Age and Geochemistry of Basite-Ultrabasite Intrusions of Saltych Anticlinorium (West Azov)

Abstract

In the Saltych anticlinorium of the West Azov, small intrusions of rocks of basic and ultrabasic composition are known in the middle reaches of the Obitochna, Kiltychiya and Burtychiya rivers and in the upper reaches of the Obitochna river. They are composed from amphibolized peridotites, pyroxenites, actinolithites, tremolithites, hornblendites, amphibole and other shales. These intrusions are considered "fractured intrusions", which are rooted in the already deployed rocks of the Archean age. In the stratigraphic scheme they are referred to the Novoselytske association. Intrusions break through the veins of syenites, pegmatites and aplite-like granites. Metaultrabasites, according to I.S. Usenko and G.L. Kravchenko, these are ultrabasic rocks of the normal series, which were formed, probably, because of differentiation of basaltic magma. The main and ultrabasic rocks of these intrusions have not been studied enough yet — their age, geodynamic conditions of formation have not been determined, the potential for minerals has not been fully revealed. For this purpose, we determined the microelement composition of meta-ultrabasites, metabasites and acid rocks by the ICP MS method and determined the age of monazite from veins of aplite-like granites that break through the metapyroxenites of the Kamyshuvatka intrusion. According to the obtained geochemical and mineralogical data, the vein rocks of medium and acid composition, which break through the intrusions of the ultrabasite-basite composition at the Saltych anticlinorium, have a core genesis. Zircon in them is relict, and syngenetic monazite was found only in the veins of aplite-like granites that break through the metapyroxenites of the Kamyshuvatka intrusion. According to the dating of this monazite, it has been determined that the upper age limit for the formation of intrusions of the ultrabasite-basite composition of the Novoselytske association is 2051.8±3.8 Ma. Peridotites and pyroxenites of these intrusions could be formed from melts of the depleted upper mantle, which were fractionated in intermediate magmatic chambers. In peridotites (#mg = 0.74-0.86) of the Kamyshuvatka intrusion and intrusion near the Reva farm, the Ni content (510-826 ppm) is lower than that of Clark for ultrabasic rocks, and the chromium content at the level of Clark and below it is Cr — 1250-2260 ppm. Positive anomalies of Ti and Eu indicate the processes of fractionation of the original magma of pyroxenites. The formation of intrusions of the ultrabasite-basite composition of the Saltych anticlinorium of the Azov megablock is probably connected with the activation of the Earth’s mantle about 2050 million years ago.