Study of landform control over land utilisation pattern     

Seelan S. Kumar  G. Ch. Chennaiah  N. C. Gautam 《Journal of the Indian Society of Remote Sensing》1983,11(1):49-53

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Peripheral bulge—a causal mechanism for the Lower/Middle Ordovician unconformity along the western margin of the Northern Appalachians     

Robert D. Jacobi 《Earth and Planetary Science Letters》1981

This report proposes a plate tectonic model that can explain the Early/Middle Ordovician erosional unconformity observed along much of the western margin of the Appalachian orogen. In order for the model to apply, the Taconic allochthons must represent an outer arc (accretionary wedge) and the related subduction zone and Benioff zone must have dipped east (this report reviews the evidence for these assumptions). If these suppositions are correct, then the observed unconformity may have resulted from upwarp along a peripheral bulge (which occurs seaward of present-day oceanic trenches) as the Ordovician continental margin drifted east into the trench. Theoretical calculations show that the amount of uplift experienced by a continental plate over a peripheral bulge is on the order of the amount of uplift observed on the unconformity in Newfoundland. Furthermore, the sequence of events in Taconic times along the western margin of the Appalachian orogen supports the hypothesis that the paleocontinental margin drifted east over a peripheral bulge and on into the trench. The Ordovician shallow-water carbonate bank on the continental margin of the North American plate was uplifted (peripheral bulge) and then rapidly down-dropped to abyssal depths (continental margin entering trench) where it was first covered by flysch and then structurally overlain by the Taconic allochthons (continental margin underthrusting the outer arc). The present western boundary of the maximum relief on the unconformity would delineate the trend and approximate position of the bulge when the craton jammed the subduction zone and ceased convergence with the island arc (in Caradocian times).  相似文献   

Radiophysical Monitoring of the Lake Baikal Ice Cover     

A. K. Tulokhonov  E. Zh. Garmaev  Yu. B. Bashkuev  Yu. L. Lomukhin  V. B. Khaptanov  M. G. Dembelov  M. V. Slipenchuk  B. Ch. Dorzhiev  O. N. Ochirov 《Geography and Natural Resources》2018,39(1):39-45

Presented are the results of the winter 2014 radiophysical expedition, within the framework of which the Baikal ice cover was investigated by electromagnetic methods. The primary objectives the expedition were to detect irregularities in the ice cover, such as cracks and thawing steamed holes in the ice, and to determine the ice thickness and structure in the area of the thawing holes by the GPR sounding method. We used in the experiments the OKO-2 ground-penetrating radar (GPR) of the decimeter band and the nanosecond radar with the wavelength of 3 cm. The measurements were made carried out from the Khivus hovercraft and from the UAZ automobile. The ice thickness of Lake Baikal was determined by non-contact electromagnetic measurement methods. Radargrams of reflected signals from the ice cover are presented. Radar patterns of reflected signals from artificial irregularities of the ice cover were obtained by the short-pulse radar method. The concept of radiophysical monitoring is suggested, which provides a means of determining the ice cover parameters of a water body with high spatial resolution. We present an integral approach to investigating the conditions of the ice cover in order to integrate different physicochemical methods for diagnosing the objects studied. A further development of the concept of integrated ice cover research, and the creation of the monitoring network involves solving a number of scientific and engineering tasks that include developing physical models and information and measurement systems as well as the rationale for an integrated monitoring network.  相似文献   

Solar EUV Irradiance Measurements by the Auto-Calibrating EUV Spectrometers (SolACES) Aboard the International Space Station (ISS)     

G. Schmidtke  B. Nikutowski  C. Jacobi  R. Brunner  C. Erhardt  S. Knecht  J. Scherle  J. Schlagenhauf 《Solar physics》2014,289(5):1863-1883

