Calcalkaline

Calcalkaline refers to a major magmatic and igneous rock series commonly formed in subduction-zone environments, especially volcanic arcs. Rocks in the calcalkaline series typically show a sequence from basalt to andesite, dacite, and rhyolite, with a characteristic increase in silica as alkalis (sodium and potassium) rise, often accompanied by relatively high calcium. The trend is often described as a calc-alkaline line on silica–alkali diagrams. Calcalkaline rocks are usually metaluminous to mildly peraluminous and commonly enriched in large ion lithophile elements (LILE) such as Rb, Ba, Sr, and K, as well as light rare-earth elements, while showing depletion in high-field-strength elements (HFSE) such as Nb, Ta and Ti. They frequently exhibit notable Ba and Sr enrichment and variable europium anomalies depending on plagioclase fractionation.

Geochemically, calcalkaline magmas reflect subduction input, hydrous conditions, and crust-mantle interactions. Their magmas are thought to form in the mantle wedge above a subducting slab, with fluids and melts added from the slab modifying melting, melting composition, and crystallization behavior. Fractional crystallization of amphibole, biotite, and plagioclase during ascent and storage enhances the characteristic chemical signature and the progression from mafic to felsic compositions.

Distribution and significance: calcalkaline magmatism is widespread in convergent plate-margin regions worldwide, including the Andes, Cascades, Japan, the Alps, and the subduction zones of Southeast Asia. The term contrasts with tholeiitic series, typical of many mid-ocean ridges, and alkaline series found in other tectonic settings. The calcalkaline suite provides key insights into arc magmatism and crustal growth processes.