Evidence of extensional metamorphism associated to Cretaceous rifting of the North-Maghrebian passive margin : the Tanger- Ketama Unit (External Rif, northern Morocco)
Vázquez, M. (Universidad de Chile. Andean Geothermal Center of Excellence (CEGA))
Asebriy, L. (Université Mohammed V. Institut Scientifique)
Azdimousa, A. (Université Mohammed I. Laboratoire LGA)
Jabaloy, A. (Universidad de Granada. Departamento de Geodinámica)
Booth-Rea, G. (Universidad de Granada. Departamento de Geodinámica)
Barbero, L. (Universidad de Cádiz. Departamento de Ciencias de la Tierra)
Mellini, Marcello (Università di Siena. Dipartimento di Scienze della Terra)
González-Lodeiro, F. (Universidad de Granada. Departamento de Geodinámica)
Consejo Superior de Investigaciones Científicas (Espanya). Instituto Andaluz de Ciencias de la Tierra

Data:	2013
Resum:	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 tracks.
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Llengua:	Anglès
Document:	Article ; recerca ; Versió publicada
Matèria:	Low-grade extensional metamorphism ; Illite crystallinity ; Kübler index ; Tanger-Ketama unit ; External Rif ; Northern Morocco
Publicat a:	Geologica acta, Vol. 11, Núm. 3 (September 2013) , p. 277-293, ISSN 1696-5728

Adreça alternativa: https://raco.cat/index.php/GeologicaActa/article/view/269670
Adreça alternativa: https://revistes.ub.edu/index.php/GEOACTA/article/view/105.000001843
DOI: 10.1344/105.000001843

18 p, 2.9 MB

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