GEOCHEMISTRY OF THE METASOMATIZED UPPER MANTLE BENEATH THE SOUTHERN TIEN SHAN AND PAMIRS, TAJIKISTAN: LI AND SN IN MANTLE XENOLITHS FROM ALKALINE BASALTOIDS

Abstract

The distribution of Li and Sn was examined in rocks (>300 and ∼150 samples, respectively) from the metasomatized upper mantle: ultramafic and mafic xenoliths in alkaline basaltoids from the area. The rocks were found to bear elevated concentrations of these elements, which are 1-1.5 orders of magnitude higher than the respective clarkes. No minerals concentrating Li and Sn were identified (the Li and Sn concentrations in the micas and amphiboles are 8-18 ppm and 1.6-2.8 ppm, respectively, and the xenoliths bear neither Li nor Sn accessory minerals). The upper mantle rocks are thought to have been enriched in the rare elements in the process of upper mantle metasomatism under the effect of mantle fluids-melts. It cannot be ruled out that some of the lithophile elements occur in the form of clusters.