Discovery of a fossil oceanic hydrothermal system in the Late Precambrian Khzama ophiolite (Siroua massif, Anti-Atlas range, Morocco)

The Khzama Precambrian ophiolite, tectonized and metamorphosed, exhibits all the lithological units of a complete ophiolite suite. The dyke complex, studied in detail in three tectonic slices, consists of isotropic to laminated, sometimes banded gabbros (about 50 %), crosscut by swarms of isolated diabase dykes with systematic chilled margins (about 50 %). This dyke complex unit shows a remarkably preserved network of fossil hydrothermal veins, consisting of quartz-epi dote-sulfides associations, mostly oriented parallel to the margins of the diabase dykes. Greenish epidosites form veins and peckers, around which the diabases are impregnated with still fresh and shining sulfides, disseminated in the dykes' groundmass. These characteristics are identical to those described in fossil hydrothermal systems of much younger ophiolites, such as the cretaceous ophiolites of Oman or Cyprus, in the lower part of the sheeted dyke complex. The Khzama fossil hydrothermal system could constitute one of the most ancient oceanic hydrothermal systems developed at an oceanic spreading centre. ((C) Academie des sciences / Elsevier, Paris.).