ALKALINE-SALICIC KURUNG COMPLEX OF THE KET-KAP-YUNA IGNEOUS PROVINCE (Aldan shied, Russia): PETROGENESIS AND GEODYNAMIC CONDITIONS OF FORMATION
V.F. Polin, D.S. Ostapenko
Far East Geological Institute, Far Eastern Branch of the Russian Academy of Sciences, Vladivostok, Russia
Keywords: Geodynamics, petrogenesis, Kurung complex, alkaline magmatism, foid and alkaline syenites, Aldan Shield
Abstract
Integrated geological data, petrogeochemical characteristics of magmatites of the Kurung complex (the Ket-Kap-Yuna igneous province of the Aldan Shield), and previously published isotopic data along with the results of geochronology and geochemistry research provide evidence for this complex evolving in the Late Cretaceous in a setting of riftogenesis (final phase) of continental margins. Similar to the Late Jurassic-Early Cretaceous polyformational volcano-plutonism of the Aldan Shield, the Late Cretaceous alkaline magmatism in the Ket-Kap-Yuna province is associated with the tectonomagmatic activation which manifested itself mainly as continental margin rifting associated with deep reorganization of the southwestern, southern and southeastern framing of the Siberian craton triggered by gravitational sliding of the lithospheric plates. Results of the petrogeochemical analysis of the studied magmatites revealed that the heterogeneous rock groups identified within this rock complex are not related to each other by fractional or other type of differentiation, thus suggesting their possible derivation as a result of fluid syntexis-type interaction between mantle-derived alkali-basite melt and felsic crustal melts. Alkali-basite parent melts are shown to have formed during partial melting of variably enriched mantle which is widely spread beneath the Aldan Shield and is varied in composition (from BSE enriched to nearly EM-I). Origination of such deep-seated melts (magma sources) was associated with the rifting processes (strike-slip tectonics) triggered by the setting of gravitational sliding of lithospheric plates. The formation of alkaline-salic magmas of the Kurung complex is associated with large-scale selective assimilation of crustal material by high-temperature fluidized mantle magmas during their ascent to the surface, possibly as a result of fluid syntexis of alkaline-basite mantle magmas and crustal smeltings formed under their influence.
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