Geology and geochronology of neoarchean anorogenic magmatism of the Keivy structure, Kola Peninsula |
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Authors: | V R Vetrin N V Rodionov |
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Institution: | 1. Geological Institute, Kola Scientific Center, Russian Academy of Sciences, ul. Fersmana 14, Apatity, 184209, Russia 2. Center of Isotopic Research, Russian Geological Institute (VSEGEI), Srednii pr. 74, St. Petersburg, 199026, Russia
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Abstract: | Anorogenic magmatic complexes were formed during protoplatformal evolution of the Keivy structure. This evolution ended with
development of aluminous schists, which were derived by deep disintegration and redeposition of the rocks from the lower parts
of the sequence and surrounding of the structure. The anorogenic rocks of the region are represented by the following magmatic
complexes: gabbro-labradorite-latite-monzonite-granites; ophitic gabbro and gabbrodiabases; quartz syenite-alkaline granites;
alkaline and nepheline syenites. The magmatic activity of this period, starting from the emplacement of gabbrolabradorite
massifs and ending with alkaline and nepheline syenite bodies, was caused by ascent of mantle asthenolith, which destructed
the Earth’s crust basement in this area. The anorogenic magmatism of the Keivy structure lasted for no more than few or few
tens of million years. The granitoid subcomplex of the gabbro-labradorite-latite-monzonite-granite complex is dated at 2674
± 6 Ma, which is comparable with an age of alkaline granites of the Ponoy and Beliye Tundry massifs (2673 ± 6 Ma). The considered
complexes are separated in time by intrusion of amphibole-biotite plagiomicrocline granites with an age of 2667 ± 8 Ma. Gabbrolabradorites
of the Shchuch’e Ozero and Tsaga massifs have close ages (2663 ± 7 and 2668 ± 10 Ma, respectively, Bayanova, 2004), but were
formed earlier than granitoids (Bayanova, 2004). Formation of alkaline syenites of the Sakharijok I Massif, which finalized
the Neoarchean anorogenic magmatism of the region, falls in the same interval. During Paleoproterozoic transformations, the
rocks of the Keivy structure were sheared and uranium was introduced in the contact zones of the alkaline granite massifs,
which caused formation of palingenetic melts and subsequent formation of pegmatites in the outer contact zones of the granite
bodies. |
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