sedimentary emplacement of gabbros as clasts, blocks and lenses of polymictic gabbroic breccias. Associated amphibolites display fine-scale parallel sedimentary bedding and represent mafic epiclastites, litharenites and mafic greywackes. The mafic beds and lenses are intercalated with aluminous pelitic schists of continental origin, quartzite and marble. It is concluded that all mafic rocks from this locality derive from the erosion of an oceanic plutono-volcanic complex of MORB affinity that was reworked in a block matrix mélange and emplaced as turbidites and debris flows during the Mesozoic. We propose a convergent plate margin setting for these formations connected with the subducted Calabrian branch of the Tethyan slab.

Comparative larval morphology in three species of Pleurodeles (Urodela: Salamandridae).

The Ribbed newts (genus Pleurodeles) are endemic to the Iberian Peninsula and northwest Africa (Raffaëlli 2013), and comprise three species: Pleurodeles nebulosus (Guichenot 1850), Pleurodeles poireti (Gervais 1836) and Pleurodeles waltl Michahelles 1830. Pleurodeles nebulosus is found in northern Algeria and Tunisia with an average size of 18 cm, while P. poireti is endemic to the Edough Massif, in northeastern Algeria and is the smallest species, with 12.9 cm in total length (Escoriza et al. 2016; Carranza & Wade 2004). Pleurodeles waltl appears on the Iberian Peninsula and Morocco (García-París et al. 2004). The eastern and western populations of P. waltl although they are not differentiated taxonomically show high levels of genetic divergence (estimated to have occurred 2.0-3.2 Ma; Carranza & Arnold 2003). The individuals of P. waltl attain large sizes (30 cm of total length) and have 8-10 cutaneous glands on both sides (Pasteur 1958), which are absent in other species of the genus.

Phylogeny, age structure, growth dynamics and colour pattern of the Salamandra algira algira population in the Edough Massif, northeastern Algeria

The distribution of the Fire Salamander in North Africa is discontinuous and the Edough Peninsula, Algeria, is considered as the eastern edge of the distribution area. In the current study, we establish a description of the Salamandra algira algira population in its type locality. In this context, an analysis of the mitochondrial DNA D-loop of 47 sequences comes to confirm the phylogenetic status of our population with regard to the other Algerian and Moroccan populations. Also, we used the skeletochronological method for establishing the age structure of the population. Maximum longevity reached 18 years, with a high frequency of young adults, which suggests a good survival of the juveniles. The growth of males is faster than that of the females, although the maximum size of the males is 180 mm, while that of the females is 210 mm. The Edough’s salamander’s phenotype is characterized by multiple small white spots dispersed in different parts of the body (belly, sides, legs and throat) and a high number of large red spots. These red spots are surrounded by a ring of small white spots on the lower part of the body and sometimes on the legs, thus creating specific eyespots that are often aligned along the lower sides.

Metamorphic diamonds in a garnet megacryst from the Edough Massif (northeastern Algeria). Recognition and geodynamic consequences

We report for the first time the discovery of diamond inclusions (5–30μm in size), identified by Raman spectroscopy and the characteristic sharp band at 1332cm−1 for crystalline diamond, in a garnet megacryst (≥5cm) from the Edough Massif (NE Algeria). The garnet is adjacent to actinolite and ultramafic boudins and slices of marbles that are inserted within a major mylonite–ultramylonite band. This tectonic contact sharply delineates the Kef Lakhal oceanic unit from the granite-gneiss core below. The host garnet is almandine-dominant and is rich in exsolution of acicular rutile needles. Major and trace elements show a gradual but significant zonation from core to rim, and a sharp increase in grossular component in the rim. Trace element analyses of prismatic rutile inclusions up to 300μm in size indicate that the host metamorphic rock was a mafic protolith of MORB affinity. The Zr-in-rutile thermometry indicates a temperature range of 724–778°C that we relate to rutile growth, either during prograde metamorphism or under peak UHP metamorphic conditions of ≥3.6GPa that were reached during subduction of the UHP-rock precursors. We suggest that the mafic protolith originates from the subducted retreating Calabrian branch of the Tethyan slab, that broke or tore, and which fragments were dragged upward and thrust onto the North African margin along with the Kef Lakhal unit, shortly followed by formation of the Edough dome and opening of the Algerian basin.

