Tectonic and magmatic control on hydrothermal distribution along the ultra-slow spreading Mohns Ridge

Hydrothermal circulation along mid-ocean ridges is primarily controlled by the interplay between magmatic and tectonic processes. The Mohns Ridge, shaped by the Jan Mayen/Iceland plume and a shift from orthogonal to oblique accretion, provides a natural laboratory to test whether melt-flux, tectonic strain, and axial volcanic ridge (AVR) maturity predict hydrothermal venting, using a multiproxy approach combining bathymetry, magnetic, gravity, and seismicity data. Variations in mantle Bouguer anomaly and bathymetry along the axis show how plume distance and ridge obliquity jointly control melt distribution, dividing the ridge into three regions: high-melt-flux south of the 71.3°N, diffuse high-melt-flux between 71.3°N and 72.2°N, and a focused but melt-limited region northward. While AVR volume appears as an unreliable proxy for melt-flux and AVR maturity, along-axis correlation between magnetic, mantle Bouguer anomalies and sediment thickness distinguishes between well-developed active, well-developed inactive, and infrequent but recently active AVRs. Melt distribution style (focused vs. diffuse) and AVR magmatic state primarily dictate hydrothermal vent distribution: well-developed active AVR in focused regions promotes high-temperature venting, while a diffuse-melt distribution appears to hinder their development. The apparent tectonic strain in the axial valley shows no significant relationship with melt-flux or magnetic anomaly, reflecting the differing timescales between crustal accretion, alteration and surface activity. Similarly, seismic activity shows no relationship with AVR maturity, melt emplacement style, or hydrothermal venting, indicating that short-term events are decoupled from the long-term evolution of AVRs. Hydrothermal activity instead correlates more closely with the long-term magmatic evolution of AVRs than with these short-term events.