Synopsis

The Loch Tay Fault in the Central Highlands of Scotland is the easternmost of six major faults that transect the Dalradian. Examination of the limited exposure along the sub-vertical fault walls in the type area demonstrates that it has undergone a history of left-lateral strike-slip as well as dip-slip. Evidence from the displacement of formation boundaries and of fold traces shows that the fault has undergone a finite history of 6.5–7.5 km of left-lateral strike-slip and a dip-slip, down to the NW, of 750–1000 m in the SW and central area, diminishing to 200 m or less in the NE. A major fault lens to the NW of the main fault (the Braes of Foss Fault Complex) has similarly undergone dip-slip (but down to the SE) and left-lateral strike-slip; however, two fault lenses to the SE of the major fault (the Glen Goulandie Fault Complex and a smaller lens to its SW) and associated splays have undergone right-lateral displacement. Displacements on the Frenich Burn Fault, a minor fault to the east of the Loch Tay Fault, are again dominantly left-lateral with small displacements down to the NW, whereas faults in an adjacent mine pit illustrate that displacements in the country rock are dominantly dip-slip. By analogy with the Tyndrum Fault, the main left-lateral and dip-slip movements are considered to be pre-Devonian, whereas the right-lateral and late extensional movements are interpreted as Carboniferous.

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