Lithium Isotope Variations in Ocean Island Basalts—Implications for the Development of Mantle Heterogeneity

Lithium elemental and isotopic compositions of 33 glass and whole-rock samples from nine oceanic island regions were determined to characterize the Li inventory of the deep mantle. The Li contents of the investigated lavas range from 1.5 to 13.3 mu g g super(-) super(1), whereas delta super(7)Li ranges from 2.4 to 4.8ppt. There are weak co-variations between the Li/Y, delta super(7)Li, and Sr-Nd-Pb isotope compositions of the lavas, indicating that the Li elemental and isotopic characteristics of ocean island basalt to some extent reflect mantle source heterogeneity. In detail, HIMU-type lavas are characterized by delta super(7)Li values (up to 4.8ppt) slightly heavier than those for average normal mid-ocean ridge basalt (3.4 plus or minus 1.4ppt) and by comparatively low Li contents; EM1-type lavas are characterized by isotopically light Li (average 3.2ppt) and relative Li enrichment, whereas EM2-type lavas tend to heavier delta super(7)Li values (up to 4.4ppt) with high Li concentrations. The Li contents and isotope characteristics of HIMU-type lavas are consistent with recycling of altered and dehydrated oceanic crust, whereas those of the EM1-type lavas can be attributed to sediment recycling. The Li characteristics of EM2-type lavas may reflect reworking of mantle wedge material that has been infiltrated by fluids derived from the subducting plate.