LATE CENOZOIC VOLCANISM OF THE UDA RIVER AREA (EASTERN SAYAN, SIBERIA): THE FIRST GEOCHEMICAL AND ISOTOPIC DATA

Volcanic eruptions within the Baikal rift of predominantly basaltic composition belong to numerous small-volume eruptions, which took place in Cenozoic in Central Asia. The great majority of these eruptions occurred within the mobile belts in the southern framing of the Siberian craton. Only few of such eruptions have happened within the cratonic margin and these are of particular interest, because volcanic rock composition may provide insights on the composition of the cratonic lithosphere. Until recently, the Uda river area with the size of ~2000 km2 located within the Biryusa block of the Siberian craton (Fig. 1) was a white spot in terms of precise geochemical and isotopic data for basalts. Here we provide such data for the first time.Volcanic eruptions within the Baikal rift of predominantly basaltic composition belong to numerous small-volume eruptions, which took place in Cenozoic in Central Asia. The great majority of these eruptions occurred within the mobile belts in the southern framing of the Siberian craton. Only few of such eruptions have happened within the cratonic margin and these are of particular interest, because volcanic rock composition may provide insights on the composition of the cratonic lithosphere. Until recently, the Uda river area with the size of ~2000 km2 located within the Biryusa block of the Siberian craton (Fig. 1) was a white spot in terms of precise geochemical and isotopic data for basalts. Here we provide such data for the first time

ДВА ЭТАПА КАЙНОЗОЙСКОГО ЩЕЛОЧНО-БАЗАЛЬТОВОГО ВУЛКАНИЗМА ДАРХАТСКОЙ ВПАДИНЫ (СЕВЕРНАЯ МОНГОЛИЯ) – ГЕОХРОНОЛОГИЯ, ГЕОХИМИЯ И ГЕОДИНАМИЧЕСКИЕ СЛЕДСТВИЯ

The isotopic data showed that there are two stages distinguished in the Cenozoic history of the Darkhad depression volcanic activity, the Late Oligocene initial stage (~28.0–26.6 Ma) and the final Late Miocene – Early Pliocene stage (~5.8–4.2 Ma). It has been stated that the rocks of the initial stage are only represented by trachybasalts; however, among the final-stage basaltoids there are series of shield-volcano hawaite-basanite-phonotephrite rocks and compex trachybasaltic "valley" lava flows, the formation of which is the last stage in the territorial volcanic evolution. It has been shown that the initial-stage trachybasaltic andesites are characterized by their enrichment of TiO2, P2O5, Sr, Zn, Ga and low concentrations of Al2O3, MnO, CaO, Sc and HREE (La/Yb=27.2–30.2). Basaltoids of the final stage have a similar rare-element distribution and show an increase in the contents of TiO2, Al2O3, P2O5, LILE, HFSE, Th, U and in the degree of fractionation of REE (La/Yb from 12.2 to 20.9) towards the rocks alkalinity enhancement. Modeling of eclogite, pyroxenite and peridotite melting processes in the La/Yb – Sm/Yb system shows that trachybasaltic andesite melts could be formed at ~7–8 % melting of eclogitic matter or at ~10–11 % melting of Grt-containing pyroxenites, with trachybasalt formed at ~3 % melting of Grt-containing peridotites. The composition distribution of rocks in coordinates (Mg# – Fe/Mn) indicates that the parental magmas are the initial-stage trachybasaltic andesite magmas as well as the Early Pliocene trachybasaltic "valley" lava flows. Sr, Nd, Pb isotope characteristics of the Darkhad depression basaltoids show significant shift of isotopic ratios in time towards the relatively enriched mantle as compared with the depleted MORB mantle. The initial formation of trachybasaltic andesite melts occurred in the Late Oligicene at the pre-rift stage of the territory development involving metasomatized mantle matter, with the pyroxenite or eclogite component contained in the magma formation source. The origin of trachybasalt magmas of the final stage is associated with the processes of decompression melting of peridotites in a weakly metasomatized lithospheric mantle at the rift stage of the Darkhad structure development.На основе данных изотопного датирования в кайнозойской истории вулканической активности Дархатской впадины Северной Монголии выделены два этапа – инициальный позднеолигоценовый этап (~28.0–26.6 млн лет) и заключительный позднемиоцен-раннеплиоценовый этап (~5.8–4.2 млн лет). Установлено, что породы раннего инициального этапа представлены исключительно трахиандезибазальтами, а среди базальтоидов заключительного этапа выделяется гавайит-базанит-фонотефритовая серия пород щитовых вулканических построек и комплекс трахибазальтов «долинных» лавовых толщ, формирование которых завершает вулканическое развитие территории. Показано, что для трахиандезибазальтов инициального этапа характерными являются их относительное обогащение TiO2, P2O5, Sr, Zn, Ga и низкие концентрации Al2O3, MnO, CaO, Sc и HREE (La/Yb=27.2–30.2). Базальтоиды заключительного этапа демонстрируют рост содержаний TiO2, Al2O3, P2O5, LILE, HFSE, Th, U и увеличение степени фракционирования REE (La/Yb от 12.2 до 20.9) в направлении увеличения щелочности пород. Моделирование процессов плавления эклогитов, пироксенитов и перидотитов в системе La/Yb – Sm/Yb показывает, что трахиандезибазальтовые расплавы могли быть сформированы при ~7–8%-ном плавлении эклогитового вещества или ~10–11%-ном – Grt-содержащих пироксенитов, а трахибазальтовые расплавы образуются при ~2–3%-ном плавлении Grt-содержащих перидотитов. Распределение составов пород в координатах Mg# – Fe/Mn указывает на то, что к исходным магмам относятся трахиандезибазальты инициального этапа и раннеплиоценовые трахибазальты «долинных» лавовых толщ. Изотопные характеристики Sr, Nd и Pb базальтоидов Дархатской впадины демонстрируют значимое смещение значений изотопных отношений во времени в направлении от относительно обогащенной мантии к деплетированной мантии MORB типа. Формирование трахиандезибазальтовых расплавов на инициальном этапе происходило в позднем олигоцене на предрифтовой стадии развития территории с вовлечением в область магмообразования вещества метасоматизированной мантии с участием пироксенитового или эклогитового компонента. Происхождение позднемиоцен-раннеплиоценовых щелочно-базальтовых магм заключительного этапа связано с процессами декомпрессионного плавления перидотитов слабометасоматизированной литосферной мантии на рифтогенной стадии развития Дархатской структуры

