Paleoproterozoic hornblende gabbro of the Gnilushinsky massif, the Kursk block, Sarmatia: geochronology, sources of melts and tectonic position

Abstract

Introduction: The Paleoproterozoic Tim-Yastrebovskaya synform of eastern Sarmatia contains gabbroid intrusions. The largest of them, the Gnilushinsky massif of hornblende gabbros, differs in age, mineralogy, and geochemistry from the gabbronorites of the Zolotukhino complex. The purpose of this article was to determine the age, sources of melts and the tectonic position of the Gnilushinsky massif hornblende gabbros. Methodology: We carried out geochemical, U-Pb, and Sm-Nd studies of the rocks from the Gnilushinsky massif to determine the age of formation and sources of basic melts. Results and discussion: The gabbros of the Gnilushinsky massif are calc-alkaline rocks, enriched in light rare earth and lithophile elements with a negative MgO – Al2O3 correlation. High-alumina varieties represent residual melts, while magnesian ones can be complementary cumulus. The age of crysta llization of the massif is 2031 Ma. It has a posttectonic position and a metasomatized mantle source. Conclusions: Post-collision tectonics inherited the active margin setting, since the Archean Sm-Nd modelage of gabbros indicates their position at the edge of the Kursk Archean block.