Hf isotope and REE compositions of zircon from jadeitite (Tone, Japan and north of the Motagua fault, Guatemala): implications on jadeitite genesis and possible protoliths

摘要: Zircon separates from one jadeitite sample (JJ) Tone, Japan and Guatemala (GJ) were studied for mineral inclusions, age dating, trace-element determination Hf isotope analysis. These zircons can be categorized into two types. Type I (igneous) are characterized by the presence of among others K-feldspar, which is not present in matrix. They also show higher Th/U ratios, larger Ce anomalies 176 Lu/ 177 ratios. II (metasomatic/solution-precipitate) contain omphacite/jadeite inclusions exhibit lower smaller Both types display high eHf( t ) values, slightly than depleted mantle evolution line. The JJ contains both type zircons. SHRIMP geochemical data indicate that this was formed through mechanism whole-sale metasomatic replacement at ~80 Ma an igneous protolith juvenile origin with 136 ± 2 Ma. GJ only may have a of, or close to, vein precipitation 98 samples therefore testify mechanisms been operation during formation. Based on composition back-calculated REE pattern presumed protolith, characteristics Tone shown to similar those oceanic plagiogranites derived partial melting cumulate gabbros subduction-zone adakitic granites originated subducted crust. latter, however, more probable candidate because former known poor K O, which, contrast, notable chemical component jadeitite. On basis available data, it suggested physicochemical conditions extent jadeitization all play role dictating variations jadeitites.