Abstract

In the west Norwegian Caledonides minor granitic sheets were intruded during obduction of the c. 443 Ma Solund–Stavfjord Ophiolite Complex. The Sogneskollen Granitic Complex is the largest intrusive complex and consists of several minor lenses and one larger lens of granodiorite. The Sogneskollen Granitic Complex samples generally have high Ba, Sr and Na2O, very low Y values (<7 ppm), negative εNd420 Ma values (c. −7 to −10.1) and 87Sr/86Sr420 Ma ratios of 0.70437–0.70705. The REE patterns are strongly HREE depleted and La/Ybn varies from 0.3 to 36. Most samples display small positive Eu anomalies, but those that are most fractionated have small negative anomalies. The main part of the Sogneskollen Granitic Complex is a white composite granodiorite which is intruded by a suite of grey biotite-granite dykes. It is suggested that this, and other similar granitic sheets in the area, most probably formed by melting of sediments in the presence of a H2O-bearing volatile phase during obduction of the ophiolite. The quartzofeldspathic source sediments most probably contained detritus from long-term Rb-depleted lower continental crust and from an island arc. The sediments were deposited in large amounts in the marginal basin now represented by the Solund–Stavfjord Ophiolite Complex. During obduction the sediments were buried beneath the hot overriding Ophiolite Complex and the associated island-arc, and yielded granitic magmas during partial melting.

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