SR-ND ISOTOPIC CONSTRAINTS ON THE PETROGENESIS OF THE CENTRAL BOHEMIAN PLUTON, CZECH-REPUBLIC

The Sr-Nd isotopic data for selected granitoids of the Central Bohemia n Pluton show a broad negative correlation with the total range of (Sr -87/Sr-86)(330) = 0.7051-0.7129 and epsilon(Nd)(330) = + 0.2 to - 8.9. The older intrusions have more depleted Sr-Nd compositions and calc-a lkaline geochemistry (Sazava suite), whereas the younger intrusions sh ift towards K-rich calc-alkaline (Blatna suite) and shoshonitic rocks (Ricany and Certovo bremeno suites) with more evolved isotopic signatu res. The distribution of the data is interpreted as reflecting a diver sity of sources and processes, rather than a single progressive crusta l contamination trend. The Sazava suite could have originated by parti al melting of metabasites, or of a mantle source with an isotopic comp osition close to bulk earth, or by hybridization of crustally-derived tonalitic and mantle-derived magmas. Variation within the Blatna suite is modelled by mixing between a moderately enriched [(Sr-87/Sr-86)(33 0) similar to 0.708, epsilon(Nd)(330) similar to -3] mantle component with either an isotopically evolved metasedimentary component, or with more evolved magmas of the suite. The Ricany suite was most probably produced by partial melting of peraluminous lithologies, possibly of t he adjacent Moldanubian unit. The Certovo bremeno suite evolved from s trongly enriched mantle-derived magmas [(Sr-87/Sr-86)(330) similar to 0.7128, epsilon(Nd)(330) similar to -7], either through closed-system fractional crystallization or interaction with magma corresponding to leucogranites of the Central Bohemian Pluton.