18 research outputs found
Tectonics and geodynamics of Gorny Altai and adjacent structures of the Altai–Sayan folded area
No full textAbstract not availableM.M. Buslov, H. Geng, A.V. Travin, D. Otgonbaatar, A.V. Kulikova, Chen Ming, G. Stijn, N.N. Semakov, E.S. Rubanova, M.A. Abildaeva E.E. Voitishek, D. A. Trofimov
On a possibility to use the remote sensing techniques for glaciological analysis in mountain regions of Uzbekistan
Get PDFThe ALOS/AVNIR-2 satellite data (2007–2010) allowed estimating areas of glaciers, change in the areas for 50 years, and the number and areas of new naturally-dammed lakes in the mountain regions of Uzbekistan. Boundaries of these gla‑ ciers together with the ALOS/PALSAR data (2010) were used as the basis to determine position of the firn line. It was revealed that since 1980s elevation range of the line gradually decreased. The relationship between average elevation of the firn line and the upper limit of the juniper tree occurrence as well as changing of this relation since 1980s are consid‑ ered. The revealed lakes served as the basis for verification of probabilistic model of the moraine-dammed lake forma‑ tions due to the glacier recessions in the basins under consideration. It was shown that the GIS-techniques based on the use of this model together with data on glaciation and the relief digital model may significantly simplify searching of new lakes. Application of a system of the mudflow movement modeling makes possible to estimate a risk level in a case of a lake bursting. Current information about changing elevations of the glacier surfaces was obtained duet to the radar inter‑ ferometry and the altimeter data. The digital model of the river Pskem upper course (the DEM) had been built using the satellite TerraSAR‑X/TanDEM‑X data (2011–2012). All datasets of the elevations were checked for horizontal shifts of the relief digital models relative to the ICESat profiles (2003–2008). Evaluation of accuracy and morphological analysis of all the relief models for the investigated region were also made. DEMs differencing, the difference between ICESat measure‑ ments and DEM, nearby ICESat footprints within one track and between the tracks were carried out to assess the change in elevations of the glacier surfaces. Average rate of the surface lowering of an individual glacier with the maximal number of footprints (7) in the track is equal to −1 m/year; on average for 7 corrie-valley glaciers with northern/north-eastern exposition, it is −1.3 m/year in the ablation zone. This rate increases toward to the glacier terminus. Average local mass balance in the ablation zone of the Barkrak Glacier is egual to −0.82±0.36 m w.e. a−1 for the period since 2000 till 2012
Evolution and loss of long-fringed petals
Get PDFBackground: The Cucurbitaceae genus Trichosanthes comprises 90–100 species that occur from India to Japan and southeast to Australia and Fiji. Most species have large white or pale yellow petals with conspicuously fringed margins, the fringes sometimes several cm long. Pollination is usually by hawkmoths. Previous molecular data for a small number of species suggested that a monophyletic Trichosanthes might include the Asian genera Gymnopetalum (four species, lacking long petal fringes) and Hodgsonia (two species with petals fringed). Here we test these groups’ relationships using a species sampling of c. 60% and 4759 nucleotides of nuclear and plastid DNA. To infer the time and direction of the geographic expansion of the Trichosanthes clade we employ molecular clock dating and statistical biogeographic reconstruction, and we also address the gain or loss of petal fringes.
Results: Trichosanthes is monophyletic as long as it includes Gymnopetalum, which itself is polyphyletic. The closest relative of Trichosanthes appears to be the sponge gourds, Luffa, while Hodgsonia is more distantly related. Of six morphology-based sections in Trichosanthes with more than one species, three are supported by the molecular results; two new sections appear warranted. Molecular dating and biogeographic analyses suggest an Oligocene origin of Trichosanthes in Eurasia or East Asia, followed by diversification and spread throughout the Malesian biogeographic region and into the Australian continent.
