Artículo de revista
Evidence of extensional metamorphism associated to Cretaceous rifting of the North-Maghrebian passive margin: The Tanger- Ketama Unit (External Rif, northern Morocco)
Fecha
2013Registro en:
G e o l o g i c a A c t a , Vo l . 1 1 , N º 3 , S e p t emb e r 2 0 1 3 , 2 7 7 - 2 9 3
D O I : 1 0 . 1 3 4 4 / 1 0 5 . 0 0 0 0 0 1 8 4 3
Autor
Vázquez Vílchez, María de las Mercedes
Asebriy, L.
Azdimousa, A.
Jabaloy Sánchez, Antonio
Booth Rea, G.
Barbaero, L.
Mellini, M.
González Lodeiro, F.
Institución
Resumen
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. 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.