Alkaline rock series

Examples of the trends characteristic of the tholeiitic and calc—alkaline rock series are also plotted in Figure 3.18. The tholeiitic trend is illustrated by Thingmuli volcano in Iceland and the calc-alkaline trend is for the average compositions of the Cascades lavas Carmichael, 1964). 

Rock compositions range from mafic to silicic, and show a calc-alkaline (CA), high-potassium calc-alkaline (HKCA) to shoshonitic (SHO) affinity. A few potassic alkaline rocks with a composition close to the Roman potassic series (KS) occur at Vulcano and Stromboli (e.g. Keller 1982 Francalanci et al. 2004). Arc tholeiites have been dredged along some seamounts (Beccaluva et al. 1982). 

Kelemen P. B. (1990) Reaction between ultramafic rock and fractionating basaltic magma I. Phase relations, the origin of calc-alkaline magma series, and the formation of discordant dunite. J. Petrol. 31, 51-98. 

Dal Negro A., Carbonin S., Molin G. M., Cundari A., and Piccirillo E. M. (1982). Intracrystalline cation distribution in natural clinopyroxenes of tholeiitic, transitional and alkaline basaltic rocks. In Advances in Physical Geochemistry, vol. 1, S. K. Saxena (series ed.), New York Springer-Verlag. 

The SiC>2 vs. K2O plot (Fig. 7.8) shows that the Lipari volcanics define a steep increase in K2O from mafic to intermediate rocks, straddling the limits between arc tholeiitic, calc-alkaline and shoshonitic series. Basaltic andesites and andesites have porphyritic textures with phenocrysts of zoned... 

A strongly silica undersaturated Na-alkaline series ranging in composition from basanite-tephrite to phonolite, with some of the most evolved rocks reaching a peralkaline composition. This is best represented by volcanic rocks from Montiferro. 

A mildly silica undersaturated to saturated series (trachybasalt to trachyte) with a moderate alkali content and a Na- to mildly K-alkaline affinity. This comprises most of the Plio-Quatemary rocks, including some lavas from Monte Arci. 

Fig. A.l. K20 vs. Si02 classification grids for arc rocks. 1 arc tholeiitic series 2a calc-alkaline series 2b high-K calc-alkaline series Field 3 shoshonitic series. Modified from Peccerillo and Taylor (1976).

---