Strontium isotope study of two supposed satellite massifs of the Egersund Anorthosite Complex: the Sjelset Igneous Complex and the Undheim Leuconorite
pp. 58-69

The Sjelset lgneous Complex is an undeformed inhomogeneous granitic body with two main rock types: biotite granite and Fe-rich pyroxene ± fayalite chamockite. The nearby Undheim Leuconorite shows only minor deformation and recrystallization and preserves a cumulate texture. Both the Sjelset lgneous Complex and the Undheim Leuconorite occur in the westemmost part of the autochthonous Proterozoic basement and probably continue below the Caledonian Nappe system. The two bodies have been dated by the Rb-Sr whole rock and mineral isochron method. Variable partial resetting of the isotopic systems of rocks and minerals took place during slow Proterozoic cooling and/or Caledonian overthrusting. Field, mineralogical, chemical and isotopic data show that the Sjelset granite (985 Ma) and Sjelset chamockite (900-930 Ma) represent two separate intrusions. Similarities with the upper (Quartz) Monozonitic Phase of the Bjerkreim-Sokndal Lopolith suggest that the Sjelset charnockites result from anorthositic magmatism. The Sjelset biotite granite is probably of crustal origin. Correlation of the Undheim Leuconorite ( 1028 Ma) with the lower anorthositic-noritic units of the Bjerkreim-Sokndal Lopolith and with the Hidra Leuconorite is uncertain. A NNW continuation of the hypersthene-in isograd in the northem part of the Rogaland isograd pattern is probably related to the NNW continuation of anorthostic magmatism.

C. Maijer 1, R. H. Verschure 2 & D. Visser
1 Instituut voor Aardwetenschappen, Vakgroep Geochemie, Universiteit Utrecht, Budapestlaan 4, 3584 CD, The Netherlands;
2Laboratorium voor lsotopen-Geologie, Vrije Universiteit, De Boelelaan 1085, 1081 HV Amsterdam, The Netherlands.