The Beni Bousera marbles, record of a Triassic-Early Jurassic hyperextended margin in the Alpujarrides-Sebtides units (Rif belt, Morocco)

The timing and process of exhumation of the subcontinental peridotites of the Gibraltar Arc (Ronda, Beni Bousera) have been discussed extensively over the last decades. In this work, we contribute to this debate through the first mapping, structural and petrological analyses, and SHRIMP U-Th-Pb dating of high-grade marbles that crop out around the Beni Bousera antiform of the Alpujarrides-Sebtides units of northern Rif (Morocco). These marbles, here termed the Beni Bousera marbles (BBMs), instead of being intercalations in the granulitic envelope (kinzigites) of the Beni Bousera peridotites, as previously described, form minor, dismembered units within a ∼30 to 300 m thick mylonitic contact between the kinzigites and the overlying gneisses of the Filali Unit (Filali–Beni Bousera Shear Zone, FBBSZ). They display silicate-rich dolomitic marbles, sandy-conglomeratic calcareous marbles and thinly bedded marble with interleaved biotite-rich schists. An unconformable contact, either of stratigraphic or tectonic origin, with the underlying kinzigites, is observed locally. Pebbles or detrital grains include K-feldspar, quartz, almandine garnet and zircon. Peak mineral assemblages consist of forsterite, Mg-Al-spinel, geikielite (MgTiO3), phlogopite and accessory zirconolite, baddeleyite and srilankite in dolomite marble, as well as K-feldspar, scapolite, diopside, titanite and accessory graphite and zircon in calcite marble. These assemblages characterize peak HT-LP metamorphic conditions close to 700–750 °C, ≤4.5 kbar. The FBBSZ includes minor ductile thrusts that determine kinzigite horses or slivers carried NW-ward over the marbles. Within the latter, NNE-trending folds are conspicuous. Brittle, northward-dipping normal faults crosscut the FBBSZ ductile structures. Detrital cores of zircon from the BBMs yield two U-Th-Pb age clusters of ∼270 Ma and ∼340 Ma, whereas their rims yield ∼21 Ma ages. Correlations with comparable settings in other West Mediterranean Alpine belts are discussed. The BBMs compare with the Triassic carbonates deposited over the crustal units of the Alpujarrides-Sebtides. The assumed Triassic protoliths may have been deposited onto the kinzigites or carried as extensional allochthons over a detachment in the Early Jurassic during the incipient formation of the Alboran Domain continental margin. Thus, it is concluded that the Beni Bousera mantle rocks were exhumed to a shallow depth during early rifting events responsible for the birth of the Maghrebian Tethys.


