Abstract

The Dalradian block, a part of the Precambrian metamorphic basement of Scotland, is thought to be exotic to Laurentia, having a provenance in Gondwana. In contrast to the rest of the Laurentian margin, which from ca. 700 to 530 Ma was undergoing extension, the Dalradian block was undergoing severe compression ca. 590 Ma. At the time of splitting of the Late Proterozoic supercontinent, both Gondwana and Laurentia shared a common history of extension; however, at ca. 670 Ma Gondwana converted to a destructive margin and underwent compression, whereas Laurentia remained in extension and passive to 500-510 Ma. The Dalradian block had two major phases of metamorphism and deformation, one in Gondwana, and the other in Laurentia. The second phase of classical Barrovian metamorphism may have been produced by thickening due to emplacement of ophiolitic and other nappes, rather than the earlier internal nappe structures. Late-stage ductile folding in the Moine basement to the north may be related to the final emplacement of the Dalradian block onto Laurentia.

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