摘要
The REE and Pb ,Sr,Nd isotopes in three xenoliths from limburgite and scoria-breccias,including spinel-lherzolite,spinel-gamet-1herzolite and phlogopite-gamet-1herzolite,were analysed.The REE contentso of the xenoliths are 1.3 to 3.3 times those of the chondrites with their REE pattems characterized by weak LREE depletion.The ^143Nd/^144Nd values of whole rocks and minerals range from 0.51306 to 0.51345 with εNd=+8.2-+15.8,^206Pb/^204Pb<18.673,and ^207Pb/^204Pb<15.574,All this goes to show that the upper mantle in Mingxi at the depth of 67-82km is a depleted mantle of MORB type,with ^87Sr/^86Sr ratios 0.70237-0.70390.In Nd-Sr diagram the data points of whole rocks are all out of the mantle array,implying that the xenoliths from Mingxi have more radiogenic Sr isotopes than those of the mantle array.
The REE and Pb, Sr, Nd isotopes in three xenoliths from limburgite and scoria-breccias, including spinel-lherzolite, spinel-gamet-lherzolite and phlogopite-gamet-lherzolite, were analysed. The REE contents of the xenoliths are 1.3 to 3.3 times those of the chondrites with their REE patterns characterized by weak LREE depletion. The ^(143)Nd/^(144)Nd values of whole rocks and minerals range from 0.51306 to 0.51345 with εNd=+8.2-+15.8, ^(206)pb/^(204)Pb<18.673, and ^(207)pb/^(204)Pb< 15.574. All this goes to show that the upper mantle in Mingxi at the depth of 67-82 km is a de- pleted mantle of MORB type, with ^(87)Sr/^(86)Sr ratios 0.70237-0.70390. In Nd-Sr diagram the data points of whole rocks are all out of the mantle array, implying that the xenoliths from Mingxi have more radiogenic Sr isotopes than those of the mantle array.
