Evolution of migmatitic granulite complexes: Implications from Lapland Granulite Belt, Part II: Isotopic dating

Abstract

The migmatitic metapelites of the Lapland granulite belt (LGB) in the NE part of the Fennoscandian Shield represent an arc-related greywacke basin metamorphosed in the granulite facies. Detrital zircons from migmatitic metapelites are derived from 1.94 etrital zircons from migmatitic metapelites are derived from 1.94 zircons from migmatitic metapelites are derived from 1.94 derived from 1.94 − 2.9 Ga old acid 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 into 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 ε Nd values of 0 to +1 and the continuous spectrum of LILE enrichment in the enderbite-series probably reflect assimilation of metasediments by magmas. Monazite U-Pb ages of migmatitic metasediments in the range 1906 − 1910 ± 3 Ma overlap the late stage of enderbite intrusion and growth of early metamorphic zircons. Garnetwhole rock Sm-Nd ages from leucosomes in the range 1880 − 1886 ± 7 Ma are concurrent with the growth of the youngest metamorphic zircons and probably indicate the crystallization of leucosomes or the influence of a fluid liberated from them. Isotopic and petrologic data reveal that the evolution of Lapland Granulite belt from the erosion of source rocks to the generation of a sedimentary basin, its burial, metamorphism and exhumation took place within ca. 60 Ma.

New data on detrital zircons from the sandstones of the lower Cambrian Brusov Formation (White Sea region, East-European Craton): unravelling the timing of the onset of the Arctida–Baltica collision

“…This is consistent with previous reports on the amount of early Palaeoproterozoic juvenile zircons found in Palaeoproterozoic sedimentary units of northeastern Fennoscandia (i.e. erosional products of the Lapland-Kola orogen and Svecofennian province) that are based on integrated isotopic (U-Pb, Sm-Nd, and Lu-Hf) investigations (Timmerman and Daly 1995;Bridgwater et al 2001;Tuisku and Huhma 2006;Lahtinen et al 2010;Andersson et al 2011;Beyer et al 2012).…”

3.3 Palaeotectonic and Palaeogeographic Evolution of Fennoscandia in the Early Palaeoproterozoic

“…Arccontinent and subsequent continent-continent collisions that generated the Lapland-Kola orogen and related highpressure metamorphic rocks mainly occurred at 1930-1910 Ma (Daly et al 2006). The U-Pb zircon studies of rocks from the Finnish part of the Lapland Granulite Belt by Tuisku and Huhma (2006) indicate that the deposition of pelitic protoliths of the belt took place later than 1940 Ma, whereas enderbitic plutons representing arc magmatism were emplaced at c. 1920-1905 Ma. Subsequent burial and orogenic metamorphism followed by exhumation up to upper crustal levels was over by c. 1880 Ma.…”

Ressources en terres rares de l’Europe et du Groenland : potentiel minier et enjeux

“…La ceinture de Tana est une zone fortement tectonisée, composée d'amphibolites, de gneiss à grenat-biotite et de gneiss arkosiques. L'ensemble a chevauché la ceinture de roches vertes de Laponie centrale aux alentours de 1,91 Ga (Tuisku et Huhma, 2006). Dans les zones de Mäkärä et Vaulo, un épais profil kaolinique s'est développé aux dépens des roches du socle, le tout étant recouvert de dépôts argileux glaciaires (tills) enrichis en La et Y (Sarapää et Sarala, 2011.…”