Conclusions: Long-fringed corollas evolved independently in Hodgsonia and Trichosanthes, followed by two losses in the latter coincident with shifts to other pollinators but not with long-distance ispersal events. Together with the Caribbean Linnaeosicyos, the Madagascan Ampelosicyos and the tropical African Telfairia, these cucurbit lineages represent an ideal system for more detailed studies of the evolution and function of petal fringes in plant-pollinator mutualisms
Erratum to “Tectonics and geodynamics of Gorny Altai and adjacent structures of the Altai–Sayan folded area” [Russian Geology and Geophysics 54 (2013) 1250–1271]
No full textThe late Quaternary slip-rate of the Har-Us-Nuur fault (Mongolian Altai) from cosmogenic Be-10 and luminescence dating
Get PDFThe Altai range (western Mongolia) accommodates NNE–SSW shortening across the northern India–Eurasia collision zone by dextral slip on faults trending NNW–SSE, and anticlockwise, vertical-axis rotations of fault-bounded blocks. However, fault slip-rates and the way in which faulting evolves over time are poorly understood, and form the motivation for this study. We focussed on the Har-Us-Nuur fault, a major transpressional fault bounding the eastern margin of the Altai. Three abandoned alluvial fan surfaces, each displaced right-laterally by the fault, were targeted for dating with cosmogenic 10Be and quartz optically stimulated luminescence (OSL). The first surface (A2) shows an exponential decrease in 10Be with increasing depth, with a significant inherited component. Modelling this profile yielded a minimum age of 74.1 ka. Material from the same sampling pit was dated at ~ 19 ka with OSL, but we consider this younger age to be incorrect, possibly due to feldspar contamination or abnormal quartz OSL characteristics. The A2 surface is displaced by 175 m, implying a (maximum) dextral slip-rate of 2.4 ± 0.4 mm yr− 1. A second fan surface (F1) was dated at ~ 6 ka with OSL and shows little variation in 10Be with depth, consistent with this young age. The inherited component is higher than for A2, indicating contrasting levels of inheritance for different periods of fan aggradation. A final surface (F2) shows scattered 10Be concentrations and lacks material suitable for OSL, so cannot be dated precisely. Using the total vertical displacement across the fault, we place the initiation of movement on the fault at ~ 2 Ma, significantly later than the late Oligocene to Miocene (28–5 Ma) onset of shortening in the Altai region. This suggests that deformation in the Altai has widened over time to incorporate new faults at the range margins (such as Har-Us-Nuur), possibly because older faults in the range interior have rotated about vertical axes into orientations that require work to be done against gravity
О возможности использования методов дистанционного зондирования Земли при расчётах гляциологических показателей для горных районов Узбекистана
Get PDFThe ALOS/AVNIR-2 satellite data (2007–2010) allowed estimating areas of glaciers, change in the areas for 50 years, and the number and areas of new naturally-dammed lakes in the mountain regions of Uzbekistan. Boundaries of these gla‑ ciers together with the ALOS/PALSAR data (2010) were used as the basis to determine position of the firn line. It was revealed that since 1980s elevation range of the line gradually decreased. The relationship between average elevation of the firn line and the upper limit of the juniper tree occurrence as well as changing of this relation since 1980s are consid‑ ered. The revealed lakes served as the basis for verification of probabilistic model of the moraine-dammed lake forma‑ tions due to the glacier recessions in the basins under consideration. It was shown that the GIS-techniques based on the use of this model together with data on glaciation and the relief digital model may significantly simplify searching of new lakes. Application of a system of the mudflow movement modeling makes possible to estimate a risk level in a case of a lake bursting. Current information about changing elevations of the glacier surfaces was obtained duet to the radar inter‑ ferometry and the altimeter