Murzinka and Dzhabyk are continental-type batholiths of the middle and southern East Uralian domain. They comprise mainly undeformed peraluminous K-rich granites whose elemental composition is similar to some late-Variscan granites of western Europe, but with much more primitive Sr and Nd isotope ratios. Murzinka (2545 Ma) is composed of silica-rich granites forming two different rock series with a 87 Sr/ 86 Sr init of 0.709 and 0.704, respectively. Both series have enormous variations in eNd 255 (±11.9 to ±0.1 and ±8.9 to +4.1) that reveal derivation from heterogeneous sources. Dzhabyk (2914 Ma) also comprises two coeval magmas which yielded voluminous granites and quartz-monzonites, respectively, with smaller differences in 87 Sr/ 86 Sr init and eNd 290 (~0.7043, +0.8 to +1.6 and~0.7049, 0.0 to +0.8). Despite their isotope compositions both batholiths lack evidence of genetic involvement of a mantle-derived parental magma. Moreover, we suggest that Dzhabyk granitoids were generated by polybaric partial melting of Paleozoic island-arc material, whereas Murzinka granitoids derived from an extremely heterogeneous source consisting mainly of Paleozoic and Proterozoic metagreywackes. This implies a relative fast reworking of juvenile arc crust and burial of the protoliths during the orogenic evolution of the Urals. Since there is neither evidence of significant extension, nor a direct link with subduction, we suggest that the main cause for late-orogenic anatexis was elevated heat production and fertility in the protolith, perhaps combined with some additional heat from unexposed mafic intrusions.
—The chemical composition of rocks of the Murzinka–Adui metamorphic complex and the Murzinka granite pluton, a reference interformational granite pluton in the Urals, is considered. A detailed comparative analysis of ancient gneisses and related granite veins included an isotope–geochemical study of zircons from both groups of rocks. Zircons are subdivided into seven age groups (I, 1588 ± 20 Ma; II, 1060 ± 28 Ma; III, 530 ± 11 Ma; IV, 380 ± 6 Ma; V, 330 ± 9 Ma; VI, 276 ± 3 Ma; and VII, 260 ± 3 Ma). The first four groups are apparently zircons from gneisses, reworked to different extents, and the other three groups are zircons crystallized during granite genesis. The gneisses and most of the granite samples contain zircons of all the above age populations, which is evidence of trapping zircons from gneisses by granite melts, on the one hand, and the occurrence of “granite-derived” zircons in gneisses, on the other.
The granitoids and gneisses of all types differ considerably in geochemical features. The behavior of trace elements and the Rb–Sr ages indicate that the formation of granites of the Murzinka massif was a discrete episode of magmatic activity. The Sr isotope ratios in the granites and gneisses indicate different degrees of the mantle–crust interaction and the participation of the material of the crystalline basement and newly formed crust in their formation.
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