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Geological studies and tomographic profiles of a locality nearby the Agoudal village (Morocco) showed the presence of a single impact crater, 500–600 m diameter, largely hidden by a limestone block, 220 m long and 40 m deep. The site was interpreted as a landslide that followed the fall of a cosmic body. The Agoudal impact crater was not affected by intense erosion. The lack of an evident impact structure, as well as the sporadic distribution of impactites and their limited occurrence, can be explained by a complex geological framework and by recent tectonics. The latter is the result of the sliding of limestone block, which hides almost two-thirds of the crater's depression, and the oblique fall of the meteoroid on sloping ground. In addition, some impact breccia dikes sharply cut the host rock in the Agoudal impact structure. They do not show any genetic relationship with tectonics or hydrothermal activity, nor are they related to any karst or calcrete formations. Altogether, the overlapping of the meteorite strewn field (11 km long and 3 km wide) with the area of occurrence of shatter cones and impact breccias, together with the presence of meteorite fragments (shrapnel) ejected from the crater, the presence of shatter cones contaminated by products of iron meteorites and the presence of impact breccias that contain meteorite fragments of the same chemical composition of the Agoudal meteorite indicate that the fall of this meteorite can be responsible for the formation of the impact structure.

Isli and Tislit, the Moroccan “Romeo and Juliette” according to a popular legend gave their name to a twin lakes in Imilchil. There we show evidences that these two lakes are impact craters. The proof as follow: 1) the fragments of iron meteorites found on both sides of Isli and Tislit lakes belong to the same parent meteorite and siderite type; 2) the sedimentary formations which are almost tabular in the area of the lakes become tilted with a centripetal sloping all around and towards Isli lake; 3) the circular shape of the Tislit lake is similar to that of the Isli lake; 4) the impact breccias found on the south of the Isli lake contain shocked quartz crystals; 5) the radial fractures of high pressure affect some sedimentary beds. All these observations give evidence of the presence of an impact crater due to the fall of meteorites.

The ternary diagram TiO 2 –FeO*–MgO (FeO* = FeO + MnO) is proposed as a quantitative objective tool for distinguishing between primary magmatic biotites and those that are more or less reequilibrated, or possibly neoformed, by or within a hydrothermal fluid. The limit of the domains of the primary magmatic biotites, the reequilibrated biotites and the neoformed biotites were determined on the basis of optical, paragenetic and chemical criteria. To cite this article: H. Nachit et al., C. R. Geoscience 337 (2005).

Extremely high abundances of BaO (up to 21.46 wt. %) and TiO 2 (up to 13.85 wt. %) are reported from brown phlogopite in calcite carbonatite inclusions from Jbel Saghro, Anti-Atlas Morocco. The substitution of Ba into the phlogopite structure can be explained by the scheme [12] Ba + [4] Al ⇔ [12] K + [4] Si. At least 50 % of the K on the interlayer sites of phlogopites from Saghro is replaced by Ba. The incorporation of Ba into phlogopite allow the occurence of kinochitalite phases. Al compensates for tetrahedral Si deficiencies, and Ti is probably limited to octahedral substitution for Mg and Fe. A substitution scheme of the type Ba 2+ + 2Ti 4+ + 3Al 3+ ⇔ K + + 3(Mg, Fe) 2+ + 3Si 4+ is proposed.

Zircon U–Pb data on post-tectonic granites that have intruded the Precambrian formations of the Kerdous inlier (western Anti-Atlas, Morocco) are Pan-African. Zircon grains from a syntectonic monzodiorite of the Tahala pluton yield a precise discordia line with an upper intercept at 2043.9 ± 1.8 Ma (MSWD = 0.67) interpreted as the emplacement age. This age is consistent with zircon U–Pb ages of granites from other inliers and confirms the existence of a widespread magmatic event at ≈2045 Ma in the Anti-Atlas. The Pan-African event left no resolvable imprint on the isotopic systems of the analysed zircons. The Kerdous Schists are, therefore, older than 2045 Ma. Rb–Sr and Sm–Nd data on the schists and the Tahala pluton suggest that both juvenile and Archaean material contributed to the generation of the Palaeoproterozoic formations in the Anti-Atlas.

