Home – Home – Jornals – Russian Geology and Geophysics 2020 number 11

Geological, petrological, isotope-geochemical (⁴⁰Ar/³⁹Ar analysis, petrochemical data, and geochemistry of trace elements and REE), and mineralogical researches testify that the formation of the early Paleozoic basalt and picrite complexes of the West Siberian Plate basement was related to the development of the Cambrian subduction zone of the Paleo-Asian Ocean. Using the compositions of clinopyroxenes and amphiboles (and also programs of computational modeling), we have established the Р-Т conditions of formation of early Paleozoic picrite complexes. Crystallization of clinopyroxenes began at significant depths (25-20 km) and at high temperatures (1300-1275 °C). Olivine might have formed at elevated pressures (8-7 kbar) and temperatures of 1540-1490 °C. Amphiboles formed, most likely, at 6.1-4.5 kbar and much lower temperatures, 1105-1060 °C. Petrochemical analysis and data on trace elements and REE in the rocks of the studied early Paleozoic complexes in West Siberia testify to their intricate formation involving magmatic systems with basalt (island-arc and back-arc basins), picrite, and shoshonite (and also WPB type) melt characteristics. Taking into account the similar geochemical characteristics of the early Paleozoic basaltoids and picrites of the West Siberian Plate basement and the Kamchatka volcanics, we suggest that a considerable part of the studied ancient complexes formed by the model implying (as in the case of the Sredinnyi Ridge in Kamchatka) the action of enriched magmatic systems during the development of a destructive window ("slab-window") under rupture of subducted plate on the background of common island-arc magmatism.