249
We started the study of the marbles in the Oued Amter valley (Fig. 4) where we had previously 250 described marble outcrops (Saddiqi, 1988). The marbles outcrops were mapped south of Taza village, 251 north of Inoualine, and at the Oued Ljouj-Oued Amter confluence (Fig. 5). As the marble outcrops 252 appeared to be linked to the upper boundary of the Beni Bousera kinzigites in the mapped area, we 253 searched for other marbles along the southwestern flank of the Beni Bousera Unit from the Oued Ljouj 254 to the crest of the massif, where we discovered a large marble outcrop in the predicted location (JN, 255 Thirty-three samples were collected within and around the marbles outcrops (Table 1) Potential zircon-bearing fractions were separated using panning, first in water and then in ethanol. 278 Only three samples yielded sufficient zircon grains to undertake SHRIMP analysis with a perspective 279 of detrital zircon study, i) MTS 5 from the metaconglomeratic bed near the base of outcrop 1a; ii) 280 MTS 6 from the impure marbles of outcrop 1b, and iii) MTS 18 from a calcschist bed of outcrop 1c 281 (Fig. 5). After extracting the magnetic fraction with a neodymium magnet, zircon grains were 282 handpicked under a binocular microscope. About 150 zircon grains for samples MTS 5 and MTS 6, 283 and 60 for MTS 18 were mounted along with standards on a 3.5 cm diameter epoxy SHRIMP 284 megamount. Zircons were polished, studied by optical (reflected and transmitted light) and scanning 285 electron microscopy (secondary electrons and cathodoluminescence images), coated with a 13-15 nm 286 thick gold layer, and analyzed for U-Th-Pb using a SHRIMP IIe/mc ion microprobe at the IBERSIMS 287 laboratory of the CIC University of Granada, Spain. The SHRIMP U-Th-Pb analytical method is 288 described in detail at www.ugr.es/ibersims. Each selected spot was rastered with the primary beam for 289 120 s prior to analysis, and then analyzed by 6 scans, following the isotope peak sequence 196  At a regional scale (Fig. 4), the marble outcrops form lens-shaped exposures (TZ, IN, OL, JN) 303 exclusively located in between the kinzigite envelope of the Beni Bousera peridotites and the 304 overlying Filali gneisses. As mentioned in section 2, we have distinguished this limit under the name 305 of Filali-Beni Bousera Shear Zone (FBBSZ). Along this contact, the most significant outcrops are 306 observed on the western bank of Oued Amter, south of Taza village, along the Amter track (Fig. 6A, 307 C), and in the narrow Oued Taza valley (Fig. 5, outcrops 1a-1c). Here, the FBBSZ is nearly 150 m 308 thick, whereas at Inoualine, on the opposite bank of Oued Amter, marble lenses 2a, 2b (Fig. 5)  Marble outcrops of the Taza and Inoualine lenses commonly exhibit bedding confirming the 313 sedimentary nature of the protoliths. This is best exemplified by the thinly bedded marbles with 314 interleaved meta-argillites (now biotite-vermiculite schists) outcropping in Oued Taza (Fig. 6B). 315 Likewise, large outcrop 1a (Fig. 5) displays conspicuous bedding marked by alternating pure and 316 siliceous/silicate-rich carbonate layers (Fig. 6C). The state of the silica component in the protolith may 317 have been diffuse (chert) and/or detrital sand (see sub-sect. 5.2), but the occurrence of a 318 metaconglomeratic bed (Fig. 6D) supports the idea of metadetrital carbonate beds in this sequence. 319 Moreover, the outcrop bedding appears to parallel the basal contact of the marbles over the tightly 320 folded kinzigites of the Beni Bousera Unit (Fig. 6C). However, this contact may be of sedimentary or 321 of tectonic origin as discussed below (sect. 5). 322

