GLIMMERITE XENOLITH IN ALKALIC BASALTIC ROCKS OF THE SOUTHERN TIEN SHAN. NEW EVIDENCE OF MANTLE METASOMATISM

Abstract

Petrologic and geochemical study of the products of deep-seated metasomatism helps to bring out inhomogeneities in the composition of the lithosphere that could be related to the redistribution and subsequent mobilization of ore components. Of definite interest, therefore, is our detection of an unusual glimmerite inclusion in the Tuvish volcanic pipe, South Gissar zone, composed of leucite-bearing melanocratic analcitite of Early Mesozoic age. Mantle xenoliths so far found in this pipe consist dominantly of green spinel pyroxenite and, less commonly, of black pyroxenite, lherzolite, granulite and quartzite [1]. The glimmerite xenolith (sp. 9200) is large (20 × 30 cm) and comparatively heavy (ca. 10 kg). The above data on the mineralogical and major- and trace-element chemical compositions of the glimmerite studied suggest that it is characteristic of zones of potassium-fluorine-barium metasomatism in the upper mantle, the possible source of the ore-forming material for some types of fluorite deposits in the region.