U-Pb baddelyit dateringar av basiska gångar längs Romeleåsen i Skåne och deras påverkan av plastisk deformation i Protoginzonen
Sammanfattning: The bedrock in the southwest of Sweden was deformed and metamorphosed during the Sveconorwegian orogeny. The Sveconorwegian Frontal Deformation Zone north of the lake Vättern and the Protogine Zone south of the lake is regarded as the eastmost boundary of Sveconorwegian reworking. South of lake Vättern the Protogine Zone is 20-30 km wide made up of a system of discrete ductile (and locally brittle) shear zones. The spatial continuation of the Protogine Zone southward from northeast Skåne is uncertain and little documented. Three generations of mafic intrusive rocks (dated at ca. 1.56 Ga, 1.2 Ga and 0.95 Ga) indicates that the Protogine Zone was repeatedly reactivated during the Mesoproterozoic (1600-1100 Ma). The purpose of this study was to investigate how far east Sveconorwegian metamorphism can be followed. In order to try to date four dolerites, located on Romeleåsen in central Skåne (Dalby, Veberöd, Stenberget and Beden), the U-Pb method on the mineral baddelyite has been used. They dykes are all affected by deformation and metamorphism (especially along the margins), which means that the crystallization age represents a maximum age of deformation seen in the quarries. With petrographic studies from the four dolerites were investigated if differences in the metamorphic influence between the dolerites in the west and those further east could be seen. The results of the study show that a Sveconorwegian imprint can be traced through all the quarries. Age data combined with structural observations in the quarries show that the Protogine Zone appears to continue south of the lake Vättern down to the middle of Skåne. No significant lateral movements have occurred along the northern faults associated with the Tornquist zone. Since there is no Sveconorwegian deformation or metamorphism on Bornholm, the eastern boundary of Sveconorwegian reworking seems to be located somewhere between Beden and Bornholm. Petrographic studies of the dated dolerites indicate that grade of metamorphism decreases from west to east. The age of the dolerites of Dalby and Veberöd suggest they may represent a southern expression of ca. 1.2 Ga Protogine Zone dolerites or dykes of the 1.27-1.25 Ga Central Scandinavian Dolerite Group. The dolerite in Beden must be older than 1.2 Ga and thus cannot represent a reworked dyke of the Protogine Zone dolerites. Alternatively the dolerites have a common generation of older dolerites that can be linked to the Kalseaa dolerite dyke at Bornholm (1326 Ma) and dolerites in Västra Götaland (ca. 1.3Ga).
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