The Dalradian rocks of the north-east Grampian Highlands of Scotland

Origin, age, and significance of deep‐seated granulite‐facies migmatites in the Barrow zones of Scotland, Cairn Leuchan, Glen Muick area

“…Abundant garnet–hornblende–clinopyroxene mafic gneisses also outcrop on the hill of Cairn Leuchan (Figures and ) and are extensively migmatized. Although initially interpreted as Precambrian basement (Ramsay & Sturt, ; Read, ; Smith, Goodman, & Robertson, ; Sturt, Ramsay, Pingle, & Teggin, ; Viete, Richards, Lister, Oliver, & Banks, ), these mafic gneisses and intercalated metapsammite, metapelite, and calcsilicate lithologies have recently been stratigraphically reassigned to the Crinan Subgroup of the Upper Dalradian Series (Stephenson, Mendum, Fettes, Smith, et al., ), and thus are considered contiguous with the rest of the lower grade Barrow zone sequence. Detailed structural investigation has shown that these metamorphosed basic sheets were intruded as dykes and sills before regional‐scale Grampian deformation, although some fine‐grained rocks exposed near the base of the Subgroup are regarded as metavolcanic (Fettes, MacDonald, Fitton, Stephenson, & Cooper, ; Stephenson, Mendum, Fettes, Smith, et al., ).…”

The source of Dalradian detritus in the Buchan Block, NE Scotland: application of new tools to detrital datasets

“…The rocks record a complex sequence of tectonomagmatic events, termed the Caledonian orogenic cycle (McKerrow et al 2000;Chew & Strachan 2014), related to the opening and closure of the Iapetus Ocean during supercontinent break-up and reassembly in the early Palaeozoic (Cambrian to Devonian) (Soper 1994;Dewey & Mange 1999;Cawood et al 2003Cawood et al , 2007aChew et al 2009;Kirkland et al 2013;Chew & Strachan 2014). Recent reviews on the Caledonides of Scotland and Ireland have been provided by Stephenson et al (2013a), Chew & Strachan (2014), Tanner (2013) and Dewey et al (2015), and of the geology of the NE Grampian Highlands, including the Buchan Block, by Stephenson et al (2013b).…”

“…2). It is bounded to the west and south by major shear zones and exhibits some profound differences compared with the rest of the Grampian Terrane (Stephenson et al 2013b). These differences include the presence of large layered mafic-ultramafic intrusions (the NE Grampian Basic Suite), numerous peraluminous granite bodies and metasedimentary migmatites from which the granites may have been derived (Johnson et al 2003), and the widespread development of low-pressure (andalusite to sillimanite) Buchan-type regional metamorphism (Read 1952;Harte & Hudson 1978) rather than Barrovian (kyanite to sillimanite) metamorphism (Barrow 1893(Barrow , 1912) that characterizes Dalradian rocks outside of the Buchan Block.…”

“…These differences include the presence of large layered mafic-ultramafic intrusions (the NE Grampian Basic Suite), numerous peraluminous granite bodies and metasedimentary migmatites from which the granites may have been derived (Johnson et al 2003), and the widespread development of low-pressure (andalusite to sillimanite) Buchan-type regional metamorphism (Read 1952;Harte & Hudson 1978) rather than Barrovian (kyanite to sillimanite) metamorphism (Barrow 1893(Barrow , 1912) that characterizes Dalradian rocks outside of the Buchan Block. Although the Buchan Block has been regarded by some as an exotic terrane thrust into place during Grampian orogenesis (Sturt et al 1977;Ramsay & Sturt 1978), it is now generally regarded as autochthonous (Johnson et al 2001b(Johnson et al , 2015Stephenson et al 2013b). At lower stratigraphic levels, rocks comprising semipelites, graphitic metapelites and psammites with minor metalimestones and metavolcanic rocks are generally ascribed to the Argyll Group, whereas at higher stratigraphic levels within the core of the Buchan Block, a thick sequence of metaturbidites belongs to the Southern Highland Group (Fig.…”

“…2). One sample (BB6) is from the Argyll Group, and is assigned to the Crinan Subgroup (Goodman 1991;Stephenson et al 2013b); the others are from the Southern Highland Group of which, based on a structural cross-section of the area (Stephenson & Gould 1995), the proximity of the samples to the Argyll Group-Southern Highland Group contact and the metamorphic grade of the rocks (which increases down-stratigraphy), BB1 is stratigraphically lowest and BB3 stratigraphically highest. BB6 is a coarse-grained granulite-facies metapelitic migmatite (Johnson et al 2001a(Johnson et al ,b, 2015; BB1 (amphibolitefacies staurolite zone) and BB3 (greenschist-facies biotite zone) are from massive psammite units interbedded with metapelite; BB5 (amphibolite-facies andalusite zone) is a semipelite containing sparse Mn-rich garnet.…”