Timing, growth and structure of a reactivated basin-bounding fault



Worthington, R.P1,2 & Walsh, J.J.1
1 - Fault Analysis Group, University College Dublin, Ireland
2 - Present Address: Statoil, Sandsliveien, 5254 Bergen, Norway

Abstract - Until recently there have been relatively few natural examples of basement fault reactivation, demonstrating convincing hard-linkage to underlying structure and a well-constrained geometry and timing of reactivation. Applying a variety of quantitative techniques, including displacement analysis and examining across-fault sequence thickening, to high quality 3-D seismic data, we describe the Cenozoic structure and growth of a reactivated Mesozoic normal fault, NW Porcupine Basin, west of Ireland. We demonstrate a previously unrecognized period of Mid-Late Eocene extensional reactivation and a tectonic, rather than the previously suggested compactional origin. E-W extensional reactivation of a N-S to NE-SW trending basement fault has led to the development of a highly segmented and systematically stepping fault array in the Cenozoic cover. A clear relationship between the displacement of hangingwall antithetic faults and the displacement along the main synthetic system is attributed to the antithetics primarily accommodating strain associated with a hangingwall roll-over anticline. Our study shows that displacement analysis provides an excellent basis for defining the kinematics of basement fault reactivation and the importance of fault segmentation and twisting during the upward propagation of reactivated faults into overlying cover sequences. Fault timing corresponds to a period of rapid differential subsidence, the magnitude of which is too large to be attributable solely to extensional reactivation of basement faults. The origin of faulting could be related to minor plate motions associated with Atlantic spreading or to the formation of mantle plumes.


In: The Geometry and Growth of Normal Faults. (Edited by Childs, C., Holdsworth, R. E., Jackson, C. A.-L., Manzocchi, T., Walsh, J. J. & Yielding, G.). Geological Society of London, Special Publication 439, doi.org/10.1144/SP439.14.