Caledonian Nappe Sequence of Finnmark, Northern Norway, and the Timing of Orogenic Deformation and Metamorphism
Caledonian Nappe Sequence of Finnmark, Northern Norway, and the Timing of Orogenic Deformation and Metamorphism B. A. STURT Geologisk Institutt, adv. A, Joachim Frielesgt. 1, Bergen, Norway I. R. PRINGLE Department of Geophysics, Madingley Road, Cambridge, England D. ROBERTS Norges Geologiske Undersakelse, Postboks 3006, Trondheim, Norway ABSTRACT and have a varying metamorphic state, reaching at least into garnet grade (Holtedahl and others, 1960). The exact relation between On the basis of regional, structural, and metamorphic studies these rocks on Mageray and the older Caledonian metamorphic combined with age determinations, it is demonstrated that the in- complex of the Kalak Nappe are, however, not yet established. ternal metamorphic fabrics of the main nappe sequence of Finn- Correlations made by a number of authors equate, with the mark, northern Norway, developed during an Early Ordovician obvious exception of the younger sedimentary rocks of Magertfy, phase of the Caledonian orogeny (Grampian?); the cleavage de- the rocks of the Finnmark nappe pile with the upper Pre- velopment in the autochthon also belongs to this phase. The final cambrian-Tremadoc sequence of the foreland autochthon. This mise-en-place of the thrust-nappe sequence, however, appears to correlation indicates that- the entire Caledonian sequence of the belong to a later phase of Caledonian orogenic development, prob- nappe pile (without Mageroy) and immediately underlying au- ably toward the end of the Silurian Period, as does the deformation tochthon is upper Precambrian, passing conformably up at least and metamorphism of the Silurian sequence of Mageray. The into the lower part of the Tremadoc. The nappe units beneath the geochronological results also give information regarding the posi- Kalak Nappe, although of lower metamorphic grade, have a simi- tioning of the lower boundaries to the Cambrian and Ordovician lar structural sequence.
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