Zusammenfassung
Aus Zentralmarokko (Zentraler Hoher Atlas, Mittlerer Atlas, Haute Moulouya) wurden, in kontinentale Rotserien des frühen Mesozoikums (Trias-Lias) eingeschaltete Tholeiite geochemisch und geochronologisch untersucht. Haupt-, Spurenund Seltene Erden-Elementgehalte klassifizieren die Vulkanite als basaltische bis andesitisch-basaltische, quarznormative Tholeiite. Einige Spurenelementverhältnisse (Zr/Nb, Zr/Y, Y/Nb, Ti/V) weisen auf eine MORB-ähnliche (P- bis N-typisch) Zusammensetzung hin. Die erhöhten LILE-Gehalte, die negative Nb-Anomalie und die87Sr/86Sr-Anfangsverhältnisse (0.7064–0.7069) zeigen eine krustale Komponente an (13–17 Gew%). Unterschiedliche87Sr/86Sr-Verhältnisse karbonatischer Mineralseparate aus verschiedenen Lavaströmen weisen auf mehrere Alterationszyklen hin, deren Alterationslösungen keine Meerwasserzusammensetzung besaßen.40Ar/39Ar-Datierungen an Plagioklasen ergaben Extrusionsalter zwischen 210.4 ± 2.1 Ma und 196.3 ± 1.2 Ma. Stratigraphisch umfaßt dies den Zeitraum zwischen Nor (Rhät?) und oberem Sinemur.
Abstract
From Central Morocco (Central High Atlas, Middle Atlas, Haute Moulouya) continental tholeiites were investigated geochemically and geochronologically. These tholeiites are intercalated within continental redbeds of the Early Mesozoic (Triassic-Liassic). The major, trace and rare earth element contents classify these volcanic rocks as basaltic to andesitic-basaltic, quartz-normative tholeiites. Some trace element ratios (e.g. Zr/Nb, Zr/ Y, Y/Nb, Ti/V) suffer a heterogeneous source with a composition similar to MORB (P- to N-type). The enriched LILE contents, the negative Nb anomaly and the inital87Sr/86Sr ratios (0.7064–0.7069) reveal the presence of a crustal component up to 13–17 wt%.87Sr/86Sr ratios of carbonate mineral separates from different lava flows show different cycles of alteration; however, the major and trace element chemistry together with Sr isotope evidence, indicate that the alteration phases are not submarine in origin.40Ar/39Ar age determinations on translucent plagioclase phenocrysts yield extrusion ages which range between 210.4 ± 2.1 Ma and 196.3 ± 1.2 Ma. These ages correspond to a stratigraphic period between the Norian (Rhaetian?) and the Upper Sinemurian.
Résumé
Des tholéiites du Maroc central (Haut Atlas central, Moyen Atlas, Haute Moulouya) ont fait l'objet d'une investigation géochimique et géochronologique. Ces tholéiites sont intercalées dans des couches rouges continentales d'âge mésozoïque inférieur (Trias-Lias). Les teneurs en éléments majeurs, en éléments en trace et en terres rares classent ces roches volcaniques comme tholéiites basaltiques à andésito-basaltiques, à quartz normatif. Certains rapports d'éléments en traces (p. ex.:Zr/Nb, Zr/Y, Y/Nb, Ti/V) indiquent une composition analogue au MORB (type P à N). La teneur élevée en LILE, l'anomalie négative du Nb et les rapports initiaux87Sr/86Sr (0,7064 à 0,7069) révèlent la présence d'un composant crustal dans la proportion de 13 à 17% en poids. Les rapports87Sr/86Sr de minéraux carbonatés séparés de diverses coulées de lave montrent l'existence de plusieurs cycles d'altération; toutefois, le chimisme des majeurs et des traces, ainsi que les données isotopiques du Sr, indiquent que ces phases d'altération ne sont pas sous-marines. Les mesures d'âge par40Ar/39Ar effectuées sur des plagioclases fournissent des âges d'extrusion compris entre 210,4 ± 2,1 Ma et 196,3 ± 1,2 Ma. Ces âges correspondent à une période située entre le Norien (Rhétien?) et le Sinémurien supérieur.
