This report provides an account of the geology of the Newtonmore-Ben Macdui district in the Grampian Highlands of Scotland, which extends from the Cairngorm massif in the north-east, west across to the Upper Spey valley and south into the upper parts of Glen Tilt and Glen Fearnach. The district is nearly all remote countryside with steep-sided glens between upland plateaus with relatively few distinct mountain peaks. The entire area lies within the Cairngorm National Park and much of the land is covered by large estates run for game conservation and recreational sports.
The bulk of the rocks are metasedimentary and most of these are assigned to the Neoproterozoic Dalradian Supergroup (Figure 1). In the north-west near Newtonmore, a ridge or ‘palaeohigh’ of older metasedimentary rocks, the Glen Banchor Subgroup, is considered to lie below the Dalradian. The Dalradian Supergroup forms a thick succession of originally clastic, carbonate and pelitic rocks. Much of the latter is graphitic and pelagic in origin. The metasedimentary rocks were intruded by relatively minor basic igneous and granitic bodies as the Rodinian palaeocontinent broke up.
At about 470 Ma the Laurentian continental margin collided with an island arc causing the Grampian Event of the Caledonian Orogeny. The orogeny is mainly manifest in four deformation phases which included early large nappe-like folds, ductile shear-zones and prograde Barrovian regional metamorphism. Most of the rocks in this district lie within the kyanite zone but, because most of the rocks are siliceous, this index mineral is scarce. Semipelitic rocks are locally migmatitic. The earlier Precambrian metamorphism in the Glen Banchor Subgroup is overprinted by the Grampian metamorphism.
The world’s mountain ranges are the clearest manifestations of long-term deformation of the continental crust. As such they have attracted geological investigations for centuries. Throughout this long history of research a few keynote publications stand out. One of the most important is the Geological Survey’s 1907 memoir, The Geological Structure of the North-West Highlands of Scotland. The papers in this Special Publication celebrate the 100th anniversary of this remarkable book, placing the original findings in a present-day context by juxtaposing them against modern studies, not only from the NW Highlands, but also from elsewhere around the world.
Synopsis The Moine Thrust Belt of the Northwest Highlands of Scotland represents the front of the Caledonian Orogeny. The exact age of this thrust belt is the source of continuing debate, and has not been fully resolved either by dating of igneous rocks within the thrust belt or by direct dating of mylonites. The Canisp Porphyry sills are porphyritic quartz–microsyenite intrusions, found in the Foreland to the Moine Thrust Belt in the Assynt region. The sills occur close to the lowest thrust, but are never seen within the thrust belt. They are thus considered to predate movement on the lowest thrusts. This paper presents a U–Pb (TIMS) zircon date of 437 ± 4.8 Ma for the Canisp Porphyry, and thus movement on the lower thrusts of the Moine Thrust Belt is constrained as having occurred after that date.
Synopsis The front cover image for this volume is a hill-shaded digital surface model (DSM) of the Ullapool area, created using NEXTMap Britain elevation data from Intermap Technologies. This is a classic area for bedrock geology, transected by the Moine Thrust Zone, and in recent years it has also been studied in detail for its glacial history. Perhaps equally important, this is one of Scotland's most iconic landscapes. The geology of the area comprises a number of distinct sequences, each of which has a characteristic landscape expression as illustrated by the DSM. This paper considers the influence of the bedrock geology on the glacial geomorphology, and shows that the interplay of the two has led to the development of the different landscape elements of this spectacular area. Surprisingly, it is not always the major geological features – such as the Moine Thrust – that have the strongest topographic expression.
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