Peridotite-gabbro-trondhjemite association of the Mid-Atlantic Ridge between 12°58′ and 14°45′N: Ashadze and Logachev hydrothermal vent fields

This study aimed at reconstructing the sequence of events in the magmatic and metamorphic evolution of peridotites, gabbroids, and trondhjemites of the oceanic core complexes of the Ashadze and Logachev hydrothermal vent fields. The study object was the collections of plutonic rocks made during cruises 22 and 26 of the R/V Professor Logachev, Cruise 41 of the R/V Akademik Mstislav Keldysh, and the Russian-French expedition Serpentine aboard the R/V Pourquoi pas? The data reported here suggest that the oceanic core complexes of the Ashadze and Logachev fields were formed via the same scenario in the two MAR regions. On the other hand, the analysis of petrological and geochemical characteristics of the rocks indicated that the oceanic core complexes of the MAR axial zone between 12°58′ and 14°45′N show a pronounced petrological and geochemical heterogeneity manifested in variations in the degree of depletion of mantle residues and the Nd isotopic compositions of the rocks of the gabbro-peridotite association. The trondhjemites of the Ashadze hydrothermal field can be considered as partial melting products of gabbroids under the influence of hydrothermal fluid. It was supposed that the presence of trondhjemites in the MAR oceanic core complexes can be used as a marker for the highest temperature deep-rooted hydrothermal systems. Perhaps, the region of the MAR axial zone in which petrologically and geochemically contrasting oceanic core complexes are spatially superimposed served as sites for the development of large hydrothermal clusters with a considerable ore-forming potential.