Краткое содержание
Провели геохимическ ие и геохронологичес кие исследования толеит ов, включенных в материковые красноц ветные свиты раннего мезозоя триаслейас и з центрального Марок ко. На основании распред еления главных и микр оэлементов, а также Редких Земель считают, что эти вулканиты мож но отнести к базальто вым до андезитно-базальт овым толеитам с нормальным содержан ием кварца. На основан ии соотношения микроэл ементов Zr/Nb, Zr/Y, Y/Nb, Тi/V предполагают сост ав, подобный MORB типа P до N. Повышенное с одержание LILE, отрицательная анома лия Nb и исходные соотношения изотопо в стронция87Sr/86Sr= 0,7064–0,7069 указывают на прису тствие компонентов коры в них (13–17 вес.-%).
Различия в соотношен иях содержания строн ция в карботных минерала х из различних потоков лав говорят о многократных циклич еских изменениях, происход ивших в эти промежутк и времени, причем содер жание элементов во внесенных раствор ах не соответствовал и составу морской воды. Определ ение возраста по изотопам аргона на пл агиоклазах указываю т на то, что возраст экст рузий составляет 210,4 ±2,1 Ма - 196,3± 1,2 Ма. Стратиграф ически этот возраст соответ ствует норийскому яр усу (рэтскому ?) и верхнему с инемюрскому ярусу.
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References
Allégre, C. J., Dupré, B., Richard, P., Rousseau, D. &Brooks, C. (1982): Subcontinental versus suboceanic mantle, II. Nd-Sr-Pb isotopic comparison of continental tholeiites with mid-ocean ridge tholeiites, and the structure of the continental lithosphère. - Earth Planet. Sci. Lett.,57, 25–34.
Berger, G. W. &Yorck, D. (1981): Geothermometry from40Ar/39Ar dating experiments. - Geochim. Cosmochim. Acta,45, 795–811.
Bertrand, H., Dostal, J. &Dupuy, C. (1982): Geochemistry of Early Mesozoic tholeiites from Morocco. - Earth Planet. Sci. Lett.,58, 225–239.
Brooks, C., Hart, S. R. &Wendt, I. (1972): Realistic use of two-error regression treatments as applied to rubidiumstrontium data. - Rev. of Geophys. and Space Phys.,2, 551–577.
Carter, S. R. Evensen, N. M., Hamilton, P. J. &O'Nions, R. K. (1978): Neodymium and strontium isotope evidence for crustal contamination of continental volcanics. - Science,202, 743–747.
Cousminer, H. L. &Manspeizer, W. (1976): Triassic pollen data Moroccan High Atlas and the incipient rifting of Pangaea as Middle Carnian. - Science,191, 943–945.
Cowie, J. W. &Bassett, M. G. (1989): Global stratigraphic chart (1989) of the IUGS. - Supplement to Episodes,12/2.
Dalrymple, G. B. &Lanphere, M. A. (1969): Potassiumargon dating: Principles, techniques and applications to Geochronology, 225 S., San Francisco, (Freeman).
Dupuy, C. &Dostal, J. (1984): Trace element geochemistry of some continental tholeiites. - Earth Planet. Sci. Lett.,67, 61–69.
—,Marsh, J., Dostal, J., Michard, A. &Testa, S. (1988): Astenosperic and lithospheric sources for Mesozoic dolentes from Liberia (Africa): trace element and isotopic evidence. - Earth Planet. Sci. Lett.,87, 100–110.
Evensen, N. M., Hamilton, P. J. &O'Nions, R. K. (1978): Rare earth abundances in chondritic metorites. - Geochim. Cosmichim. Acta,42, 1199–1212.
Faure, G. (1982): The marine-strontium geochronometer. - In: Odin, G. S. (ed.), Numerical dating in stratigraphy, 73–79, New York, (John Wiley & Sons).
— (1986): Principles in isotope geology, 589 S., 2d edition, New York, (Wiley & Sons).
Fiechtner, L. (1990): Geochemie und Geochronologie frühmesozoischer Tholeiite aus Zentral-Marokko. - Berliner geowiss. Abh.,118, 76 S., Berlin.
Hammerschmidt, K. (1986): 40Ar/39Ar dating of young samples. - In: Hurford, A. J., Jäger, E. & Ten Cate, J. A. M. (eds.), dating young sediments. - CCOP/TP,16, 339–357, Bangkok.
Hauptmann, M. (1990): Untersuchungen zur Mikrofazies, Stratigraphie und Paläogeographie jurassischer Karbonatgesteine im Atlas-System Zentralmarokkos. - unveröffentl. Dissertation, 150 S., Berlin.