data. The digital model of the river Pskem upper course (the DEM) had been built using the satellite TerraSAR‑X/TanDEM‑X data (2011–2012). All datasets of the elevations were checked for horizontal shifts of the relief digital models relative to the ICESat profiles (2003–2008). Evaluation of accuracy and morphological analysis of all the relief models for the investigated region were also made. DEMs differencing, the difference between ICESat measure‑ ments and DEM, nearby ICESat footprints within one track and between the tracks were carried out to assess the change in elevations of the glacier surfaces. Average rate of the surface lowering of an individual glacier with the maximal number of footprints (7) in the track is equal to −1 m/year; on average for 7 corrie-valley glaciers with northern/north-eastern exposition, it is −1.3 m/year in the ablation zone. This rate increases toward to the glacier terminus. Average local mass balance in the ablation zone of the Barkrak Glacier is egual to −0.82±0.36 m w.e. a−1 for the period since 2000 till 2012.Рассматриваются вопросы использования спутниковой информации для решения нескольких задач: расчёта площади ледников Республики Узбекистан и скорости понижения их поверхности; поиска связи между высотой фирновой линии и верхней границей арчи; применения модели возможного формирования моренных озёр при отступании ледников и модели движения селевого потока в случае прорыва ледниковых озёр
ГЛУБИННОЕ СТРОЕНИЕ ГОРНОГО АЛТАЯ И СОВРЕМЕННЫЕ МОДЕЛИ ГРАВИТАЦИОННОГО ПОЛЯ
Get PDFThe results of the ground-based absolute gravity and space geodetic measurements for the Altai Mountains were considered in combination with EIGEN-6C4 Global Geopotential Model (ETOPO1 Global Relief Model) generated from the satellite data. Analysis was made on different kinds of data: model values for the vertical component of gravity, values of Bouguer and Faye gravity reductions, variations of the vertical gravity gradient, and changes in altitude of the measurement sites. With EIGEN-6C4 model for Bouguer reduction, the crustal thickness curve was drawn along the Novosibirsk (southern West Siberia) – Ukok Plateau (Altai Mountains) line with a length of 800 km. The Moho depth increases from 40 km in the northwest of the area to 51 km in the southeast. For the homogeneous crust model, there was obtained the Moho depth distribution in the Altai Mountains and their foothills.The analysis of the results of modeling Bouguer and Faye reductions, the data on quasigeoid heights and the relationship between relief height and Bouguer anomalies implies that the Altai Mountains area as a whole is isostatically compensated. Non-compensated are some intermountain basins, such as, for example, the Kurai and Chuya valleys.Результаты наземных измерений в районах Горного Алтая, полученные методами абсолютной гравиметрии и космической геодезии, рассматривались совместно с моделью геопотенциала EIGEN-6C4 (модель рельефа ETOPO1), построенной по спутниковым данным. Анализировались различные виды данных: модельные величины вертикальной составляющей силы тяжести, значения силы тяжести в редукциях Буге, Фая, вариации вертикального градиента силы тяжести и изменения высот пунктов. С использованием модели EIGEN-6C4 в редукции Буге построен график мощности земной коры по линии Новосибирск (юг Западной Сибири) – плато Укок (Горный Алтай) длиной 800 км. Глубина границы Мохоровичича увеличивается от 40 км на северо-западе территории до 51 км на юго-востоке. Для модели однородной коры получено распределение глубин по поверхности Мохоровичича в Горном Алтае и его предгорьях.Анализируя результаты построений в редукциях Буге и Фая, данные о высотах квазигеоида и соотношение высоты рельефа и аномалий Буге, следует сделать вывод, что в целом территория Горного Алтая изостатически скомпенсированна. Являются нескомпенсированными отдельные межгорные впадины, например Курайская и Чуйская долины
ВЗАИМОДЕЙСТВИЕ ГАББРОИДНОЙ И ГРАНИТОИДНОЙ МАГМ ПРИ ФОРМИРОВАНИИ ПРЕОБРАЖЕНСКОГО ИНТРУЗИВА, ВОСТОЧНЫЙ КАЗАХСТАН
