Reply to the comment by Michard et al. on "Evidence of extensional metamorphism associated to Cretaceous rifting of the North-Maghrebian passive margin : The Tanger-Ketama Unit (External Rif, northern Morocco) by Vázquez et al., Geologica Acta 11 (2013), 277-293"

Michard et al. (this issue) commented on certain aspects of the Alpine metamorphism and structural evolution of the Rif belt (Morocco) that were briefly noted in Vázquez et al. (2013). In particular, they criticize our interpretation of an extensional setting during the main metamorphic recrystallization of the Tanger-Ketama Unit that we considered related to slaty cleavage (S1) parallel to the lithological layering generated during the Cretaceous. Michard et al. (this issue) interpret the S1 syn-metamorphic foliation as being related to compressional folds, and the peak metamorphism temperatures, in the Lower Cretaceous sediments, as ranging between 200-300°C. Therefore, they conclude that recrystallization of the Ketama Unit occurred during Miocene thrust nappe tectonics. We explain our view in the following sections

Evidence of extensional metamorphism associated to Cretaceous rifting of the North-Maghrebian passive margin : the Tanger- Ketama Unit (External Rif, northern Morocco)

The distribution pattern of diagenetic conditions to very low-grade metamorphism in the eastern Rif has been determined based on a study of clay-mineral assemblages and illite crystallinity of Mesozoic metapelites. Low-grade conditions were reached in marbles and also in the Beni-Malek serpentinites, as suggested by the mineral assemblages present in the marbles and antigorite growth in serpentinites. Previous thermochronological data are based on i) 40Ar/39Ar in amphiboles from greenschists, ii) K/Ar in white micas from metasandstones, and iii) fission tracks in apatites and zircons from metasandstones. These data indicate a Late Cretaceous age (∼80 Ma) for the very low- to low-grade metamorphism. We propose an evolutionary model for the Tanger-Ketama Unit consisting of a Lower Cretaceous sequence deposited in half-graben basins over an exhumed serpentinized mantle in a setting similar to the West Galician non-volcanic margin. The sediments underwent diagenesis to very low-grade metamorphism under relatively high heat flow in this extensional setting. Miocene contractional deformation of the Tanger-Ketama Unit resulted in a penetrative crenulation cleavage associated to asymmetric inclined folds. This crenulation developed, mostly by solution-transfer processes, without significant mineral growth. Miocene metamorphism reset the apatite fission-tracks, but metamorphic conditions were not high enough to reset either the K/Ar ages or the zircon fission track

Evidence for surface uplift of the Atlas Mountains and the surrounding peripheral plateaux: Combining apatite fission-track results and geomorphic indicators in the Western Moroccan Meseta (coastal Variscan Paleozoic basement)

This work represents an initial attempt to link the evolution of the topography in relation to the general tectonic framework of western Morocco. For this purpose, in a section of the Western Moroccan Meseta different tools are combined in order to attain the general objective. Apatite fission-track (AFT) data of granitic rocks of the Rabat–Khenifra area give ages around 200 Ma with track length distributions which are compatible with the thermal models already established for the area. An inverse correlation between AFT ages and elevation is observed which is compatible with previous models indicating northward tilting of the whole Western Moroccan Meseta which is younger than 20–25 Ma. In order to test this possibility a detailed analysis of the topography at different scales in the Western Moroccan Meseta has been performed. Results indicate that two open folds with different amplitudes are recognized and that the one with wider wavelength could correspond to a lithospheric fold as previously stated by other authors on the basis of independent geological arguments. The northward tilting proposed based on the AFT data agrees with the results obtained in the analysis of the topography which reinforces the presence of a very open fold with a wavelength of 200–300 km in the north-western limb of the Western Moroccan Meseta

Reply to the comment by Michard et al. on “Evidence of extensional metamorphism associated to Cretaceous rifting of the North-Maghrebian passive margin: the Tanger-Ketama Unit (External Rif, Northern Morocco) by Vázquez et al., GeologicaActa 11 (2013)...

Non

Evidence of extensional metamorphism associated to Cretaceous rifting of the North-Maghrebian passive margin: The Tanger- Ketama Unit (External Rif, northern Morocco)

Articulo de publicación ISIThe distribution pattern of diagenetic conditions to very low-grade metamorphism in the eastern Rif has been determined based on a study of clay-mineral assemblages and illite crystallinity of Mesozoic metapelites. Lowgrade conditions were reached in marbles and also in the Beni-Malek serpentinites, as suggested by the mineral assemblages present in the marbles and antigorite growth in serpentinites. Previous thermochronological data are based on i) 40Ar/39Ar in amphiboles from greenschists; and ii) K/Ar in white micas from metasandstones, and iii) fission tracks in apatites and zircons from metasandstones. These data indicate a Late Cretaceous age (∼80Ma) for the very low- to low-grade metamorphism. We propose an evolutionary model for the Tanger-Ketama Unit consisting of a Lower Cretaceous sequence deposited in half-graben basins over an exhumed serpentinized mantle in a setting similar to the West Galician non-volcanic margin. The sediments underwent diagenesis to very lowgrade metamorphism under relatively high heat flow in this extensional setting. Miocene contractional deformation of the Tanger-Ketama Unit resulted in a penetrative crenulation cleavage associated to asymmetric inclined folds. This crenulation developed, mostly by solution-transfer processes, without significant mineral growth. Miocene metamorphism reset the apatite fission-tracks, but metamorphic conditions were not high enough to reset either the K/Ar ages or the zircon fission tracks