Structures 323
Syn-to post-metamorphic structures are observed within the marbles and at their contacts with 324 the surrounding units. Of particular interest is the lower contact of marble lens 2a (Fig. 5), which 325 within a few square meters shows, i) a marble bed unconformably overlying the kinzigites of the Beni 326 Bousera Unit, and ii) two juxtaposed, northwest-ward verging kinzigite-marble duplexes (Fig. 7A). 327 on the other bank of Oued Amter (Fig. 6C) or at outcrop 1b (Fig. 8C, D). In contrast, the upper limit of 329 lens 1c (Fig. 5) shows superposed gneiss, kinzigite and marbles bodies sheared beneath the Filali 330 gneiss unit. There, over some tens of meters along the slope, the boudinage of gneissic mylonites (Fig.  331 S1 in Supplementary Material, SM) in the juxtaposed calc-mylonite (Fig. 7B) and the ductile, 332 asymmetric folding of previously boudinaged silica-rich beds (Fig. 7D) are observed. Two types of 333 folds are illustrated within the same marble lens 1c: i) isoclinal recumbent folds (P 1 ) whose axial-334 planes coincide with the main foliation S m = S 0 -S 1 (Fig. 7C), and ii) open, upright folds (P 2 ) that 335 deform Sm (Fig. 6B). In more massive marbles, syn-D 2 crenulation cleavage and brittle-ductile 336 microfaults contribute to flattening of the main foliation, which again parallels bedding S 0 (Fig. 7E). 337 Both the ductile and brittle-ductile structures are overprinted by place by late, east-trending brittle 338 faults with gouge ( Fig. 7F) or breccia and striated mirror (Fig. 8E). 339 The JN outcrop at the source of Oued Jnane Nich (Fig. 4 for location) displays a complex 340 structure involving both kinzigitic and calc-mylonitic sheets (Fig. 7G). These alternating sheets feature 341 isoclinal folds and sheath folds deformed by late, but still ductile open folds. The core of the major 342 isoclinal fold is filled by a calc-mylonitic meta-breccia that contains small shreds and fragments of 343 kinzigite-like material (Fig. 7H). 344 In the Oued Ljouj outcrop (OL, Fig. 4), the marbles are reduced to shreds in the shear zone 345 beneath the Filali gneisses. Some lens-shaped blocks of siliceous marbles can be seen in a sheared 346 kinzigite matrix (Fig. 8A-B). 347 To summarize, the marbles and the intercalated kinzigite and gneiss bodies (duplexes or slivers) 348 that delineate a decametric corridor at the base of the Filali gneisses are all marked by strong ductile 349 deformation ( Fig. S1 in SM), which justifies the name we proposed above for this major contact, i.e., 350 Filali-Beni Bousera Shear Zone (FBBSZ). In the kinzigite slivers, ductile deformation is characterized 351 by recrystallised quartz ribbons, elongate garnet and feldspar porphyroclasts with typical core-and-352 mantle structure due to dynamic recrystallization. 353 5, 9B). In the FBBZ, kinematic criteria such as asymmetrical folding or C/S structures are indicative 355 of thrusting toward the west (Fig. 7A, B, D; Fig. 8). 356 The data plot collected from different stations shows that the main foliation and marble bedding 357 (Taza marbles) trend NW-SE with an opposite dip consistent with the Beni Bousera anticline (Fig. 9  358 A). Three sets of folds are observed at the regional scale, NW-SE, NE-SW, and E-W ( Fig. 9 C), 359 reflecting late polyphase FBBSZ activity 360 361

Petrology 362
The marbles frequently display alternating beds of pure and silicate-rich facies (Figs. 6, 7), which 363 demonstrates unequivocally their sedimentary origin (Kornprobst, 1974). The critical problem to 364 tackle within the marble samples is to distinguish clastic from metamorphic minerals. A sketchy 365 description of samples is given in Table 1 and we address below four main rock types: conglomeratic 366 marble, standard calcite marble, dolomite marble and siliceous marble. 367

