Journal of the Virtual Explorer

The concentrations of major elements of the studied rocks are presented in Table 4. Based on both (Na₂O + K₂O) vs SiO₂ (Le Bas et al., 1986) and R1-R2 diagrams (De La Roche et al., 1980) all the samples are classified as rhyolites, rhyodacite, dacites and rarely andesite (Fig.4a, 4b). In terms of aluminum saturation concept (A/CNK molecular ratios), they are predominantly metaluminous to mild peraluminous (0.62- 1.08). Based on Irvine and Baragar’s classification (1971), all the analysed rocks plot in the subalkaline and calc-alkaline fields. The content of SiO₂ in these rocks varies from 56.27 to 70.08 wt%.

Figure 4. Classification of the studied volcanic rocks.

Total alkali-silica diagram (TAS: Le Bas et al., 1986) for the volcanic rocks. Dashed line = subalkaline- alkaline divide (Irvin and Baragar, 1971);

R1-R2 diagram (De La Roche et al., 1980)

Figure 5. Harker variation diagrams

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Harker variation diagrams (Major oxides) for the studied volcanic rocks.

In all the samples, the K₂O content increases with increasing SiO₂, whereas the amounts of CaO, Al₂O₃, MgO, TiO₂ and Fe₂O₃ decrease, reflecting the fractional crystallization of hornblende, plagioclase and biotite (Fig.5).

It seems that partial melting of the continental crust led to the formation of dacite parent magma which intruded into shallow-level magma chambers and fractionated. The dacite parent magma mingled with the small volume of mafic magma intruded into magma chamber.