Get PDFThe paper reports on studies of the Preobrazhensky gabbro‐granitoid intrusion, East Kazakhstan, com‐ posed of the rocks that belong to four phases of intrusion, from quartz monzonites and gabbroids to granite‐ leucogranites. Specific relationships between basite and granitoid rocks are usually classified as the result of interac‐ tions and mixing of liquid magmas, i.e. magma mingling and mixing. Basite rocks are represented by a series from biotite gabbros to monzodiorites. Granitoids rocks are biotite‐amphibole granites. Porphyric granosyenites, com‐ bining the features of both granites and monzodiorites, are also involved in mingling. It is established that the primary granitoid magmas contained granosyenite/quartz‐monzonite and occurred in the lower‐medium‐crust conditions in equilibrium with the garnet‐rich restite enriched with plagioclase. Monzodiorites formed during fractionation of the parent gabbroid magma that originated from the enriched mantle source. We propose a magma interaction model describing penetration of the basite magma into the lower horizons of the granitoid source, which ceased below the viscoplastic horizon of granitoids. The initial interaction assumes the thermal effect of basites on the almost crystal‐ lized granitic magma and saturation of the boundary horizons of the basite magma with volatile elements, which can change the composition of the crystallizing melt from gabbroid to monzodiorite. A ‘boundary’ layer of monzodiorite melt is formed at the boundary of the gabbroid and granitoid magmas, and interacts with granitoids. Due to chemical interactions, hybrid rocks – porphyric granosyenites – are formed. The heterogeneous mixture of monzodiorites and granosyenites is more mobile in comparison with the overlying almost crystallized granites. Due to contraction frac‐ turing in the crystallized granites, the heterogeneous mixture of monzodiorites and granosyenites penetrate into the upper rock levels. Examples of the magma interaction causing the formation of mingling structures at the middle and upper crust levels can be viewed as indicative of ‘fast’, active processes of the mantle‐crust interaction, when the mantle magmas actively drain the lithosphere and melt the substance of the lower‐middle crust. An important role is played by the temperature gradient in the sublithospheric mantle. It directly affects the degree of its melting and the volumes of basite magmas. Nonetheless, the permeability of the lithosphere is also important – the above‐described scenario is possible if the lithosphere is either thin or easily permeable due to the development of strike‐slip and extension fractures. In the Late Paleozoic, the territory of East Kazakhstan was part of the Altai collision system of hercinides. The late stages of its evolution (300–280 Ma) were accompanied by large‐scale mantle and crustal magma‐ tism corresponding to the formation of the Late Palaeozoic large igneous province related to the activity of the Tarim mantle plume. The influence of the mantle plume on the lithospheric mantle led to an increase in the temperature gradient, and the lithosphere weakened by shear movements of the collapsing orogenic structure was permeable to mantle magmas, which caused the processes of mantle‐crustal interaction.Приведены результаты исследования Преображенского габбро‐гранитоидного интрузива в Восточном Казахстане. В его строении участвуют породы четырех интрузивных фаз, от кварцевых монцонитов и габброидов до гранит‐лейкогранитов. Между базитовыми и гранитоидными породами наблюдаются специфические взаимоотношения, которые принято классифицировать как результат взаимодействия в жидком состоянии и смешения магм (процессы минглинга и миксинга). Базитовые породы представлены рядом от биотитовых габбро до монцодиоритов, гранитоидные – биотит‐амфиболовыми гранитами. В минглинг‐взаимодействии определены также порфировидные граносиениты, сочетающие в себе черты как гранитов, так и монцодиоритов. Установлено, что первичные гранитоидные магмы имели граносиенитовый/кварцево‐монцонитовый состав и были сформированы в нижне‐среднекоровых условиях в равновесии с обогащенным плагиоклазом гранатсодержащим реститом. Формирование монцодиоритов происходило при фракционировании родоначальной габброидной магмы, которая произошла из