Chemical variation in a Proterozoic suite of granitoids extending across a mobile belt — craton boundary |
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Authors: | Anders Lindh Roland Gorbatschev |
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Institution: | (1) Present address: Geologiska Institutionen, Sölvegatan 13, S-223 62 Lund, Sweden |
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Abstract: | Contrary to earlier opinions, the southwestern margin of the Baltic Shield was formed after the Svecokarelian orogenic event (2.2-1.8 Ga). During the initial stages of its formation (1.7-1.6 Ga), granitoid rocks intruded the southwestern margin and simultaneously also the already cratonized part of the shield. Among these granitoids, the most important chemical difference is between calc-alkalic differentiated granitoids to the west and alkalicalcic more evolved granites to the east of an intraorogenic “suture” (the Mylonite Zone). The chemical differences between alkali-calcic granites found on both sides of the interorogen boundary proper (the Protogine Zone) are less significant. As yet, a final choice cannot be made between wholly actualistic and non-actualistic, possibly intracratonic(?) variants of precursory plate-tectonic processes. |
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