372
Of particular interest is the layer marked with a red star in Fig. 6C. A clastic input is undisputable 373 for this bed as the 30 cm-thick layer contains pebbles of 0.5-4 cm in diameter (Fig. 6D). In sample 374 MTS5 from this layer, the pebble studied (Figs. 10, 11A) comprises a minor quartz-rich part with 375 plagioclase (~An 60 ) and diopside (XMg = Mg/(Mg+Fe) ~ 0.7) and a main part bearing a complex 376 assemblage of K-feldspar, sodic plagioclase, diopside (XMg = ~ 0.7 to 0.4), quartz, titanite, garnet (ca. 377 Alm 53 Grs 29 Prp 16 Spe 2 ), allanite, zircon (with small rounded quartz + plagioclase + K-feldspar 378 inclusions), apatite and late prehnite and pumpellyite. The matrix around the pebble is a recrystallized 379 calcite groundmass containing rounded clasts (?) of K-feldspar, finely polycrystalline globular 380 aggregates of a low-birefringence, Al-free and Si-rich Mg-silicate with an Mg/Si atomic ratio close to 381 latter commonly showing a thin rim of grossular garnet and/or clinozoisite. A conspicuous reaction 383 rim developed around the pebble, essentially along its quartz-rich part (Fig. 10). The rim comprises 384 quartz-calcite intergrowths (former wollastonite?), K-feldspar, sodic plagioclase and diopside in a 385 fine-grained groundmass of Mg-Si-rich sheet-silicate (palygorskite?). 386 In a more common, less obviously metadetrital marble type such as sample SR123, collected ~50 387 m to the north of MTS5 along the same outcrops of the Oued Amter dirt road south of Taza, a coarse-388 grained calcite groundmass bears abundant phlogopite lamellae and minor scapolite (Fig. 11B), 389 titanite, diopside, and graphite, with accessory pyrrhotite and zircon, and rare thorian uraninite. 390 Titanite is Al-F bearing (up to ~20 mol% CaAlSiO 4 F) and consistently shows reddish-brown to 391 colorless inverse pleochroism. Similar samples may bear less or no phlogopite in the calcite matrix but 392 commonly contain isolated K-feldspar grains (clasts?) and, less commonly, isolated quartz grains, 393 usually rimmed by diopside or (e.g., Jnane Nich, Fig   shapes, usually rounded and light, whereas overlying rims are darker, have no internal structure or just 453 a weak zonation (Fig. 12). 21.58 ± 0.18 Ma (MSWD = 2.6) for the 207-correction method (Fig. 13A3); all ages are within errors 464 of the intersection age. These Alpine ages were obtained in either uniform grains (Fig. 12, zircon 1) or 465 the outer rims of older cores (Fig. 12, zircon7). 466 Ages older than the Alpine orogeny range from ~250 to ~700 Ma and form three poorly defined 467 clusters (Fig. 13A1, A2). The first and best defined comprises 7 points in the range of 250-283 Ma, 468 yields a mode of ~270 Ma, and represents the main relict population. A further 8 points fall in the 469 range of 420-515 Ma (Fig. 13A1, A2). Two analyses, younger than 250 Ma and near concordant ages, 470 likely resulted from lead loss and/or mixed ages between a 270 Ma core and a very close to concordia 471 21 Ma rim. These older than Alpine ages were obtained in entirely inherited zircons (Fig. 12, zircons 2  472 and 3) or in inherited cores that were partially transformed during Alpine metamorphism (Fig. 12,  473 zircons 4, 5, 6, and 7). 474

MTS 6 475
Zircon grains from this sample form medium to long prismatic morphologies with rounded 476 pyramidal terminations and average 100-150 μm length. They are light-colored, clear and free of 477 inclusions or fractures. Under CL (Fig. 12), most appear as uniform light grey grains with no internal 478 structure or just with faint oscillatory zonation. Some of these zircons contain a relict inner core, 479 which is usually rounded and, in many cases, too small for analysis. Other zircons are darker, with or 480 without zonation, and most contain an irregular inherited core (Fig. 12). These Alpine ages were obtained in rims mantling inherited cores (Fig. 12, zircons 1, 2, 3, and 6) or 490 rarely in almost entirely transformed, Alpine grains (Fig. 12, zircon 8). 491 Pre-Alpine ages are mainly Permo-Triassic, but there is a small Carboniferous population, and 492 older isolated points (Fig. 13B1, B2). Permo-Triassic ages are, by far, the more abundant in this 493 sample. Thirty-one analyses fall between 227 and 290 Ma and yield a mode of 270 Ma with a 494 weighted mean 206 Pb/ 238 U age of 266 ± 7 Ma. The distribution of this population is not symmetric, 495 being tailed to the younger ages. This explains the high error of the average. These ages are found at 496 any location inside the grains: in unzoned grey rims over inherited cores of different ages (Fig. 12, 497 zircons 4, 5, and 7), in relict cores mantled by Alpine rims (zircons 1, 3, and 6) or even in entirely 498 uniform grains. The Carboniferous population comprises a small, nearly concordant but not very 499 consistent cluster peaking at ~340 Ma (Fig. 13B1, B2). These ages always appear in inherited cores of 500 variable size and shape, mantled by Permo-Triassic, or less frequently, by Alpine age rims (Fig. 12, 501 zircons 2 and 4). 502

