Sources of devonian magmatism in the Minusa Trough based on geochemical and Sr-Nd isotopic characteristics of basites

Abstract

The results of geochemical and isotopic (Sr-Nd) studies of the rocks comprising the structure of igneous associations of Minusa Trough are presented. They allowed us to identify the heterogeneity of igneous sources. Similar heterogeneity is determined by mixing of at least two sources of source melts. The first one corresponds, by the geochemical parameters, to the OIB composition with a high content of noncoherent lithophile elements and to the PREMA type mantle in its isotopic parameters. Another source is comparable to the lithospheric mantle that was metasomatized in above subduction conditions. Participation of a second source melt in magma formation led to the appearance of IAB geochemical features (typical depletion in high charge hydrophobic Ti, Nb, and Ta, and enrichment in Ba, common and radiogenic Sr) for basite melts. The performed studies give us ground to attribute the magmatism of Minusa Trough to the Altai-Sayan plume evolution beneath the convergent boundary within the limits of the southwestern margin of the Sibe rian continent.

Isotope (U–Pb, Sm–Nd, Rb–Sr) geochronology of alkaline basic plutons of the Kuznetsk Alatau

“…One of the possible reasons for this fact is metasomatism and erosion of the lower lithosphere by initial plume, followed by the partial melting of the lithosphere in ~100 Ma, with the preservation of zircons formed at the previous magma generation stage in the newly generated alkaline magma. This model eliminates the main plate tectonics contradiction, namely, the development of polychronous magmatism with similar initial parameters ε Nd (T) ≈ +4.8 to +5.7 and T Nd (DM) ≈ 0.8-0.9 Ga (Vorontsov et al, 2011;Vrublevskii et al, 2012b) within an area of 4500 km 2 commensurate in dimensions with a classical hot spot. We admit that the plume ascending at the Cambrian-Ordovician boundary generated only primary alkaline basaltic melts, and the Devonian alkaline intrusions resulted from the later melting of the metasomatized material of the Early Caledonian continental lithosphere.…”