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A zone of mylonite and related ductile deformation beneath the alpujarride nappe complex, betic cordilleras, S. Spain

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Zusammenfassung

Im Liegenden des Deckengebäudes der Alpujarriden findet sich an vielen Stellen eine Mylonitzone. Der Kontakt mit den unterlagernden nevado-filabriden Gesteinen ist durch Kalkmylonite, Dolomitbrekzien, eisenreiche Karbonate und Marmore markiert. Diese liegen auf einer dünnen Zone von Ultramylonit, der sich aus nevado-filabriden Glimmerschiefern entwickelt hat. Diese plastische Verformung nimmt zum Liegenden hin ab, kann aber bis zu 400 m unterhalb des Deckenkontaktes reichen. Sie erzeugt eine charakteristische, plattige Schieferung, eine stark ausgeprägte Streckungslineation und eine protomylonitische Mikrostruktur. Mit einer kinematischen Analyse dieser Gesteine kann die Transportrichtung der Deckeneinheiten bestimmt werden.

Die Glimmerschiefer und Phyllite alpujarrider Zuordnung besitzen keine mylonitische Mikrostruktur, obwohl sie stark deformiert sind. Dies deutet darauf hin, daß, im Gegensatz zum intrakristallinen Gleiten in den nevado-filabriden Protomyloniten, vor allem Drucklösung als Deformationsmechanismus anzusehen ist.

Abstract

A zone of mylonite is commonly developed beneath the Alpujarride nappe complex. The contact with the underlying Nevado-Filabride Complex is marked by a zone of calc mylonite, dolomitic breccia, iron-rich carbonate rocks, and marble. These lie on a thin zone of ultramylonite derived from Nevado-Filabride schist. Related ductile deformation decreases downwards, but may extend up to 400 m beneath the contact. This deformation produces a characteristic platy foliation, a strong elongation lineation, and a proto-mylonitic microstructure. Kinematic analysis of these rocks may help determine the direction of nappe transport.

Mylonitic or protomylonitic microstructures are not developed in the Alpujarride rocks, although these are strongly deformed adjacent to the contact. Microstructural evidence suggests that deformation occurred by pressure-solution in these rocks, and not by the crystal-plastic processes that operated in the Nevado-Filabride protomylonitic schists.

Resumen

Bajo el complejo de mantos de los Alpujárrides se observa comunmente el desarrollo de una zona milonitica. El contacto de dicho complejo con el de Nevado-Filabride está señalado por una zona de calcomilonitas, brechas dolomiticas, rocas carbonatadas ricas en hierro y mármoles. Estos se situan en una zona estrecha de ultramilonitas que se derivan de los esquistos del Nevado-Filabride, La deformación dúctil asociada decrece en sentido descendente, pero puedo extenderse hasta 400 m por debajo del contacto. Esta deformation produce una foliación planar characterística, una lineación de extensión muy pronunciada y una microestructura protomilonítica. Los análisis cinemáticos de éstas rocas pueden ayudar a determinar la dirección de transporte de los mantos.

Las microestructuras miloníticas y protomyloníticas no se desarrollan en las rocas Alpujárrides, aunque dichas rocas están fuertemente deformadas junto al contacto. Las observaciones microestructurales sugieren que la deformación tuvo lugar por «pressure-solution» y no por procesos de plasticidad cristalina como los operantes en los esquistos protomiloníticos del Nevado-Filabride.

Краткое содержание

В подошве покрова Аль пухаррид встречают многочисленные зоны милонизации. Контакт с подлежащим и породами Невадо-фил абрид отмечен известковым и милонитами, доломитовыми брекчи ями, богатыми железом карбонатами и мрамором. Они залега ют на тонкой зоне в ультр амилоните, который ра звился из слюдянистого сланца Неведо-филабрид. Такое пластическое п реобразование умень шается по направлению к подошв е, но может быть еще отме ченным до 400 м ниже конт акта с покровом. Они образую т характерное, пластич еское сланцевание, с с ильно выраженной линиацие й растяжения и протомилонитическ ой микроструктурой. П ри кинематическом анал изе этих пород можно определить нап равление переноса ед иниц покрова. Слюдянистый сланец и филлиты Альпухаррид не обладают милонитн ой микроструктурой, хот я они и сильно деформированы. Это го ворит о том, что в противоположность к интракристаллиновы м скольжениям в Невадо-филабридах протомил онита механизм деформации здесь следует считать сколом, вызва нным давлением.

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Author notes

  1. J. P. Platt

    Present address: Department of Geology and Mineralogy, Oxford University, Parks Road, OX1 3PR, Oxford, UK

  2. J. H. Behrmann

    Present address: B.P. Minerals International, Lower William Street, SO1 1QE, Northam, Southampton, UK

  3. J. -M. M. Martínez

    Present address: Department of Petrology, University of Granada, Granada, Spain

  4. R. L. M. Vissers

    Present address: Institute for Earth Sciences, State University of Utrecht, P.O. Box 80.021, Utrecht, The Netherlands

Authors and Affiliations

  1. Department of Geology and Mineralogy, Oxford University, Parks Road, OX1 3PR, Oxford, UK

    J. H. Behrmann

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Platt, J.P., Behrmann, J.H., Martínez, J.M.M. et al. A zone of mylonite and related ductile deformation beneath the alpujarride nappe complex, betic cordilleras, S. Spain. Geol Rundsch 73, 773–785 (1984). https://doi.org/10.1007/BF01824981

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