by Gudmundur Ómar Fridleifsson, Wilfred Allan Elders

A consortium of Icelandic companies initiated the IDDP to investigate very deep geothermal resources and has invited participation by international scientists. This project will provide the first opportunity worldwide to achieve two long-standing goals of the Ocean Drilling Program, albeit on land, that is sampling the transition from oceanic layer 2 to layer 3, and direct investigation of high-temperature hydrothermal reaction zones at mid-ocean ridges. A member of the consortium has offered a 2.7 km deep geothermal well being drilled on the Reykjanes Peninsula for deepening by the IDDP. This well, currently at ~ 2000 m depth, will be completed and flow tested in 2005. In 2006-7, the IDDP proposes to drill and spot core this well, or another candidate well, to 4.0 km depth, and carry out a second flow-test. In 2007-8 the science program will continuously core that borehole from 4.0 km to 5.0 km, and carry out another flow test. The total costs of drilling, sampling, and logging, and flow testing this well are estimated to be ~ 19 million USD, out of which the costs to the science program are estimated about 25%. This proposal seeks a contribution towards the incremental costs of drilling, sampling, and measurement essential for the science program. This drill site at the southwestern tip of Iceland, where the Mid-Atlantic Ridge emerges from the ocean, is ideally situated for a long-term study of the formation of oceanic crust and its interaction with high-temperature (~ 450oC) hydrothermal fluids. The compositions of fluids in this geothermal field are similar to those produced from seafloor hydrothermal vents. The flux of seawater through mid-ocean rift hydrothermal systems is an important component of lithosphere/hydrosphere interactions. However ocean drilling has penetrated only ~ 2 km into marine hydrothermal systems. In contrast, the IDDP will produce drill cuttings, cores and fluid samples from as deep as 5.0 km that should reveal the integrated record of basalt-seawater interactions. The drilling to 4.0 km should approach conditions similar to those in the source regions of black smokers on oceanic spreading centers. Coring below 4.0 km is designed to penetrate into layer 3 of oceanic crust and study supercritical fluids that couple hydrothermal systems with their magmatic heat sources. Supercritical fluids have greatly enhanced rates of mass transfer and chemical reaction. The active processes in such a deep mid-ocean ridge environments have never before been available for comprehensive direct study and sampling.

• Formation of oceanic crust and the processes operating in the upper 5 km of the Mid-Atlantic Ridge. How well does the ophiolite model explain the seismic layering of ocean crust? What is the nature of the boundary between layers 2 and 3. Basalt-seawater reactions and direct observation, sampling and modeling of the transition from greenschist to amphibolite facies on mid-ocean rifts. Major, minor and trace element and isotopic exchange between basalts and seawater and solution-mineral equilibria up to 450°C. Mid-ocean rift hydrothermal systems and their coupling with their magmatic heat sources. For example, what controls the depth to which hydrothermal cells penetrate? The nature of, and controls on, permeabilty with increasing depth and temperature in response to fracturing, transitions to ductile behaviour, and self-sealing due to fluid-rock reactions, etc. The environment of natural supercritical phenomena; “superconvection” and its importance in mass and energy transfer. Observation and modeling of mass and energy transfer in the mid-ocean ridge environment. Formation of hydrothermal sulphide ore bodies. The feasibility and economic potential of deep geothermal resources. Technical problems of drilling, well completion and logging and downhole sampling tools in hot hostile environments. Scientific, economic, and educational spin-offs worldwide, wherever high-temperature geothermal resources exist.

High Temperature Hydrothermal, ICDP-2005/02, Iceland, IDDP, Mid-Ocean Ridges, Reykjanes, Supercritical Fluids

Latitude: 65.71587, Longitude: -16.76452