Future directions (from 2011)

The research on AMOR will partly be exploratory (mapping new areas and searching for new novel vent fields), and partly process-oriented (relating to tectonic, magmatic and hydrothermal processes). A new research activity has also been added concerning the numeric modelling of subsurface and seabed fluid flow.

Specific sub-themes for the Deep-sea hydrothermal systems and geodynamics theme are:

Volcano-tectonic evolution and ridge-plume-continent interactions at the AMOR:

The magma production at mid-ocean spreading ridges is overall in balance with the spreading rate. As a result, the thickness of the oceanic crust is relatively uniform and around 6 km. However, at ultraslow spreading rates (below 20 mm/y), the magma supply decreases to a level where the crust becomes thinner than normal and locally disappears so that the mantle is locally exposed at the seafloor. Volcanic material, sampled along the AMOR by CGB-researchers and colleagues at other institutions, show features not observed at faster spreading ridges. Examples include: 1) magma fractionation appears to occur at higher pressures and partly at mantle depths; 2) during ascent to the surface, the magma is repeatedly at the verge of freeze-up, and 3) explosive eruptions occur at more than 3000 meters water depth, suggesting extremely high CO₂ contents and very low degrees of partial melting. These and other observations are important for understanding this end-member type of magmatism on Earth. The picture is still fragmented, and during the next five-year period we will continue to systematically sample and analyse volcanic constructions along the AMOR and perform a range of geochemical studies. Isotopic tracer studies will be used to also reveal ridge-plume-continent interactions, and this will be carried out as part of an international collaborative project. In addition, we will continue to use the unique time record provided by sedimentary deposits in the rift valley and along the flanks of the AMOR to constrain the interplay between tectonic and magmatic processes, and also using broad-band seismic arrays to link active processes. The new research plan includes the following objectives:

• Resolve the influence of the Icelandic hot spot on the AMOR in time and space by comparing the geochemistry of the basalts from the active spreading ridge with that of the extinct Aegir Ridge
• Compile all existing seismic data and acquire additional data in key areas to understand the variability in crustal thickness, and use the seismic stratigraphy from the sedimented part of the ridge to understand tectonic processes in time and space  
• Use broad-band seismic methods to image microseismicity at and between segment centres to reveal the interplay between magmatic and tectonic accretion

Extent and Diversity of hydrothermal activity:

The extent of hydrothermal activity along the global mid-ocean ridge system is immense. Some estimates suggest the flux through the crust is around 1/7 of the riverine input to the oceans. The extent of hydrothermal activity at ultraslow spreading ridges, which make up 20% of the global spreading ridge system, is poorly constrained. New findings suggest that hydrothermal activity along these most slow-spreading parts of the global ridge system is more abundant then expected. Relative to the magmatic productivity, it appears that hydrothermal activity at ultraslow spreading ridges is more extensive than at faster spreading ridges, and the reason for this is poorly understood. CGB findings suggest that a much larger proportion of the crust is convectively cooled at ultralow spreading ridges than at ridges spreading at faster rates.  Due to the effect of the Icelandic hot-spot, the crustal thickness along the AMOR decreases from 10 km at the southernmost parts to 3-4 km further north, with the mantle becoming exposed at local cold-spots. To document the extent of hydrothermal activity and how this relates to magma productivity and crustal thickness, we will collaborate with US partners to systematically document the extent of hydrothermal activity along the AMOR from the Icelandic hot spot in the south - to the cold spot in the north. The diversity in hydrothermal systems at ultra-slow spreading ridges is expected to be large due to the variability in crustal thickness and geology. CGB has been involved in the discovery and the initial studies of four out of the five vent fields located and visited thus far along these most slow-spreading parts of the ridge system. The systematic along-ridge search for hydrothermal activity at the AMOR first by towed vehicles, and then by AUV and ROV at potential venting areas, will undoubtedly result in the discovery of new vent fields and new vital information on the diversity of hydrothermal systems at slow spreading ridges. The new research plan includes the following specific objectives:

• Document the extent of hydrothermal venting from Iceland to the Gakkel Ridge by using Miniature Autonomous Plume Recorder (MAPR) and relate the frequency to lithospheric thickness and volcanic and tectonic style
• Locate and characterise new novel vent sites on and off-axis along the AMOR using AUV and ROV

Seafloor and sub-seafloor fluid flow:

Subsurface and seabed fluid flow is a fundamentally important Earth-system process. Extensive fluid flow occurs at oceanic ridges as part of hydrothermal systems and also at continental margins, where the seabed flow of geo-fluids may result from leakage from subsurface reservoirs or from compaction and diagenesis of sediments. CGB has geo-expertise on seabed fluid flow systems at both continental margins and at oceanic ridges. UiB has also a strong group involved in mathematical modelling of subsurface fluid flow. This expertise has been developed as part of a Centre of Excellence in Petroleum Research (CIPR). CGB has recently joined forces with this group to work on modelling subsurface fluid flow, fluid flow across the seabed and the dispersion of geo-fluids and geo-gases into the water column. The work is funded through several national and international projects related to subsurface CO₂ sequestration (SUCCESS, ECO2, CO2-BASE). The research aims to better understand fluid-flow through fractured rocks and soft sediments in order to predict the behaviour of both single and multiphase upward fluid flow in various settings. New mathematical tools are being developed for vertical single and multiphase fluid flow; knowledge about fault-facies and soft sediment fluid flow systems is being reviewed, and both cold seeps and hot vents will be used as natural laboratories for constraining fluxes and subsurface fluid flow using both seawater acoustic and subsurface seismic methods. The objectives of this new element to the CGB research plan are:

• Characterise the fault and fracture distribution in hydrothermal areas from ultrahigh resolution bathymetry and broad band seismometry

Use new mathematical methods developed for modelling fluid flow in reservoir cap rocks to model physical and geochemical aspects of fluid flow in hydrothermal systems in different settings

Projected milestones

• Deployment of a lander system for hydrothermal research
• Synthesis of data obtained on the frequency of hydrothermal activity along AMOR
• Deployment of broadband seismometers for detecting microseismic activity related to hydrothermal, volcanic and tectonic activity at key study areas at the AMOR
• Deep Sea expeditions aimed at discovery, diversity and geobiology of hydrothermal activity along the AMOR.
• Synthesis of seismic and geochemical data relating to crustal structure and plume-ridge-continent interaction along the AMOR.
• Modelling activities on fluid flow at hydrothermal and cold-seep settings