Early Triassic Episode of the Kresty Volcano–Plutonic Complex Formation in the Maymecha-Kotuy Alkaline Province, Polar Siberia: Geochemistry, Petrology and Uranium–Lead Geochronology.

The Kresty volcano–plutonic complex (KVPC) is one of the representatives of the alkaline–ultrabasic magmatism in the Maymecha-Kotuy Alkaline Province in Polar Siberia. The geological structure of the KVPC consists of intrusive formations of olivinite–pyroxenite and melilitolite–monticellitolite bodies, a series of rocks that break through dikes of trachydolerites, syenites, granosyenites, alkaline picrites and lamprophyres. This paper summarizes the results of the authors' long-term research on the geological structure and features of the material composition of the intrusive magmatic rocks, including geochemistry, mineralogy, distribution of rare earth elements (REE), as well as the results of isotope studies. The multielement composition of the KVPC intrusions demonstrates a complex geodynamic paleoenvironment of the formation as plume nature with signs of subduction and collision. For the ultrabasic series with normal alkalinity from the first phase of the KVPC, a Sm-Nd isochron age yielded an Early Triassic (T₁) result of 251 ± 25 Ma. Here, we present U-Pb dating of zircons and perovskite of high-calcium intrusive formations and a dyke complex of alkaline syenites. Thus, for the intrusion of kugdite (according to perovskite), the age determination was 249 ± 4 Ma, and for the crosscutting KVPC dykes of syenites (according to zircon) 249 ± 1 Ma and 252 ± 1 Ma. The age of the most recent dike is almost identical to the age of the main intrusive phases of the KVPC (T₁), which corresponds to a larger regional event of the Siberian LIP—251 Ma. According to isotopic Sr-Nd parameters, the main source of KVPC magmas is a PREMA-type material. For dyke varieties, we assume there was an interaction of plume melts with the continental crust. The new age results obtained allow us to further constrain the episodes of alkaline–ultrabasic intrusions in Polar Siberia, taking into account the interaction of mantle plume matter and crustal material. [ABSTRACT FROM AUTHOR]