ИСТИНА

he Early Cambrian mafic magmatism commonly known as the Kharaulakh event has been documented in the north-east of the Siberian platform in the Olenek uplift and in the frontal thrust sheets of the Verkhoyansk fold-and-thrust belt in the Kharaulakh Mountains. Intrusions of the Kharaulakh event are sills that typically cut Neoproterozoic succession. The uppermost magmatic body is located within the lowermost Cambrian sedimentary rocks and is interpreted to be a volcanic flow. U-Pb age of pebbles ranges from 545 to 525 Ma showing that duration of the Kharaulakh event-related magmatism was close to 20 My (Khudoley et al, 2013, Prokopiev et al, 2016). New study of the sills of the Neleger River valley expands existing database on the chemical composition of the Kharaulakh event magmatic rocks. They are enriched in titanium with TiO2 ranging from 3.7% to 6.2%. Studied magmatic rocks have very similar patterns when plotted on the mantle-normalized multy-element diagram and follow OIB trend. Some Neleger sills samples are characterized by positive Ti, P and Eu anomalies and negative Sr anomaly. Chondrite-normalized REE distribution shows LREE enrichment with (La/Lu)n and (La/Sm)n values averaging at 5,84 and 1,69 respectively and no or slightly positive Eu anomaly. Mafic sills from the westernmost exposures have higher concentrations of V as well as lower concentrations of SiO2 and Al2O3 compared to the bodies of the western part of the study area. Such chemical compositions of the basaltic magma are typical for the continental rifts, and Kharaulakh event correlates well with the latest Neoproterozoic – Early Cambrian rifting of the south-east margin of the Siberian platform. Gradual variation in chemical composition of the intrusions is typical for magma formed at the different stages of rift evolution, likely pointing that sills are getting younger westward. The study was supported by the RSF grant 18-17-00240