Pillow lavas from Demir Kapija ‒ Udovo area belong to Guevgueli ophiolite complex. This complex is part of ophiolites in the area of eastern Vardar, which was an ocean during late‒middle Jurassic period. Outcrops of pillow lavas can be traced along the regional road in the river Vardar valley. We collected samples of small pillows on two locations, near Demir Kapija and in the town of Udovo.
The determination of petrological, mineralogical and geochemical characteristics of rock samples was carried out using four analytical methods. Optical microscopy under plane polarized light was used in order to define major mineral phases and rock textures. Detailed mineralogica composition was determined with the X‒ray powder diffraction method (XRD) and with scanning electron microscope in combination with energy dispersive X‒ray spectroscopy (SEM/EDS). Geochemical analysis was performed with X‒ray fluorescence analysis (XRF).
Hypohyaline and intersertal textures are present in the examined rocks samples. Matrix constitutes about 50 % of the rock samples. Hyalophitic and corona textures are also present. Some plagioclase crystals exhibit swallow tail texture and some pyroxene crystals show skeletal growth. We determined plagioclase of albite compozition and Ca‒Mg pyroxenes that belong to augite as main rock forming minerals. Other minerals include calcite, amphiboles, pyrite, titanite, hematite, spinel and epidotes. Clay minerals were most commonly found in recrystalized and altered matrix.Chlorites, smectites and kaolinite are the most abundant clay minerals.
Rock samples from the location near Demir Kapija are more coarsely grained with less matrix present than rocks from the town of Udovo. Furthermore, the differences in mineral phases between margins and cores tend to be more pronounced in pillows from the location near Demir Kapija. Ratios of SiO2, Al2O3 and especially TiO2 of the samples from the Demir Kapija location are higher. Albite is the rock forming mineral of pillows from both locations, hence we classified examined rock samples as spilite basalts. According to the average values of SiO2 and FeO*/MgO ratio, examined rock samples belong to tholeiitic magmatic series.