Sm-Nd, Rb-Sr, K-Ar and Re-Os isotopic constraints on the origin of PGE mineralization in the Konder massif, Khabarov region, Russia.

摘要

Rb-Sr and Sm-Nd isochron ages (122.6+-1.5 Ma and 93+-47 Ma, respectively) as well as (~(87)Sr/~(86)Sr)_0=0.70393+-5 and ε_(Nd) =+5.6 are determined for pyroxenite and gabbro-pegmatite from the Konder platinum bearing mafic-ultramafic massif. K-Ar ages for biotite (132+-8 and 115+-6 Ma) from ultramafic rocks and gabbros are in accordance with the above values. Sm-Nd results from ultramafic rocks are heterogeneous and in disagreement with the isochron model. At the same time a model initial isotope composition of Sr for dunite and olivine clynopyroxenite are identical to that for gabbro-pegmatite and pyroxenite. Os isotope composition was determined directly on platinum minerals rich in Os. The compositions obtained turned out to be the same in five different samples, they are (~(187)Os/~(188)Os)= 0.1251+-0.0003. This value suggests an unusual source for the ore-bearing melt, it differs from the mantle reservoir (identical to CHUR) in significantly lower Re/Os ratio. This might be explained by migration of Os and other PGE into the mantle substrate long before melting.