Geochemistry of the eclogites of the Maksyutov Complex, South Urals, and genetic nature of their protoliths

Abstract

Detailed mineralogical-petrographic and petrogeochemical characteristics are reported for eclogites of the Maksyutov Metamorphic Complex (MMC). It was established that protoliths of different varieties of eclogites (high-Ti, moderate- and low-Ti eclogites, graphite eclogites, and eclogites of the layered body) were mafic magmatic rocks of different affinity. The petrogeochemical comparison of MMC eclogites with the Early Paleozoic lithotectonic complexes of the South Urals shows that the eclogites are close to basalts formed in different geodynamic settings that existed in the region in the Cambrian (?)-Ordovician-Silurian(?) time. Subduction of oceanic crust and subsequent rise to the surface resulted in the spatial juxtaposition of bodies, the protoliths of which were formed at the initial and island arc stages of the evolution of the Paleo-Ural Ocean. Thermodynamic calculations of mineral assemblages of eclogites showed that low-Ti eclogites (680–700°C, 24 kbar), graphite eclogites (660–710°C, 17–18.8 kbar), and eclogites of the layered body (610–730°C, 16–18 kbar; 410–430°C, 12.5–13 kbar) were formed at similar temperatures but at a large scatter in pressure. It was concluded that the pressure variations were caused by the tectonic juxtaposition of bodies during exhumation of eclogites formed at different depths of subducted plate.