Magmato-tectonic variability along the Mohns Ridge: Insights into the controls on hydrothermal circulation

The Mohns Ridge is located in the Norwegian-Greenland Sea, between the Jan Mayen Transform Fault and the Mohns-Knipovich Bend. It is an ultra-slow spreading ridge section with a full spreading rate of 15 to 17 mm/yr. Over its 580 km, the variations in axis depth and crustal thickness attest of the overall decrease of magma supply associated with the distance from the Jan Mayen Hotspot. In parallel seafloor ages based on sediment thickness and sedimentation rate in the axial valley attest of the relatively young volcanic activity (<180 ka) experienced by the entire ridge axis. Utilizing a multi-proxy approach, we aim to provide new insights into the magmato-tectonic interplay along the Mohns Ridge, including its transient nature and controls on hydrothermal circulation. We investigate: (i) the variability in relative tectonic and magmatic extension by deciphering seafloor morphology extracted from the bathymetric data; (ii) the variability in magma supply and volcanic activity by analyzing gravimetry and magnetic anomalies, and (iii) the distribution and intensity of the recent crustal activity affecting the ridge based on the 40 years of seismicity record. The analyses highlight two significant trends. First, a regional trend linked to the Jan Mayen and Iceland plumes controlling the distance between volcanic centers (i.e., axial volcanic ridges – AVRs) and the focus of the volcanic activity. Second, a local trend associated with AVR maturity controlling AVR volume and related faulting patterns. Combining these observations with the location of known hydrothermal vents, we find no evidence of the regional magma budget variability impacting the distribution of hydrothermal vents. Instead, the locations of hydrothermal vents appear to be related to AVRs with recent and voluminous volcanic activity. This suggests that hydrothermal activity is linked to recent phases of the AVR construction over shorter time scales than to overall melt supply and along-axis gradients, over longer timescales. Finaly, although the seismic activity has been stable over the last 40 years, the lack of correlation with the hydrothermal vent distribution or AVR geometry, suggests that it is related to transient processes over shorter time scales than that of the AVR construction and associated hydrothermal activity.