ПЕТРОЛОГІЯ ГАБРОЇДІВ ЗАТОКИ ЖИРАР (ПІВОСТРІВ КИЇВ БЕРЕГА ГРЕЯМА, ЗАХІДНА АНТАРКТИКА).

Several new gabbroid intrusions were discovered in the process of geological surveying in the area of the Ukrainian research station in the West Antarctica. One of them is located in the hard-to-reach Girard Bay on the western coast of the Kyiv Peninsula. The authors investigated the mode of occurrence, petrography and mineral chemistry of Girard Bay gabbroids in order to clarify their geological position and petrogenetic conditions of their formation. It was found that the newly discovered gabbroids make up a stock-like intrusive body with a horizontal dimension of more than 3 km. Gabbroids unconformably intrude the Kyiv Peninsula volcanic formation. The apical part of this gabbroid intrusion is exposed fragmentarily on the southern coast of Girard Bay. The petrographic diversity of the studied gabbroids depends on the heterogeneous manifestation of local low-temperature hydrothermal transformations (amphibolization, prenitization and silicification). In addition, the presence of hidden magmatic layering, which is characteristic of other gabbroid intrusions of the region, is assumed. The main petrographic representatives are gabbronorites and amphibolized gabbros, among which mesocratic and leucocratic varieties have been identified. The gabbronorites exposed on the southern coast of Girard Bay represent one of the lowest degrees of the post-magmatic transformation. Mineralogical and petrographic features point to hypabyssal depths of their formation. The chemistry of pyroxenes and plagioclases indicates the most high-temperature conditions of crystallization in comparison with other representatives of gabbroids both on the Kyiv Peninsula and on the neighbouring Wilhelm Archipelago. The geological age of Girard Bay gabbroids is preliminarily defined as post-Jurassic and requires further clarification using the isotopic geochronology methods. Given the possible post-magmatic re-equilibration of primary mineral paragenesis, zircon is recommended as a chronometer mineral. [ABSTRACT FROM AUTHOR]