Fluids and Deformation at a Divergent Plate Setting (Iceland, Reykjanes Peninsula)
Abstract
From a detailed 5-months seismic survey in a divergent plate setting in Iceland (Reykjanes Peninsula), we propose a spatial relationship between highly deformed crustal columns and seismogenic areas of low Vp and/or low Vp/Vs ratio. These areas are best explained by the existence of high-enthalpy fluids at the base of the upper crust. We question the interplay between crustal deformation and fluid content at depth in the oceanic-in-type crust. Combining available geological, geothermal and geophysical observations, we suggest that a deep low-permeability fluid reservoir (depth over 2-3km) is fed top-to-bottom by a high- permeability superficial reservoir when large faults in the high-T areas (centers of volcano-tectonic segments) are triggered by dynamical stresses from high-magnitude regional earthquakes. At the same time, high-enthalpy fluids would mix upward with colder brine from the upper reservoir. Such temporary increases in the bulk upper-crust permeability are consecutive to diffuse dilatation along and around the triggered faults. During the post-seismic stage, the fluids are trapped in the lower reservoir, probably at supercritical conditions, increasing in turn the capacity of the rocks to deform through cracking and faulting. We thus suggest that the cooling of oceanic crust is dependent on extensional tectonics at slow-spreading ridges.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.T43B2033G
- Keywords:
-
- 7245 Mid-ocean ridges;
- 7270 Tomography (6982;
- 8180);
- 8010 Fractures and faults;
- 8045 Role of fluids;
- 8135 Hydrothermal systems (0450;
- 1034;
- 3017;
- 3616;
- 4832;
- 8424)