The structure and metamorphism of the area between Clunie Lodge and the Cairnwell, Aberdeenshire

Abstract

The results of detailed mapping confirm the Dalradian Succession suggested by E.B. Bailey, but his structural interpretation of the area proves to be incorrect. Mapping of the Baddoch Burn area indicates that the suggestion by Bailey of a complex system of slides contemporaneous with the original folding occurring in this region is also erroneous. It is shown from further field evidence that the region is affected by two major thrusts which, in this area of study, are developed on either side of the Blair Atholl Series. These thrusts divide the schists into three structural levels. The highest of these, the Morrone Nappe, is a primary structure in which the Ben Eagach Schist is overlain by the older Perthshire Quartzite. The thrust at the base of the Morrone Nappe is gently folded. The thrust-bounded Blair Atholl Series are squeezed out in the Clunie Lodge region, where the upper and lower thrusts merge, and bring the Morrone Nappe in contact with a lower nappe. In this locality the Ben Eagach Schist and the Perthshire Quartzite are exposed at a lower structural level. Three episodes of folding preceded the thrusting, and the main metamorphism was synchronous with, and overlapped the second folding. Garnet growth occurred during this F2 period, and was accompanied by kyanite and staurolite when these movements ceased. Contemporaneous with the third folding, many of the earlier formed minerals were replaced by chlorite. Biotite was also formed during this period and both minerals continued growing after this deformation. The thrust movements were followed by a sinistral folding about a near vertical axis, causing a marked change of strike in the vicinity of the Cairnwell. Finally normal faulting and brecciation of the country rock was associated with the intrusion of a suite of acid and intermediate dyke rocks.