LATE CENOZOIC VOLCANISM OF THE UDA RIVER AREA (EASTERN SAYAN, SIBERIA): THE FIRST GEOCHEMICAL AND ISOTOPIC DATA

Volcanic eruptions within the Baikal rift of predominantly basaltic composition belong to numerous small-volume eruptions, which took place in Cenozoic in Central Asia. The great majority of these eruptions occurred within the mobile belts in the southern framing of the Siberian craton. Only few of such eruptions have happened within the cratonic margin and these are of particular interest, because volcanic rock composition may provide insights on the composition of the cratonic lithosphere. Until recently, the Uda river area with the size of ~2000 km2 located within the Biryusa block of the Siberian craton (Fig. 1) was a white spot in terms of precise geochemical and isotopic data for basalts. Here we provide such data for the first time

MICROSTRUCTURAL AND FUNCTIONAL ABNORMALITIES IN THE BRAIN OF PATIENTS WITH TEMPORAL LOBE EPILEPSY AS REVEALED WITH MR IMAGING

Diagnosis of epilepsy remains a challenging task facing physicians of various specialties. When epilepsy is suspected, neuroimaging is one of the major diagnostic tests able to localize the epileptic site and identify the underlying pathology; this information is indispensable in making the diagnosis and predicting the prognosis of the disease. Magnetic resonance imaging (MRI) is the most common modality widely used due to its high sensitivity and specificity in detecting of subtle abnormalities in the brain structure. In addition to the structural pulse sequences, the epilepsy-specific MRIprotocol incorporates a number of recently introduced techniques for the assessment of local functional abnormalities. In this report, the epilepsy-specific protocol that includes the updated pulse sequences technique was used in patients suspected of having temporal lobe epilepsy. Using this technique, characteristic changes in the structure and function of local brain segments in temporal epilepsy were demonstrated

IDENTIFICATION OF EPILEPTOGENIC ABNORMALITIES USING A HIGH-FIELD MR-SCANNER

Objective: to estimate the role of MR – tomography in epilepsy diagnostics. We have analyzed the main protocol used for examination of patients with epileptic seizures in anamnesis, as well as a number of modern techniques,  which help to get additional information about both structural and functional changes in the brain. We have described several types of pathological changes detected by us during examination of the patients from this group

THE ROLE OF METHODS FOR QUANTITATIVE ANALYSIS OF MAGNETIC RESONANCE IMAGING DATA IN THE DIAGNOSIS OF ALZHEIMER'S DISEASE AT AN EARLY STAGE

Alzheimer's disease (AD) is leading in the prevalence in the structure of neurodegenerative diseases and is the most common cause of dementia in the population. It is advisable to conduct therapy at an early stage of the disease, since at the terminal stage of the disease treatment becomes ineffective. In the present situation, timely and accurate diagnostics of AD on early stages of the disease becomes most important. One of the key places in diagnostics of this disease is assigned to neuroimaging methods, in particular, magnetic resonance imaging (MRI). In the submitted systematic review, a search was carried out in electronic databases and scientific electronic libraries Cyberleninka, PubMed, OVID, the Cochrane Collaboration database. The modern aspects of early diagnosis of AD using MRI are assessed. The modern aspects of early diagnostics of AD using MRI are assessed. A number of Russian and foreign articles and metaanalyses devoted to the quantitative evaluation of MR-tomography data at an early stage of AD were analyzed and highlighted