Neoproterozoic flood basalts of Zabolottya and Babino Beds of the volcanogenic Volhynian Series and Polesie Series dolerites in the western margin of the East European Craton

Abstract

In the Volhynia region, on the western slope of the Ukrainian Shield, occurs a large complex of Lower Neoproterozoic III (Lower Vendian) effusive-tuffogenic rocks, referred to the Volhynian Series. This series belongs to a large province of flood basalts extending over an area of ca 140 000 km2 in the western part of the East European Craton. The series is underlain by the terrigenous rocks of the Polesie Series, with volcanic ashes and dolerites in its upper part. The effusive-tuffogenic rocks of both series, together with hypabyssal dolerites, represent the Volhynian Trap Formation. Within the lower – Zabollotya and Babino Beds of the Volhynian Series there have been found alkali basalts and olivine tholeiites, whereas the basalts of the upper, Ratno Beds are quartz tholeiites exclusively. All the basalts are mainly within plate continental basalts. The diversity of basalt composition within the Volhynian Series suggests that in the Early Vendian, during the process of formation of parent magmas for basalts of particular beds, the mantle material beneath Volhynia has been melted to various degrees. Distinct variability can also be observed in basaltic pyroxene composition (particularly in the Babino and Ratno Beds) as well as in variations of REE distribution patterns in the studied basalts. Most likely, the strongly differentiated pyroxenes were not in a state of equilibrium with the magma. The native copper mineralization of basalts from the Ratno, Babino and Zabolottya Beds is described. Higher concentration of Au and Ag in the rocks with a high content of copper supports the hypothesis that the mineralizing hydrothermal solutions originated in a common igneous source. The Vendian magmatic activity in the study area was associated with the last stages of breakup of the Rodinia supercontinent.