Late Paleozoic alkaline magmatism in Western Transbaikalia,Russia:Implications for magma sources and tectonic settings

This paper presents the results of geochronological (⁴⁰Ar-³⁹Ar, U–Pb SHRIMP II), petrological and geochemical studies of the Late Paleozoic complexes of alkaline rocks (Zimovechinsky, Tuchinsky and Koma) located within the Vitim Plateau (the western part of the Mongol-Okhotsk Orogenic Belt). The rocks were formed at 310–280 ?Ma. It is coeval with Late Paleozoic magmatism within the Central Asian Orogenic Belt. The ε_Nd(T) values show large variations from ?2.1 to +3.3 as well as the initial Sr(I) isotopic ratios from 0.7042 to 0.7138, that demonstrate strong isotopic heterogeneity of the magmatic source. The geochemical characteristics of the rocks show pronounced positive Pb and negative Ti, Zr–Hf anomalies that can be explained by involvement of the subducted component in primary melts. The rocks intruded in a setting of extension at the active continental margin of the Siberian Craton during subduction of Mongol-Okhotsk oceanic crust under the Siberian Craton.