Fault-zone evolution in layered basalt sequences: a case study from the Faroe Islands, NE Atlantic Margin

• Published in: Geological Society of America Bulletin
• Main Authors: Walker, Richard James, Holdsworth, Robert E., Imber, Jonathan, Ellis, David
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Geological Society of America 2012
• Subjects: QE Geology; Faroe Islands; Wall Rocks
• Online Access: https://orca.cardiff.ac.uk/id/eprint/31338/; http://gsabulletin.gsapubs.org/content/124/7-8/1382; https://doi.org/10.1130/B30512.1

Few studies have focused on the geological characterization of exhumed sub-surface faults and fractures within continental flood basalt provinces. We present field and microstructural observations of basalt-hosted fractures and faults from the Faroe Islands, NE Atlantic margin. For a given displacement, the thickness of these highly mineralized faults varies by over three orders of magnitude. Fault zone thickness and displacement data from the Faroe Islands span nearly 4 orders of magnitude in displacement, but there is no strong positive correlation between fault zone thickness and displacement. Fault rock characterization reveals important breccia distinctions, including collapse/infill, crush/wear/abrasion, and implosion breccias, each with a respective increase in sealing potential. Collapse/infill breccias indicate sustained fluid-migration pathways, as they require open, subterranean cavities that are formed faster than mineral precipitation can seal them. Crush/wear/abrasion and implosion breccias record crack-seal behaviour during successive slip events. Despite having distinctly different fault rock assemblages, fault zone thickness and displacement data from basalt-hosted faults are indistinguishable from comparable data obtained from sediment-hosted faults. This observation suggests that the first-order controls on fault development are the same in layered basalts and sediments, namely fault surface bifurcation and linkage, asperity removal, and the accommodation of geometrically-necessary strains in the wall rocks.