Petrological features of near-contact changes in the Pervomaisky intrusion massif (Crimean Mountains)

Abstract

Introduction: The aim of the work is a physical and chemical study of the near-contact zones in the Pervomaisky intrusive massif. The research is relevant due to a lack of information about the compositional structure and hydrothermal-metasomatic transformations in the contact zones of minor intrusions in the Crimean Mountains with the host rocks. The performed studies will allow identifying the formation model of minor intrusions in the valley of the Bodrak river and can be used in the future to support the learning process in practical trainings for geology students. Experimental: Rock samples included lumps of rock selected from bedrock exposures. The most representative samples were studied on the micro level. The chemical composition of the minerals was determined by an "INCA-250" energy dispersive spectrometer (VSU, Physicochemical Research Methods Laboratory). Analysis conditions: accelerating voltage was 20 kV, measuring current was 1.2 nA, spectrum collection time was 70 sec, the beam diameter was normally 5 μ m. Results and discussion: The massif is primarily composed of altered intermediate rocks close to microdio-rites and diorite-porphyrites. The main rock-forming minerals include basic and intermediate plagioclase, hornblende, barium-containing microcline; the main accessory rocks are titanomagnetite and zircon. Among secondary minerals are chlorite, calcite, kaolin, and zeolites in plagioclase cracks. On the contacts with host rocks there are thin (15-20 cm), clear cataclasis zones made of quartz-carbonate-kaolin substance with chlorite and rare pyrite crystals. Host rocks in the area of exocontact are represented by pressed brownish agrillites consisting of kaolinite and calcite with throughout accumulations of glomeroblastic albite (adinole). The formation of adinoles, albitisation pelites at the contact with mafic intrusions is associated with sodium metasomatism. The mechanism of sodium metasomatism of agrillites of Eskiorda series can be described by the following reaction: sericite + quartz = albite. Normally, zoned plagioclase crystals in microdiorites and homogeneous titanomagnetite grains with a moderate content of TiO 2 = 15 wt.%. indicate a high rate of magma rise and crystallisation in the Pervomaisky intrusion massif. Conclusions: The intrusion of the Pervomaisky intrusion massif did not result in large-scale metasomatic changes in the host agrillites and led to the formation of thin (15-30 cm) zones accentuated by the adinolisa-tion processes.