This project will investigate boninite series and basalt to rhyolite glasses recording the formation of island arc crust over a 50 Ma period in the Izu-Bonin-Marianas (IBM) arc. IBM arc glasses inform our knowledge of island arc crust geochemical evolution and crustal growth rates. Importantly, the volatile elements in glasses provide a window into volcanic processes (effusive vs. explosive; subaerial vs. submarine events) and alteration processes that influence our models for subduction zone volatile cycling, rates for continental crust formation, and the geodynamic properties of subduction zones.
Past researchers assumed that the glass fragments lost (degassed) most of their volatile species to the atmosphere and were then transported from subaerial volcanoes to form tephra deposits and by water to form volcaniclastic turbidite deposits (Fig.). Indeed, volatiles are low in modern glass rims on dredged submarine lavas and in glass inclusions in the IBM arc. However, glass volatile contents may be higher than assumed because: 1) modern, volatile-rich submarine volcanoes are observed in the IBM arc; and 2) glasses from tephras in the IBM forearc have 91-~100% electron probe totals suggesting volatile contents of up to 9 wt. %.
The student will test if glasses in forearc tephras erupted from submarine volcanoes, where they retained their original volatile contents as the melt quenched to glass under seawater pressure. The student will quantify and map H2O, CO2, SO2 and Cl in select glasses and compare the values with open and closed system degassing models and melt inclusion data (accounting for volatile solubility as a function of composition, temperature and pressure). These data will be used to further constrain arc volatile budgets and inform tephrostratigraphy and provenance studies that can then be used to understand crust formation and geochemical evolution.