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Tatiana Donskaya, Institute of the Earth?s Crust, Siberian Branch of the Russian Academy of Sciences (Russian Federation)
Dmitry Gladkochub, Institute of the Earth?s Crust, Siberian Branch of the Russian Academy of Sciences (Russian Federation)
Anatoly Mazukabzov, Institute of the Earth?s Crust, Siberian Branch of the Russian Academy of Sciences (Russian Federation)
Sergei Pisarevsky, The University of Edinburgh (United Kingdom)
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It is generally accepted that the Siberian craton was formed at Paleoproterozoic by a collision of mainly Archean terranes. This is broadly coincides in time with similar events in Laurentia, so some paleogeographic reconstructions juxtapose Archean blocks and Proterozoic orogenic belts of two continents. However, the scale of the Siberian crustal growth during the assembly is still under debate. The continental growth takes place both in active margin setting and in intraplate or post-collision extension. Study of igneous complexes produced under these tectonic settings in the southern Siberian craton allow us to separate two main episodes of Paleoproterozoic continental growth in the studied area. Traces of both episodes are preserved within the Akitkan and Angara orogenic belts of the South Siberia. The Paleoproterozoic continental growth occurred along active margins of the Archean terranes before their assemblage into the Siberian craton. The ca. 2.0 Ga island arc related granitoids of the Akitkan orogenic belt and 1.9 Ga subduction related ophiolite of the Angara orogenic belt are considered as indicators of the first crustal forming episode. The Akitkan belt was thought to be built exclusively by a Paleoproterozoic juvenile crust. However, several Neoarchean Nd model ages were reported from various localities in this belt and 2.88 Ga foliated granitoids were found recently in its basement. In contrast to Akitkan belt, the Angara belt was suggested only by the reworked Archean crust. New geochronological and isotopic data testify that both the Paleoproterozoic juvenile crust and fragments of strongly reworked Archean crust present in both belts. This alleged history of the Angara belt does not contradict the idea of considering this belt as a continuation of some coeval belt in Laurentia. However, the suggested presence of an ocean outward the Akitkan belt put some tension on its juxtaposition to the Thelon belt, as proposed in some reconstructions.
Another the Paleoproterozoic continental growth in the studied area was related to the post-collision extension after the assembly of the Siberian craton and its possible amalgamation with Laurentia. Numerous 1.88-1.84 Ga post-collision granitoids and coeval mafic and felsic volcanics were found along the southern margin of the Siberian craton in recent years. We suggest that the amalgamation of Laurentia and Siberia were independent events and the collision of these two continents occurred shortly after their formation. Most of the post-collision granitoids in southern Siberia and coeval felsic volcanics geochemically correspond to A-type granites. Geochemical and isotopic characteristics of these A-type rocks testify that they were produced by addition of mantle-derived magmas to the crustal sources. This mantle contribution could be caused by underplating and intrusion of mantle-derived magmas into the continental crust.
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