Geomorphological and geophysical characterization of the MARNOK region (Mid-Atlantic Ridge north of the Kane Fracture Zone: 23°50′N-25°15′N)

The MARNOK region of the Mid-Atlantic Ridge (23°50′N to 25°15′N), located north of the Kane transform fault, presents a valuable setting for investigating the interplay of magmatic and tectonic processes in oceanic lithosphere formation. This study integrates high-resolution bathymetric data, structural mapping, gravity anomalies (MBA and RMBA), and lithological observations from rock dredges and submersible Nautile dives to characterize accretionary styles across six ridge segments delineated by non-transform discontinuities. The region displays both orthogonal and oblique spreading geometries, enabling direct comparison between distinct accretion modes along a single ridge section. Our results show that orthogonal segments (1 and 6), at the south and north terminations of the ridge section, are transitioning from a magmatically robust phase to a tectonic-dominated regime, as evidenced by the absence of active axial volcanic ridges, symmetrical fault patterns, along with crustal thinning near segment centers. In contrast, oblique segments (2–5) located in between the orthogonal segments are increasingly magmatic, characterized by robust axial volcanic ridges, a thickened crust, and highly negative gravity anomalies. Segment 2 illustrates a transitional case, where relict large-offset faulting and recent volcanism coexist, suggesting a recent shift from tectonic to magmatic dominance. V-shaped mantle Bouguer anomaly patterns and off-axis fault traces support the southward migration of the non-transform discontinuity at the boundary between segments 1 and 2, potentially driving the progressive narrowing of segment 1. These findings illustrate the spatial and temporal variability of accretionary processes at slow-spreading ridges, controlled by fluctuations in magma supply, stress regime reorientation, transform fault influences, cooling and lithospheric heterogeneity. The MARNOK area thus provides critical insights into how spreading geometry and segmentation interact to govern the dynamic architecture of the oceanic lithosphere in a context of slow-spreading accretion.