Alteration hydrothermale et deformation ductile des roches volcaniques acides associees au gisement sulfure de draa sfar (Jebilet Centrales, Maroc)

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Zinbi, Y. ; Maacha, L. ; Elharfi, M. ; Hibti, M. ; El Boukhari, A. ; Ben Aissi, L. (2005)
  • Publisher: Consejo Superior de Investigaciones Científicas
  • Journal: Estudios Geologicos (issn: 0367-0449, eissn: 1988-3250)
  • Related identifiers: doi: 10.3989/egeol.05613-652
  • Subject: Rhyodacite | Shear zones | hydrothermal alteration | chemical mobility | Hercynian | Morocco | Rhyodacite | Zone de cisaillement ductile | Altération hydrothermale | Mobilit&#233 | chimique | Hercynien | Maroc | Geology | QE1-996.5

The volcanics and volcanoclastic rocks of Draa Sfar (Central Jebilet, Moroccan hercynian belt) are affected by ductile stress and hydrothermal alteration accompanied by a weak degree of metamorphism (greenschist facies). Some N-S oriented shearing zones, affect locally these formations while being the site of an important hydrothermal activity. The consequences of these transformations from a non to slightly- deformed rhyodacite, show that through these ductile shearing zones: (1) the mineralogical assemblage of hydrothermal alteration is essentially formed by chlorite, sericite, quartz and magnetite; (2) the gradual increase of the alteration indexes is accompanied by the destruction of the phenocrists and the recrystallization of the matrix by phyllosilicates and quartz; (3) the progressive transfer of material is more intense in the more deformed zones where the values of Ti, Al and Zr remain constant. These shearing zones played a very important role in the circulation of fluids and the transformation of the rhyodacite of Draa Sfar.<br><br>Les roches volcaniques et volcanoclastiques de Draa Sfar (Jebilet centrales, Maroc hercynien) sont affect&eacute;es par une d&eacute;formation ductile accompagn&eacute;e d&rsquo;un m&eacute;tamorphisme de faible degr&eacute; (faci&egrave;s schistes verts) et d&rsquo;une alt&eacute;ration hydrothermale. Des zones de cisaillement de direction N-S, ont affect&eacute; localement ces formations tout en &eacute;tant vecteurs d&rsquo;une importante activit&eacute; hydrothermale. Le suivi de ces transformations &agrave; partir de la rhyodacite non ou peu d&eacute;form&eacute;e, montre qu&rsquo;&agrave; travers ces zones de cisaillements ductiles : (1) l&rsquo;assemblage min&eacute;ralogique d&rsquo;alt&eacute;ration hydrothermale est form&eacute; essentiellement de chlorite, de s&eacute;ricite, de quartz et de magn&eacute;tite ; (2) l&rsquo;augmentation graduelle des indices d&rsquo;alt&eacute;ration s&rsquo;exprime par la destruction des ph&eacute;nocristaux au profit d&rsquo;une matrice recristallis&eacute;e en phyllosilicates et quartz ; (3) le transfert progressif de la mati&egrave;re est plus intense dans les zones d&eacute;form&eacute;es o&ugrave; Ti, Al et Zr restent constants. Ces zones de cisaillements ductiles ont jou&eacute; un r&ocirc;le tr&egrave;s important dans la circulation des fluides &agrave; l&rsquo;origine de la transformation en phyllosilicates de la rhyodacite de Draa Sfar.
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