SolACES is part of the ESA SOLAR ISS mission that started aboard the shuttle mission STS-122 on 7 February 2008. The instrument has recorded solar extreme ultraviolet (EUV) irradiance from 16 to 150 nm during the extended solar activity minimum and the beginning solar cycle 24 with rising solar activity and increasingly changing spectral composition. The SOLAR mission has been extended from a period of 18 months to >?8 years until the end of 2016. SolACES is operating three grazing incidence planar grating spectrometers and two three-current ionization chambers. The latter ones are considered as primary radiometric detector standards. Re-filling the ionization chambers with three different gases repeatedly and using overlapping band-pass filters, the absolute EUV fluxes are derived in these spectral intervals. This way the serious problem of continuing efficiency changes in space-borne instrumentation is overcome during the mission. Evaluating the three currents of the ionization chambers, the overlapping spectral ranges of the spectrometers and of the filters plus inter-comparing the results from the EUV photon absorption in the gases with different absorption cross sections, there are manifold instrumental possibilities to cross-check the results providing a high degree of reliability to the spectral irradiance derived. During the mission a very strong up-and-down variability of the spectrometric efficiency by orders of magnitude is observed. One of the effects involved is channeltron degradation. However, there are still open questions on other effects contributing to these changes. A survey of the measurements carried out and first results of the solar spectral irradiance (SSI) data are presented. Inter-comparison with EUV data from other space missions shows good agreement such that the international effort has started to elaborate a complete set of EUV-SSI data taking into account all data available from 2008 to 2013.  相似文献   

Morphology and Structural Features of the Subduction Zone in the Vicinity of Kuril–Kamchatka–Aleutian Junction     

Baranov  B. V.  Tsukanov  N. V.  Gaedicke  Ch.  Freitag  R.  Dozorova  K. A. 《Oceanology》2022,62(4):528-539

Oceanology - The specific morphology of the inner and outer slopes of the eastern Kuril–Kamchatka Trench were revealed based on joint study of bathymetry and seismic profiles obtained in two...  相似文献   

Iron speciation in minerals and glasses probed by $$\hbox{M}_{2/3}$$-edge X-ray Raman scattering spectroscopy     

A.?NyrowEmail author  C.?Sternemann  M.?Wilke  R.?A.?Gordon  K.?Mende  H.?Yava?  L.?Simonelli  N.?Hiraoka  Ch.?J.?Sahle  S.?Huotari  G.?B.?Andreozzi  A.?B.?Woodland  M.?Tolan  J.?S.?Tse 《Contributions to Mineralogy and Petrology》2014,167(5):1012

We present a spectroscopic study of the iron \(\hbox{M}_{2/3}\)-edge for several minerals and compounds to reveal information about the oxidation state and the local coordination of iron. We describe a novel approach to probe the iron \(\hbox{M}_{2/3}\)-edge bulk sensitively using X-ray Raman scattering. Significant changes in the onset and shape of the Fe \(\hbox{M}_{2/3}\)-edge were observed on ferrous and ferric model compounds with Fe in octahedral and tetrahedral coordination. Simulation of the spectra is possible using an atomic multiplet code, which potentially allows determination of, e.g., crystal-field parameters in a quantitative manner. A protocol is discussed for determination of the Fe oxidation state in compounds by linear combination of spectra of ferric and ferrous end members. The presented results demonstrate the capabilities of Fe \(\hbox{M}_{2/3}\)-edge spectroscopy by X-ray Raman scattering to extract information on the ratio of trivalent to total iron \(\hbox{Fe}^{3+}/\sum \hbox{Fe}\) and local coordination. As X-ray Raman scattering is performed with hard X-rays, this approach is suitable for in situ experiments at high pressure and temperature. It thus may provide indispensable information on oxidation state, electronic structure and local structure of materials that are important for physical and chemical processes of the deep Earth.  相似文献   

Early Cambrian granitoids of North Gondwana margin in the transition from a convergent setting to intra-continental rifting (Ossa-Morena Zone,SW Iberia)     

T. Sánchez-García  M. F. Pereira  F. Bellido  M. Chichorro  J. B. Silva  P. Valverde-Vaquero  Ch. Pin  A. R. Solá 《International Journal of Earth Sciences》2014,103(5):1203-1218

