TEMPORAL GEOCHEMICAL TRENDS IN NORTHERN LUZON ARC LAVAS (PHILIPPINES)- IMPLICATIONS ON METASOMATIC PROCESSES IN THE ISLAND ARE MANTLE

Neogene and Quaternary lavas from Batan, Babuyan de Clavo, Camiguin an d Calayan islands (northern Luzon are) display temporal increases in i ncompatible elements including Cs, Rb, Ba, K, La, Ce, Th, U, Ta, Hf an d Zr from volcanoes older than 3 Ma to younger ones. These enrichments occur either within a single island (Batan) or within an island group (from Calayan to Camiguin and Babuyan). We show that these enrichment s result from incompatible element input into the mantle wedge rather than from partial melting or fractionation effects. The fact that high ly incompatible elements display temporal enrichment patterns in Batan lavas whatever their chemical properties indicates that hydrous fluid s are not the only metasomatic agents operating in the mantle wedge an d that slab-derived melts (adakitic magmas) may also be involved. The coupled temporal variation patterns of large ion lithophile elements a nd Sr-Nd isotopes su est that the metasomatic budgets beneath the sout hern group of islands are mainly controlled by hydrous fluid inputs. I n contrast, young Batan lavas likely derive from a mantle source mostl y metasomatized by adakitic magmas.