Structure of Spreading Segments of the Mid-Atlantic Ridge between the Arkhangelsky and Bogdanov Transform Faults, Equatorial Atlantic

The paper presents new data on the Doldrums megatransform fault located in the northern Equatorial Atlantic (6.5°–9° N), which consists of four transform faults with large offsets: Doldrums, Vernadsky, Pushcharovsky, and Bogdanov. Several types of spreading segments of the Mid-Atlantic Ridge (MAR) displaced by transform faults were identified by analyzing seafloor bathymetric survey results from a multibeam echo sounder on cruise 45 of the R/V Akademik Nikolaj Strakhov in 2019. Depending on the depth of the axial spreading zone, the structure of segments varies from typical for mid-oceanic ridges to intratransform spreading centers. The shallowest spreading segments south of the Bogdanov FZ and north of the Vernadsky FZ correspond to spreading cells with small neovolcanic rises and abyssal hills in combination with oceanic core complexes on the flanks of the MAR. The deepest intra-transform spreading center formed between two branches of the double Pushcharovsky FZ. This center is characterized by the largest neovolcanic rise, a nonstationary position, and origination of new spreading centers in areas of pull-apart basins, which form under the influence of extension directed towards the intra-transform domain of the Pushcharovsky FZ. Segments intermediate in depth and structure form between the Vernadsky, Pushcharovsky, and Bogdanov Fracture zones. The segments are characterized by large neovolcanic rises in the axial zone and asymmetrical structure of the flanks. The eastern flank exhibits oval rises, which are mostly composed of serpentinized ultramafic rocks; the western flank shows rare rift ridges (former neovolcanic rises). We analyzed the oblique structures with respect to the spreading direction, which are abundant in the studied region, and considered possible reasons for their origination in Equatorial Atlantic.