THE CHEMISTRY OF ROCK-FORMING MINERALS AS AN INDICATOR IN THE CASE OF GEOLOGICAL DIVISION AND CORRELATION OF THE UKRAINIAN SHIELD INTRUSIVE FORMATIONS
Keywords:
rock-forming minerals, magmatic rocks, geological division and correlation, Ukrainian Shield.Abstract
We systematically investigated the rock-forming minerals of three fundamentally different petrographic objects that are typical representatives of the Ukrainian Shield intrusive formations: 1)olivine gabbro and ultramafites from Kropyvenska Ti-bearing intrusion (Korostenskyi anortho-site-rapakivi-granite pluton in the North-Western part of the Ukrainian Shield); 2) anorthosites, norites and gabbro-norites from the Gorodyshchenskyi gabbro-anorthosite massif (Korsun-Novomyrhorodskyi anorthosite-rapakivi-granite pluton localized in the central part of the Ukrain-ian Shield); 3) olivine dolerites and gabbro-dolerites from the Bobrynetskyi dyke belt (intrude the Precambrian basement in the Southern part of the Inhulskyi megablock of the Ukrainian Shield; the host rocks in the North-Western part of the belt are granitoids of Novoukrainskyi pluton, in the South-Eastern – granites and migmatite of Kirovohradskyi complex). The purpose of this study was to determine the possibility of using data about the chemical composition of rock-forming minerals for solving the problems of geological division and corre-lation of intrusive formations of the Ukrainian Shield and other Precambrian regions. The chemi-cal composition of rock-forming minerals has been studied by electron probe X-ray spectral mi-croanalysis on the focused beam electron microscope REMMA-202 equipped with energy-dispersive X-ray spectrometer “Link systems”. The chemistry of feldspars, pyroxenes, olivine and Fe-Ti oxide ore minerals has been studied in detail. Completed studies have demonstrated extensive capabilities in using of data about the chemical composition of rock-forming minerals in the solution of applied problems arising in the course of geological survey and exploration in the areas of intrusive-magmatic formations devel-opment. It have been shown that the ratio #Ca = Ca/Ca+Na in plagioclase, the ratio #Mg = Mg/Mg+Fe in pyroxenes and content of Ti in Ti-magnetites can serve as an important indicator sign to iden-tify hidden stratification in Ti-bearing gabbroid intrusions belong to the anorthosite-rapakivi-granite association of the Ukrainian Shield, such as Kropyvnenska ones. Data about #Ca-ratio in plagioclase as well as #Mg-ratio in pyroxenes and olivine are not less informative for the identification of intrusive phases in the multiple intrusions, for example in Proterozoic anorthosite massifs of the Ukrainian Shield, such as Gorodyshchenskyi ones. These ratios also can be used for the correlation of spatially disconnected intrusive bodies such as individual mafic dikes as well as their groups and dyke swarms. For some petrographic objects (for example, Ti-bearing gabbroids of the Kropyvnenska intrusion and dolerites of the Bobrinets dyke belt) the data on the chemistry of the rock-forming minerals can serve as an addi-tional criterion to determine the potential ore content of intrusive bodies or their separate parts.
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