The Upper Kedon Area of Intraplate Cenozoic Alkaline Basaltoids, Northeast Russia

Abstract

This study is concerned with the structure and composition of a sheet of Cenozoic alkaline basaltoids (basanites and trachybasalts) in the upper reaches of the Kedon River, in the Kedon Uplift of the Omolon Massif. Mineralogical and geochemical data provide evidence of an intraplate, poorly differentiated type of magmas. Geochronologic isotope data (⁴⁰Ar/³⁹Ar and K-Ar methods) indicate a Late Miocene age for the eruptions in the time span between 9 and 7 ± 1 Ma. The magma source contained a considerable percentage of pyroxenites and, judging from the isotopic composition of Sr, Nd, and Pb volcanics, it is similar to the PREMA mantle component that is also characteristic for other Cenozoic alkaline basalt occurrences in Northeast Asia. The potential temperature of the mantle beneath the volcanic area is similar, judging from theoretical calculations, to the mean value of an unexcited mantle, and is consistent with the scenario of lithospheric extension initiated by remote tectonic events.