Upper Katian (Ordovician) bentonites in the East Baltic, Scandinavia and Scotland: geochemical correlation and volcanic source interpretation

摘要: Altered volcanic ash interbeds (bentonites) in the upper Katian of Baltoscandia indicate significant activity neighbouring tectonically active areas. bentonites East Baltic can be reliably correlated using sanidine phenocryst composition. Ratios immobile trace elements TiO2, Nb, Zr and Th to Al2O3 enable extension correlations Scandinavia, where late diagenetic alterations could have caused recrystallization phenocrysts. At least seven eruptions were recognized Baltoscandian sections. Several found deep-sea sediments are absent shallow-sea sediments, indicating extensive breaks sedimentation erosion during Hirnantian times. The areal distribution pattern indicates a source from north or northwest (present-day orientation) margins Iapetus Palaeo-Ocean. Signatures ultra-high-pressure metamorphism Seve Nappe (Central Sweden) intrusions Helgeland Complex Central Norway been proposed as potential sources magmas that generated ashes deposited Geochemical similarities between Dob's Linn southern Scotland suggest common