TRANSITIONAL (2.1 GA) FE-THOLEIITIC THOLEIITIC MAGMATISM IN THE FENNOSCANDIAN SHIELD SIGNIFYING LITHOSPHERIC THINNING DURING PALAEOPROTEROZOIC EXTENSIONAL TECTONICS

Citation
Vm. Nykanen et al., TRANSITIONAL (2.1 GA) FE-THOLEIITIC THOLEIITIC MAGMATISM IN THE FENNOSCANDIAN SHIELD SIGNIFYING LITHOSPHERIC THINNING DURING PALAEOPROTEROZOIC EXTENSIONAL TECTONICS, Precambrian research, 70(1-2), 1994, pp. 45-65
Citations number
72
Categorie Soggetti
Geology
Journal title
ISSN journal
03019268
Volume
70
Issue
1-2
Year of publication
1994
Pages
45 - 65
Database
ISI
SICI code
0301-9268(1994)70:1-2<45:T(GFTM>2.0.ZU;2-G
Abstract
The Palaeoproterozoic sedimentary cover of the Archaean basement compl ex in the Fennoscandian Shield is intruded by several stages of mantle -derived magmas. The 2.1 Ga Fe-tholeiitic magmatism, which is characte rized by hypabyssal intrusions, dykes and volcanic flows intersecting the cover, also forms a widespread dyke swarm within the basement in N orth Karelia, eastern Finland. There are certain differences between t hese age-related sets of dykes, suggesting lithospheric thinning resul ting from extensional tectonics during 2.1 Ga events. REE abundances o f the Fe-tholeiitic dykes within the basement range from 10 to 40 time s chondritic, with gently dipping REE patterns ([La/Yb](N)=1.2 to 3.8) . The dykes intersecting the epicontinental sediments of the cover hav e total REE abundances ranging from 10 to 70 times chondritic, with LR EE-enriched, gently or steeply dipping REE patterns ([La/Yb](N)=2.8 to 4.1), whereas the dykes intersecting the shallow-marine sediments wit hin the cover have total REE abundances from 5 to 55 times chondritic, with almost flat REE patterns ([La/Yb](N)=1.2 to 1.8). On the basis o f the REE patterns and modelling the melting it is suggested that the melt generation occurred in a transitional tectonic setting, where bot h garnet- and spinel-bearing mantle lherzolites were involved due to l ithospheric thinning during Palaeoproterozoic extensional tectonism.