U-Pb age of titanite from diorit of Osnytsky Block (Volyn Megablock of Ukrainian Shield)

Abstract

The Osnytsky block is a constituent part of the Osnytsky-Mikashevytsky volcano-plutonic belt. The leading place in the geological structure of the Osnytsky block is occupied by the rock association, which includes a number of plutonic formations from gabbro to leucocratic granites (gabbro-diorite-granodiorite-granite association), formed in the Paleoproterozoic — 1,98—1,95 Ga. The results of lead-lead isotope dating of titanites from diorites, opened by the RPZ-5 quarry, located in the northwestern vicinity of the village Tomashhorod. Diorites were formed in the second phase, after gabroids, before the beginning of the formation of granitoids. The age of 1975 ± 9,1 Ma was obtained for them. The age calculated based on previously published data is 1973 ± 8,3 Ma, which is in good agreement with the U-Pb isotopic age of the zircons of these diorites 1974 ± 1,2 Ma. It was found that to determine the isotopic age of titanites with a high content of ordinary lead, it is enough to use only the isotopic composition of lead, calculating the age in the coordinates of the graph 207Pb/204Pb — 206Pb/204Pb, by the tangent of the angle of inclination of the regression line.