Clinopyroxenites (diopsidites) and metabasites from the East Sarmatian Orogen, East European Craton

Abstract

The East Sarmatian Orogen was built through successive subduction and collision processes at the junction of the Sarmatia and Volga-Uralia segments of the East European Craton. In this paper we present petrological and geochemical characteristics of diopsidites and host amphibolites from the central part of this orogen. We report a new occurrence of metabasites (meta-gabbros and amphibolites) and anorthite–bytownite-bearing diopsidites from the Palaeoproterozoic Vorontsovka terrane of the East Sarmatian Orogen. The diopsidites occur as networks of veinlets and dykes within the metabasite layers (thickness up to 100 m) and are composed predominantly of high-Mg diopside (Mg# up to 0.87) and calcic plagioclase (An99–73) with traces of K-feldspar, titanite, calcite, quartz with retrograde chlorite and epidote. The diopsidites are low in Ti and K and high in Mg (Mg# greater than 0.82) rocks. They have low REE; positive Ce, U and Sr anomalies; and negative Th, Nb and Ti anomalies. The meta-gabbros and amphibolites are composed of calcic amphibole, albite, quartz, biotite, zoisite, prehnite and ore minerals (sulphides + ilmenite). The amphibolites are low Al, low K, magnesian–ferroan (Mg# = 0.46–0.75) and medium Ti (TiO2 0.75–1.37 wt.%) (SiO2 40.1–47.3 wt.%). The meta-gabbros exhibit slight LREE and LILE enrichment, particularly in Rb, Ba and Sr. The amphibolites are tholeiitic in composition and have N-MORB-like REE and HFSE features, with high 143Nd/144Nd (0.512736) and positive eNd(T) (6.0). The diopsidites reported in our study compare with convergent-margin rocks formed via metasomatic processes associated with slab subduction. The metabasite protoliths represent oceanic crust with N-MORB-type features with the LILE enrichment accompanying the subduction zone process. Copyright © 2016 John Wiley & Sons, Ltd.