We investigated the microstructural and crystallographic features of quartz from complex vein systems associated with the development of thrust and shear deformations in Western Transbaikalia using electron back scatter diffraction (EBSD) and optical microscopy. Vein quartz systems were studied to obtain insights on the mechanisms and localization of strains in quartz, in plastic and semibrittle conditions close to the brittle–ductile transition, and their relationship to the processes of regional deformations. Five types of microstructures of vein quartz were distinguished. We established that the preferred mechanisms of deformation of the studied quartz were dislocation glide and creep at average deformation rates and temperatures of 300–400 °C with subsequent heating and dynamic and static recrystallization. The formation of special boundaries of the Dauphiné twinning type and multiple boundaries with angles of misorientation of 30° and 90° were noted. The distribution of the selected types in the differently oriented veins was analyzed. The presence of three generations of vein quartz was established. Microstructural and crystallographic features of vein quartz aggregates allow us to mark the territory’s multi-stage development (with the formation of syntectonic and post-deformation quartz).

Water distribution in the structure of vein quartz formed as a result of successive plastic deformations associated with dislocation slip and subsequent recrystallization was estimated using infrared microspectroscopic (μFTIR) mapping. Water contained in quartz demonstrates a broad absorption band in the IR range at 2800–3750 cm⁻¹, which indicates its molecular state and suggests the presence of water bearing water inclusions. In addition to water, the presence of an absorption band located at 2341 cm⁻¹ seems to be due to the presence of carbon dioxide in a molecular state. A necessary step before assessing the distribution of volatile components in the quartz structure was to calibrate the boundaries obtained by calculating the intensity ratios of the peaks at 1118 and 1160 cm⁻¹ in the reflectance spectrum and using electron back scatter diffraction (EBSD). A variety of fluid distributions in different elements of the structure was observed. At medium temperatures and medium strain rates, dislocation mass transfer is effective during dislocation slip. At low strain rates and elevated temperatures, the contribution of diffusion creep gradually increases, which facilitates the interaction of volatile components with migrating boundaries. It was found that in the process of successive rearrangements, migration of fluid components occurs within the main elements of the structure due to the redistribution of dislocations between defects of different scale levels. Redistribution of fluid from fluid inclusions as a result of plastic deformations in the quartz structure is one of the ways of relaxing intracrystalline stresses during strengthening of the structure.

—The behavior of fluids during plastic deformation is studied from the morphology and distribution of fluid inclusions in quartz grains of different microstructure types from a vein system controlled by thrusting and strike-slip faulting in the eastern Sayan–Baikal fold area. The analytical work includes electron backscatter diffraction (EBSD) for quartz microstructure and crystallography, as well as Linkam heating-and-freezing analysis and Raman spectroscopy for the composition of fluid inclusions. The studied fluid inclusions are of seven types that differ in morphology and position in the deformed quartz structure. A model is suggested to describe successive structural changes of quartz aggregates during dislocation sliding and subsequent creep-related recrystallization associated with redistribution of fluid. Fluid inclusions undergo qualitative and quantitative changes due to water leakage at all stages of plastic deformation. The changes occur by two main mechanisms: (i) mass transfer during dislocation sliding at medium temperatures and strain rates and (ii) diffusion creep at low strain rates and high temperatures. The contribution of creep increases gradually with temperature, which maintains the interaction of inclusions with migrating grain boundaries.

Link for citation: Bukharova O. V., Kungulova E.N. Typomorphism of minerals of vein Vezdarinskaya (southwestern Pamir) as an indicator of physico-chemical processes of pegmatite formation. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2021, vol. 332, no. 12, рр. 64-75. In Rus. The relevance of the work is caused by the need to clarify the conditions for formation of a unique pegmatite object – the Vezdarinskaya miarolitic pegmatite vein. This object gave the world a large number of rare mineral species, which indicates special physico-chemical parameters of the mineral formation medium. The main aim of the research is to characterize the formation of structural-material complexes of the pegmatite vein by typomorphic features of feldspar, tourmalines, garnets, micas. Objects: rock-forming and secondary mineral species of the pegmatite vein Vezdarinskya. Methods. Quantitative analysis of the chemical composition of minerals was performed using X-ray spectral microanalysis on the JXA-8100 microprobe and on scanning electron microscopes Tescan Mira 3 LMU and VEGA II LMU, combined with INCA Energy350 Oxford spectrometers, the structural state of feldspars was calculated based on the results of X-ray analysis on the XPert PRO (PANalytical) diffractometer. Results. The authors have obtained the complex data on the mineral composition of the pegmatite vein Vezdarinskaya (4 mineral species of mica, 4 species of tourmalines, 2 species of plagioclases were identified and refined), generations of mineral species were identified, new minerals for this pegmatite (andalusite, bertierine) were recorded, the association with which is typomorphic. A scenario for formation of a nearmiarolic vein aggregate is proposed and the role of remobilization of host rocks in the formation of pegmatite (its mineral associations) is analyzed. According to the association of mineral phases, the formation temperatures of the structural-material complexes of the vein were determined. The tipochemism of secondary minerals records the presence of a heterogeneous pegmatite-forming medium, which has undergone separation into silicate and silicate-fluid parts. The geochemistry of pegmatite and its mineral set are caused by a change in the chemistry of the pegmatite melt under the influence of the rocks of the Shugnan formation of the Shahdarinskaya series that contains it. Ссылка для цитирования: Бухарова О.В., Кунгулова Э.Н. Типоморфизм минералов Вездаринской жилы (Юго-Западный Памир) – репер физико-химических процессов пегматитообразования // Известия Томского политехнического университета. Инжиниринг георесурсов. – 2021. – Т. 332. – № 12. – С. 64-75. Актуальность работы обусловлена необходимостью уточнения условий формирования уникального пегматитового объекта – Вездаринской миароловой пегматитовой жилы, давшей миру большое количество редких минеральных видов, что указывает на особенные физико-химические параметры среды минералообразования. Цель: дать характеристику формирования структурно-вещественных комплексов пегматитовой жилы по типоморфным признакам полевых шпатов, турмалинов, гранатов, слюд. Объекты: породообразующие и второстепенные минеральные виды Вездаринской пегматитовой жилы. Методы. Количественный анализ химического состава минералов выполнен на основе рентгеноспектрального микроанализа на микрозонде JXA-8100 и на сканирующих электронных микроскопах Tescan Mira 3 LMU и VEGA II LMU, совмещенных со спектрометрами INCA Energy350 Oxford, структурное состояния полевых шпатов рассчитывалось по результатам рентгеновского анализа на дифрактометре XPert PRO (PANalytical) Результаты. Получены комплексные данные по минеральному составу Вездаринской пегматитовой жилы (определены и уточнены 4 минеральных вида слюд, 4 вида турмалинов, 2 вида плагиоклазов), выделены генерации минеральных видов, зафиксированы новые для этого пегматита минералы (андалузит, бертьерин), ассоциация с которыми является типоморфной. Предложен сценарий образования околомиаролового агрегата жилы и проанализирована роль ремобилизации вмещающих пород при формировании пегматита (его минеральных ассоциаций). По ассоциации минеральных фаз определены температуры образования вещественно-структурных комплексов жилы. Типохимизм второстепенных минералов фиксирует наличие гетерогенной, подвергшейся разделению на существенно силикатную и...