Мінеральні ресурси України (May 2022)
The leucogranulite formation and zelenolevadivska siute of the Buh area granulite complex (western part of the Ukrainian shield). Article 2. Concomitant and superimposed phenomena, isotopic dating and age
Abstract
The article continues the discussion of the origin of the leucogranulite formation of the Buh Area granulite complex and the possibility of distinguishing it as an independent stratigraphic unit – zelenolevadivska suite – in the scheme of the dismemberment of the Lower Precambrian of the Ukrainian Shield. In a previous article, data from many years of research were presented, including the results of state geological mapping (SGK–200), indicating the initial stratigenic nature of the leucogranulite formation. This article discusses the arguments presented in a collective publication [29] to substantiate alternative ideas about the occurrence of a leucogranulite formation as a result of endogenous processes. The authors of the article [29] believe that the leucogranulite formation has a dynamometamorphic origin and arose due to the transformation of rock associations of a different primary composition. The leading role in the origine of the formation was played by faults and associated processes of diaphthoresis and metasomatism, and the age of the formation is 2,04 billion years. All the phenomena cited by the authors of [29], which they consider to be decisive in the formation of the leucogranulite formation, have been noted by many researchers before, but were considered as the result of secondary superimposed processes. This article shows that the areas of development of the leucogranulite formation have non-linear forms in most of its distribution area and are not structurally and genetically related to faults. Their directions coincide only within the Holovanivskyi block, in which both folded and fault structures have a common northwestern strike. The processes of diaphthoresis, which are recorded mainly by the transformations in the rocks of dark-colored minerals, could not significantly change the composition and appearance of the leucogranulite formation, since leucocratic gneisses dominate in it. The ultrametamorphic granitoids associated with the leucogranulite formation are mainly not of an allochthonous metasomatic, but of an autochthonous crystalloblastic nature. Based on the position of the leucogranulite formation (zelenolevadivska suite) in the section, of the Buh Area complex, its stratigraphic age is at least 3,8 billion years. Younger dating is associated with lengthy processes of metamorphism and ultrametamorphism up to 2,0–1,9 billion years.
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