Isotopic (Nd, Sr, Pb) Composition of the Permo–Triassic and Late Cretaceous Basaltoids in the Minusa Depression (Southern Siberia, Kop’evo Uplift): Heterogeneity of Mantle Sources of Mafic Magmas

Abstract

––We have studied the isotopic composition of Nd, Sr, and Pb in Permo–Triassic subalkaline dolerites and Late Cretaceous basanites of the northern part of the Minusa depression. The wide variations in the primary isotope parameters of dolerites (ɛNd = 6.6–8.5, 87Sr/86Sr = 0.7031–0.7061, 206Pb/204Pb = 18.13–18.72, 207Pb/204Pb = 15.51–15.55, 208Pb/204Pb = 37.88–38.07) and basanites (εNd = 5.3–9, 87Sr/86Sr = 0.7026–0.7054, 206Pb/204Pb = 18.63–19.09, 207Pb/204Pb = 15.54–15.56, 208Pb/204Pb = 38.40–39.01) indicate both heterogeneity of mantle mafic melts and their partial crust contamination. Doleritic magma was presumably generated predominantly from a substance from a moderately depleted mantle source, which is similar in isotopic composition to the PREMA component of sublithospheric plumes. The basanitic magma might have formed through the melting of the material of the subcontinental lithospheric mantle modified as a result of plume activity in the Paleozoic–early Mesozoic. The similar isotopic compositions of Pb in basanites and the derivates of the enriched lithospheric mantle (EM 2 type) are due to the mixing of different substances of the SCLM substratum.