The article discusses the classification and evolution of volcanic rock series in island arcs and active continental margins. Three main volcanic rock series are identified: calc-alkalic (CA), tholeiitic (TH), and alkalic. The first two are collectively termed non-alkalic. The CA series shows a steeper increase in SiO₂ and lower FeO* enrichment compared to the TH series. Both series include basalt, andesite, dacite, and rhyolite. In immature island arcs, TH series basalts and basaltic andesites dominate, while well-developed arcs with thick continental-type crust show TH and CA series andesites and dacites. Continental margins mainly have CA series andesites, dacites, and rhyolites. The proportion of CA series rocks increases with the development of continental-type crust. Alkalic series rocks are rare in slow-converging arcs. The average SiO₂ and K₂O contents of volcanic rocks increase with the development of continental-type crust. This trend is due to the increasing proportion of CA series rocks, which have higher SiO₂ than TH series. The primary magmas of TH and CA series form independently, with the increase in CA series magmas due to the depletion of the upper mantle wedge over a descending slab. Some ophiolitic complexes are remnants of early volcanic masses. The K₂O and Na₂O + K₂O contents, and the (Na₂O + K₂O)/Al₂O₃ ratio of volcanic rocks increase toward the continent. However, silica saturation varies widely in alkalic rocks. The increasing alkalicity is controlled by pressure and decreasing melt percentage in magma generation. Degassing of the deeper mantle may contribute to increased alkalicity. The distinction between CA and TH series is based on the slope of variation diagrams. The CA series has a steeper slope, while the TH series has a gentler slope. The boundary between the two series is defined by a straight line in figure 1A. The CA and TH series are defined as having compositions above and below this line, respectively. The CA and TH series are composed of basalt, andesite, dacite, and rhyolite. TH series rocks have higher FeO* and color index than CA series rocks. The CA series is more common in arcs with thick continental-type crust. The TH series is more common in arcs with thin, oceanic-type crust. The evolution of island arcs and continental margins is influenced by the rate of plate convergence and the development of continental-type crust. Arcs with rapid convergence (group I) have more TH series rocks, while those with slower convergence (group III) have more CA series rocks. The proportion of CA series rocks increases with the development of continental-type crust, leading to more silicic volcanic rocks and higher average SiO₂ percentages. The increase in CA series rocks is not due toThe article discusses the classification and evolution of volcanic rock series in island arcs and active continental margins. Three main volcanic rock series are identified: calc-alkalic (CA), tholeiitic (TH), and alkalic. The first two are collectively termed non-alkalic. The CA series shows a steeper increase in SiO₂ and lower FeO* enrichment compared to the TH series. Both series include basalt, andesite, dacite, and rhyolite. In immature island arcs, TH series basalts and basaltic andesites dominate, while well-developed arcs with thick continental-type crust show TH and CA series andesites and dacites. Continental margins mainly have CA series andesites, dacites, and rhyolites. The proportion of CA series rocks increases with the development of continental-type crust. Alkalic series rocks are rare in slow-converging arcs. The average SiO₂ and K₂O contents of volcanic rocks increase with the development of continental-type crust. This trend is due to the increasing proportion of CA series rocks, which have higher SiO₂ than TH series. The primary magmas of TH and CA series form independently, with the increase in CA series magmas due to the depletion of the upper mantle wedge over a descending slab. Some ophiolitic complexes are remnants of early volcanic masses. The K₂O and Na₂O + K₂O contents, and the (Na₂O + K₂O)/Al₂O₃ ratio of volcanic rocks increase toward the continent. However, silica saturation varies widely in alkalic rocks. The increasing alkalicity is controlled by pressure and decreasing melt percentage in magma generation. Degassing of the deeper mantle may contribute to increased alkalicity. The distinction between CA and TH series is based on the slope of variation diagrams. The CA series has a steeper slope, while the TH series has a gentler slope. The boundary between the two series is defined by a straight line in figure 1A. The CA and TH series are defined as having compositions above and below this line, respectively. The CA and TH series are composed of basalt, andesite, dacite, and rhyolite. TH series rocks have higher FeO* and color index than CA series rocks. The CA series is more common in arcs with thick continental-type crust. The TH series is more common in arcs with thin, oceanic-type crust. The evolution of island arcs and continental margins is influenced by the rate of plate convergence and the development of continental-type crust. Arcs with rapid convergence (group I) have more TH series rocks, while those with slower convergence (group III) have more CA series rocks. The proportion of CA series rocks increases with the development of continental-type crust, leading to more silicic volcanic rocks and higher average SiO₂ percentages. The increase in CA series rocks is not due to