The effects of variable sources, processes and contaminants on the composition of northern EPR MORB (8-10 degrees N and 12-14 degrees N): Evidence from volatiles (H2O, CO2, S) and halogens (F, Cl)

New volatile (H2O, CO2, S), halogen (F, Cl) and trace-element data for selected fresh MORB glasses are reported from two geologically and geophysically well-studied regions on the East Pacific Rise (8-10 degrees N and 12-14 degrees N) with distinct differences in spreading rate and magma supply. Sample locations include on-axis and young off-axis eruptions, as well as off-axis fissures, abyssal hills and pillow mounds. H2O, F, S and trace-element concentrations increase with decreasing MgO content, displaying over-enriched liquid lines of descent consistent with combined fractional and in-situ crystallization. A negative correlation between CO2/Nb and MgO indicates simultaneous degassing and magma crystallization, while broadening of this correlation to lower CO2/ Nb at constant MgO indicates shallow degassing and CO2 loss during magma transport to the seafloor.