Two distinct Cambrian magmatic pulses are recognized in the Ossa-Morena Zone (SW Iberia): an early rift-(ER) and a main rift-related event. This Cambrian magmatism is related to intra-continental rifting of North Gondwana that is thought to have culminated in the opening of the Rheic Ocean in Lower Ordovician times. New data of whole-rock geochemistry (19 samples), Sm–Nd–Sr isotopes (4 samples) and ID–TIMS U–Pb zircon geochronology (1 sample) of the Early Cambrian ER plutonic rocks of the Ossa-Morena Zone are presented in this contribution. The ER granitoids (Barreiros, Barquete, Calera, Salvatierra de los Barros and Tablada granitoid Massifs) are mostly peraluminous granites. The Sm–Nd isotopic data show moderate negative εNdt values ranging from ?3.5 to +0.1 and TDM ages greatly in excess of emplacement ages. Most ER granitoids are crustal melts. However, a subset of samples shows a transitional anorogenic alkaline tendency, together with more primitive isotopic signatures, documenting the participation of lower crust or mantle-derived sources and suggesting a local transient advanced stage of rifting. The Barreiros granitoid is intrusive into the Ediacaran basement of the Ossa-Morena Zone (Série Negra succession) and has yielded a crystallization age of 524.7 ± 0.8 Ma consistent with other ages of ER magmatic pulse. This age: (1) constrains the age of the metamorphism developed in the Ediacaran back-arc basins before the intrusion of granites and (2) defines the time of the transition from the Ediacaran convergent setting to the Lower Cambrian intra-continental rifting in North Gondwana.  相似文献   

Neoproterozoic complexes of the shelf cover of the Dzabkhan terrane basement in the Central Asian Orogenic Belt     

I. K. Kozakov  A. B. Kuznetsov  Ch. Erdenegargal  E. B. Salnikova  I. V. Anisimova  Ju. V. Plotkina  A. M. Fedoseenko 《Stratigraphy and Geological Correlation》2017,25(5):479-491

The formation stages of high-grade metamorphic complexes and the related granitoids of the Dzabkhan terrane basement are considered. The age data (U–Pb method, TIMS) of zircons from the trondhjemite block of the eastern part of the Dzabkhan terrane, which is directly overlain by the dolomite sequence of the Tsagaan Oloom Formation, are given. Trondhjemites yield the U–Pb zircon age of 862 ± 3 Ma. In their structural position, they are assigned to typical postmetamorphic formations that determine the formation and cratonization of rocks of the host block. The geochronological study of trondhjemites gives grounds to distinguish fragments of the continental crust in the Dzabkhan terrane basement, the formation of which occurred at different periods of time: ～860 and ～790 Ma. Geological–geochronological and Sm?Nd isotope–geochemical studies indicate that the Dzabkhan terrane basement is not a single block of the Early Precambrian continental crust, but a composite terrane, comprising Neoproterozoic ensialic and island-arc structural and compositional complexes. Correlation of Sr isotopic characteristics with the ⁸⁷Sr/⁸⁶Sr variation curve in the Neoproterozoic and Cambrian seawater shows that carbonate deposits accumulated at the eastern margin of the Dzabkhan terrane near the end of the Neoproterozoic, 700–550 Ma, and in the central part of the terrane in the Early Cambrian, 540–530 Ma.  相似文献   

Book reviews: Black Hole Gravitohydrodynamics. By Brian Punsley     

Ch. Fendt 《Astronomische Nachrichten》2003,324(5):507-508

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The sulfur species in hot rocky exoplanet atmospheres     

L. J. Janssen  P. Woitke  O. Herbort  M. Min  K. L. Chubb  Ch. Helling  L. Carone 《Astronomische Nachrichten》2023,344(10):e20230075

The first JWST observations of hot Jupiters showed an unexpected detection of SO ${}_2$ in their hydrogen-rich atmospheres. We investigate how much sulfur can be expected in the atmospheres of rocky exoplanets and which sulfur molecules can be expected to be most abundant and detectable by transmission spectroscopy. We run thermochemical equilibrium models at the crust–atmosphere interface, considering surface temperatures 500–5000 K, surface pressures 1–100 bar, and various sets of element abundances based on common rock compositions. Between 1000 and 2000 K, we find gaseous sulfur concentrations of up to 25% above the rock in our models. SO ${}_2$, SO, H ${}_2$S, and S ${}_2$ are by far the most abundant sulfur molecules. SO ${}_2$ shows potentially detectable features in transmission spectra at about 4 $\mu$m, between 7 and 8 $\mu$m, and beyond 15 $\mu$m. In contrast, the sometimes abundant H ${}_2$S molecule is difficult to detect in these spectra, which are mostly dominated by H ${}_2$O and CO ${}_2$. Although the molecule PS only occurs with concentrations ppm, it can cause a strong absorption feature between 0.3 and 0.65 $\mu$m in some of our models for high surface pressures. The detection of sulfur molecules would enable a better characterization of the planetary surface.  相似文献