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Older than you think: Using U-Pb calcite geochronology to better constrain basin-bounding fault reactivation, Inner Moray Firth Basin, W North Sea

Tamas, A.; Holdsworth, R. E.; Tamas, D. M.; Dempsey, E. D.; Hardman, K.; Bird, A.; Roberts, N.M.V.; Lee, J.; Underhill, J. R.; McCarthy, D.; McCaffrey, K. J. W.; Selby, D.

Authors

A. Tamas

R. E. Holdsworth

D. M. Tamas

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Dr Eddie Dempsey E.Dempsey@hull.ac.uk
Senior Lecturer in Structural Geology and Geohazards

K. Hardman

N.M.V. Roberts

J. Lee

J. R. Underhill

D. McCarthy

K. J. W. McCaffrey

D. Selby



Abstract

Like many rift basins worldwide, the Inner Moray Firth Basin (IMFB) is bounded by major reactivated fault zones, including the Helmsdale Fault and the Great Glen Fault (GGF). The Jurassic successions exposed onshore close to these faults at Helmsdale and Shandwick preserve folding, calcite veining and minor faulting consistent with sinistral (Helmsdale Fault) and dextral (GGF) transtensional movements. This deformation has been widely attributed to Cenozoic post-rift fault reactivation. Onshore fieldwork and U–Pb calcite geochronology of five vein samples associated with transtensional movements along the Helmsdale Fault and a splay of the GGF show that faulting occurred during the Early Cretaceous (c. 128–115 Ma, Barremian–Aptian), while the Helmsdale Fault preserves evidence for earlier Late Jurassic sinistral movements (c. 159 Ma, Oxfordian). This demonstrates that both basin-bounding faults were substantially reactivated during the episodic NW–SE-directed Mesozoic rifting that formed the IMFB. Although there is good evidence for Cenozoic reactivation of the GGF offshore, the extent of such deformation along the north coast of the IMFB remains uncertain. Our findings illustrate the importance of oblique-slip reactivation processes in shaping the evolution of continental rift basins given that this deformation style may not be immediately obvious in interpretations of offshore seismic reflection data.

Citation

Tamas, A., Holdsworth, R. E., Tamas, D. M., Dempsey, E. D., Hardman, K., Bird, A., …Selby, D. (in press). Older than you think: Using U-Pb calcite geochronology to better constrain basin-bounding fault reactivation, Inner Moray Firth Basin, W North Sea. Journal of the Geological Society, 180(5), Article jgs2022-166. https://doi.org/10.1144/jgs2022-166

Journal Article Type Article
Acceptance Date Jun 19, 2023
Online Publication Date Jun 26, 2023
Deposit Date Jul 18, 2023
Publicly Available Date Sep 25, 2023
Journal Journal of the Geological Society
Print ISSN 0016-7649
Electronic ISSN 2041-479X
Publisher Geological Society
Peer Reviewed Peer Reviewed
Volume 180
Issue 5
Article Number jgs2022-166
DOI https://doi.org/10.1144/jgs2022-166
Public URL https://hull-repository.worktribe.com/output/4335495