U-Pb baddeleyite ages and Hf, Nd isotope chemistry constraining repeated mafic magmatism in the Fennoscandian Shield from 1.6 to 0.9 Ga

Summary, in English

The Palaeoproterozoic (1.90 - 1.60 Ga) crust of central Fennoscandia was intruded repeatedly by dolerite dikes and sills during the Neo- and Mesoproterozoic eons. We report 17 new baddeleyite U - Pb dates comprising six generations of dolerites ( in Ma): Blekinge-Dalarna dolerites 946 - 978 Protogine Zone dolerites 1,215 - 1,221 Central Scandinavian Dolerite Group 1,264 - 1,271 Tuna dikes and age equivalents in Dalarna 1,461 - 1,462 Varmland dolerites similar to 1,568 Breven-Hallefors dolerites similar to 1,595 The favoured tectonic model implies that the majority of these suites were related to active margin processes somewhere west ( and possibly south) of the Fennoscandian Shield. Dolerite intrusions are interpreted to reflect discrete events of back-arc extension as the arc retreated oceanward. Initial Hf and Nd isotope compositions of the dolerite swarms fall between CHUR and normal-depleted mantle, and suggest a variably depleted and re-enriched mantle as the source for the here investigated 1.6 to 0.95 Ga old mafic rocks. Repeated recycling of older crustal components, mainly sediments ( dominated by material with short residence ages) in earlier subduction systems may have been very efficient at producing geochemically and isotopically variably enriched lithospheric mantle sections beneath the Fennoscandian Shield.

• Author: Ulf Söderlund; CE Isachsen; Göran Bylund; LM Heaman; PJ Jonathan Patchett; JD Vervoort; UB Andersson
• Department/s: Lithosphere and Biosphere Science
• Publishing year: 2005
• Language: English
• Pages: 174-194
• Publication/Series: Contributions to Mineralogy and Petrology
• Volume: 150
• Issue: 2
• Links: http://dx.doi.org/10.1007/s00410-005-0011-1
• Document type: Journal article
• Publisher: Springer
• Topic: Geology
• Status: Published
• ISBN/ISSN/Other: ISSN: 0010-7999