Abstract
Island arc low-K tholeiites are basaltic magmas erupting from frontal arc volcanoes of juvenile arcs associated with the subduction of old and cold plates. We investigated the origins of geochemical variation in volcanic rocks having multiple phase saturated liquid compositions from the Izu-Oshima volcano in the northern Izu arc. The geochemical variations in the liquids fall between two endmember trends, namely higher- and lower-Al/Si trends. Polybaric differentiation of H2O-saturated melts between a 4-km-deep magma chamber and degassed melts near the surface should be responsible for the observed variation in the liquids.
Highlights
With a worldwide average of 3 to 5 wt.% H2O, island arc magmas are characterized by higher volatile concentrations than magmas erupting from other tectonic settings with
We investigated the conditions of crystallization differentiation, the dissolved H2O concentration in melts by considering previously reported chemical compositions for volcanic rocks from the Izu-Oshima volcano, a frontal arc volcano in the northern Izu arc, along with the results of hydrous melting experiments on relevant magmas to evaluate the dissolved H2O concentration in island arc low-K tholeiitic melts
Implications for the origin of the lower-K subgroup liquids Three types of magma have been identified in island arc low-K tholeiites from the Izu-Oshima volcano: (i) a lower-K subgroup, (ii) higher-Al/Si trend of a higher-K subgroup, and (iii) lower-Al/Si of a higher-K subgroup
Summary
With a worldwide average of 3 to 5 wt.% H2O, island arc magmas are characterized by higher volatile concentrations than magmas erupting from other tectonic settings with
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