NJG58-4-02
1978
A Rb/Sr whole-rock isochron date from the lowermost gneiss complex of the Gaular area, west Norway and its regional implications
58
4
259-265

The Precambrian rocks within the Gaular area can be tectonically divided into two major rock units; a lower complex (Jostedal Complex), which largely consists of migmatites and gneiss-granites, and an overlying largely metasupracrustal sequence. The latter unit, which may be subdivided into the Holsen Gneiss (mainly quartz-rich paragneisses) and the Vevring Complex (mainly amphibolites, paragneisses, and eclogitic rocks), has been interpreted as a thurst sheet, the Sunnfjord nappe. The Jostedal Complex yields a metamorphic Rb/Sr whole-rock isochron date of 1625 ±75 m.y. An initial 87Rb/86Sr ratio of o.70 1 ± 0.002 excludes an extended crustal history prior to the major metamorphism. Two biotite/whole-rock ages of 392 ± 15 m.y. and 396 ± 15 m.y. provide evidence for a Caledonian influence in the area. It is assumed that the emplacement of the Sunnfjord nappe took place late in the Sveconorwegian (Grenvillian) orogeny.

0029-196X
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