обогащенного мантийного источника. Предложена модель взаимодействия магм, описывающая внедрение в нижние горизонты гранитоидного очага базитовой магмы, которая остановилась под вязкопластичным горизонтом гранитоидов. Начавшееся взаимодействие предполагало тепловое воздействие базитов на почти закристаллизованную гранитную магму и насыщение пограничных горизонтов базитовой магмы летучими, что могло привести к изменению состава кристаллизующегося расплава от габброидного до монцодиоритового. На границе габброидной и гранитоидной магм возник «пограничный» слой монцодиоритового расплава, который вступил во взаимодействие с гранитоидами. Результатом химического взаимодействия явилось образование гибридных пород – порфировидных граносиенитов. Сформированная гетерогенная смесь монцодиоритов и граносиенитов оказалась более подвижной по сравнению с вышележащими практически закристаллизованными гранитами, а возникновение в последних контракционных трещин обусловило проникновение и подъем гетерогенной смеси граносиенитов и монцодиоритов на более верхние уровни. Примеры взаимодействия магм с формированием минглинг‐структур на средне‐ и верхнекоровых уровнях могут рассматриваться как индикатор «быстрых», активных процессов мантийно‐корового взаимодействия, когда мантийные магмы активно дренируют литосферу и плавят вещество нижней‐средней коры. Определяющее значение имеет температурный градиент в подлитосферной мантии, который напрямую влияет на степени ее плавления и объемы базитовых магм, однако немаловажную роль играет и проницаемость литосферы: для реализации рассмотренного сценария литосфера должна быть либо маломощна, либо хорошо проницаема вследствие сдвигово‐раздвиговых движений. Территория Восточного Казахстана в позднем палеозое являлась частью Алтайской коллизионной системы герцинид, поздние стадии эволюции которой (300–280 млн лет назад) сопровождались проявлением масштабного мантийного и корового магматизма, отвечающего формированию поднепалеозойской крупной изверженной провинции, связанной с активностью Таримского мантийного плюма. Воздействие мантийного плюма на литосферную мантию привело к повышению температурного градиента, а ослабленная сдвиговыми движениями литосфера коллапсирующего орогенного сооружения оказалась проницаемой для мантийных магм, что вызвало процессы мантийно‐корового взаимодействия
Позднепалеозойские деформации пород Курайского блока: структурно‐кинематический анализ (верховья реки Курайка, Горный Алтай)
Get PDFIn the Kurai ridge located in the southeastern Gorny Altai (Altai Mountains, Russia) metamorphic rocks of the Kurai complex are widely developed: granite‐gneisses, crystalline schists and amphibolites, including widespread Early Carboniferous mylonites and blastomylonites. Oriented samples of blastomylonites were taken from the upper reaches of the Kuraika river for the microstructural study aimed to determine the kinematics of movements. The analyses of thin cut samples show structural‐kinematic indicators that suggest two deformation events (left‐lateral shearing, then right‐lateral shearing).В пределах Курайского хребта юго‐восточной части Горного Алтая широко распространены метаморфические породы курайского комплекса. Он представлен гранитогнейсами, кристаллическими сланцами и амфиболитами, среди которых развиты раннекарбоновые милониты и бластомилониты. По отобранным в верховьях реки Курайка ориентированным образцам бластомилонитов проведено микроструктурное исследование с целью определения кинематики движений. В шлифах по структурно‐кинематическим индикаторам зафиксировано наличие двух деформационных событий: более раннее – левостороннее и более позднее – правостороннее
TECTONICS AND GEODYNAMICS OF THE ALTAI-JUNGGAR OROGEN IN THE VENDIAN-PALEOZOIC: IMPLICATIONS FOR THE CONTINENTAL EVOLUTION AND GROWTH OF THE CENTRAL ASIAN FOLD BELT
Get PDFIn the end of the 20th century folded structures of central Asia were regarded as formed by accretion and collision of the Paleo-Asian oceanic plate and Siberia continent.In the end of the 20th century folded structures of central Asia were regarded as formed by accretion and collision of the Paleo-Asian oceanic plate and Siberia continent
