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Unravelling the kinematic evolution of segmented rift systems

Bubeck, Alodie 2016. Unravelling the kinematic evolution of segmented rift systems. PhD Thesis, Cardiff University.
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Abstract

Normal fault systems within incipient rifts comprise an array of small-­‐scale structures, including networks of fractures and small displacement faults (<15 m) that represent the incremental strains that develop during rift propagation. To constrain the evolution of volcanic rift systems, I investigate rift-­‐fault propagation and localisation at a range of scales using laboratory-­‐based mechanical characterisation of host rocks, and high-­‐resolution structural mapping of faults, and fault-­‐related deformation in an incipient (Koa’e fault system, Hawai’i), and evolved (Krafla fissure swarm, Iceland) rift system. Experimental analysis of pahoehoe lava from Kilauea’s south flank, Hawai’i, highlight a distinctive physical and mechanical stratigraphy related to the volume, and geometry, of voids within the lava. The resulting variability in intact strength produces the effect of a multi-­‐layered sequence within a single lava, and will exert significant control on the segmentation and linkage of initial cracks (mm-­‐scale or less) that develop. High-­‐ resolution mapping of the distribution, geometry, and kinematics of cm-­‐ to km-­‐scale extensional strains in the Koa’e fault system (Hawai’i) and the Krafla fissure swarm (Iceland) also reveals evidence for segmented fault propagation, linkage and non-­‐coaxial strain. This segmentation is a function of the varying natural mechanical anisotropy of the deforming sequence and non-­‐uniform strain rates. Results from the Koa’e and Krafla rifts are compared with break-­‐up related deformation from the NE Atlantic margins to model the evolution of non-­‐coaxial fault sets at the margin scale. Fault and intrusion data from the Faroe Islands and East Greenland highlights geometrically and kinematically comparable structural sets, implying an analogous kinematic evolution of inter-­‐rift strains. I infer that stress transfer during NE Atlantic opening took place by sub-­‐basin scale ancillary faults and dikes, associated with two overlapping, active rift systems in the Paleogene – a NE-­‐propagating Reykjanes ridge, and a SW-­‐ propagating Aegir ridge – rather than via transfer fault segmentation.

Item Type: Thesis (PhD)
Date Type: Publication
Status: Unpublished
Schools: Earth and Ocean Sciences
Subjects: Q Science > QE Geology
Date of First Compliant Deposit: 11 October 2016
Last Modified: 20 Oct 2017 01:30
URI: http://orca.cf.ac.uk/id/eprint/95297

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