• journal_title：Geology
• Contributor：Maya B. Kamenetsky ; Alexander V. Sobolev ; Vadim S. Kamenetsky ; Roland Maas ; Leonid V. Danyushevsky ; Rainer Thomas ; Nikolai P. Pokhilenko ; Nikolai V. Sobolev
• Publisher：Geological Society of America
• Date：2004-
• Format：text/html
• Language：en
• Identifier：10.1130/G20821.1
• journal_abbrev：Geology
• issn：0091-7613
• volume：32
• issue：10
• firstpage：845

Kimberlite magmas, as the deepest probe into Earth's mantle (>150 km), can supply unique information about volatile components (hydrogen, carbon, chlorine, sulfur) in mantle-derived melts and fluids. All known kimberlite rocks are not suitable for studies of mantle volatiles because of their pervasive postmagmatic alteration; however, this study discusses an exceptionally fresh group I kimberlites (<0.5 wt% H₂O) from the Udachnaya-East diamondiferous pipe in Siberia. Kimberlite groundmass, in addition to euhedral olivine and calcite, is extremely enriched (at least 8 wt%) in water-soluble alkali chlorides, alkali carbonates, and sulfates (ratio 5:3:1), and often shows immiscibility textures. A primary magmatic origin of alkali chlorides and alkali carbonates is confirmed by the study of strontium isotopes in the water- and dilute acid–leachates of the groundmass (⁸⁷Sr/⁸⁶Sr = 0.7069 and 0.7050) that contrast with much more radiogenic isotope composition of the Cambrian platform sedimentary rocks and the Udachnaya-East mine-site brines. Melt inclusions in groundmass olivine, composed of halite, sylvite, alkali-Ca carbonates, phlogopite, olivine, and CO₂ fluid, were used to determine the composition and evolution of the kimberlite melt prior to emplacement. Melt inclusions show immiscibility between chloride and carbonate liquids at <600 °C in heating stage experiments. The chloride and carbonate enrichment in the kimberlite parental magma suggests the presence of a powerful agent for chemical modifications (metasomatism) in the mantle and crust.