MTS 18 503
Zircons from this sample are short to medium, prismatic or round, always with rounded 504 terminations, and are, generally, relatively short (averaging <100 μm). Most of the grains are 505 heterogeneous in age, with discordant rims over irregular cores. A few are uniform, with no internal 506 structure (Fig. 12). Fifty-seven analyses were performed in rims and cores of 52 grains. Eleven had a 507 discordance >10% and were rejected for age calculations. The remaining 46 analyses show a 508 polymodal distribution with a main peak at ~273 Ma, smaller peaks at ~457, 584, 813 Ma, and isolated 509 old ages up to 3088 Ma (Fig. 13, C1 and C2). No Alpine ages are recorded in this sample. Fifteen 510 analyses plot in the range of 220-320 Ma and define a wide cluster yielding a mode at 273 Ma and a 511 weighted mean 206 Pb/ 238 U age of 273 ± 14 Ma. This population shows a symmetric distribution, so 512 mode and mean are coincident, but the mean age error is large because of the high dispersion. These 513 grains (zircons 4, 5, and 8). Between 350 to 700 Ma ages plot in an almost continuum, with small and 515 poorly defined groups having low statistical significance. A separate small group of analyses peak at 516 813 Ma. These pre-Permian ages are mainly found in inherited cores (Fig. 12, zircons 2, 6, 7, 9, and 517 10) and rarely in entire grains. 518

5.
Interpretation and discussion layers whose texture and mineralogy are compatible with a detrital origin (Fig. 11C). In contrast, the 533 northern, lower part of the marbles displays mingled kinzigite-like and calc-mylonite sheets folded 534 together (Fig. 7G), which may be explained by the occurrence of calcareous beds within the pelitic 535 protolith of the kinzigites. However, at this time, we prefer a hypothesis involving tectonic mingling 536 during the HT mylonitic deformation that prevails along the FBBSZ. 537 Secondly, a sharp, unconformable contact is observed in two outcrops (marble lenses 1a and 2a, 538  (Figs. 6C, 7A). 539 unconformities or low-angle detachment contacts. In any case, these contacts are at odds with a 541 hypothesis of initial continuity between carbonates and pelites before the granulite-facies 542 metamorphism that affected the kinzigites during the Variscan orogeny (Rossetti et al., 2020). whereas the absence of corundum is logical in case they had only an Alpine history. We did not find 560 corundum, nor was it reported by Kornprobst (1974). This is regarded as tentative, but not compelling, 561 evidence for a simple prograde low-P evolution of the marbles. In any event, the main forsterite + 562 calcite assemblage developed in spinel dolomite marble is consistent with the LP-HT conditions of an 563 Alpine imprint. 564 Therefore, based only on these geological/mineralogical arguments, we assume that the BBMs 565 were derived from a sedimentary formation younger than the granulitic envelope of the Beni Bousera 566 The sedimentary lithology of the carbonate formation is therefore characterized by shallow 581 marine facies, such as dolomitic limestones and dolostones, sandstones, clastic limestones with 582 sandstones layers and rare argillites. The coarse clastic, pebbly marbles located just above one of the 583 marbles basal contacts (Fig. 6C), apparently support the notion of unconformable sedimentation on top 584 of the kinzigites. However, the K-feldspar clasts and the pebbles bearing quartz, K-feldspar and 585 almandine may have a different origin than the underlying kinzigites, possibly a source similar to the 586 Filali garnet-bearing gneisses. As for the globules of palygorskite/sepiolite scattered in some of the 587 clastic marbles (e.g., Fig. 11A), they could form from the retrogression of metamorphic forsterite (Fo 588 98% in sample MTS13; Table 1) rather than from detrital olivine sourced from the peridotites (Fo 589 90%; Obata, 1980). Therefore, in contrast to it being previously expressed (Saddiqi et  several mountains named after their white cliffs, such as the Sierra Blanca and Sierra de Las Nieves 600 (see Fig. 16 below). These carbonate series are less recrystallized in units to the east than in the west. 601 In the eastern Alpujarrides nappes, the Sierra de Gador (Fig. 1 for location)  Bousera-Ronda units belong to the typical Alpujarride-Sebtide domain, we may at first suggest a 612 Middle-Late Triassic age for the BBMs. However, the occurrence of younger deposits (Early 613 Jurassic?) cannot be excluded for thinly-bedded facies such as those illustrated in Fig. 6B. 614

