LAM-ICPMS analysis on clinopyroxenes of peridotite xenoliths from Hannuoba and its significance on lithospheric mantle evolution

The compositions of the whole rocks and trace elements of minerals in peridotites can reflect the characters of lithospheric mantle. The nature and evolution of the Cenozoic lithospheric mantle beneath Hannuoba, which is located on the north edge of the intra-North China orogenic belt, are mainly discussed based on the in situ, LAM-ICPMS detected trace element compositions of clinopyroxenes in the Hannuoba peridotitic xenoliths, combined with detailed petrographic and petrochemical studies. The Hannuoba lithospheric mantle was formed by different partial melting of the primitive mantle. Most of the samples reflect a partial melting degree of lower than 5% with a few samples of 15%-20%. Major element compositions of the whole rocks and geochemical compositions of clinopyroxenes reveal the coexistence of both fertile and depleted mantle underneath the Hannuoba region during the Cenozoic. This was probably caused by the asthenospheric mantle that replaced the aged craton mantle through erosion, intermingling and modification. Our conclusion is further supported by the existence of both carbonatitic magmatic material and silicate melt/fluid metasomatism as magnified by the trace element compositions of the clinopyroxenes from the Hannuoba lithospheric mantle.8 page(s