The Revsegg and Kvitenut allochthons, Scandinavian Caledonides: origins and evolution in the Caledonian Wilson cycle

Abstract

The Caledonian Orogen preserves the record of a complete Wilson cycle from rifting to continent–continent collision and orogenic collapse. The Revsegg Allochthon, the uppermost tectonostratigraphic unit of the Hardangervidda–Ryfylke Nappe Complex of the southern Scandinavian Caledonides, is an understudied example illustrating the key temporal and tectonic stages in a Wilson cycle. It overlies 1600–1500 Ma gneisses of the Kvitenut Allochthon, which were deformed, metamorphosed and juxtaposed onto the Dyrskard Allochthon at 1000 Ma. The Revsegg Allochthon consists of leucosome-bearing mica schists with metasandstone, and amphibolite and granitoid lenses. The timing of sedimentation of the metasedimentary rocks is constrained to the period 780–495 Ma, but its association with a 495 Ma bimodal mafic and felsic intrusive suite suggests concurrent sedimentation in a Cambrian extensional setting. The Revsegg Allochthon underwent peak metamorphism at 480–470 Ma, followed by several metamorphic stages from 460 to 440 Ma, probably at an active margin outboard of Baltica, as postulated for the eclogite-bearing Jæren Nappe to the SE. The Revsegg Allochthon was thrust onto the Kvitenut–Dyrskard duplex from 437 to 434 Ma during an early Scandian phase, which is also recognized in the Seve Nappe. Syn-deformational pegmatites, emplaced at 428 Ma, represent the final stage in the development of the nappe stack.Thematic collection: This article is part of the Caledonian Wilson cycle collection available at: https://www.lyellcollection.org/cc/caledonian-wilson-cycle