M.A. PROSKURNINA, V.F. PROSKURNIN, D.N. REMIZOV, A.N. LARIONOV (VSEGEI)

Ring intrusions of the Bespamyatnaya Areal: manifestations of shoshonite­latite magmatism in Northern Taimyr

Petrographic, mineralogical, petrochemical and isotope geochronological studies of typical intrusions in the Bespamyatnaya River mouth have been carried out. The results showed that the intrusions had been formed by association of rocks from monzogabbro, monzodiorite, monzonite to syenite and quartz syenite. Granitoids are enriched with LILE (Ba, Sr, Rb, K, Cs), LREE and volatile components, such as F, P₂O₅, have negative geochemical Ti and Ta­Nb anomalies of suprasubduction nature. They differ from classical types of granites and correspond to intrusive counterparts of the shoshonite­latite series or shoshonite granitoids. Results of the U­Pb zircons dating from different intrusive phases indicate that they postdate the Siberian trap basalts being emplaced at 241–233 Ma (T_2–3) and are close by their age to the main phase of the Early Cimmerian orogeny in the Byrranga Mountains. The obtained results prompt for revision of paleogeodynamic reconstructions of the Pangea (North Siberian parts) and Paleopacific in the Late Permian – Early Triassic time with the trap (superplume) magmatism and Middle­Late Triassic with orogeny and formation of postorogenic intrusions of the shoshonite­latite series of the Bespamyatnaya Areal.
Keywords: ring intrusions, monzogabbro, monzodiorite, monzonite, syenite, quartz­syenite, shoshonite granitoid, Ta­Nb anomaly, U­Pb dating, Middle­Late Triassic magmatism, Early Cimmerian orogeny, the Bespamyatnaya Areal.