Plagioclase and apatite from exsolution structures in minerals from mantle xenoliths

Abstract

483 Chlorine and alkali bearing minerals unusual for the kimberlitic matrix from nonserpentinized kimber lite of the Udachnaya pipe (Yakutia) with an anoma lously low concentration of water [1] were described in the groundmass [2], as chloride–carbonate nodules [3], and in melt inclusions in olivines from this kim berlite [4]. Phlogopite, apatite, calcite, djerfisherite [5], and sodalite [5, 6] were observed in xenoliths of deformed lherzolites from the Udachnaya pipe; tetra ferriphlogopite, halite, sylvite, alkaline carbonates, and sulfates were registered in melt inclusions from all primary minerals of these xenoliths [5]. Graphite bearing megacrystalline garnet orthopyroxenite con tained three generations of phlogopite, sylvite between orthopyroxene and phlogopite, apatite, sodalite, and potassic feldspar among the minerals of the rim around garnet, calcite in an orthopyroxene inclusion in garnet, and tetraferriphlogopite in a microfracture with djerfisherite and rusvumite, which was not previ ously reported in xenoliths [7]. Extremely nonequili brated ilmenite ultrabasic rock contained several gen erations of phlogopite, sodalite, apatite, calcium car bonate, and djerfisherite [8]. The presence of these minerals in deep xenoliths of mantle rocks is explained either by the interaction with the kimberlitic melt [5] or by metasomatic alteration of rock before it was cap tured by kimberlite [6–8]. In any case we deal with the mantle (probably multistage) process with a signifi cant role of alkalis and chlorine. The depth of this pro cess is confirmed by the finds of phlogopite, apatite, carbonate, and K sulfide inclusions in diamond [9]; the multistage nature, by quite a wide range of PT conditions of equilibrium in mantle rocks, in which alkali and chlorine bearing minerals were registered, as well as by the presence of several generations of phl ogopite in xenoliths and combination of water soluble sylvite and water bearing phlogopite in the same xenolith [7].