Abstract
Abstract The Palaeoproterozoic sedimentary cover of the Archaean basement complex in the Fennoscandian Shield is intruded by several stages of mantle-derived magmas. The 2.1 Ga Fe-tholeiitic magmatism, which is characterized by hypabyssal intrusions, dykes and volcanic flows intersecting the cover, also forms a widespread dyke swarm within the basement in North Karelia, eastern Finland. There are certain differences between these age-related sets of dykes, suggesting lithospheric thinning resulting from extensional tectonics during 2.1 Ga events. REE abundances of the Fe-tholeiitic dykes within the basement range from 10 to 40 times chondritic, with gently dipping REE patterns [La/Yb]N=1.2 to 3.8). The dykes intersecting the epicontinental sediments of the cover have total REE abundances ranging from 10 to 70 times chondritic, with LREE-enriched, gently or steeply dipping REE patterns ([La/Yb]N=2.8 to 4.1), whereas the dykes intersecting the shallow-marine sediments within 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 of the REE patterns and modelling the melting it is suggested that the melt generation occurred in a transitional tectonic setting, where both garnet- and spinel-bearing mantle lherzolites were involved due to lithospheric thinning during Palaeoproterozoic extensional tectonism.
Published Version
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