Geochemistry and petrology of metamorphosed submarine basic ashes in the Edough Massif (Cap de Garde, Annaba, northeastern Algeria)

The study presents the first evidence of metamorphosed submarine ashes in the Edough Massif, in northeastern Algeria. It occurs below the greenschist-facies Tellian units that represent the thrusted Mesozoic to Eocene passive paleomargin of northern Africa deposited on thinned continental crust. The metamorphic complex consists of tectonically superposed units composed of gneisses (lower unit) and micaschists (upper unit). At the Cap de Garde, these units enclose an “intermediate unit” composed of micaschists and meter-thick layers of marbles, which are sometimes intercalated with amphibolites. The latter occur as discontinuous small lenses and layers. The amphibolites are parallel to the primary bedding of the marbles and the main foliation. Chemical markers and field observations indicate that they are metamorphic equivalents of basic igneous rocks. The lenticular character, low thickness and multiple intercalations with marine sediments and the unusual high lithium concentrations suggest subaqueous near-source basaltic ash-fall deposits in a marine environment.

Geochemical study (major, trace elements and Pb–Sr–Nd isotopes) of mantle material obducted onto the North African margin (Edough Massif, North Eastern Algeria): Tethys fragments or lost remnants of the Liguro–Provençal basin?

Abstract The Maghrebides, Betics and some parts of the Calabrian, NE Sicilian and Tuscan allochtons constitute dismembered fragments of the Alpine belt that resulted from the Cenozoic collision between Africa and Eurasia and the opening of the Western Mediterranean basin. Mineral and whole-rock geochemical analyses have been performed on three distinct outcrops of mantle material from the Edough Massif of NE Algeria, namely the Bou Maiza (BM) gabbros, the La Voile Noire (LVN) amphibolites and the Sidi Mohamed (SM) peridotites. In all samples, Sr isotopes are largely affected by seawater alteration (87Sr/86Sract. > 0.70384 and up to 0.70888) and cannot be used to evaluate the nature of the source reservoirs. SM peridotites display variable depleted mantle Nd isotopic signatures (eNdact. from + 7.0 to + 12.2) and geochemical features suggesting no significant chemical depletion as a result of partial melting and melt extraction (Mg# + 7.9) and are likely cogenetic, but without filiation with the SM peridotites. Pb isotopes indicate a contribution of sediments in the source reservoir, which is attributed to contamination solely by hydrous fluids released from a sedimentary component. This observation, together with a LILE-enrichment, suggests a back-arc basin environment. These results indicate that BM and LVN units were obducted onto the North African margin and subsequently fragmented, probably during doming and exhumation of the lower continental crust of the Edough massif. Doming resulted in opposite movements of the overlying oceanic units, southward for the BM units and northward for LVN amphibolites.

The Sidi Mohamed peridotites (Edough Massif, NE Algeria): Evidence for an upper mantle origin

The Hercynian Edough massif is the easternmost crystalline massif of the Algerian coast. It consists of two tectonically superposed units composed of micaschists, gneisses, and peridotite. This study concentrates on the small and isolated Sidi Mohamed peridotite outcrop area (0.03 km2). The Sidi Mohamed peridotite is composed mainly of harzburgites (Mg-rich olivine and orthopyroxene as major minerals). The Ni (2051–2920 ppm), Cr (2368–5514 ppm) and MgO (~28–35 wt.%) whole-rock composition and the relative depletion in Nb make these harzburgites comparable to depleted peridotites related to a subduction zone. We suggest that the Sidi Mohamed ultramafic body was derived directly from the upper mantle and tectonically incorporated into the gneiss units of the Edough metamorphic core complex in a subduction environment.

