Articles | Volume 8, issue 6
Research article
22 Nov 2017
Research article |  | 22 Nov 2017

Extension parallel to the rift zone during segmented fault growth: application to the evolution of the NE Atlantic

Alodie Bubeck, Richard J. Walker, Jonathan Imber, Robert E. Holdsworth, Christopher J. MacLeod, and David A. Holwell

Abstract. The mechanical interaction of propagating normal faults is known to influence the linkage geometry of first-order faults, and the development of second-order faults and fractures, which transfer displacement within relay zones. Here we use natural examples of growth faults from two active volcanic rift zones (Koa`e, island of Hawai`i, and Krafla, northern Iceland) to illustrate the importance of horizontal-plane extension (heave) gradients, and associated vertical axis rotations, in evolving continental rift systems. Second-order extension and extensional-shear faults within the relay zones variably resolve components of regional extension, and components of extension and/or shortening parallel to the rift zone, to accommodate the inherently three-dimensional (3-D) strains associated with relay zone development and rotation. Such a configuration involves volume increase, which is accommodated at the surface by open fractures; in the subsurface this may be accommodated by veins or dikes oriented obliquely and normal to the rift axis. To consider the scalability of the effects of relay zone rotations, we compare the geometry and kinematics of fault and fracture sets in the Koa`e and Krafla rift zones with data from exhumed contemporaneous fault and dike systems developed within a > 5×104 km2 relay system that developed during formation of the NE Atlantic margins. Based on the findings presented here we propose a new conceptual model for the evolution of segmented continental rift basins on the NE Atlantic margins.

Short summary
We present a field-based study of relay zone development using examples from the Koa’e fault system (Hawai’i) and the Krafla fissure swarm (Iceland). We show the evolution of second-order deformation within these zones and illustrate the effects of horizontal (heave) displacement gradients in evolving continental rift systems. Data are consistent with faults and intrusions from the Faroe Islands and E Greenland. We propose a new model for the evolution of segmented basins along the NE Atlantic.