UDC 549.552.331 (477)

Kryvdik S.G. (1), Sharygin V.V. (2, 3), Gatsenko V.O. (1), Lunev E.S. (1)
(1) 1 M.P. Semenenko Institute Geochemistry, Mineralogy and Ore Formation of the NAS of Ukraine
34, Acad. Palladin Av., Kyiv-142, Ukraine, 03680
(2) Sobolev Institute of Geology and Mineralogy, Siberian Branch of RAS
3, Acad. Koptyuga Av., Novosibirsk, Russia, 630090
(3) Novosibirsk State University
1, Pirogova Str., Novosibirsk-90, Russia, 630090
Mineralogical journal 2016, 38 (3): 24-38

Abstract: Devonian Pokrovo-Kyriyivo massif is located in the junction of Azov megablock of the Ukrainian Shield and the folded structure of Donbas. This massif is composed of subalkaline and alkaline rocks: pyroxenites, vehrlites, gabbros, malignites, nepheline syenites and pseudoleucites and their dyke counterparts. Clinopyroxenes are the main femic minerals for almost all types of rocks of the Pokrovo-Kyriyivo massif. However, despite the fairly satisfactory knowledge of different types of minerals, pyroxenes are examined partially. The object of our study is the chemical composition of pyroxenite and dyke malignites from Pokrovo-Kyriyivo massif. The aim of this paper is to present new results of detailed microprobe studies of pyroxenes and dyke malignites from the Pokrovo-Kyriyivo massif and petrogenetic conclusions. Research methods. The chemical composition of pyroxenite is determined by microprobe analysis: scanning electron microscope JSM-6700F, equipped with energodispersive system for microanalysis JED-2300 (JEOL, Japan), scanning electron microscope REMMA-202 equipped with energodispersive X-ray spectrometer Link systems and scanning electron microscope 3 MIRA LMU (Tescan Ltd), equipped with microanalysis system INCA Energy 450 XMax-80 (Oxford Instruments Ltd). Based on these and published data it is shown that the chemical composition of clinopyroxene evolves from diopside-titanium salite (called titanium augite) throw sodium (aegirine) salite to isomorphic varieties of diopside-series hedenbergite-acmit to the direction of subalkaline peridotite, pyroxenite, gabbro through malignites to nepheline syenites (juvites). In dyke rocks of basite and ultrabasite composition (subalkaline habroides, pyroxenites) pyroxene are saturated with TiO2 (up to 5.1 wt. %) and Al2O3 (up to 6.6 wt. %) and represented by titanium salite, while in holocrystalline peridotite, and gabbro pyroxenites they correspond belong to the diopside-salite with moderate or low content of TiO2 (up to 2.4 wt. %) and Al2O3 (up to 3 wt. %). Nepheline syenites and pyroxenites from malignites are enriched with acmite minal (70—75 %) and depleted of TiO2 and Al2O3. In malignites the pyroxene phenocrysts are zonal, central part is consists of the diopside-titanium salite, peripherals — consist of aegirine-salite. Microlite pyroxene in the bulk species belong to the diopside-hedenbergite-acmite series. The content of acmite is up to 75 %. The observed evolution of pyroxene is explained by the melt alkalinity and its quick crystallization. In the final stages of the massif formation nepheline syenites with accessory minerals (gotzenite enriched by titanium, Na, Sr-apatite), characteristic of this type of rocks, are crystallized by oversaturated alkali (agpaitic ratio >1). Formation peculiarities of the complex massif are shown on the example of pyroxenes from the Pokrovo-Kyriyivo massif. Its first intrusive phases are represented by subalkaline vehrlites, pyroxenites and gabbro and the final ones — by alkaline, including agpaitic rocks.

Keywords: Pokrovo-Kyriyivo massif, malignites, pyroxenes diopside-hedenbergite-acmite series.


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