Lead Isotopes and the Sources of Granitic Magmas: The Sveconorwegian Granite and Pegmatite Province of Southern Norway

Abstract

Lead isotope analyses of K-feldspar from late Sveconorwegian (900–1000 Ma) granitic pegmatites and A-type, ferroan granitic intrusions in four different areas of southern Norway analyzed by laser-ablation inductively coupled plasma source mass spectrometry (LA-ICPMS) give compositions in the range 206Pb/204Pb = 16.637 to 17.555, 207Pb/204Pb = 15.445 to 15.534, 208Pb/204Pb = 36.317 to 37.459. These compositions broadly overlap with the initial compositions estimated from previously published solution TIMS whole-rock and feldspar Pb isotope analyses of late Sveconorwegian granitic plutons across the region, suggesting that magmas forming A-type granite plutons and granitic pegmatites have been derived from broadly similar source rocks, i.e., from a continental crust that initially formed in Palaeoproterozoic time (ca. 2.10–1.86 Ga), and subsequently underwent intracrustal partial melting, differentiation and rejuvenation via mafic underplating in Mesoproterozoic time.