Oceanic Crust Formation in the Mid-Atlantic Ridge Segment between Azores and Icelandic Plumes: Results of Geological and Petrogeochemical Studies

Abstract

The structure of the ocean floor and the composition of basalts and dolerites of the MAR segment between the Maxwell and Charlie Gibbs FZs (North Atlantic) were studied based on the data of the 53rd cruise of the R/V “Akademik Nikolaj Strakhov”. It was found that in this segment, along the spreading axis, areas of greater and lesser magmatic productivity alternate, which correspond to higher and lower bottom relief. In areas of high relief, spreading cells form in the axial zone, and rises of various nature dominate in the ridge zone: from tectonic to volcanic. In areas of low relief, the rift valley consists of deep rift basins, and low ridges are developed on the flanks, separated by wide depressions. Oceanic tholeites N, T and E-MORB are distinguished among the studied volcanites. The first of them are ubiquitous and were melted from mainly depleted mantle (source DM). Basalts and dolerites of E-MORB are found in areas of high relief. Their mantle substrate is formed by a mixture of DM and EM-2 material with the subordinate role of HIMU. T-MORB volcanites are mainly localized on large volcanic rises in the southern part of the studied MAR segment and were melted from a substrate formed by a mixture of DM and HIMU material with the subordinate role of EM-2. Two types of mantle inhomogeneities involved in melting are reconstructed: passive and active. The former are represented by blocks of the transformed continental lithosphere that are similar in composition to the EM-2 mantle source. Active inhomogeneities associate with the uplift near Maxwell FZ of the microplume of the enriched mantle with a composition close to HIMU and with its subaxial flow in the north direction up to the Charlie Gibbs FZ.