STRONTIUM ISOTOPE STUDY OF 2 SUPPOSED SATELLITE MASSIFS OF THE EGERSUND ANORTHOSITE COMPLEX - THE SJELSET IGNEOUS COMPLEX AND THE UNDHEIM LEUCONORITE

The Sjelset Igneous Complex is an undeformed inhomogeneous granitic bo dy with two main rock types: biotite granite and Fe-rich pyroxene +/- fayalite charnockite. The nearby Undheim Leuconorite shows only minor deformation and recrystallization and preserves a cumulate texture. Bo th the Sjelset Igneous Complex and the Undheim Leuconorite occur in th e westernmost part of the autochthonous Proterozoic basement and proba bly continue below the Caledonian Nappe system. The two bodies have be en 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 Sjelse t granite (985 Ma) and Sjelset charnockite (900-930 Ma) represent two separate intrusions. Similarities with the upper (Quartz) Monozonitic Phase of the Bjerkreim-Sokndal Lopolith suggest that the Sjelset charn ockites result from anorthositic magmatism. The Sjelset biotite granit e is probably of crustal origin. Correlation of the Undheim Leuconorit e (1028 Ma) with the lower anorthositic-noritic units of the Bjerkreim -Sokndal Lopolith and with the Hidra Leuconorite is uncertain. A NNW c ontinuation of the hypersthene-in isograd in the northern part of the Rogaland isograd pattern is probably related to the NNW continuation o f anorthostic magmatism.