Abstract
Many rifts develop in response to multiphase extension with numerical and physical models suggesting that reactivation of first-phase normal faults and rift-related variations in bulk crustal rheology control the evolution and final geometry of subsequent rifts. However, many natural multiphase rifts are deeply buried and thus poorly exposed in the field and poorly imaged in seismic reflection data, making it difficult to test these models. Here we integrate recent 3D seismic reflection and borehole data across the entire East Shetland Basin, northern North Sea, to constrain the long-term, regional development of this multiphase rift. We document the following key stages of basin development: (i) pre-Triassic to earliest Triassic development of multiple sub-basins controlled by widely distributed, NNW- to NE-trending, east- and west-dipping faults; (ii) Triassic activity on a single major, NE-trending, west-dipping fault located near the basins western margin, and formation of a large half-graben; and (iii) Jurassic development of a large, E-dipping, N- to NE-trending half-graben near the eastern margin of the basin, which was associated with rift narrowing and strain focusing in the Viking Graben. In contrast to previous studies, which argue for two discrete periods of rifting during the Permian–Triassic and Late Jurassic–Early Cretaceous, we find that rifting in the East Shetland Basin was protracted from pre-Triassic to Cretaceous. We find that, during the Jurassic, most pre-Jurassic normal faults were buried and in some cases cross-cut by newly formed faults, with only a few being reactivated. Previously developed faults thus had only a limited control on the evolution and geometry of the later rift. We instead argue that strain migration and rift narrowing was linked to the evolving thermal state of the lithosphere, an interpretation supporting the predictions of lithosphere-scale numerical models. Our study indicates that additional regional studies of natural rifts are required to test and refine the predictions of physical and numerical models, more specifically, our study suggests models not explicitly recognising or including thermal or rheological effects might over emphasise the role of discrete pre-existing rift structures such as normal faults.
Highlights
Continental extension marks the first stage of ocean basin formation, being associated with normal faulting and the development of rift basins (e.g. Nagel and Buck, 2007)
Because sedimentary basins formed during the early stages of multiphase rifting are progressively buried and structurally overprinted during later stages of rifting, it can be difficult to assess the role pre-existing faults play in controlling subsequent rift geometry
Subsurface studies utilising long (10’s to 100 km), widely spaced (>5 km) 2D seismic profiles allow us to define the basin-scale geometry of structures associated with individual tectonic phases in multiphase rifts, but these lack the spatial detail needed to investigate how pre-existing faults behave on the scale of individual fault systems (e.g., Badley et al, 1988; Coward, 1993; Thomas and Coward, 1995; Færseth, 1996; Reston, 2005)
Summary
Continental extension marks the first stage of ocean basin formation, being associated with normal faulting and the development of rift basins Outcrop studies can reveal the geometry and kinematic development of large rift-related fault arrays (i.e., a kinematically linked group of faults that are 10’s to 100 km of length) at a relatively high-level of spatial and temporal precision (e.g., Strecker et al, 1990; Gawthorpe et al, 2003; Morley et al, 2004) Such studies are typically limited by the quantity and quality of outcrop, with structures and stratigraphy associated with only one rift stage being exposed. Subsurface studies utilising long (10’s to 100 km), widely spaced (>5 km) 2D seismic profiles allow us to define the basin-scale geometry of structures associated with individual tectonic phases in multiphase rifts, but these lack the spatial detail needed to investigate how pre-existing faults behave on the scale of individual fault systems (i.e., kinematically linked group of faults that are 1-to several 10’s of km long) (e.g., Badley et al, 1988; Coward, 1993; Thomas and Coward, 1995; Færseth, 1996; Reston, 2005). Unlike most previous studies (see above), our extensive, high-quality dataset allows us to document how pre-existing normal faults throughout a regional fault array accommodate later extension
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
