Evidence from Rb–Sr mineral ages for multiple orogenic events in the Caledonides of Shetland, Scotland

Evidence for an Early Silurian Synorogenic Basin Within the Metamorphic Hinterland of the North Atlantic Caledonides: Insights From the U‐Pb Zircon Geochronology of the Funzie Conglomerate, Shetland, Scotland

“…The latter is broadly correlative with the Dalradian Supergroup of the Grampian Terrane in mainland Scotland (Figure a; Flinn, ; Strachan et al, ). Rb‐Sr mineral ages of 480–440 Ma constrain the main metamorphic assemblages and deformation fabrics to have formed during Grampian orogenic events (Walker et al, ). The earliest stage of Grampian orogenic activity corresponds to the obduction of the Unst ophiolite (Figure b; Flinn, , , ; Spray & Dunning, ; O'Driscoll et al, , ).…”

“…The transport direction is thought to have been toward the west, parallel to an L1 lineation only preserved in northwest Unst (Figure c; Cannat, ; Flinn & Oglethorpe, ; Flinn, ). This was followed by the reworking of low‐angle thrust‐related fabrics into a regionally steep orientation across Yell and Mainland Shetland (Walker et al, ). Peak pressure‐temperature conditions were approximately 10 kbar and 775 °C (Cutts et al, ). “Grampian II” amphibolite facies metamorphism of the footwall metasedimentary successions at ca.…”

“…Peak pressure‐temperature conditions were approximately 10 kbar and 775 °C (Cutts et al, ). “Grampian II” amphibolite facies metamorphism of the footwall metasedimentary successions at ca. 450–445 Ma (Walker et al, ). Development of a greenschist facies foliation and associated NNE trending L2 mineral lineation forms the single and dominant deformation fabric within the Funzie Conglomerate (Figure c). Top‐to‐the‐NNE kinematic indicators parallel to L2 are well developed (Cannat, ; R. A. S., unpublished data).…”

Evidence from U–Pb zircon geochronology for early Neoproterozoic (Tonian) reworking of an Archaean inlier in northeastern Shetland, Scottish Caledonides

“…1) and resulted in the Grampian orogenic event (Lambert & McKerrow 1976;Chew et al 2010). This caused widespread metamorphism and deformation of the Moine and Dalradian Supergroups and equivalent units in Shetland (Dewey & Shackleton 1984;Dewey & Ryan 1990;Kinny et al 1999;Oliver et al 2000;Cutts et al 2011;Tanner 2013;Walker et al 2016). The subsequent Silurian collision of Laurentia with Baltica resulted in the c. 435 -425 Ma Scandian orogenic event.…”

“…In mainland Scotland, regional deformation and metamorphism of the Moine Supergroup was followed by its northwestward translation along the Moine Thrust (Coward 1990;Dallmeyer et al 2001;Dewey & Strachan 2003). The relative paucity of Silurian mineral ages in Shetland is attributed to a likely location at a high structural level in the regional nappe pile relative to mainland Scotland (Walker et al 2016).…”