Triple oxygen isotope constraints on the origin of ocean island basalts

 

Understanding the origin of ocean island basalts (OIB) has important bearings on Earth’s deep mantle. Although it is widely accepted that subducted oceanic crust, as a consequence of plate tectonics, contributes material to OIB’s formation, its exact fraction in OIB’s mantle source remains ambiguous largely due to uncertainties associated with existing geochemical proxies. We have shown, through theoretical calculation and examining published data, that unlike many known proxies, triple oxygen isotope compositions (i.e. Δ¹⁷O) in olivine samples are not affected by crystallization and partial melting. This unique feature allows olivine Δ¹⁷O values to identify and quantify the fractions of subducted ocean sediments and hydrothermally altered oceanic crusts in OIB’s mantle source. In this work, new Δ¹⁷O measurements for OIB will be presented, and the implications will be discussed.