Volatile components (H2O, CO2, Cl, F, and S) in magmas of intermediate andacid compositions from distinct geodynamic settings: Evidence from melt inclusions and chill glasses

Generalized data on the chemistry of melt inclusions and chill glasses were used to evaluate the average concentrations of H2O, CO2, Cl, F, and S and the variations in these concentrations in natural magmas of intermediate an d acid compositions from oceanic islands, island arcs, active continental m argins, continental rifts, hotspots (continental areas), and continental co llision zones. The highest average concentrations of H2O in magmas of inter mediate and acid compositions were detected in island arcs (2.2 and 4.4 wt %, respectively) and active continental margins (2.4 and 2.8 wt %, respecti vely). These values for other volatiles are as follows: Cl-0.19 and 0.39% ( oceanic islands) and 0.37 and 0.23 wt % (continental areas); F-2.80 and 2.0 6 wt % (continental collision zones), 1.58 and 0.73 wt % (continental areas ), and 0.45 and 0.70 wt % (active continental margins); S-0.09 wt % (contin ental areas); and CO2-up to 1.42 wt % (active continental margins). Variati ons in the concentrations of volatile components in magmas are controlled b y the compositions of the magma sources and their differentiation and degas sing degrees. The contents of volatiles in intermediate and some acid magma s of oceanic islands, continental areas, and island arcs depend on the diff erentiation of mafic magmas, and these values for acid magmas of active con tinental margins and continental areas are related to the processes of migm atization and anatexis in the crust, i.e., processes in which micas are act ively involved. The highest contents of H2O, Cl, and F were encountered in strongly differentiated intermediate and acid magmas, which are characteriz ed by the lowest concentrations of S. The outgassing of magmas can be detec ted by comparing the average concentrations of H2O, Cl, S, and CO2 in melt inclusions and chill glasses. The volatiles of spreading-zone magmas from o ceanic ridges and backarc basins, oceanic islands, and continental areas we re provided by either mantle amphibole and micas or mantle fluids and magma s, which inherited the proportions of volatiles and the ratios of volatiles to K from the amphiboles and micas. The sources of water in magmas of isla nd arcs and active continental margins were fluids of the hydrated mantle.