Pre-existing intra-basement shear zones influence growth and geometry of non-colinear normal faults, western Utsira High–Heimdal Terrace, North Sea

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Edoseghe Osagiede, Atle Rotevatn, Robert Leslie Gawthorpe, Thomas Kristensen, Christopher Aiden-Lee Jackson , Nicola Marsh


Pre-existing intra-basement shear zones can induce mechanical and rheological heterogeneities that may influence rifting and the overall geometry of rift-related normal faults. However, the extent to which physical and kinematic interaction between pre-existing shear zones and younger rift faults control the growth of normal faults is less-well understood. Using 3D reflection seismic data from the northern North Sea and quantitative fault analysis, we constrain the 3D relationship between pre-existing basement shear zones, and the geometry, evolution, and synrift depositional architecture of subsequent rift-related normal faults. We identify NE-SW- and N-S-striking rift faults that define a coeval Middle Jurassic – Early Cretaceous, non-colinear fault network. NE-SW-striking faults are parallel to underlying intra-basement shear zone. The faults either tip-out above or physically merge with the underlying shear zone. For faults that merges with the basement shear zone, a change from tabular to wedge-shaped geometry of the hangingwall synrift strata records a transition from non-rotational to rotational extension faulting, which we attribute to the time of rift fault’s linkage with the shear zone, following downward propagation of its lower tip. N-S-striking faults are oblique to, and offset (rather than link with) intra-basement shear zones. These observations highlight the selective influence pre-existing intra-basement shear zones have on evolving rift-related normal faults



Earth Sciences, Geology, Physical Sciences and Mathematics, Tectonics and Structure


Seismic reflection data, extensional tectonics, normal fault, rift basin, North Sea, Fault growth, normal fault growth, northern North Sea, crystalline shear zone, Utsira High


Published: 2019-05-06 17:59

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CC BY Attribution 4.0 International

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