The structural history of a transtensional basin: Inner Moray Firth, NE Scotland

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Abstract
The isostatically-uncompensated Moray Firth Basin forms the western arm of the North Sea rift. Unlike other parts of the rift the Moray Firth opened not by dip-slip movements on basin-bounding faults, but as a result of dextral strike-slip motion on the sub-vertical Great Glen Fault Zone, which during basin opening was probably pinned at its intersection with the Wick Fault. Thus the Caithness Ridge and Northern Highland blocks were stable relative to each other, while the Central Highland and Northern Highland blocks accommodated dextral slip. Previous calculations have shown that a cumulative 8 km of displacement have occurred on the Great Glen Fault Zone since the Permian. Approximately 2 km of this displacement may have formed a small Permian half-graben at the centre of the present basin, the remaining c. 6 km occurred largely during the Late Jurassic, but Triassic and Early Cretaceous displacement is also inferred. Although much of the internal structure of the Inner Moray Firth is dominated by tilted-fault-block structures, displacement analysis indicates that the majority of faults within the basin have accommodated significant oblique-slip motion. An understanding of the kinematics of the basin allows structures attributable to oblique-slip movement to be explained, a number of these are illustrated with seismic reflection examples.