Henderson, P. (1984): Rare earth element geochemistry, 510 p., Amsterdam-Oxford-New York-Tokyo, (Elsevier).
Hergt, J. M., Chappell, B. W., Faure, G. &Mensing, T. M. (1989): The geochemistry of Jurassic dolerites from Portal Peak, Antarctica. - Contrib. Mineral. Petrol.,102, 298–305.
Houten van, F. B. (1977): Traissic-Liassic deposits of Morocco and eastern North America: comparison. - Am. Ass'n Petrol. Geol. Bull.,61, 79–99.
Ingamells, C. O., &Engels, J. C. (1977): Preparation, analysis and sampling constants for a biotite. - In: Accuracy in trace analysis: Sampling, sample handling and anlaysis. - National Bureau of Standards, Special Pub,402, pp 401–419.
Jacobshagen, V., Görler, K. &Giese, P. (1988): Geodynamic evolution of the Atlas System (Morocco) in postPalaeozoic times. - In: Jacobshagen, V. (ed.), The Atlas System of Morocco. - Lecture Notes in Earth Sciences, 481–499, Berlin Heidelberg New York London Paris Tokyo, (Springer Verlag).
Jaques, A. L. &Green, D. H. (1980): Anhydrous melting of peridotite at 0–15 kb pressure and the genesis of tholeiitic basalts. - Contrib. Mineral. Petrol.,73, 287–310.
Kuno, H. (1950): Petrology of Hakone volcano and the adjacent areas, Japan. - Geol. Soc. Bull.,61, 957–1020.
Langmuir, Ch. H., Bender, J. F. Bence, A. E., Hanson, G. N. &Taylor, S. R. (1977): Petrogenisis of basalts from the Fameous Area: Mid Atlantic Ridge. - Earth Planet. Sci. Lett.,36, 133–156.
Liou, G. J.,Maruyama, S. &Moonsup, C. (1987): Very low grade metamorphism of volcanic and volcaniclastic rocks — mineral assemblages and mineral mineral faciès. - In: Frey, M.: Low temperature metamorphism. pp 59–112. Blackie, Glasgow, London.
Lorenz, J. (1988): Synthesis of Late Paleozoic and Triassic red-bed sedimentation in Morocco. - In: Jacobshagen, V. (ed.), The Atlas System of Morocco, 139–168, Berlin Heidelberg New York London Paris Tokyo, (SpringerVerlag).
Manspeizer, W., Puffer, J. H. &Cousminer, H. L. (1978): Separation of Morocco and eastern North America: A Triassic-Liassic stratigraphic record. - Geol. Soc. Am. Bull,89, 901–920.
Maurer, P. (1973): 40Ar/39Ar-Kristallisationsalter und 37Ar/ 38Ar-Strahlungsalter von Apollo 11-, 12- und 17-Steinen und dem Apollo 17 » orange soil«. - Unpub. Lizentiatsarbeit, 91 S., Bern.
Mattauer, M., Tapponier, P. &Proust, F. (1977): Sur les mécanismes de formation des chaines intracontinentales. L'exemple des chaines atlasiques dú Maroc. - Bull. Soc. géol. France, (VII),19, 521–526, Paris.
Mattts, A. F. (1977): Nonmarine Triassic sedimentation, Central High Atlas Mountains, Morocco. - J. Sediment. Petrol.,47, 107–119.
McDonald, G. A. &Katsura, T. (1964): Chemical composition of Hawaiian lavas. - J. Petrol.,5, 82–133.
McIntryre, D. B. (1963): Precision and resolution in geochronometry. - In: Albritton, C. C. (ed.): The fabric of geology, 112–134, (Addison-Wesley).
Menzies, M. &Seyfried, Jr.,W. E. (1979): Basalt-seawater interaction: trace element and strontium isotopic variations in experimentally altered glassy basalts. - Earth Planet. Sci. Lett.,44, 463–472.
Menzies, M. A., Leeman, W. P. &Hawkesworth, Ch. J. (1983): Isotope geochemistry od Cenozoic volcanic rocks reveals mantle heterogeneity below western USA. - Nature,303, 205–209.
Meschede, M. (1986): A method of discriminating between different types of mid-ocean ridge basalts and continental tholeiites with the Nb-Zr-Y diagram. - Chem. Geology,56, 207–218.
