The Nature of Enderbites From Bug Area According to the Data of Sm-Nd, U-Pb and Lu-Hf Methods

Abstract

As a result of the mineralogical and isotopic-geochemical study of U-Pb, Lu-Hf, isotopic systems of zircons from Pobug enderbites, the existence of crustal and juvenile enderbites was established. Negative values of (εNd) and negative values of εHf in zircons from enderbito-gneisses of the Middle Bouh area, Lityn enderbite, and Sabariv enderbite indicate their crustal nature, origin by account of older (Eoarchean?) rocks series, the protolith for which was probably mafic protocrust. The transformation of these rocks occurred pulsatingly 3.6-3.4, 3.0-2.8 and 2.1-1.9 billion years ago. The presence of "typomorphic" zircons in enderbites is also evidence of their crustal nature. Juvenile enderbites 117/79, from the quarry in Tyvriv and 127/79 from the quarry in the village of Holoskove have positive εNd and positive εHf values in zircons, indicating their formation from a juvenile source. They are 2080 and 2070 million years old, respectively. It is believed that it is the juvenile rocks that give increase to the continental crust, which is consistent with the idea that the growth of continents was accompanied by the addition of new sialic material from the mantle. At the same time, rocks that are an addition to the сгust may not differ in composition from older rocks. The available isotopic-geochemical and geological data indicate at least three stages of formation of enderbites (TTG association) within the Pobug granulite belt. The oldest of them is represented by enderbites (enderbito-gneisses) of the Haivoron complex. The next TTG association (Lityn complex, ~2.8 billion years ago) is more widespread, and in general forms a wide "shell" around the protocontinental core, formed by the rocks of the Haivoron complex. The youngest TTG association in the borders of the Pobug granulite belt (Berdychiv complex) is often represented by numerous intrusive bodies of juvenile enderbites, with xenoliths of more ancient rocks.