Ancient and modern subduction zone contributions to the mantle sources of lavas from the Lassen region of California inferred from Lu-Hf isotopic systematics

Hafnium isotopic compositions have been determined on a suite of calc-alkaline and high-alumina-olivine tholeiitic lavas from the Lassen region of California and are used, in conjunction with previously published mineralogical, geochemical, and isotopic data, to constrain their petrogenesis. Positive correlation between ε_Hf values and geochemical indices of the modern subduction component indicates that the isotopic compositions of the calc-alkaline lavas record addition of radiogenic Hf from the subducted slab. However, the addition of the modern subduction component increases the ε_Hf values of most calc-alkaline lavas by