Evolution of Migmatitic Granulite Complexes: Implications

The migmatitic metapelites of the Lapland granulite belt (LGB) in the NE part of the Fenno-scandian Shield represent an arc-related greywacke basin metamorphosed in the granulite facies. Detrital zircons from migmatitic metapelites are derived from 1.94 − 2.9 Ga old ac-id source rocks (U-Pb SIMS ages). The clustering of detrital zircon ages between 1.97 and 2.2 Ga is problematic, because abundant felsic crust of this age is absent in the shield. The metasediments are characterized by Sm-Nd model ages of ca. 2.3 Ga. A younger, 1905 − 1880 Ma population of homogeneous zircons was formed during regional metamorphism. The peak high-grade metamorphism took place at ~1900 Ma and the latest chronological record from subsequent decompression and cooling phase is from ca. 1870 Ma. The norite-enderbite series of the LGB represents arc-magmas, which were intruded in-to the metasediments at ~1920 − 1905 Ma ago according to zircon U-Pb ages and were probably an important heat source for metamorphism. Older, zoned zircon grains in a quartz norite vein, initial εNd values of 0 to +1 and the continuous spectrum of LILE enrich-ment in the enderbite-series probably reflect assimilation of metasediments by magmas