Caledonian structure and magmatism of the Southern Uplands

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Stone, P, McMillan, A A, Floyd, J D, Barnes, R P, and Phillips, E R. 2012. British regional geology: South of Scotland. Fourth edition. Keyworth, Nottingham: British Geological Survey.

Introduction[edit]

Stages in the closure of the Iapetus Ocean . P912315.
Deep crustal sections across the Iapetus Suture Zone. P912318.
Palaeogeographical reconstructions from the Ordovician to the Cretaceous. P912314.

As the Iapetus Ocean closed, collisional events at its margins caused episodes of deformation and metamorphism. Two main events can be identified. The Grampian Event (which peaked at about 470 Ma) was caused by the arrival at the Laurentian margin of arc terranes represented, in small part, by the Upper Ordovician Ballantrae Complex ophiolite (P912315b). The Scandian Event (about 430 Ma) resulted from the collision of Laurentia with Baltica but its effects are largely restricted to northern Scotland. The slightly later convergence of Laurentia with Avalonia and the final elimination of the Iapetus Ocean was a much less dramatic affair that is barely identifiable in the tectonic record. Though it might be anticipated to have had a profound effect in the Southern Uplands terrane, the leading edge of Laurentia, the deformation seen therein is mostly the result of the Late Ordovician to mid Silurian, diachronous accretionary process (P912315c,d). One possible effect of the collision, implicit in P912318, was the north-directed thrust emplacement of the accretionary complex onto Laurentian crystalline basement. Farther to the north, more demonstrable north-directed thrust movements probably instigated by the collision produced the large-scale, Wenlock (about 425 Ma) thrust reactivation of faults affecting the Girvan sequence. The coming together of Laurentia and Avalonia was then followed during the Early Devonian (at about 400 Ma) by the Acadian orogenic event, which was initiated much farther south by the arrival of another Gondwanan continental fragment at the southern margin of Avalonia as the Rheic Ocean closed (P912314c). Acadian effects are most pronounced in northern England and Wales but some tectonic features of the Southern Uplands were influenced by that event. Of particular importance was the transtensional regime that, between about 410 Ma and 397 Ma, focused the intrusion of dyke swarms and granitic plutons.

Bibliography[edit]

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Related articles[edit]

Obduction of the Ballantrae Complex
Deformation of the Girvan succession
Southern Uplands accretionary complex
Late Caledonian dyke swarms
Late Caledonian plutonic rocks