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- Widenfalk, Lennart, et al.
(författare)
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A multidisciplinary investigation of the Notträsk Gabbro, northern Sweden
- 1985
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Ingår i: Geologiska föreningens i Stockholm förhandlingar. - : Informa UK Limited. - 0016-786X. ; 107:2, s. 109-126
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Tidskriftsartikel (refereegranskat)abstract
- The differentiated, sulfide-bearing gabbro near the city of Boden in northern Sweden has been investigated in order to get a plausible model for its formation, shape and age. The gabbro is associated with a major fault system along which several intrusive bodies occur. The largest of these has been traversed by a gravimetric, magnetometric and geological profile. The investigated intrusion is undeformed and oval-shaped and covers some 20 km2. The outer parts of the body consist of a norite in contact with older meatasediments and granites of varying age. Inside the norite occurs a magnetite-rich gabbro, which forms a ring around the centre of the massif, which in turn consists of leucogabbro-olivine gabbro. Fe, Ti and K are low in the centre where Mg and Cr have their highest contents. Impregnations of sulfides and a massive pyrrhotite vein with some 1 % Ni are located in the norite. A number of intrusion models have been tested by computer modelling combining gravimetric and magnetic field data. The most probable model seems to be a funnel-shaped body pointing downwards. The different gabbro types dip steeply inwards indicating vertical zones rather than horizontal. Palaeomagnetic measurements show that the intrusion has a similar orientation of magnetization as other gabbros of the Haparanda series in northern Sweden (1800-1900 Ga, Rb-Sr). Furthermore, the pole distributions show that the rock cooled slowly, which may indicate that the present outcrop is a deep part of an eroded intrusion. The massif is supposed to have been formed by a diapiric re-emplacement of primary horizontal cumulates formed in the sequence olivine gabbro-leucogabbro-magnetite-bearing gabbro-norite.
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