Impact de l’alteration sur le bilan chimique des diatexites du Massif de l’Edough (Annaba, NE Algérien)

The studied section, located on the eastern part of the Edough massif (region of Annaba, Algeria), is characterized by a Mediterranean climate and the area is one of the most humid of Algeria (precipitation between 750 and 1200 mm/year). It consists of diatexites with homogeneous petrographic and metamorphic facies. The primary minerals are quartz, feldspar, oligoclase and biotite whereas weathering products are mostly represented by illite and montmorillonite. Although all samples comprise the same mineral composition, due to changes in the mode, the chemistry of this diatexites is very heterogeneous. The chemical analyses of the rocks reveal a progressive evolution in the composition in terms of gains and losses in Ca, Na, K, Fe, Mg and in trace elements. The values of the Chemical Index of Change (CIA = 62.79 - 68.32, of the Chemical index of Weathering (CIW = 63.92 - 70.79), the Freshness Index (IFRAIS = 76 - 46.35) and the high value of the loss of ignition (L.O.I > 2%) as well as the Rb/Sr ratio >1 indicate that the distribution of the chemical elements along the section is entirely controlled by weathering (bisiallitisation alteration type) during a long time.

Stability of the association fayalite + calcite within metamorphosed banded iron formations: The case of the magnetite ores of Edough massif (N-E Algeria)

We interpret the mineral assemblages observed in iron magnetite deposits, and in particular the association fayalite+calcite, which result from the metamorphism of iron carbonate. The variety of mineral assemblages is explained in terms of compositional differences in the parent rock as well as by the intensity of both the reduction and decarbonation processes. The Ca-Fe-Si-C-O system is considered. Phase diagrams are constructed with μO2 and μCO2 as coordinates (mobile components), the elements Ca, Fe and Si being inert. The method is applied to the Edough massif, the easternmost crystalline massif of the Algerian coast. This massif hosts ancient deposits of magnetite±hematite ores hosted in kyanite-staurolite-garnet schists. The main minerals of the ore bodies are magnetite, hematite, siderite, quartz, calcite, fayalite, hedenbergite and garnet, resulting from the metamorphism of siderite+calcite+quartz rocks containing variable proportions of the starting minerals. The stability of the fayalite+calcite assemblage coexisting with magnetite and other minerals is suggested from phase relations observed in the iron formations of the Edough massif. Although this association is generally regarded as impossible, it has been described in a number of studies. The thermodynamic calculations reported here demonstrate the existence of a stability domain for the association fayalite+calcite.

Determination of the source rocks for the diatexites from the Edough Massif, Annaba, NE Algeria

The crystalline Edough Massif is located in the oriental part of the Algerian coastline. It consists of two tectonically superposed units of gneisses, augen-gneisses and migmatitic gneisses in the lower unit and micaschists in the upper unit. The crystalline rocks underwent a low to moderate degree of metamorphism; the gneisses suffered partial melting. They display migmatitic features such as nebulitic structures with contorted leucosome layers and K-feldspar porphyroblasts and thus can be classified as diatexites. The mineralogical composition of these rocks is very homogenous and consists of K-feldspar, micas and quartz. The feldspar-rich, arkosic nature of the outcrop implies a granitic source rock. High K2O/Na2O ratios and high A/CNK>1.1 indicate an S-type granite source and a peraluminous composition of the protolith respectively. Chondrite normalized REE distribution patterns of the Edough diatexites show gently inclined patterns with a minor negative Eu anomaly (Eu/Eu*=0.36–0.49), which points to a very slightly differentiated granitic source. The REE pattern and trace element data of the diatexites are similar to those of average Proterozoic upper continental crust, which suggests that they are derived mainly from upper continental crust and were deposited in continental margins.

