The Process of Serpentinization in Beni Bousera Massif (Internal Rif, Morocco)

Zaineb Hajjar1, Amina Wafik1, Abderrahim Essaifi1 and Marc Constantin2, (1)DLGR Laboratory (Unit associated to CNRST, URAC 43), Department of Geology, Marrakech, Morocco, (2)Laval University, Quebec City, QC, Canada

Contact First Author: Zaineb Hajjar; zaineb.hajjar@edu.uca.ma

Abstract ID#: 34298

 

English Abstract:
The Beni Bousera massif is part of the Sebtide units in the internal Rif (Morocco). It is mainly composed by mantle peridotites surrounded by crustal metamorphic series (kinzigites, micaschists, schists). Intensity of ductile deformation in the peridotites allows recognizing from bottom to top: 1) coarse grained porphyroclastic to granular spinel peridotites including spinel pyroxenites layers; 2) spinel porphyroclastic peridotites with layers of garnet pyroxenites; 3) garnet and spinel mylonites.

Serpentinization is superimposed on the ductile deformation. Following the exhumation, fluid circulations induced serpentinization of the peridotites. Serpentinization is concentrated at the top of the peridotites, along the mylonitized zone, and decreases towards the bottom of the massif. It is manifested by the formation of mesh texture and hourglass texture in foliation plans in the high serpentinized peridotites to brecciaed texture in low serpentinized peridotites. Pyroxene is still intact marked by few serpentine veins. This differential serpentinization reflects a low silica activity.

The study of the Raman shifts indicates that, in the low wavenumber region, four main peaks (near 230, 390, 690 and 1100 cm-1) characterize the spectra of lizardite and chrysotile. The differences between chrysotile and lizardite spectra could be clearly identified by sharpness of the Raman lines. In particular, a single band at 1100 cm-1 is observed at chrysotile whereas several convoluted bands are observed between 1060 and 1100 cm-1 at lizardite. Therefore the serpentine showed a brecciaed texture in the bottom of the massif and the mesh texture, hourglass texture and vein texture in the top of the massif correspond to lizardite type, whereas the serpentine filling the fracture is a chrysotile.

Regarding the tectono-metamorphic evolution of Beni Bousera massif we can relate the serpentinization phenomenon to the thermal event between 19 to 14 Ma as defined by Zircon and Apatite Fission Track.

Keyword: Lizardite, Raman spectroscopy, thermal event, Beni Bousera,

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