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Trabajo presentado en el 2nd International congress on Permian and Triassic, celebrado en Casablanca (Marruecos), del 25 al 27 de abril de 2018, The Permian volcanism of the Eastern Rehamna massif (Western Meseta) displays two large outcrops: (i) Mechra Ben Abbou to the N and (ii) Benguerir to the S. The volcanism of Mechra Ben Abbou is often interbedded in Stephanian/Autunian sandstones/conglomerates (e.g., Gigout, 1952; Hoepffner, 1982; etc.), and appears as massive/fluidal andesitic lava flows and rhyolitic domes (e.g., the Bled Mekrach garnet-bearing rhyolitic dome). The thickness of these volcanics varies from a few tens of to 500 meters depending on their proximity to the effusive centers. The latter are situated either on/near the N40E lateorogenic dextral strike-slip Wadi Tarfa fault (Hoepffner, 1982) or along the half-graben bounding the Nahilat normal fault (e.g., El Kamel and Muller, 1987; Muller et al., 1990). In the southeastern Rehamna, east of the Benguerir City, there are also massive/fluidal lava flows (andesites) and isolated volcaniclastics overlying the Autunian conglomerates (similar to those of Mechra Ben Abbou). Rhyolitic domes intruding andesitic lava flows with mingling structures at their interface also occur, showing that the rhyolitic domes and the andesitic, ava flows were synchronous (Baudin et al., 2003). Another outcrop of andesitic lava flows overlies an hercynian outcrop (the Jbel Kharrou structure). Late-Hercynian microgranite and microdiorite dyke swarms and sill complexes are also present in Rehamna trending N-S to N30 (more rarely N90 to N130; Gigout, 1952; Hoepffner, 1982; etc.). They fill subvertical fractures (dykes) or more frequently cleavage (sills) with thicknesses varying from 1 to 10 m (reaching 20 m). They can be lenticular over a few meters or extend over several kilometers (Hoepffner, 1982). They were emplaced after the lower Permian molasses and before the Triassic: they intrude the Rehamna granite (268 ± 6 Ma; Mrini et al., 1992) and do not crosscut the Triassic cover. One of these dykes penetrates an overlapping contact affecting the first Permian detrital deposits of Formation 1. This overlapping fault is sealed by the last terms of this Formation (El Kamel and Muller, 1987, Muller et al., 1990). The microgranitic dykes display intraplate and calco-alkaline affinities and were emplaced at 285.4 ± 6.1 Ma (Baudin et al., 2003; Bensalah, 2012). We provide new insights into the mineralogy, geochemistry and geochronology of the Rehamna volcanism affecting the northwestern Gondwanaland Permian margin. The studied volcanics are typical orogenic calc-alkaline magmatism. The origin of garnet in the Bled Mekrach rhyolites (phenocrysts, xenocrysts, restites, or secondary reaction products) will be discussed on the basis of their textures, mineral relationships and chemistry data. We determined U-Pb zircon ages by Sensitive High-Resolution Ion Microprobe (SHRIMP) on the Bled Mekrach garnet-bearing rhyolitic dome. The sample BM 20 (GPS: 32°38'19.21"N, 7°45'5.23"W) yielded two predominant ages (611 ± 20 Ma and 285.3 ± 4.9 Ma): the last age is more concordant, being interpreted as the age of crystallization of rhyolites, while 611 Ma indicate inherited zircon that is sourced from the Pan-African crust under the Rehamna. The 285 Ma rhyolite age is very similar to that one obtained on the microgranitic dykes.

Trabajo presentado en el 2nd International Congress on Permian and Triassic, celebrado en Casablanca (Marruecos), del 24 al 27 de abril de 2018, The NE-SW Tsesdai basin (110 km to the SE of Rabat) is the third largest Late Palaeozoic continental trough in the northern Central Moroccan Meseta. It is, (i) the volcanic complex is Permian s.l. (post-Carboniferous and pre-Triassic, presumably Stephanian/Permian) a percept based on (a) the intrusion of rhyolites into the Visean deep marine siliciclastics of the basement (shark-fin rhyolitic dome of Ari el Mahsar extrusive and its satellite dykes); (b) the angular unconformity between the red detritic sediments and the Visean siliciclastics folded during the late Westphalian A; (c) the presence of reworked rhyolitic/andesitic pebbles in the red sediments of the Tsesdai basin and their absence in the detrital sediments of the Westphalian C/ D preserved nearby in the Sidi Kacem graben; (d) the angular unconformity between the Triassic and the red detritals; and (d) strike-slip fault that postdates the basin sedimentary/volcanic formations and predates the Triassic/Cenozoic. (ii) the distinction of 3 major volcanic pulses: the first one (mainly andesitic) predates the Permian series; witnesses of this pulse can still be observed in Tiddas, but most material is reworked in the conglomerates; the second pulse is synsedimentary, displays different petrographic characteristics, and it is remarkable for its andesitic lava flows interbedded with the detritals. The third pulse of intrusive rhyolitic dykes precedes the Ari el Mahsar rhyolitic dome emplacement and the dacitic flows. (iii) identification of three intra-permian tectonic events. The close relationship between volcanism and fracturation is obvious: dykes and effusive centers are located in relation with N40-N70 faults, mostly strike-slip. We present new insights on the petrology and geochronology of the Tsesdai Permian volcanism affecting the northwestern Gondwanaland margin. The studied volcanic has typical orogenic calc-alkaline signatures. For the last volcanic pulse we determined U-Pb ages of zircon by Sensitive High-Resolution Ion Microprobe (SHRIMP). The shark fin rhyolitic extrusive dome of Ari el Mahsar (sample ARM15/GPS: 33°39'51.48"N, 6° 4'2.06"W) yielded two predominant ages (603 ± 25 Ma and 286.4 ± 4.7 Ma): the young age is more concordant, being interpreted as the crystallization age of rhyolites, while