Zircon dates 615
The SHRIMP U-Th-Pb analyses of zircon collected from three marble samples at different 616 outcrops in the Taza and Inoualine areas (Fig. 5, outcrops 1a, 1c, 2b)  number of zircon grains and is considered tentative. Therefore, we maintain that the ~270 Ma peak 646 recognized in the core of the zircon grains from the BBMs is not a metamorphic age, but rather the 647 above proposal of a Triassic age for most of these protoliths. 649 On a kilometer scale (Fig. 4), the contact between the Beni Bousera kinzigites and the Filali 657 gneiss, namely the FBBSZ, is a syn-metamorphic low-angle thrust fault locally assisted by the high 658 ductile properties of the calc-mylonites (see the classic example of the Jurassic calc-mylonites beneath 659 the Helvetic nappe of Glarus; Ebert et al., 2007). In contrast, due to the strong metamorphic and 660 tectonic overprint, the nature of the sharp contact locally observed between the marbles and the 661 underlying kinzigites is somewhat ambiguous. As mentioned previously (sub-sect. 5.1), there may be 662 two alternative interpretations to explain this relationship, either stratigraphic or tectonic. Accordingly, 663

Early exhumation of the Beni Bousera peridotites
we propose hereafter two alternative scenarios for the early exhumation of the peridotites (Fig. 14).  For the first possible hypothesis (Fig. 14A), we assume that the kinzigites were exposed (and then For the second possible hypothesis (Fig. 14B), we refer to the hyperextension models of the Adria 676 Ghomarides, at the northern border of the Maghrebian Tethys (Fig. 15B, location is shown in Fig.  715 15A). This proposal is consistent with the nature and moderate thickness of the crustal rocks that form 716 the Alpujarrides-Sebtides basement, i.e., a few thousand meters of schists, gneiss, and granulites 717 affected by high-grade Variscan metamorphism (see also Whitehouse, 1999, 2002;Sánchez-718 Navas et al., 2017). In this framework, the occurrence of Triassic unconformable deposits or rafts 719 upon the Beni Bousera granulites, as proposed above (Fig. 14), is likely. We assume that the al., 2020) and is also recorded in the BBMs (Fig. 7F). Two areas of the Ronda peridotite massif could be candidates for similar settings, i.e., the southern 758 part of the massif (Estepona-Benahavis-Guadaiza area) and its frontal part at the contact with the Las 759 Nieves carbonates (Fig. 16). Sierra Bermeja massif at their contact with the Nieves unit (Fig. 16). The latter is a ~1500 m thick, with the Ronda peridotites can presently be used to corroborate or refute the notion of an early 805 exhumation of the Beni Bousera peridotites as presented in this paper. 806

