The name given to a suite of rocks comprising the volcanic association basalt–andesite–dacite–rhyolite, or the plutonic association gabbro–diorite–granodiorite–granite. The suite is defined chemically using a graph depicting the variation of CaO and (Na₂O + K₂O) with SiO₂ (wt. %), and is classified as calc-alkaline if the SiO₂ value at the intersection of the CaO and (Na₂O + K₂O) trends is between 56 and 61 SiO₂ wt. %. (Less than 51 SiO₂ wt. % and the rock suite is classed as belonging to the alkalic series, 51–56 SiO₂ wt. % to the alkali-calcic series, and more than 61 SiO₂ wt. % to the calcic series.) Calc-alkaline rocks are typically developed on the continental side of plate subduction zones, well-known examples occurring in the Andes of S. America and in Japan.