The lithospheric architecture of Africa consists of several Archean cratons and smaller cratonic fragments, stitched together and flanked by younger fold belts. The three larger cratons (West Africa, Congo and Kalahari Cratons) are underlain by Sub Continental Lithospheric Mantle (SCLM) extending to ≥300 km depth and having a prevailing depleted composition. Three series of spinel peridotite xenoliths from Waw-En-Namus (Libya; LB hereafter), Tafraoute and Bou-Ibalrhatene (Morocco; MOR), Barombi Mbo and Lake Nyos (Cameroon; CA) have been investigated to provide a new knowledge of the mantle beneath North-Western Africa continent. In particular MOR and LB should reflect peri- and meta-cratonic conditions, respectively while CA are from the Cameroon volcanic line whose products outcrop within a polycyclic mobile belt. According to their chemistry, the spinels from CAM and MOR xenoliths are magmatic cumulates while LB are representatives of ambient lithospheric peridotites. From a structural point of view, the CAM and MOR spinels are rather similar having comparable cell edges and oxygen positional parameters. The cation distribution allows the determination of an intracrystalline temperature in the range 560-750 °C. Spinels from LB can be divided in two groups with very different oxygen positional parameter and cell edges. The intracrystalline temperature is 680 °C for the second. There is a similarity of Vcell between the CAM, MOR and LBI cpx (< 434 Å3) while those from LBII show Vcell >435 Å3. According to their REE contents, CAM cpx can be divided in 2 groups (depleted and enriched in LREE compared to CPX-DMM), in MOR there are two, both enriched, but with different behavior of the LREE suggesting evolutions starting from a DMM like composition. LB cpx show 4 groups, all of them being more or less depleted. The OH contents are lowest for the LB cpx (100-300 ppm H2O), while the CAM samples are intermediate (200-400 ppm H2O) and the MOR samples show the highest contents (380-610 ppm H2O). Boron is nearly absent apart from two samples (one olivine and one cpx) from CAM. The xenoliths sampled from a probably juvenile lithosphere at the edge of the Cameroon and Morocco lithospheric roots apparently have cumulus-like spinels probably crystallized in situ from percolating melts and thus do not represent a real spinel-peridotites facies; on the contrary peridotite mantle xenoliths from Libya exhibit spinels with features compatible with a slow ascent of a mantle plume. The juvenile behaviors shown by CAM and MOR spinels seem also to be reflected by the cpx-HREE patterns showing typical DMM features. As opposed, for LB ones, where very depleted HREE patterns appear, recent chemical changes seem to have been superimposed to ancient (and/or deeper?) depletion. Funding was provided by the FRA 2013 project of the Trieste University.

International audience; Surface nanosecond dielectric barrier discharge has been studied in air and at pressures ranging from 1 to 5 bar, with a coaxial geometry of the electrodes for positive and negative polarities of the high-voltage pulses. Pulses of a 24-55 kV amplitude on the electrode, positive or negative polarity, 20 ns duration, 0.5 ns rise time and 10 Hz repetitive frequency were used to initiate the discharge. ICCD images of the discharge development have been taken with a 2 ns gate. In the case of discharges in nitrogen, the emissions of molecular bands of the first negative and second positive systems of molecular nitrogen have been measured, and the dependence of their ratio versus pressure and distance from the high-voltage electrode has been analyzed. A comparison of the discharge development has been made in the case of negative and positive polarities at the high-voltage electrode. Ignition delay times under the action of a high-voltage nanosecond discharge have been studied and compared with autoignition delays in a rapid compression machine (RCM). The nanosecond Surface Dielectric Barrier Discharge (SDBD) was initiated in a quasi-uniform radial geometry in the proximity of the end plate of the combustion chamber of the RCM. Experiments were performed for methane and n-butane containing mixtures diluted by Ar or N2 for temperatures and pressures at the end of compression respectively ranging from 650 to 1000 K and 6 to 16 bar. A significant decrease of the ignition delay time is observed, when compared to autoignition experiments. The possibility to ignite lean mixtures is demonstrated. Preliminary experiments in the region of negative temperature coefficient for stoichiometric n-butane:oxygen mixture diluted with argon, are performed. The threshold voltage for plasma ignition, over which the ignition delay is decreased, is studied for different mixtures.