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51.
Leaf fragments of Herbifolia antiqua A. Frolov et Enushchenko gen. et sp. nov. from the Middle Jurassic (Aalenian) of the Irkutsk Coal Basin (Eastern Siberia, Russia) are reported. The following features are characteristic of H. antiqua gen. et sp. nov.: the presence of leaf sheaths, linear smooth-edged leaves with parallel venation, anastomoses between the veins, anomocytic stomata, rhomb-shaped ordinary epidermal cells. Such a combination of characters is widespread in modern monocotyledonous plants and is absent in fossil and modern cryptogam and gymnosperms. Due to the lack of evidence of an enclosed ovule in H. antiqua gen. et sp. nov.we attribute it to a typological angiosperm, based on its unique leaf structure characteristic of monocotyledons. The leaf epidermal structure of Herbifolia gen. nov. is most similar to those of modern Asparagales and Liliales. 相似文献
52.
Coupled hydrological and atmospheric modeling is an efficient method for snowmelt runoff forecast in large basins. We use short-range precipitation forecasts of mesoscale atmospheric Weather Research and Forecasting(WRF) model combining them with ground-based and satellite observations for modeling snow accumulation and snowmelt processes in the Votkinsk reservoir basin(184,319 km2). The method is tested during three winter seasons(2012–2015). The MODIS-based vegetation map and leaf area index data are used to calculate the snowmelt intensity and snow evaporation in the studied basin. The GIS-based snow accumulation and snowmelt modeling provides a reliable and highly detailed spatial distribution for snow water equivalent(SWE) and snow-covered areas(SCA). The modelling results are validated by comparing actual and estimated SWE and SCA data. The actual SCA results are derived from MODIS satellite data. The algorithm for assessing the SCA by MODIS data(ATBD-MOD 10) has been adapted to a forest zone. In general, the proposed method provides satisfactory results for maximum SWE calculations. The calculation accuracy is slightly degraded during snowmelt periods. The SCA data is simulated with a higher reliability than the SWE data. The differences between the simulated and actual SWE may be explained by the overestimation of the WRF-simulated total precipitation and the unrepresentativeness of the SWE measurements(snow survey). 相似文献
53.
Luca Bindi Ekaterina A. Sirotkina Andrey V. Bobrov Fabrizio Nestola Tetsuo Irifune 《Physics and Chemistry of Minerals》2016,43(2):103-110
The crystal structure and chemical composition of a crystal of (Mg14?x Cr x )(Si5?x Cr x )O24 (x ≈ 0.30) anhydrous Phase B (Anh-B) synthesized in the model system MgCr2O4–Mg2SiO4 at 12 GPa and 1600 °C have been investigated. The compound was found to be orthorhombic, space group Pmcb, with lattice parameters a = 5.900(1), b = 14.218(2), c = 10.029(2) Å, V = 841.3(2) Å3 and Z = 2. The structure was refined to R 1 = 0.065 using 1492 independent reflections. Chromium was found to substitute for both Mg at the M3 site (with a mean bond distance of 2.145 Å) and Si at the octahedral Si1 site (mean bond distance: 1.856 Å), according to the reaction Mg2+ + Si4+ = 2Cr3+. Such substitutions cause a reduction in the volume of the M3 site and an increase in the volume of the Si-dominant octahedron with respect to the values typically observed for pure Anh-B and Fe2+-bearing Anh-B. Taking into account that Cr3+ is not expected to be Jahn–Teller active, it appears that both the Cr3+–for–Mg and Cr3+–for–Si substitutions in the Anh-B structure decrease the distortion of the octahedra. Electron microprobe analysis gave the Mg13.66(8)Si4.70(6)Cr0.62(4)O24 stoichiometry for the studied phase. The successful synthesis of this phase provides new information for the possible mineral assemblages occurring in the Earth’s deep upper mantle and shed new light on the so-called X discontinuity that has been observed at 275–345 km depth in several subcontinental and subduction zone environments. 相似文献
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Nadezhda KANYGINA Andrey TRETYAKOV Dmitriy ALEXEIEV Kirill DEGTYAREV Anfisa SKOBLENKO Natalia SOLOSHENKO Boris ERMOLAEV 《《地质学报》英文版》2024,98(1):67-82
The combined petrographic, petrological, geochemical and geochronological study of the Neoproterozoic gneisses of the Sarychabyn and Baskan complexes of the Junggar Alataw of South Kazakhstan elucidate the Precambrian tectonic evolution of the Aktau–Yili terrane. It is one of the largest Precambrian crustal blocks in the western Central Asian orogenic belt. The U-Pb single-grain zircon ages indicate that granite-gneisses formed from the same source and crystallised in the early Neoproterozoic ca. 930–920 Ma. The chemical composition of gneisses corresponds to A2-type granites. The whole-rock Nd isotopic characteristics (εNd(t) = ?4.9 to ?1.0 and TNd(DM-2st) = 1.9 to 1.7 Ga) indicate the involvement of Paleoproterozoic crustal rocks in magma generation. Early Neoproterozoic ca. 930–920 Ma A-type granitoids in the Aktau–Yili terrane of South and Central Kazakhstan might reflect within-plate magmatism adjacent to the collisional belt or a local extension setting in back-arc areas of the continental arc. 相似文献
57.
