Barium isotope compositions of altered oceanic crust from the IODP Site 1256 at the East Pacific rise

Abstract

This study reports barium (Ba) isotope compositions of intact altered oceanic crust (AOC) recovered from Integrated Ocean Drilling Program (IODP) Site 1256, East Pacific Rise (EPR), to investigate the behavior of Ba isotopes during both low-temperature seawater alteration and high-temperature hydrothermal alteration processes in the oceanic crust. The Ba isotope compositions of the volcanic section and sheeted dike complex have large variations and are mostly heavier than those of the fresh EPR MORB, with δ138/134Ba ranging from −0.01‰ to +0.39‰, which may be attributed to the modification of Ba isotopes by seawater and hydrothermal fluid during low-temperature and high-temperature alteration. The samples from the plutonic complex display much lighter Ba isotope compositions than the fresh EPR MORB, having δ138/134Ba values of −0.22‰ to −0.06‰, which may reflect the influence of late magmatic fluids. Because of the large Ba isotope variation in the AOC and the obvious difference in Ba isotope compositions between the AOC and the upper mantle, the recycling of the AOC could result in Ba isotope heterogeneity in the mantle and further indicate the application of Ba isotopes for tracing crustal material recycling in the Earth's mantle.