Geochemical evolution of Caledonian volcanism recorded in the sedimentary rocks of the eastern Baltic region
T. Kiipli, A. Soesoo, T. Kallaste, 2014. "Geochemical evolution of Caledonian volcanism recorded in the sedimentary rocks of the eastern Baltic region", New Perspectives on the Caledonides of Scandinavia and Related Areas, F. Corfu, D. Gasser, D. M. Chew
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This article describes the occurrence, bulk geochemistry and phenocryst compositions of Caledonian volcanic ash beds (bentonites) in the sedimentary sections of the Palaeozoic Baltic sedimentary basin. Four periods of volcanism are recognized in the eastern Baltic region: (a) Late Sandbian with sources derived from the convergent margin between Avalonia and Baltica; (b) Late Katian with sources from the margin of the Iapetus Ocean (Norwegian Caledonides); (c) Aeronian (with extension into Telychian and Sheinwoodian) with sources in the Central European Caledonides; and (d) Telychian to Early Ludlow with sources derived from the convergent margin between Laurentia and Baltica (Norwegian Caledonides). Trace element compositions in bentonites indicate mostly evolved source magmas of rhyolitic and dacitic composition. The volcanism in the Aeronian is characterized by less evolved basaltic and trachyandesitic compositions. Sanidine compositions indicate the existence of potassium-dominated (over sodium) source magmas in Late Sandbian and from the late Homerian to Early Ludlow. During other periods both potassium- and sodium-dominated source magmas occur. The presence of sodium-rich sanidine in many bentonites combined with the scarcity of biotite suggests that the source magmas were water-undersaturated. Biotite phenocrysts are mostly Mg-rich, but Fe-rich varieties occur in the Late Sandbian and Early Telychian.
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New Perspectives on the Caledonides of Scandinavia and Related Areas
The Caledonides are a major orogenic belt that stretches from the Arctic, through Scandinavia, East Greenland, Britain and Ireland into the Atlantic coast of North America. Following the break-up of Rodinia, the Caledonides formed in the Palaeozoic by the drifting of various continents and their eventual aggregation in the Silurian and Devonian. The orogen subsequently fragmented during the opening of the Atlantic Ocean. This volume brings together 25 papers presenting the results of modern research that investigates the orogenic processes and the provenance of specific components of the belt. The contributions reflect different lines of research, linking traditional field studies with modern analytical techniques. In addition three overview papers summarize the main features of the belts in Scandinavia, Svalbard, East Greenland, Britain and Ireland, highlighting the advances made since the last major synthesis of the Scandinavian Caledonides 30 years ago, and discussing important open questions.