Ard Mor, Bettyhill
Geological Conservation Review site | GCR #2971 | Structural and Metamorphic Geology | Moine
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Summary
At this site we can see good exposures of typical lithologies of the Bettyhill assemblage migmatised metasediments, amphibolites, granites and pegmatites, showing the effects of polyphase deformation and metamorphism. There are many examples of granite and pegmatite veins within this area, both foliated and unfoliated, which clearly crosscut and are later than the early (D1) regional migmatisation. At least four phases of deformation can be distinguished. The early (D1) regional gneissification and migmatisation produced fabrics which are folded by later tight folds (F2). These are both refolded by later (F3) folds, eg [NC698630]. Other F3 folds are well-displayed at Creag Ruadh [NC696630] where tight upright folds are accompanied by a remarkable (?F2) eye fold [NC696630] which shows extreme hinge curvilinearity, a feature of the local (F2) folds. On the east side of Creag Ruadh a variety of late crosscutting pegmatites, microgranites and lamprophytic sheets occur. The Ard Mor amphibolite forms a series of discontinuous bodies extending along the strike through the area. This has been shown to be part of the early (pre-D1) tholeiitic intrusive suite. The early D1 metamorphism produced a moderately coarse garnet amphibolite, whilst later deformation and metamorphism progessively reduces this to fine grained hornblende schist. Discontinuously developed in the vicinity of the amphibolite is a singular quartz-biotite rock which has been explained as a high-strain restite produced from the partial melting of psammitic gneiss. The essence of this site is that is exemplifies the polyorogenic migmatitic gneisses, amphbolite and granite veins which make up the Bettyhill assemblage. This is most probably a high grade lateral equivalent of part of the Morar Division.
Related geosites
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