Age, geochemistry, and origin of the mid-Proterozoic Häme mafic dyke swarm, southern Finland

We have reappraised the age and composition of mid-Proterozoic Häme dyke swarm in southern Finland. The dominant trend dykes this is NW to WNW. Petrographic observations geochemical data indicate uniform, tholeiitic low- Mg parental magmas for all dykes. Nevertheless, variability incompatible trace element ratios, such as Zr/Y La/Nb, provides evidence changing mantle melting conditions variable crustal contamination. Our ID-TIMS 207Pb/206Pb ages four low-Zr/Y-type emplacement at 1639 ± 3 Ma, whereas most reliable previously published suggest high-Zr/Y-type 1642 2 Ma. propose that swarm, possibly also other mid- Proterozoic mafic swarms Finland, records a progressive decrease values due magma generation under developing areas thinned lithosphere. consider formation was probably associated with upwelling hot convective an extensional setting related nearby Gothian orogeny. below continental lithosphere promoted by elevated temperature underneath Nuna supercontinent. speculate origin relatively small swarms, anorthosites, rapakivi granites, rocks found across similarly triggered plate tectonics convection anomalous upper