NMR Spectral Characteristics of Ultrahigh Pressure High Temperature Impact Glasses of the Giant Kara Crater (Pay-Khoy, Russia)

In this study, we carried out the analysis of the impact melt vein glasses from the Kara impact crater (Russia) in comparison to low-pressure impact melt glasses (tektites) of the Zhamanshin crater (Kazakhstan). 27Al, 23Na, and 29Si MAS NMR spectra of the samples of these glasses were analyzed. The samples of the natural glass contained inclusions of crystalline phases, paramagnetic elements that greatly complicate and distort the NMR signals from the glass phase itself. Taking into account the Mossbauer distribution of Fe in these glasses, the analysis of the spectra of MAS NMR of glass network-former (Si, Al) and potential network-modifiers (Na) of nuclei leads to the conclusion that the Kara impact melt vein glasses are characterized by complete polymerization of (Si,Al)O4 tetrahedral structural units. The NMR features of the glasses are consistent with the vein hypothesis of their formation under conditions of high pressures and temperatures resulting in their fluidity, relatively slow solidification with partial melt differentiation, polymerization, and precipitation of mineral phases as the impact melt cools. The 70 Ma stability of the Kara impact vein glass can be explained by the stabilization of the glass network with primary fine-dispersed pyroxene and coesite precipitates and by the high polymerization level of the impact glass

Dispersed organic matter characteristics as an indicator of rock alteration degree of the Safyanovskoe copper-sulphide deposit

Relevance of the study is due to the importance of composition and maturity of the dispersed organic matter (DOM) as indicators of rock forming conditions, which may contribute to the paleoecological reconstruction of sedimentation conditions for rocks in the ore-bearing stratum of the Safyanovskoe deposit. Objective: to analyze the composition and characteristics of DOM in carbon-siliceous rocks of the ore-bearing stratum of the Safyanovsky copper-pyrite deposit. The obtained characteristics of the DOM make it possible to reveal the source of original accumulation and the level of its transformation under the influence of various geological processes. Conclusions. DOM of carbon-siliceous rocks of the Safyanovsky deposit is genetically the same, its type is mainly sapropelic and accumulation is associated with marine conditions. A characteristic feature is, on the one hand, its high polymerization, which is typical for DOM of the stage of late mesocatagenesis, and, on the other hand, its molecular composition does not allow us to talk about the maturation of DOM in the process of natural regional metamorphism.26-3

ЭПР и 57Fe-мёссбауэровская спектроскопия SrBi2Nb2O9б допированного железом

Solid solutions of Bi2SrNb2−2xFe2xO9−δ have been obtained by solid-phase synthesis. The electronic state and nature of the local environment of iron atoms in the SrBi2Nb2O9 matrix with a layered perovskite-like structure were studied by ESR and M¨ossbauer spectroscopy. In the ESR spectra of samples of Bi2SrNb2−2xFe2xO9−δ (х60.04) solid solutions an intensive asymmetric line in the lowfield region with the main feature at g=4.27, weakly pronounced peak g=6.15 and shoulder g∼9, and also an intensive broad (ΔBpp ∼50–150 мТ) band centered around g∼2.0 is present. The M¨ossbauer spectrum of the compound Bi2SrNb2−2xFe2xO9−δ is represented by an asymmetric doublet with isomer shift (IS)∼0.3, and quadrupole splitting (QS)∼0.5 mm/s. The shape of the doublet is reproduced by the superposition of two doublets with small and high IS and QS values. About 85% of the spectral area of the paramagnetic part of the spectrum is represented by the doublet Fe3+(1) with IS=0.31±0.04, QS = 0.45±0.04 mm/s correlated with Fe3+ ions in regular axial positions. The remaining part is represented by the doublet Fe3+(2) with IS=0.5±0.1, QS = 0.7±0.2 mm/s from the Fe3+ ions in defect environmentТвердофазным методом синтеза получены твердые растворы Bi2SrNb2−2xFe2xO9−δ. Методами ЭПР и мёссбауровской спектроскопии исследовано электронное состояние и характер локального окружения атомов железа в матрице SrBi2Nb2O9 со слоистой перовскитоподобной структурой. В спектрах ЭПР образцов твердых растворов Bi2SrNb2−2xFe2xO9−δ (x 6 0.04) присутствует интенсивная асимметричная линия в области низких полей с главной особенностью при g = 4.27, слабо выраженными пиком g = 6.15 и плечом g∼9, а также интенсивная широкая (ΔBpp ∼50–150 мТ) полоса с центром около g∼2.0. Мёссбауэровский спектр соединения Bi2SrNb2−2xFe2xO9−δ представлен асимметричным дублетом с изомерным сдвигом (IS)∼0.3 и квадрупольным расщеплением (QS)∼0.5 мм/с. Форма дублета воспроизводится суперпозицией двух дублетов с малыми и высокими значениями IS и QS. Около 85 % спектральной площади парамагнитной части спектра приходится на дублет Fe3+(1)) with IS = 0.31±0.04, QS = 0.45±0.04 мм/с, соотнесенный с ионами Fe3+ в регулярных аксиальных позициях. Оставшаяся часть представлена дублетом Fe3+(2) с IS = 0.5 ± 0.1, QS = 0.7 ± 0.2 мм/с от ионов Fe3+ в дефектном окружени