Geochronology and geochemistry of the enderbite series in the Lapland Granulite Belt: generation, tectonic setting, and correlation of the belt1NORDSIM Publication No. 322.

Abstract

The Lapland Granulite Belt of the northeastern Fennoscandian Shield is dominated by blastomylonitic migmatitic metagreywackes and a deformed, structurally conformable norite–enderbite series. The belt contains minor granodiorites and one major anorthosite massif and is crosscut by post-tectonic granite plutons and diabase dykes. The major and trace element composition of the enderbite series is similar to that of arc-related igneous rocks. Magmatically zoned zircon yield U–Pb secondary ion mass spectrometry ages of 1.91–1.92 Ga, while homogeneous metamorphic zircon domains are aged 1.88–1.90 Ga. Major enderbite bodies reveal only a few older inherited, xenocrystic zircon cores or grains, mainly Archaean in age, while a tonalite body and a narrow quartz norite vein have abundant inherited zircons comparable with the detrital zircon population in the metagreywackes. The intrusive series has slightly positive initial εNdvalues, while the tonalite body has a slightly negative initial εNd, consistent with the occurrences of inherited zircon grains. The major intrusive series, interpreted to have been emplaced in an arc environment, has juvenile character and assimilated only a minor amount of older crustal material during ascent, intrusion, and cooling. Narrow veins and more evolved bodies had more interaction with the metasediments and other crustal rocks. The enderbite series of the Lapland Granulite Belt may be correlated with arc-related plutonism in the Nagssugtoqidian and Torngat orogens, but metamorphic and structural evolution took place considerably later in Greenland and the northeastern Canadian Shield, with the exception of the Inglefield Belt of northwestern Greenland.