Volcano-tectonic controls of hydrothermalism on a hot spot-influenced mid-ocean ridge : Insights from Iceland and Reykjanes Ridge

Hydrothermal systems along mid-ocean ridges play an important role in the evolution of our planet by contributing to planetary cooling, geochemical mass balance, the formation of ore deposits and influencing the biogeography of the deep-sea ecosystems. The primary aim of this thesis was to investigate the abundance and volcano-tectonic controls of low-temperature, off-axis hydrothermal activity along the flanks of an active divergent plate boundary, initially using the subaerial Westfjords region of Iceland as a proxy. A secondary aim was to put constraints on the age of features controlling hydrothermal circulation in off-axis setting. A third aim was to postulate where hydrothermal venting along the Reykjanes Ridge may occur and determine if and where more high-temperature systems could be present. Icelandic hot springs were used as direct analogues for seafloor hydrothermal systems and results of on-land observations extrapolated to the adjacent Reykjanes Ridge. Field observations were collected in two field seasons in 2013 and 2014, mainly from the off-axis Westfjords (NW Iceland) but also from the on-axis Reykjanes Peninsula (SW Iceland). Dating of vents-hosting features was done using the 40Ar/39Ar method. The bathymetry of the northern Reykjanes Ridge was interpreted for volcano-tectonic status and hydrothermal prospecting, based on on-land observations

Detailed Mapping and Sampling of the Reykjanes Ridge, Cruise No. MSM75, 29 June 2018 - 8 August 2018, Reykjavik - Reykjavik, REYKJANES

Hotspot-influenced spreading axes are characterized by a shallow axis, thickened crust, and possibly by higher-than-normal eruption frequency, all signs of an excess of magma and heat being supplied to such ridges by the hotspot. Despite this, these ridges are also characterized by an apparently lower-than-average incidence of high-temperature hydrothermal venting, raising questions about their thermal budget. The type example for hotspot-ridge interaction is the Reykjanes Ridge south of Iceland, which shows abnormally shallow bathymetry between the Reykjanes Peninsula at ca. 63°N and the Charlie Gibbs Fracture Zone at 53°N.The seafloor surrounding the present spreading axis is also characterized by V-shaped bathymetric ridges, thoughtto be produced by regions of excess melting migrating along the axis through time. Cruise MSM75aimed to produce geological maps of four key areas along the ridge -one with thickened crust where a V-shaped ridge intersects the present-day axis, one with thickened crust but no on-axis V-shaped ridge anomaly, a third with more normal crustal thickness and an axial valley and a fourth at the only known, but up to present unsampled, Reykjanes hydrothermal site Steinaholl. This geological mapping is to be usedto investigate questions of variations in eruption size or frequency away from Iceland, the interplay between magmatism and tectonism, the axial volcanology of V-shaped ridges and how thick crust is cooled in the apparent paucity of high-temperature vent fields

Hydrothermal activity in Tertiary Icelandic crust: Implications for cooling processes along slow-spreading mid-ocean ridges

Known hydrothermal activity along the Mid–Atlantic Ridge is mostly high–temperature venting, controlled by volcano–tectonic processes confined to ridge axes and neotectonic zones ~15km wide on each side of the axis (e.g. TAG or Snake Pit). However, extensive exploration and discoveries of new hydrothermal fields in off–axis regions (e.g. Lost City, MAR) show that hydrothermalism may, in some areas, be dominated by off–axis venting. Little is known about nature of such systems, including whether low–temperature “diffuse” venting dominates rather than high–temperature black-smokers. This is particularly interesting since such systems may transport up to 90% of the hydrothermal heat to the oceans. In this study we use Icelandic hot springs as onshore analogues for off–shore hydrothermal activity along the MAR to better understand volcano-tectonic controls on their occurrence, along with processes supporting fluid circulation. Iceland is a unique laboratory to study how new oceanic crust cools and suggests that old crust may not be as inactive as previously thought. Our results show that Tertiary (>3.3 Myr) crust of Iceland (Westfjords) has widespread low–temperature hydrothermal activity. Lack of tectonism (indicated by lack of seismicity), along with field research suggest that faults in Westfjords are no longer active and that once sealed, can no longer support hydrothermal circulation, i.e. none of the hot springs in the area occur along faults. Instead, dyke margins provide open and permeable fluid migration pathways. Furthermore, we suggest that the Reykjanes Ridge (south of Iceland) may be similar to Westfjords with hydrothermalism dominated by off–axis venting. Using bathymetric data we infer dyke positions and suggest potential sites for future exploration located away from neotectonic zone. We also emphasise the importance of biological observations in seeking for low-temperature hydrothermal activity, since chemical or optical methods are not sufficient

Role of Hydrothermal systems in Development of the Oceans. Where to find them on the seafloor?

Hydrothermal activity along Mid–Ocean Ridges is dominated by high–temperature venting mostly confined to ridge axis and neotectonic zone extending ~15km on each side of the axis. However, extensive exploration and discoveries of new hydrothermal fields in off–axis regions (e.g. Lost City, MAR) show that hydrothermal activity may be dominated by off–axis venting. Hence, little is known about controls and nature of such systems, for example, weather low–temperature “diffuse” venting dominates? Such systems may transport even 90% of hydrothermal heat to the oceans. This makes them a great potential source of renewable energy. However, we need to know where to look for them on the seafloor? On Iceland 95% of hydrothermalism takes place through low-temperature venting, therefore as subaerial part of the Mid-Atlantic Ridge, Iceland can help us better understand underwater hydrothermalism. Unfortunately, the technology to detect these systems is rudimentary. Therefore we need to develop an inexpensive and precise method for detecting low-temperature venting that will have very little impact on environment but will help us accurately assess potential of these systems. Observations of Icelandic systems helped me to develop predictive model for locating low-temperature venting on the Reykjanes Ridge (south of Iceland) based on existing bathymetry maps. This method could potentially be applied to other mid-ocean ridges worldwide. Seafloor of Reykjanes Ridge is easy to reach due to shallow depth. With high resolution maps we can focus investigations to pre-targeted areas of interest. Biological observations can significantly improve this method since detecting signals created by low-temperature fluids is very difficult with only geological, acoustic and optic measurements. Visual observations of bacteria mats or mussels (e.g. Bathymodiolus) can help directly locating sites where fluids escape from the crust

Multibeam bathymetry raw data (Kongsberg EM 712 entire dataset) of RV MARIA S. MERIAN during cruise MSM75

Multibeam bathymetry raw data was recorded in the North Atlantic during cruise MSM75 that took place between 2018-06-29 and 2018-08-08. The data was collected using the ship's own Kongsberg EM 712. This data is part of the DAM (German Marine Research Alliance) underway research data project. Underway data is collected continuously on German research vessels and can include data from transits or from the entire cruise. Underway data is shared in line with the FAIR principles

Multibeam bathymetry raw data (Kongsberg EM 122 entire dataset) of RV MARIA S. MERIAN cruise MSM75

Multibeam bathymetry raw data was recorded in the North Atlantic Ocean during cruise MSM75 that took place between 2018-06-29 and 2018-08-08. The data was collected using the ship's own Kongsberg EM 122. Sound velocity profiles (SVP) were applied on the data for calibration. SVP data are part of this dataset publication. This data is part of the DAM (German Marine Research Alliance) underway research data project