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Wenlock metabentonites from Gotland, Sweden: geochemistry, sources and potential as chemostratigraphic markers

Published online by Cambridge University Press:  01 November 1999

R. A. BATCHELOR
Affiliation:
School of Geography and Geosciences, University of St Andrews, North Haugh, St Andrews, Fife KY16 9ST, UK
L. JEPPSSON
Affiliation:
Department of Geology, Division of Historical Geology and Paleontology, Sölvegatan 13, S-223 62 Lund, Sweden

Abstract

Two metabentonite suites occur within the Wenlock limestones and marls of Gotland, one within the Slite Formation (M. belophorus to the C. ellesae biozones) and the other in the Mulde Formation (G. nassaM. dubius Biozone). Their geochemical characteristics based on rare-earth element (REE) distributions in apatite crystals separated from the metabentonites suggest origins from three separate volcanic sources. One of these sources has an alkaline affinity, reflected in relatively high levels of Th, Nb and Zr, which suggests that it may have lain over thickening continental crust during the waning stages of the closure of the Tornquist Sea, while the other two represent calc-alkaline magmas. The source of the volcanic ash is placed some 400 km to the southwest of Gotland, on the Tornquist–Teysseyre Zone, which is the northernmost expression of the Trans-European Suture Zone. Distinctive differences in REE distribution in apatite from these metabentonites should assist in future correlation studies in Wenlock stratigraphy, both within the Baltic region and further afield.

Type
Research Article
Copyright
© 1999 Cambridge University Press

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