Miocene incorporation of peridotite into the Hercynian basement of the Maghrebides (Edough massif, NE Algeria): Implications for the geodynamic evolution of the Western Mediterranean

A laser ablation ICP-MS U–Pb age of 17.84 ± 0.12 Ma (late Burdigalian) was obtained from monazites separated from a leucocratic diatexite collected in close proximity to a small peridotite massif incorporated into the lower crustal sequence of the Edough Massif (north-eastern Algeria), a southern segment of the peri-Mediterranean Alpine Belt. Monazites extracted from a neighbouring deformed leucogranite intruding early Paleozoic phyllites yield a consistent age of 17.4 ± 1.3 Ma. Zircons occurring in the same leucogranite, with magmatic characteristics, have an age of 308 ± 7 Ma interpreted as dating magmatic crystallisation of the leucogranite and reflecting partial melting during the Hercynian orogeny. Low Th/U domains (Th/U < 0.10) from the same grains substantiate recrystallisation during a younger metamorphic event whose upper age limit is 286 ± 11 Ma. These results emphasize the polycyclic evolution of basement rocks preserved in the crystalline units of the western Mediterranean and indicate that part of their metamorphic features were inherited from older, Hercynian, events. Taken together with published Ar–Ar dates, the late Burdigalian age of monazites indicates a rapid cooling rate of c. 370 °C/Ma and is regarded as closely approximating the emplacement of the peridotites into the Hercynian basement. The monazite ages are significantly younger than those recorded for orogenic peridotites from the Betic-Rif orocline and for the timing of lithospheric extension forming the Alboran sea. It is also younger than rifting and back-arc extension opening the Liguro–Provençal basin. The late Burdigalian age is interpreted as dating the incipient rifting event that opened the Algerian basin, which is consequently not a continuation of the Liguro–Provençal basin. At the scale of the western Mediterranean, these observations concur with current models supporting slab roll-back and an eastwards migration of extension in the western Mediterranean, but suggest that the Algerian basin opened as a result of torsion and stretching of the Thethyan slab due to its steepening under the Alboran microplate.

Edoughnura rara n.gen., n.sp., an enigmatic genus of Neanurinae Collembola from the Edough Massif (Algeria)

A new genus and new species of Neanurinae Collembola, Edoughnura rara, is described from the Edough massif in Algeria. It combines a number of unusual or unique features : additional chaetae on head; mandible as a long, thin, ciliated lamella; chaetae Di of Th. II-III in line; tubercles Di fused on axis from Abd.III to Abd.V. Its affinities within the tribe Neanurini remains obscure.

Stable isotope study of the igneous, metamorphic and mineralized rocks of the Edough complex, Annaba, Northeast Algeria

The petrogenesis of igneous, metamorphic and mineralized rocks in the Edough massif, NE Algeria, indicates an interplay between crustal and magmatic sources, and magmatic and surface fluids, as determined by sulphur and oxygen isotopic analyses. The Tertiary igneous rocks (microgranites and rhyolites) show a tendency towards I-type granitoids with δ 34S values of +5.4±2.2 ‰ (1 σ) and δ 18O between +5.6 ‰ and +6.9 ‰, with the most hydrothermally altered rocks having the lowest δ 18O values. This is indicative of seawater being a major component of the hydrothermal fluids. Seawater interaction with the granitoids produced enrichment in 34S of sulphide-sulphur in both the microgranites and associated skarn mineralization. However, in the Beleleita W–Sn–(Au) deposit, magmatic fluids dominated the mineralization, reflected by δ 34S values of +1.7 ‰ and +1.8 ‰. The basement amphibolites of Kef Lakhal indicate derivation from a basaltic magma with δ 18O ranging from +4.9 ‰ to +8.6 ‰. Locally altered amphibolite has the lowest δ 18O values suggestive of meteoric water interaction, whereas the highest δ 18O indicate the incorporation of crustal material during the genesis of the amphibolites. Crustal contamination is also reflected in their δ 34S of −18 ‰ to +2.1 ‰, with the most contaminated rocks having the lowest δ 34S. Host Palaeozoic mica schists with δ 18O of +12.7 ‰ and δ 34S of −13.2 ‰ and associated marbles ( δ 34S −9.9 ‰ to −17.4 ‰) are thought to be the most likely contaminants. At the Ain Barbar Fe–Cu–Pb–Zn deposit, δ 34S values range between −9.6 ‰ and −10.8 ‰, indicating that the sulphide-sulphur and base-metals were likely leached from the host Cretaceous flysch and/or the underlying mica schists, with local Tertiary magmatic rocks providing the heat for local convection cells. At Boumaiza Fe-deposit, δ 34S values of the sulphide-sulphur extend from −1.2 ‰ to −8.1 ‰ indicative of magmatic sulphur with the incorporation of substantial amounts of sulphur derived from the host mica schists.