807
The Pyrenees offer a remarkable example of an orogen with subcontinental mantle rocks (e.g., the 808 famous lherzolites of Lherz) exhumed during the opening of an axial rift, which was later mildly 809 inverted (Fig.17). Nowadays, this rift and its paleomargins correspond to the North Pyrenean Fault In Calabria (Fig. 1, insert; Fig. 2B), the easternmost equivalent of the Alboran Domain is widely 845 exposed in the Sila and Serre crustal massifs that overlie the ophiolitic Ligurian units (Rossetti et al., 846 2001;Vitale and Ciarcia, 2013). The sedimentary cover of the Sila massif is preserved and includes 847 "Verrucano"-type deposits, overlain by carbonate Triassic-Sinemurian successions followed by 848 Pliensbachian-Toarcian marly-olistolitic facies. The Middle Liassic extension is recorded by neptunian 849 dykes that penetrate down to the Paleozoic basement (Bouillin and Bellomo, 1990). The Paleozoic 850 massifs include a ~7 km-thick basal section which equilibrated in the medium-pressure granulite field 851 (Schenk, 1984). Lenticular bodies of ultramafics are widespread in the lower part of the section. 852 Siliceous marbles and calcsilicate rocks represent a minor proportion of these lower crustal rocks in 853 the form of lenses ranging in thickness from a few centimeters to several tens of meters. These 854 marbles are regarded as Paleozoic or older alike the host metapelites, whose HT-MP metamorphism is 855 In the Western Alps (Fig. 18 1995; Bianchi et al., 2003;Pelletier et al., 2008). These mantle rocks are exposed in the overturned 880 Monte Leone nappe of the Simplon culmination (Fig. 18). When restored to their pre-orogenic 881 position, these peridotites appear to be overlain by a thinned gneissic crust, which is covered by early 882 syn-rift Triassic sediments and younger syn-rift breccias (Fig. 19). Thus, the restored Geisspfad setting 883 is strongly suggestive of the possible Beni Bousera setting prior to Alpine events. 884

885
In Corsica (Fig. 18), the transition zone between the European margin and the Ligurian Tethys is 886 exposed in the Santa Lucia nappe, which shows a 2-4 km thick layered "Mafic Complex" whose base

898
The BBMs are exposed in small outcrops around the granulitic envelope (kinzigites) of the Beni 899 Bousera subcontinental peridotites. Despite their modest extent, a study of these marbles leads to 900 revisiting current models that interpret the exhumation of the Gibraltar Arc mantle rocks as a basically 901 Cenozoic process. 902 The marbles are not intercalated in the kinzigites, but rather pinched within a mylonitic thrust 903 contact between the kinzigites and the overlying Filali mid-crustal unit. The Filali-Beni Bousera Shear 904 Zone (FBBSZ) can no longer be considered as extensional and equivalent to the deeper Kinzigites-905 Peridotites Shear Zone (KPSZ). The protoliths of the most typical BBMs formed a series of sandy and 906 sometimes pebbly carbonates, dolostones, and magnesian limestones locally interlayered with 907 argillites. They are comparable with the Triassic series of the less recrystallized Alpujarrides-Sebtides 908

units. 909
Zircons from the BBMs exhibit cores of detrital origin with rim overgrowths dated at ~21 Ma. 910 The youngest age cluster from the cores peaks at ~270 Ma, which suggests the erosion of Middle 911 Permian magmatic sources, and supports a Triassic age for the marble protoliths. 912 At this stage, we consider two alternative explanations for the presence of these marbles in the 913 FBBSZ: either the likely Triassic beds were deposited unconformably onto the kinzigites, or they were 914 emplaced as extensional allochthons above the detachment allowing the granulitic crust to be exhumed 915     to the peridotites, whereas those on the right belong to a second-order sliver included in the FBBSZ. 1552 The unconformable contact below the marbles looks like a stratigraphic unconformity, but could 1553 alternatively be a low-angle fault. D: Close view of the metaconglomeratic marble bed, ~1 m above 1554 the base of the marbles (red star in C). E: View of the uppermost part of the Oued Jnane Nich marbles 1555   Fig. 6D. S m : regional foliation molded on the pebble in the pressure shadow. The matrix is 1587 calcite-rich, whereas the pebble shows a feldspar-rich brownish part and a quartz-rich, lighter layer. 1588 The dark, foliated aureole (rim) around the pebble mainly consists of quartz-calcite intergrowths. 1589       The natural cross-section is overturned (Monte Leone nappe). See location in Fig. 16.