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 obtained during the 53rd cruise of the R/V Akademik Nikolaj Strakhov organized and performed by the Geological Institute of the Russian Academy of Sciences over the period of July 7–August 15, 2022. In this segment, areas of greater and lesser magmatic productivity, which correspond to higher and lower bottom relief, alternate along the spreading axis. In high-relief areas, spreading cells form in the axial zone, and rises of tectonic and volcanic genesis dominate in the crest zone. In low-relief areas, the rift valley consists of deep rift basins; low ridges are developed on the flanks, which are separated by wide depressions. Oceanic N- and T-type tholeiites and E-MORB-type basalts and dolerites are distinguished among the studied volcanics. The N-tholeiites are widespread and were derived from mainly depleted mantle (source of DM). E-MORB-type basalts and dolerites are found in high-relief areas. Their mantle substrate is formed by a mixture of DM and EM-2 material with the subordinate role of HIMU. T-MORB volcanics 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.