Detrital zircon U–Pb ages in the Rif Belt (northern Morocco): Paleogeographic implications

This dataset include detrital zircon U-Pb zircon age distributions in Mesozoic and Cenozoic rocks from the External Rif and Maghrebian Flysch Complex (Rif belt, Morocco) to test if they from part of the north-western African paleomargin, or if they are related to the Alpine Allochtonous Internal terranes. The data set show ages in the text, tables, and figures. The ages are quoted as 206Pb/238U dates for zircons younger than 1500 Ma and as 207Pb/206Pb dates for zircons older than 1500 Ma. Figures include the U–Pb concordia and the youngest zircon population plots for the studied samples. Zircons were separated using standard heavy-liquid and magnetic techniques in the Department of Geodynamics of the University of Granada. Grains were handpicked and mounted in epoxy, polished, cleaned and gold coated for cathodoluminescence (CL) imaging on a Mira3 FESEM instrument at the John de Laeter Centre (JdLC), Curtin University, Perth, Australia. LA-ICP-MS data collection was performed at the GeoHistory Facility, JdLC, Curtin University, Perth, Australia

Origine, qualité chimique et normes législatives des eaux de sources et des eaux minérales embouteillées au Maroc

International audienc

Origine, qualité chimique et normes législatives des eaux de sources et des eaux minérales embouteillées au Maroc

International audienc

Origin of Bentonite Deposits in the Eastern Rif Belt (morocco): Constraints From New Mineralogical, Geochemical and Stable Isotopic Data

The eastern Rif Belt in Morocco represents an important economic region in North Africa due to its extensive bentonite deposits. This study aimed to elucidate the formation processes and mechanisms of Providencia bentonite deposits, classified as yellow and white bentonites, surrounding the Upper Miocene rhyolitic Tidiennit Massif. Multidisciplinary approaches, integrating structural, lithostratigraphic, mineralogical, petrographical and geochemical analyses have been utilized to examine the properties of the bentonites and precursor (host) rocks. The X-ray diffraction analyses of the tuffs, perlites and rhyolites show that the presence of smectite, feldspar, amorphous silica (Opal-A and Opal-CT) and biotite in tuffs, feldspar, quartz, cristobalite and pyroxene in rhyolites, and amorphous silica, pyroxene, feldspar in perlites. The clay fraction patterns of yellow and white bentonites indicate the bentonites are composed of pure or nearly pure dioctahedral (Al-rich) smectite minerals. The characteristic bands observed in Fourier transform infrared spectroscopic analyses were also confirmed the presence of Al-rich smectites in the bentonites. The thermogravimetric and differential thermal analysis data show a total mass loss of 15.7% and 18.13%, and endothermic peaks of 698 °C and 678 °C representing the smectite from white and yellow bentonite, respectively. The major element concentrations indicate the sub-alkaline series, and the composition of dacite to rhyolite for tuffs, whereas rhyolite for perlites and rhyolites. The alteration index (AI) and the chlorite-carbonate-pyrite index (CCPI) data suggest a clear trend towards argillization of the volcanic tuffs surrounding the Tidiennit Massif. The chemical compositions of bentonites and precursor (host) rocks show an increase in Fe2O3, MgO, Al2O3, TiO2, P2O5, Nb, Y, Zn, Zr, total REE from rhyolites-perlites via tuffs to bentonites. The immobile element (Zr, Ti, Nb, Y in ppm) compositions of the bentonites represent a subduction zone (syn-collision and volcanic arc granites) environment. Bentonites and host rocks exhibit a negative Eu anomaly with respect to the chondrite and upper continental crust composition indicating the chemical fractionation from the rhyolitic/rhyodacitic source rocks through removal of Eu by plagioclase fractionation in a reducing environment. The structural formulas of smectites in yellow and white bentonites indicate the montmorillonite-beidellite series of smectite composition. The δ18O and δD isotope data of the smectites show that bentonitization was formed as a result of hydrothermal alteration (hypogene origin) of tuffs interacting with hydrothermal fluids at temperature conditions of 127–165 °C for yellow bentonites and 153–174 °C for white bentonites. Oxygen and hydrogen isotope compositions of smectite-forming fluids indicated that yellow bentonites formed from fluids with a relatively high magmatic water component, and subsequent dilution of the hydrothermal fluids, primarily composed of meteoric waters, caused the formation of white bentonites (re-bentonitization). The obtained data indicate that the bentonite deposits are the result of heat flux transmission to the host by conduction and triggering of a convective geothermal circuit facilitated by extensive tectonics favoring hydrothermal fluid circulation. The hydrothermal fluids, that migrated across the N-NE oriented normal faults, were mainly controlled the formation of the bentonites. © 2025 Elsevier Lt

Datación por trazas de fisión de circones rosados asociados a la secuencia volcano-sedimentaria de Irra (Caldas)

Volcaniclastic sequences, mainly andesitic, belonging to the Irra Formation. Member B. crop out in the eastern margin of the Cauca River west of Manizales. Fission track dating of pink zircons yields ages close to the Miocene-Pliocene limit and indicate volcanic activity intermediate between the Combia Formation (10-8 Ma) and the base of the Ruiz-Tolima Complex (4 Ma).Secuencias volcanoclásticas predominantemente andesiticas pertenecientes a la Formación Irra, miembro B. afloran en la margen Oriental del Rio Cauca al Occidente de Manizales. Datación por trazas de fisión en circones rosados reportan edades cercanas al límite Mioceno-Plioceno e indican actividad volcánica entre la Formación Combia (10-8 Ma) y la base del Complejo Ruíz Tolima (4 Ma)