Metamorphic evolution, partial melting and Miocene exhumation of lower crust in the Edough metamorphic core complex, west Mediterranean orogen, eastern Algeria

The Edough massif is the easternmost crystalline massif of the Maghrebides which represent the southeastern part of the west Mediterranean orogen. It emerges from below the greenschist–facies Tellian units that represent the thrusted Mesozoic to Eocene passive paleomargin of northern Africa deposited on the thinned continental crust. The top of the crystalline pile of the Edough massif is characterised by metasedimentary rocks affected by medium- to high-pressure (12–14 kbar) and medium-temperature metamorphic conditions of ca. 600 °C. The northern part of the massif as well as the overlying allochthonous amphibole–peridotite unit in the north is characterised by high-pressure granulite facies ( T∼800 °C and P≥12 kbar). Nearly isothermal decompression is documented in metapelites by late- to post-kinematic crystallisation of sillimanite and andalusite overprinting kyanite. The core of the dome comprises essentially diatexite and granite gneisses. A late low-pressure evolution and overprinting (2–3 kbar) took place in Paleozoic rocks in proximity to granite–gneisses. The predominant igneous mineralogy of granite–gneisses suggests that they represent synmetamorphic and syn-kinematic sheeted intrusions generated through a high-degree melting of metasediments. Geochronology of the metamorphic rocks (U–Pb on monazite, Sm–Nd on garnet–WR pairs, 40Ar/ 39Ar on amphiboles and micas) yields ages bracketed between 24 and 16 Ma, suggesting that regional metamorphism of the Edough massif took place during the Late Tertiary, synchronous with the greenschist–facies metamorphism recorded in the overlying Mesozoic Tellian units. The Edough massif represents a metamorphic core complex exhumed through tectonic denudation assisted by syn- to late-metamorphic low-angle, N-dipping normal ductile shear zones. An exhumation rate of 6–8 km/Ma and associated cooling rate of 200–300 °C/Ma is implied. We conclude that the Edough massif represents part of the former thinned continental crust of Africa involved in a Late Eocene northward subduction beneath the suboceanic domain that separated Paleo-Europe and Africa in Mesozoic time. The upward syn-metamorphic tectonic emplacement at ∼40–45 km depth of slices of spinel peridotites detached from the lower mantle may be responsible for the local granulite facies occurrences. Their emplacement is a consequence of the long-lived transtensional (sinistral, then dextral) kinematics having taken place between the African and European plates.

Métamorphisme miocène de granites panafricains dans le massif de l'Edough (Nord-Est de l'Algérie)

The Edough Massif is the easternmost crystalline core of the Maghrebides that represents the African segment of the west Mediterranean Alpine belt. U-Pb zircon dating provides upper intercept ages of 595 ± 51 My and 606 ± 55 My for an orthogneiss of the lower unit and a deformed leucogranite of the upper pelitic unit, respectively. These ages suggest emplacement of the two granitoids during the Pan-African orogeny. Monazites from a paragneiss sample gave a 18 ± 5 My U-Pb age that points to a Miocene age of the high-temperature metamorphism.