Os-Hf-Sr-Nd isotope and PGE systematics of spinel peridotite xenoliths from Tok, SE Siberian craton:: Effects of pervasive metasomatism in shallow refractory mantle

Os-Hf-Sr-Nd isotopes and PGE were determined in peridotite xenoliths carried to the surface by Quaternary alkali basaltic magmas in the Tokinsky Stanovik Range on the Aldan shield. These data constrain the timing and nature of partial melting and metasomatism in the lithospheric mantle beneath SE Siberian craton. The xenoliths range from the rare fertile spinel lherzolites to the more abundant, strongly metasomatised olivine-rich (70-84%) rocks. Hf-Sr-Nd isotope compositions of the xenoliths are mainly within the fields of oceanic basalts. Most metasomatised xenoliths have lower Nd-143/Nd-144 and Hf-116/Hf-177 and higher Sr-117/Sr-86 than the host basalts indicating that the metasomatism is older and has distinct sources. A few xenoliths have elevated Hf-176/Hf-177 (up to 0.2838) and plot above the Hf-Nd mantle array defined by oceanic basalts.