Brune Sascha Ladage Stefan Babeyko Andrey Y. Müller Christian Kopp Heidrun Sobolev Stephan V. 《Natural Hazards》2010,54(2):547-562
Our analysis of new bathymetric data reveals six submarine landslides at the eastern Sunda margin between central Java and
Sumba Island, Indonesia. Their volumes range between 1 km3 in the Java fore-arc basin up to 20 km3 at the trench off Sumba
and Sumbawa. We estimate the potential hazard of each event by modeling the corresponding tsunami and its run-up on nearby
coasts. Four slides are situated remarkably close to the epicenter of the 1977 tsunamigenic Sumba M
w
= 8.3 earthquake. However, comparison of documented tsunami run-up heights and arrival times with our modeling results neither
allows us to confirm nor can we falsify the hypothesis that the earthquake triggered these submarine landslides. 相似文献
58.
Andrey A. Gurenko Kaj A. Hoernle Alexander V. Sobolev Folkmar Hauff Hans-Ulrich Schmincke 《Contributions to Mineralogy and Petrology》2010,159(5):689-702
The Canary Island primitive basaltic magmas are thought to be derived from an HIMU-type upwelling mantle containing isotopically
depleted (NMORB)-type component having interacted with an enriched (EM)-type component, the origin of which is still a subject
of debate. We studied the relationships between Ni, Mn and Ca concentrations in olivine phenocrysts (85.6–90.0 mol.% Fo, 1,722–3,915 ppm
Ni, 1,085–1,552 ppm Mn, 1,222–3,002 ppm Ca) from the most primitive subaerial and ODP Leg 157 high-silica (picritic to olivine
basaltic) lavas with their bulk rock Sr–Nd–Pb isotope compositions (87Sr/86Sr = 0.70315–0.70331, 143Nd/144Nd = 0.51288–0.51292, 206Pb/204Pb = 19.55–19.93, 207Pb/204Pb = 15.60–15.63, 208Pb/204Pb = 39.31–39.69). Our data point toward the presence of both a peridotitic and a pyroxenitic component in the magma source.
Using the model (Sobolev et al. in: Science 316:412–417, 2007) in which the reaction of Si-rich melts originated during partial
melting of eclogite (a high pressure product of subducted oceanic crust) with ambient peridotitic mantle forms olivine-free
reaction pyroxenite, we obtain an end member composition for peridotite with 87Sr/86Sr = 0.70337, 143Nd/144Nd = 0.51291, 206Pb/204Pb = 19.36, 207Pb/204Pb = 15.61 and 208Pb/204Pb = 39.07 (EM-type end member), and pyroxenite with 87Sr/86Sr = 0.70309, 143Nd/144Nd = 0.51289, 206Pb/204Pb = 20.03, 207Pb/204Pb = 15.62 and 208Pb/204Pb = 39.84 (HIMU-type end member). Mixing of melts from these end members in proportions ranging from 70% peridotite and 30%
pyroxenite to 28% peridotite and 72% pyroxenite derived melt fractions can generate the compositions of the most primitive
Gran Canaria shield stage lavas. Combining our results with those from the low-silica rocks from the western Canary Islands
(Gurenko et al. EPSL 277:514–524, 2009), at least four distinct components are required. We propose that they are (1) HIMU-type
pyroxenitic component (representing recycled ocean crust of intermediate age) from the plume center, (2) HIMU-type peridotitic
component (ancient recycled ocean crust stirred into the ambient mantle) from the plume margin, (3) depleted, MORB-type pyroxenitic
component (young recycled oceanic crust) in the upper mantle entrained by the plume, and (4) EM-type peridotitic component
from the asthenosphere or lithosphere above the plume center. 相似文献
59.
Michael J. Benton Andrey G. Sennikov 《Proceedings of the Geologists' Association. Geologists' Association》2010,121(3):313-318
Roderick Impey Murchison named the Permian Period in 1841 based on his work on Lower Permian marine sediments around the city of Perm’, on the west flank of the Ural Mountains. However, he had observed post-Carboniferous red beds earlier, around the town of Vyazniki, west of Moscow, lying above the classic Carboniferous limestones of the Moscow Basin. Murchison's notebooks and papers show that he and colleagues equivocated about the exact age of these red beds, whether latest Permian or early Triassic, but he always favoured the former view. So, his initial observation of the Vyazniki redbeds provided a marker for the top of the Permian and base of the Triassic in the European Russian platform. 相似文献
60.