Granodiorite-granite Intrusions in Central and Southern Rudny Altai (Eastern Kazakstan): Age, Composition, and Geodynamic Setting

The granodiorite-granite intrusions included in Late Paleozoic Zmeinogorsk complex have been studied within central and southern part of Rudny Altai (territory of Eastern Kazakhstan). U–Pb dating (LA-ICP-MS) of zircons allowed to determine age of intrusions in 370–358 Ma interval that corresponds to Late Devonian (Famennian). This correlates with the age of the Zmeinogorsk complex granitoid intrusions in the northwestern (Russian) part of Rudny Altai. Granodiorites and plagiogranites predominate in the volume of intrusions; their geochemical features correspond to I-type granites. Granodioritic-plagiogranitic magmas may have formed because of partial melting of meta-basalts or meta-andesites under influence of mantle-derived magmas. Biotite leucocratic granites form the later intrusive phases; and they may have classified as fractionated I-type granites. They may have formed during fractionation in deep magma chambers with F-bearing fluid presence. Analysis of geological and geochemical data allows to conclude that the Famennian granodiorite-granite magmatism is most likely associated with subduction of the Ob–Zaisan Ocean lithosphere under the Altai active margin, which could have occurred obliquely (transform) to the continental margin.