吉林汪清和龙岗新生代岩石圈地幔的含水性和元素地球化学特征

首次报道了来自东北地区岩石圈地幔水含量的数据。通过对吉林龙岗和汪清新生代玄武岩中的橄榄岩包体矿物进行电子探针(EMP)和激光熔蚀等离子体质谱(LA-ICPMS)的分析，得到了矿物的主量元素和微量元素的数据，结果显示这些橄榄岩是原始地幔经历了不同程度部分熔融的残余，大部分样品的熔融程度可能<10%。橄榄岩样品在后期还经历了地幔交代作用，大部分样品受到硅酸岩熔体的交代，少部分样品受到碳酸岩熔体的交代。显微傅里叶变换红外光谱(FTIR)的分析结果显示，橄榄岩样品中的单斜辉石、斜方辉石均含有以结构羟基形式存在的水，而橄榄石中没有明显的羟基吸收峰。龙岗样品中单斜辉石的水含量为(48~464)×10^-6(H₂O, 质量分数)，斜方辉石水含量为(28~104)×10^-6；汪清样品中单斜辉石的水含量为(34~403)×10^-6，斜方辉石的水含量为(13~89)×10^-6；所有样品全岩水含量为(8~92)×10^-6。样品的水含量可以代表龙岗和汪清地区岩石圈地幔的水含量信息，并且水含量变化范围较大，造成这种变化的原因可能是由于地幔源区初始水含量的不均一，以及部分熔融和地幔交代作用叠加的结果。

Water content and element geochemistry of peridotite xenoliths hosted by Cenozoic basalt in Longgang and Wangqing,Jilin Province

This paper presents major and trace element data of minerals (clinopyroxene (Cpx), orthopyroxene (Opx), olivine (Ol), and spinel (Spl)) from peridotite xenoliths hosted by Cenozoic basalts in Longgang and Wangqing, Jilin Province, which were obtained by EMP and LA ICPMS respectively. Covariances in element contents of peridotite minerals suggest that the peridotite xenoliths are relicts of primary mantle after different degrees of partial melting. Elevated content of highly incompatible elements in some clinopyroxenes demonstrates that the Longgang and Wangqing lithospheric mantle has undergone subsequent mantle metasomatism; the major metasomatic agent was silicate melt and/or with minor carbonatite melt. Both clinopyroxene and orthopyroxene show prominent absorption bands in the range of 3 0003 700 cm-1, which are due to hydroxyl defect in their crystal structure; no discernable OH peaks can be found in olivine grains. The water content (H₂O wt.) of clinopyroxene and orthopyroxene from Longgang are calculated to be ranging from 48×10^-6 to 464×10^-6 and 28×10^-6 to 104×10^-6 respectively; that of same minerals from Wangqing ranges from 34×10^-6 to 403×10^-6 and 13×10^-6 to 89×10-6 respectively. Based on the water content and mineral model, it is estimated that the whole rock water contents of the Longgang and Wangqing peridotites vary in the range of (892)×10^-6. The water contents of peridotites can reflect the information on lithospheric mantle in this region, and the large variations in the water content may be resulted from the heterogeneity of the primary water content in the mantle source and combined with the superimposition of partial melting and metasomatism events.