Petrology, geochemistry and source characteristics of the Burpala alkaline massif, North Baikal

Abstract

The Burpala alkaline massif contains rocks with more than 50 minerals rich in Zr, Nb, Ti, Th, Be and rare earth elements (REE). The rocks vary in composition from shonkinite, melanocratic syenite, nepheline and alkali syenites to alaskite and alkali granite and contain up to 10% LILE and HSFE, 3.6% of REE and varying amounts of other trace elements (4% Zr, 0.5% Y, 0.5% Nb, 0.5% Th and 0.1% U). Geological and geochemical data suggest that all the rocks in the Burpala massif were derived from alkaline magma enriched in rare earth elements. The extreme products of magma fractionation are REE rich pegmatites, apatite–fluorite bearing rocks and carbonatites. The Sr and Nd isotope data suggest that the source of primary melt is enriched mantle (EM-II). We correlate the massif to mantle plume impact on the active margin of the Siberian continent.