Physical and chemical conditions of basaltic magmatism of archipelago Franz Josef Land

Abstract

As a result of mineralogical and thermobarogeochemical researches of different-age basaltic complexes of Archipelago Franz Josef Land (FJL) regular changes in time of compositions of plagioclases, clinopyroxenes and melt inclusions are established. Chemical compositions of inclusions directly testify to prevalence in Early Jurassic of plateau basaltic melts similar (according to the content of the basic components, and also trace and rare-earth elements) to typical basalt tholeiitic magma of the Siberian platform. In Early Cretaceous melts already had the enriched subalkaline character. Calculations of conditions of magma generation, spent on the basis of the data on melt inclusions, have shown evolution from Early Jurassic to Early Cretaceous (with allocation of three peaks of magmatic activity: 192.2±2.8, 157.4±3.5 and 131.5±0.8 million years) depths and temperatures (accordingly: 70-110 km and to 120 km, 1430-1580°С; 60-110 km, 1390-1580°С; 50-140 km, 1350-1690°С) of mantle melting with formation of deep sources of the FJL magmas.