949 ISSN 1028-334X, Doklady Earth Sciences, 2017, Vol. 475, Part 2, pp. 949–952. © Pleiades Publishing, Ltd., 2017. Original Russian Text © A.A. Tomilenko, D.V. Kuzmin, T.A. Bul’bak, N.V. Sobolev, 2017, published in Doklady Akademii Nauk, 2017, Vol. 475, No. 6, pp. 680–684. Primary Melt and Fluid Inclusions in Regenerated Crystals and Phenocrysts of Olivine from Kimberlites of the Udachnaya-East Pipe, Yakutia: The Problem of the Kimberlite Melt A. A. Tomilenko a *, D. V. Kuzmin a,b , T. A. Bul’bak a , and Academician N. V. Sobolev a,b Received November 28, 2016 Abstract—The primary melt and fluid inclusions in regenerated zonal crystals of olivine and homogeneous phenocrysts of olivine from kimberlites of the Udachnaya-East pipe, were first studied by means of micro- thermometry, optic and scanning electron microscopy, electron and ion microprobe analysis (SIMS), induc- tively coupled plasma mass-spectrometry (ICP MSC), and Raman spectroscopy. It was established that oliv- ine crystals were regenerated from silicate–carbonate melts at a temperature of ~1100°C. DOI: 10.1134/S1028334X17080281 To identify the nature of kimberlite melts, the physicochemical conditions of their evolution at the stage of uplift to the surface and crystallization at the final stage of kimberlite formation have been deter- mined; the role of water and fluids of complex struc- ture in these processes is the subject of long-term stud- ies, which have been presented in numerous published works and reviews [1–3]. In connection with this, we believe that studying melt and fluid inclusions in kim- berlite minerals will make it possible to obtain new information on the composition of primary, interme- diate, and residual kimberlite melts, as well as on the PT-conditions of kimberlite formation. One such mineral of hypabyssal kimberlites from the Udachnaya-East pipe that is confined to the Upper Devonian stage of productive kimberlite magmatism, including all acting diamond deposits (367 ± 3.0 Ma according to isotope dates [4, 5]), is unchanged mag- nesian olivine (F o = 85–94 mol %) contained in the kimberlites as isolated round or idiomorphic xenocrystals and as phenocrysts (idiomorphic inclu- sions) that are usually less than 1.0 mm in size [6–10]. However, according to our estimates, typical phe- nocrysts are less than 5%, which is considerably differ- ent from the other estimates [3]. The chemical com- position of the groundmass of kimberlite is the follow- ing, % wt: SiO 2 28.1–29.6, TiO 2 2.1–1.54, Al 2 O 3 2.43–2.58, FeO tot. 8.9–13.0, MnO 0.21, MgO 28.1– 32.2, CaO 10.7–17.3, Na 2 O 1.4–3.61, K 2 O 0.8–1.3, P 2 O 5 0.5–1.0, which is similar to the composition of the groundmass of the kimberlite in [11]. This work is focused on study of the primary melt and fluids inclusions in regenerated olivines and newly formed phenocrysts of olivine by means of microther- mometry, optic and scanning electron microscopy (SEM), electron and ion microprobe analysis (SIMS), inductively coupled plasma mass-spectrometry (ICP MSC), and Raman spectroscopy. These inclusions were found in previous studies [7, 9]. The procedure for the analysis of melt and f luid inclusions in minerals by inductively coupled plasma mass-spectrometry (ICP MS) was published in [12]. Olivine xenocrystals are characterized by a heter- ogenous dominant central part of irregular shape and a narrow outer edge having a zonal structure (Fig. 1а) [6]. All newly formed phenocrysts of olivine are non- zonal (Fig. 1b). The compositions of the outer zones and the relicts of the central parts (cores) of the regen- erated olivines with inclusions of clinopyroxene and pyrope (Cr 2 O 3 from 1.4 to 9.14 wt %) that prove the high-pressure genesis of the central parts of olivines were presented in detail in [6]. The isotopic composition of oxygen (δ 18 О) in the regenerated megacrystals of olivine varies from 5.02 to 5.28 ‰ V-SMOW, and in the olivine phenocrysts, it is 5.05‰ V-SMOW; i.e., they conform to the mantle values. A similar δ 18 О was determined for the fresh (unchanged) olivines from the mantle xenoliths in the same kimberlite pipe. GEOCHEMISTRY a Sobolev Institute of Geology and Mineralogy, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia b Novosibirsk State University, Novosibirsk, Russia *e-mail: tomilen@igm.nsc.ru