Odin, G. S., Curry, D., Gale, N. H. &Kennedy, W. J. (1982): The Phanerozoic time scale in 1981. - In: Odin, G. S. (ed.), Numerical Dating in Stratigraphy,2, 957–960, New York, (John Wiley & Sons).
Pearce, J. A., Gorman, B. E. &Birkett, T. C. (1977): The realtionship between major element chemistry and tectonic environment of basic and intermediate volcanic rocks. - Earth Planet. Sci. Lett.,36, 121–132.
Roche de la, H., Leterrier, J., Grandclaude, P. &Marchal, M. (1982): A classification of volcanic and plutonic rocks using R1 R2-Diagram and major element analyses. - Its realtionship with current nomenclature - Chem. Geology,29, 183–210.
Roex Le, A. P. (1987): Source regions of mid-ocean ridge basalts: Evidence for enrichment processes. - In: Menzies, M. A. & Hawkesworth, C. J. (eds.), Mantle Metasomatism, 389–419, London, (Academic Press Harcourt Brace Jovonovich Publisher).
Salvan, H. M. (1974): Les séries salifères du Trias marocain; charactères généraux et possibilités d'interprétation. - Bull. Soc. Géol. France,7, 724–731.
Schermerhorn, L. J. G., Priem, H. N. A., Boelrijk, A. I. M., Hebeda, E. H., Verdurmen, E. A. Th. &Verschure, R. H. (1978): Age and origin of the Messejana dolerite fault-dike system (Portugal and Spain) in the light of the opening of the north atlantic ocean. - J. Geology,86, 299–309.
Steiger, R. H. &Jäger, E. (1977): Subcommission on geochronolgy: convention on the use of decay constants in geoand cosmochronology. - Earth Planet. Sci. Lett.,36, 359–362.
Stets, J. &Wurster, P. (1981): Zur Strukturgeschichte des Hohen Atlas in Marokko. - Geol. Rdsch.,70, 801–811.
Stettler, A., Eberhardt, P., Geiss, J., Grögler, N. &Maurer, P. (1973):39Ar-40Ar ages and37Ar-38Ar exposure ages of lunar rocks. - Proc. Lunar Sci. Conf. 4th,2, 1865–1888.
— &Allègre, C. J. (1979):87Rb-87Sr constrains on the genesis and evolution of the Cantal continental volcanic system (France). - Earth Planet. Sci. Lett.,44, 269–278.
Sun, S. S. &Nesbitt, W. R. (1977): Chemical heterogeneity of the archaean mantle, composition of the earth and mantle evolution. - Earth Planet. Sci. Lett.,35, 429–448.
— &Sharaskin, A. Y. (1979): Geochemical characteristics of mid-ocean ridge basalts. - Earth Planet. Sci. Lett.,44, 119–138.
Taylor, S. R. &McLennan, S. M. (1985): The continental crust: its composition and evolution, 312 S., Palo Alto Oxford London Edinburgh Boston Victoria, (Blackwell Scientific Publications).
Thompson, R. N., Morrison, M. A., Dickin, A. P. &Hendry, G. L. (1983): Continental flood basalts ... arachnids rule OK?. - In: Hawkesworth, C. J. & Norry, M. J. (eds.), Continental basalts and mantle xenoliths, 158–185, Cheshire, (Shiva Publishing Limeted).
—,Morrison, M. A., Hendry, G. L. &Parry, S. J. (1984): An assessment of the relative roles of a crust and mantle in magma genesis: an elemental approach. - Phil. Trans. Royal Soc. Lond., A310, 549–590.
Turner, G. (1971):40Ar/39Ar ages from the lunar maria. - Earth Planet. Sci. Lett.,11, 169–191.
Warme, J. E. (1988): Jurassic carbonate faciès of the central and eastern High Atlas rift, Morocco. - In: Jacobshagen, V. (ed.), The Atlas System of Morocco. - Lecture Notes in Earth Sciences, 481–499, Berlin Heidelberg New York London Paris Tokyo, (Springer Verlag).
Wedepohl, K. H. (1988): Spilitization in the oceanic crust and seawater balances. - Fortschr. Miner.,66, 129–146.
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Fiechtner, L., Friedrichsen, H. & Hammerschmidt, K. Geochemistry and geochronology of Early Mesozoic tholeiites from Central Morocco. Geol Rundsch 81, 45–62 (1992). https://doi.org/10.1007/BF01764538
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DOI: https://doi.org/10.1007/BF01764538