A preliminary study on the Cenozoic lithospheric mantle beneath the northern part of the western North China Craton

Petrology and major- and trace-element compositions of minerals of the peridotite xenoliths from the Liangcheng, Siziwangqi, Sanyitang and Datong suggest that the lithospheric mantle beneath the northern parts of the Western Block and Central Zone of the North China Craton mainly consists of transitional peridotites. It is the relict of the primitive mantle having experienced initial melt extraction and subsequent metasomatism. The lithospheric mantle beneath the Liangcheng has been subjected to the lowest degree of melt extraction and intermediate metasomatism, which is in accordance with the lower Cr-# of spinets and lower Mg-# of coexisting clinopyroxenes in the Liangcheng peridotites. The lithospheric mantle beneath the Sanyitang has experienced the highest degree of melt extraction and the strongest metasomatism. The Sanyitang clinopyroxenes, even within one single sample, show large variations in La/Yb and chondrite-normalized REE patterns (from LREE-depleted to LREE-enriched), and the Sanyitang peridotitic minerals show marked enrichment in some trace elements on the rim than in the core. The Datong and Siziwangqi lithospheric mantles have experienced intermediate melt extraction, but weaker metasomatism than the Liangcheng and Sanyitang lithospheric mantles. The lithospheric mantles were mainly affected by silicate melt metasomatism, and only the lithospheric mantle beneath the Sanyitang was probably affected by carbonatite melt metasomatism as well.