| Реферат: | eng: Taking advantage of the common occurrence of superdeep mineral inclusion assemblages, we examined core-to-rim primary zonation in 69 diamonds from the alluvial deposits of the Sao-Luis River (Juina, Brazil). Syngenetic inclusions were represented by phases of superdeep paragenesis. The dominant inclusions are majoritic garnets, ferropericlases and CaSi- and CaSiTi-perovskites. Rare inclusions of MgSi-perovskites, olivines, clinopyroxenes, TAPP, phases of SiO2, kyanites, AlSi-phases, KFsp (K-hollandite?), CF, NAL, grossular, merwinite, native iron, Fe-sulphides, magnesite and CaCO3 + CaMgSi2O6 (composite inclusions) were also found. The diamonds from Sao-Luis display wide variations in carbon isotopic compositions (delta C-13), from +2.7 to -25.3 parts per thousand. The diamonds with inclusions of ferropericlase have a very narrow range of delta C-13 values, from -2.1 to -7.7 parts per thousand, which are close to the "normal" mantle values. In many cases, diamonds with inclusions of calcic majoritic garnet and CaSi- and CaSiTi-perovskites display marked differences from this range. Low delta C-13 values (-10 to -25 parts per thousand) were observed exclusively in a series of diamonds with majorite garnets, Ca-silicates, aluminous silicates and SiO2. The delta C-13 values from the cores to rims in certain individual crystals varied substantially, indicating multiple stages of growth. The highly negative delta C-13 values in the cores (-20 to -25 parts per thousand) potentially represent organic matter in metasediments of altered oceanic crust, and the lower delta C-13 values may represent mixing trends towards "normal" mantle compositions. In this study, we also found a set of diamonds that display an opposite trend of change of the carbon source, from primordial mantle to subducted/crust (either biotic or abiotic carbon). (C) 2013 Elsevier B.V. All rights reserved.
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