Extremely high abundances of BaO (up to 21.46 wt. %) and TiO2 (up 13.85 wt. %) are reported from brown biotite in calcite carbonatite inclusions from Jbel Saghro, Anti-Atlas Morocco. The substitution of Ba into the biotite structure can be explained by the scheme Ba + Al ↔ K + Si. At least 50 % of the K on the interlayer sites of biotites from Saghro is replaced by Ba. Al compensates for tetrahedral Si deficiencies, and Ti is probably limited to octahedral substitution for Mg and Fe. A substitution scheme of the type Ba + 2Ti + 3Al ↔ K + 3(Mg, Fe) + 3Si is proposed.

The analysis by electron microprobe allows the evaluation of the quantity of Fe 3+ in spinels with considerable errors. The use of a correction equation which is based on a the calibration of analyses with an electron microprobe in relation to those carried out with Mossbauer spectroscopy gives more precise evaluations of Fe 3+ . In fact, it allows a calculation of the oxygen fugacity in peridotitic xenoliths. The obtained results show that peridotites of the French Central Massif crystallised under oxygen fugacities which were higher than those of the Moroccan AntiAtlas.

Summary In alkaline lavas, the chemical zoning of megacrystals of spinel is due to the cationic exchange between the latter and the host lava. The application of Fick's law to cationic diffusion profiles allows to calculate the time these crystals have stayed in the lava. Those which are in a chemical equilibrium were in contact with the lava during 20 to 30 days, whereas megacrystals lacking this equilibrium were in contact only for 3 or 4 days. The duration of the rise of an ultrabasic nodule in the volcanic chimney was calculated by applying Stokes' law.

New meteorite prospections at different places in the region of Imilchil showed that (1) besides the Ataxite of Tasraft all the other collected specimens belong to the same and only IIAB iron mother meteorite (2) the strewn field of the meteorite has a length of about 38 km into north-south direction (3) the small crater of Agoudal as well as the impact crater of Isli are situated on a parallel north-south axis, if not put together with the strewn field of the Imilchil meteorite (4) these two structures might be the result of the fall of the same and only mother meteorite of the IIAB type.

We discuss the significance of igneous layering with respect to pluton growth processes. The case study is the Tarcouate Laccolith (Morocco), whose core consists of modally layered hornblende granodiorites with high amount of monzodioritic enclaves, contrasting with peripheral, non-layered biotite granodiorites with low amount of enclaves. Rhythmic layering, with modal grading, cross-stratification and trough layering is associated with monzodioritic layers and wraps around mafic enclaves. Its steep dips ≥ 45° result from tilting that occurred above solidus conditions, as indicated by sub-vertical and synmagmatic granite, aplite and monzodiorite dykes cutting across the layering. The systematic association of igneous layering with mafic enclaves in calc-alkaline plutons suggests that layering originates from recurrent injection of mafic magma. Viscosity calculations suggest that the physicochemical properties of magma alone cannot account for the presence of layering in the central hornblende granodiorite and its coeval absence in the peripheral biotite granodiorite of the Tarcouate Laccolith. Intermittent pulses of hot mafic magma into crystallizing granodiorite likely produced thermal perturbations able to trigger local convection, formation of mafic enclaves and development of igneous layering through protracted crystallization.

The Tarcouate pluton (Anti-Atlas, Morocco) is an inversely zoned laccolith emplaced 583 Ma ago into low-grade metasediments, with the following succession: leucocratic granites, biotite–granodiorites (±monzodiorites), hornblende–granodiorites (±monzodiorites) and monzodiorites syn-plutonic dykes. These rocks form two distinct, chemically coherent, units: (1) A main unit consists of layered (57

From Barrois (1884) to Barriere (1980) it is has been classical to divide Armorican Granites into three main units (Fig. 1): 1. A leucogranite belt which extends from the Pointe du Raz to Bressuire and Parthenay, emplaced during activity on the South Armorican Shear Zone (SASZ, Cogne 1960) and of its subsidiary faults. 2. A red-granite belt which extends along the northern shore of Brittany from Aber Ildut to the Cotentin Peninsula over 300 km in length. In its western part, it is parallel to the Porspoder-Guisseny mylonitic zone (Chauris 1965). 3. Middle-Armorican Batholith, with large elliptic plutons of porphyritic gray granites, extending westwards from the Mancellia Cadomian formations, emplaced during activity on the North Armorican Shear Zone (NASZ, Hirbec 1979).