Tracking the evolution of shallow crustal permeability using repeated surveys of hydrothermally active rift zones: Insights into the R2K focus sites via analysis of Iceland rift zones

The location of hydrothermal vents at the earth's surface is a direct expression of the architecture of permeable conduits in the shallow crust, primarily (but not exclusively) active faults and associated fracture systems. The character of fault populations along hydrothermally active segments of rift zones should therefore exert significant control on the spatial relationships between hydrothermal vents at the surface and deeper structural and magmatic components of spreading/rifting systems. Local tectonic or magmatic activity such as eruptions, intrusions, and/or fault slip should cause systematic changes in vent location and behavior as a result of changes in the geometry, connectivity, and permeability of shallow, fracture-controlled conduits. By analyzing repeated surveys of faults, fractures and surficial deposits in hydrothermally active settings with respect to vent locations and characteristics (i.e. temperature, flow rate, chemistry), we gain a first-order understanding of the structural influence on outflow sites and the impact of changes in shallow crustal architecture on hydrothermal activity. Determination of earthquake locations and the boundaries of shallow crustal magma bodies further enhance our understanding of the tectonic context of hydrothermal flow. Understanding how hydrothermal systems respond to geological events over short time scales is a key aspect of the R2K ISS initiative. As an initial step toward creating a time-integrated view of these systems, we analyzed data from a variety of well-mapped hydrothermal sites along several sections of the Iceland rift zone, where there is an extensive body of long-term observation, repeat mapping, and geological and geophysical data. Analyses of historical and recent data from hydrothermal systems in the Krafla, Reykjanes, and Hveragerdi areas indicate changes in the surface expression of hydrothermal activity (both location and behavior of vents) associated with magmatic intrusion, earthquake swarms, fissure eruptions, and fault slip. Integrating these events and associated changes in vent location and behavior over time in conjunction with fault population analysis provides a strong foundation for synthesizing a wide array of existing data sets (seafloor maps, hydrothermal vent locations, chemical, thermal and fluid flow properties, and subsurface geophysical/seismological data) gathered from the R2K focus sites.