Abstract:

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.

Key words:  peridotite xenolith, Wangqing, Longgang, Cenozoic basalt, major element, trace element, constitutional water