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Dmitry Gladkochub, Institute of the Earth?s Crust, Siberian Branch of Russian Academy of Sciences (Russian Federation)
Tatiana Donskaya, Institute of the Earth?s Crust, Siberian Branch of Russian Academy of Sciences (Russian Federation)
Eugene Sklyarov, Institute of the Earth?s Crust, Siberian Branch of Russian Academy of Sciences (Russian Federation)
Jennifer Tait, The University of Edinburgh (United Kingdom)
Sergei Pisarevsky, The University of Edinburgh (United Kingdom)
Anatoliy Mazukabzov, Institute of the Earth?s Crust, Siberian Branch of Russian Academy of Sciences (Russian Federation)
Michael Wingate, Geological Survey of Western Australia (Australia)
Sergei Sergeev, Karpinsky Russian Geological Research Institute (VSEGEI) (Russian Federation)
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Geological, geochronological, geochemical, and paleomagnetic studies of mafic dyke swarms provide significant information on the tectonic evolution of ancient cratons. These swarms mark large-scale extensional events. In some cases, these events lead to continental breakup, hence coeval and geochemically similar sub-swarms can provide 'piercing points' for paleogeographical reconstructions. Mafic dykes are also amongst the best targets for paleomagnetic studies - the only quantitative means for retrieving precise rotation parameters for such reconstructions.
New geochronological data from mafic dyke swarms in southern Siberia have greatly improved our knowledge of the region. The dyke swarms fall into seven major groups and we suggest the following geodynamic environments for their emplacement:
1. The oldest dyke swarm, at c. 1.91 Ga, is located in Urik graben, which is bordered by the Sharizhalgai and Biryusa basement salients. This swarm intruded the extensional basin between these two blocks well before their collision at about 1.88 Ga.
2. A c. 1.85 Ga dyke swarm in the Baikal block marks post-collisional extension and delamination of a lithospheric mantle root.
3. A c. 1.67 Ga swarm reflects mafic underplating beneath marginal areas of the craton thinned during delamination.
4. Dyke swarms dated at 0.78 - 0.74 Ga in the Sharizhalgai, Biryusa, and Baikal blocks probably correspond to the first stages of rifting between Siberia and adjoining parts of Rodinia.
5. Dykes dated at 0.65 - 0.61 Ga in Sharizhalgai, Urik graben, and the Aldan shield were emplaced during an advanced stage of rifting, or during the initial stage of Rodinia breakup and development of the passive margin.
6. Dykes in the Biryusa block, dated at c. 0.50 Ga, are probably related to post-collisional extension resulting from at c. 0.55 Ga accretion of the Kan and Arzybei blocks to the Siberia margin.
7. The youngest dykes, dated at c. 275 Ma, in the Sharizhalgai block and Urik graben were emplaced along an active Siberian margin during closure of the Mongol-Okhotsk Ocean.
There is a significant 'magmatic gap' of about one billion years (from 1.67 to 0.78-0.74 Ga) in southern Siberia. We suggest that, during this period, southern Siberia occupied an internal position within a Proterozoic mega-continent, and that this may explain the absence of magmatic activity. Recent paleomagnetic studies suggest that Siberia and Laurentia were parts of this mega-continent since at least c. 1.5 Ga. The absence of a continuation within Siberia of the giant 1.27 Ga Mackenzie dyke swarm of Laurentia can be explained by the presence of smaller continental fragments between northern Laurentia and southern Siberia, as suggested by paleomagnetic data.
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