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排序方式: 共有240条查询结果,搜索用时 390 毫秒
151.
Victor P. Nechaev Evgene V. Sklyarov Yukio Isozaki Nikolay N. Kruk Alexey V. Travin Yukiyasu Tsutsumi Eugenia V. Nechaeva 《Island Arc》2021,30(1):e12426
More than 30 mafic dykes crop out in the Sergeevka belt in the coastal South Primorye, Far East Russia, of which geologic settings have been unclear for years. This study conducted major- and trace elements characterization, Sr–Nd isotope analyses, and Ar–Ar amphibole and U–Pb zircon datings for these rocks in order to identify their origin. The results demonstrated that all dykes are characterized by high Ba/Yb and low Nb/Y, Zr/Y, and Th/Yb ratios, which suggest their origin from arc melts derived from thin wedge mantle and shallow-dipping slab. These dykes are clearly separated into two distinct age/geochemistry suites; that is, the Paleogene and Early Cretaceous one with dolerites/basalts and adakitic rocks, and the Permian–Triassic one with high-Mg and high-Al gabbro-dolerite varieties. Their geochemistry suggests that the older suite was sourced from a primitive depleted MORB mantle (DMM)-type mantle, whereas the younger suite from an enriched mantle II (EM2)-type mantle domain. The transition in source type from DMM to EM2 occurred during the Jurassic-earliest Cretaceous time, probably by a strong influence of a mantle plume onto the long-continuing subduction-related magmatism. The plume influence reached the maximum when the unique meimechite-picrite complex formed in the region. 相似文献
152.
We calculated equilibrium chemical composition of a mixture of meteoritic vapor and air during fireball events, i.e. during penetration of large meteoroids into terrestrial atmosphere. Different types of fireballs were considered, and calculations were performed for wide ranges of temperatures and pressures. Chemical composition at the quenching point was estimated by comparison of hydrodynamic and chemical reaction time scales. For the typical fireball temperatures of 4000-5000 K, most elements are expected to be in the form of atoms and ions. Notable exceptions are Si and C, which are expected to be mainly in the form of SiO and CO. Other molecules abundant at these temperatures are N2 and NO. Metal monoxides are most abundant at 2000-2500 K and are formed during the cooling phase. Conditions for formation of other molecules such as , CN, C2 and OH were also considered. The composition of freshly ablated meteoroid material was studied using the MAGMA code. 相似文献
153.
L. S. Kuchment A. N. Gel’fan V. N. Demidov P. Yu. Romanov 《Russian Meteorology and Hydrology》2011,36(9):630-637
A technique is proposed of precomputing the snowmelt runoff hydrograph on the basis of physical and mathematical models of
river runoff formation, available standard data of surface hydrometeorological measurements, and satellite measurements of
Earth’s surface conditions. The computations were carried out for two regions including the basins of the Vyatka and Don rivers.
It is demonstrated that, in spite of the possible errors and gaps depending on meteorological conditions, the satellite snow
cover measurements can be an important addition to the surface measurements for simulating a spatial picture of the runoff
formation. The use of physical and mathematical models of the runoff formation enables to reduce the errors of satellite snow
cover data and to ensure the spatiotemporal continuity of its monitoring. 相似文献
154.
Lake-margin ecosystems of saline lakes of the Borzya group (Zabaikalsky Krai,Russia) during the initial filling phase 总被引:1,自引:0,他引:1
Evgenia R GORLACHEVA Gazhit Ts. TSYBEKMITOVA Alexey V. AFONIN Natalya A. TASHLIKOVA Ekaterina Yu. AFONINA Alexey P. KUKLIN Natalia V. SALTANOVA 《中国海洋湖沼学报》2014,32(4):871-878
This article presents the results ofhydrochemical and hydrobiological studies of shallow saline lakes of the Borzya group (Zabaikalsky K_rai, Russia) at the initial filling phase. The lake-margin ecosystems of the studied lakes are characterized by varying degrees of salinity from polyhaline to brine water. Cyclical variations of meteorological conditions and high salinity determined that the compositions of the aquatic organisms are specific, mostly between stenohaline and euryhaline species, the quantities are low, and the community structures are simple. 相似文献
155.
156.
