Moine Thrust Belt
Mountains within the belt display complexly folded and faulted layers and the width of the main part of the zone varies up to ten kilometres (six miles), although it is significantly wider on Skye.
After further fieldwork, Nicol changed his mind and advocated instead that the contact at the base of the upper gneisses was tectonic, starting what was known as the Highlands Controversy.
The results of the mapping proved conclusively to Peach and Horne that the contact was tectonic and they were eventually able to persuade Geikie when he visited them briefly in the field in October 1884.
[2] The Moine Thrust Belt was formed during the Scandian orogenic phase Caledonian Orogeny cycle as part of the collision between Laurentia and Baltica.
The relationship between the Moine Thrust Belt and other Scandian age structures in Scandinavia and East Greenland remains unclear, due to uncertainties associated with the Great Glen Fault zone.
This major sinistral (left-lateral) strike-slip fault was also active during the late stages of the orogeny, but continued to move during the early Devonian and appears to truncate the southern end of the thrust belt.
The total late Caledonian displacement on the Great Glen Fault is poorly constrained, making reconstruction of the southern part of the orogenic belt difficult.
The overlying Pipe Rock Member is a distinctive quartz arenite with many white weathering skolithos trace fossils that act as strain markers in areas of more ductile deformation.
The distinctive character of this sequence enabled detailed mapping, even in areas of relatively poor exposure and allowed sections repeated by thrusting to be recognised.
The Morar Group forms the lowest tectonostratigraphic unit of the Neoproterozoic metasediments, lying tectonically beneath the younger Loch Ness Supergroup.
Unlike the other thrusts, there is a broad zone (up to 600 m in thickness) of the Morar Group in the hanging-wall that is intensely deformed into mylonite, indicating that it originated at a significantly deeper crustal level.
The exposures on the flank of Ben Arnaboll have particular importance as it was here that Lapworth first described the highly deformed rock type mylonite and also where Geikie coined the term "thrust plane".
The presence of half graben basins in the hanging walls of these faults was interpreted to represent Devonian and Mesozoic extensional reactivation of the Caledonian thrust structures.
Onshore in Shetland the Wester Keolka Shear was proposed to represent the Moine Thrust,[9] although more recent radiometric dating results suggest that this is unlikely to be the case.
[11] In respect of it being 'the classic orogenic front of significant importance in both modern and historical tectonics research', the International Union of Geological Sciences (IUGS) included the 'Moine Thrust Zone' in its assemblage of 100 'geological heritage sites' around the world in a listing published in October 2022.
