Paleoproterozoic Gabbros of the Kursk Block, Sarmatia: Age, Sources of Melts, and Tectonic Position

The Paleoproterozoic Tim-Yastrebovka synform of Eastern Sarmatia contains gabbroid intrusions. The largest of them is the Gnilushinskii massif of hornblende gabbros, which are calc-alkaline rocks, enriched in light rare earth and lithophile elements with a negative stable MgO–Al2O3 correlation. High-aluminous varieties represent residual melts, while magnesian ones can be complementary cumulus. The crystallization age of the massif is 2031 Ma. The massif has a post-tectonic position and a metasomatized mantle source. Post-collisional tectonics inherited the environment of the active margin, since the Archean Sm–Nd model age of gabbros indicates its position at the margin of the Kursk Archean block.