A whole rock Rb-Sr isotope study of the Kleivan granite, Farsund area in south Norway, has determined an age of 930 ± 7 m. y., and an initial strontium ratio of . 7052 ± 2. This result is in accord with recent estimates of the major plutonic episode of the Rogaland Province, southwestern Norway. · The age and initial Sr-ratio is markedly different from that of the Farsund charnockite, which from other geological and geochemical evidence seems strong!y related. Possible explanations for the difference in initial Sr-isotope ratios are discussed. These suggest a two-step generation which involves isotope-disequilibrium melting and/or a selective 87Sr-extraction, accompanying the generation of melt from a common, lower crustal source rock.
Strontium-isotope study of the Kleivan granite, southern Norway