The depletion in Ti-Nb-Ta (TNT) contents of island arc basalts and subduction related ophiolitic lavas are explained as either due to the presence of TNT bearing mantle phases or as mantle source signature. A consistent depletion in Ti content from the Coto Volcanics, exhibiting transitional MORB - island arc characteristics, to the Coto Dikes then to the Acoje Volcanics, characterized by island arc signatures of the Zambales Ophiolite Complex is also observed. Petrographic analyses of the different residual peridotite units did not reveal the existence of any TNT-bearing phase. Bulk chemical analyses, together with available mineral chemistry and REE data, suggest increasing degree of partial melting of the sources of the Coto Volcanics, Coto Dikes and Acoje Volcanics, respectively. This, coupled by the multistage melting history of this ophiolite complex, suggest that the decreasing Ti-content observed is a mantle source signature and not due to the presence of TNT-bearing mantle phases.