Isotopic compositions of the peridotitic xenoliths from the Nushan area,Anhui Province:Constraints on the age of subcontinental lithospheric mantle beneath the East China
安徽女山地幔橄榄岩捕虏体的同位素组成:中国东部新生代岩石圈地幔时代制约

Nushan volcano, located in Anhui Province, contains abundant and various mantle-derived peridotitic xenoliths, including spinel lherzolite, garnet lherzolite and spinel-garnet lherzolite, with minor harzburgite. Some spinel lherzolites contain amphibole, phlogopite and apatite, indicating that they had experienced mantle metasomatism. Petrological, mineralogical and geochemical data of the spinel lherzolites and harzbuigites revealed that the former are fertile and the latter are refractory. Depleted Sr-Nd-Hf isotopic characteristics of the spinel lherzolites indicate that they are typical of oceanic peridotites, rather than of Archean lithospheric mantle. Furthermore, most spinel lherzolites have high 187Os/188Os ratios. Although the lithospheric mantle beneath the Nushan are has been strongly metasomatismed by fluids/melts, the Os isotopes and PGE (Platinum Group Element) data display that the Os isotopic composition of the Nushan peridotites are not significantly affected by later mantle metasomatism processes. All these geochemical data of most spinel lherzolites indicate that the lithospheric mantle beneath Nushan are young (Phanerozoic) additions to the subcontinental lithospheric mantle (SCLM) from the convective asthenospheric mantle. However, one harzburgite has relatively lower 187Os/188Os ratio of 0.1184 and ancient Re-depletion age of 1.5Ga, suggesting existence of some ancient component in the asthenosphere.