Xuke Hu Hongchao Fan Alexey Noskov Zhiyong Wang Alexander Zipf Fuqiang Gu Jianga Shang 《Transactions in GIS》2021,25(1):71-111
Semantically rich maps are the foundation of indoor location‐based services. Many map providers such as OpenStreetMap and automatic mapping solutions focus on the representation and detection of geometric information (e.g., shape of room) and a few semantics (e.g., stairs and furniture) but neglect room usage. To mitigate the issue, this work proposes a general room tagging method for public buildings, which can benefit both existing map providers and automatic mapping solutions by inferring the missing room usage based on indoor geometric maps. Two kinds of statistical learning‐based room tagging methods are adopted: traditional machine learning (e.g., random forests) and deep learning, specifically relational graph convolutional networks (R‐GCNs), based on the geometric properties (e.g., area), topological relationships (e.g., adjacency and inclusion), and spatial distribution characteristics of rooms. In the machine learning‐based approach, a bidirectional beam search strategy is proposed to deal with the issue that the tag of a room depends on the tag of its neighbors in an undirected room sequence. In the R‐GCN‐based approach, useful properties of neighboring nodes (rooms) in the graph are automatically gathered to classify the nodes. Research buildings are taken as examples to evaluate the proposed approaches based on 130 floor plans with 3,330 rooms by using fivefold cross‐validation. The experiments conducted show that the random forest‐based approach achieves a higher tagging accuracy (0.85) than R‐GCN (0.79). 相似文献
157.
Jens Hopp Mario Trieloff Uli Ott Ekaterina V. Korochantseva Alexey I. Buykin 《Meteoritics & planetary science》2014,49(3):358-372
Ar‐Ar isochron ages of EL chondrites suggest closure of the K‐Ar system at 4.49 ± 0.01 Ga for EL5 and 6 chondrites, and 4.45 ± 0.01 Ga for EL3 MAC 88136. The high‐temperature release regimes contain a mixture of radiogenic 40Ar* and trapped primordial argon (solar or Q‐type) with 40Ar/36ArTR ~ 0 , which does not affect the 40Ar budget. The low‐temperature extractions show evidence of an excess 40Ar component. The 40Ar/36Ar is 180–270; it is defined by intercept values of isochron regression. Excess 40Ar is only detectable in petrologic types >4/5. These lost most of their primordial 36Ar from low‐temperature phases during metamorphism and retrapped excess 40Ar. The origin of this excess 40Ar component is probably related to metamorphic Ar mobilization, homogenization of primordial and in situ radiogenic Ar, and trapping of Ar by distinct low‐temperature phases. Ar‐Ar ages of EH chondrites are more variable and show clear evidence of a major impact‐induced partial resetting at about 2.2 Ga ago or alternatively, prolonged metamorphic decomposition of major K carrier phases. EH impact melt LAP 02225 displayed the highest Ar‐Ar isochron age of 4.53 ± 0.01 Ga. This age sets a limit of about 25–45 Ma for the age bias between the K‐Ar and U‐Pb decay systems. 相似文献
158.
159.
Ekaterina V. KOROCHANTSEVA Mario TRIELOFF Cyrill A. LORENZ Alexey I. BUYKIN Marina A. IVANOVA Winfried H. SCHWARZ Jens HOPP Elmar K. JESSBERGER 《Meteoritics & planetary science》2007,42(1):113-130
Abstract— Radiochronometry of L chondritic meteorites yields a rough age estimate for a major collision in the asteroid belt about 500 Myr ago. Fossil meteorites from Sweden indicate a highly increased influx of extraterrestrial matter in the Middle Ordovician ~480 Myr ago. An association with the L‐chondrite parent body event was suggested, but a definite link is precluded by the lack of more precise radiometric ages. Suggested ages range between 450 ± 30 Myr and 520 ± 60 Myr, and can neither convincingly prove a single breakup event, nor constrain the delivery times of meteorites from the asteroid belt to Earth. Here we report the discovery of multiple 40Ar‐39Ar isochrons in shocked L chondrites, particularly the regolith breccia Ghubara, that allow the separation of radiogenic argon from multiple excess argon components. This approach, applied to several L chondrites, yields an improved age value that indicates a single asteroid breakup event at 470 ± 6 Myr, fully consistent with a refined age estimate of the Middle Ordovician meteorite shower at 467.3 ± 1.6 Myr (according to A Geologic Time Scale 2004). Our results link these fossil meteorites directly to the L‐chondrite asteroid destruction, rapidly transferred from the asteroid belt. The increased terrestrial meteorite influx most likely involved larger projectiles that contributed to an increase in the terrestrial cratering rate, which implies severe environmental stress. 相似文献
160.
Previous simulations of martian global dust storms with a simple low-order model showed the desired interannual variability of storms if one of the model parameters—the threshold wind speed for starting saltation and lifting dust from the surface—was finely tuned. In this paper we show that the fine-tuning of this parameter could be the result of negative feedback in which processes associated with global dust storms raise the threshold and small-scale processes like dust devils, which are active in years between the storms, lower the threshold. 相似文献