Paleomagnetic constraints on the paleogeography and oroclinal bending of the Devonian volcanic arc in Kazakhstan   总被引：1，自引：0，他引：1  

Alexandra Abrajevitch  Rob Van der Voo  Natalia M. Levashova  Mikhail L. Bazhenov   《Tectonophysics》2007,441(1-4):67-84

Numerical modelling, incorporating coupling between surface processes and induced flow in the lower continental crust, is used to address the Quaternary evolution of the Gulf of Corinth region in central Greece. The post-Early Pleistocene marine depocentre beneath this Gulf overlies the northern margin of an older (Early Pleistocene and earlier) lacustrine basin, the Proto Gulf of Corinth Basin or PGCB. In the late Early Pleistocene, relief in this region was minimal but, subsequently, dramatic relief has developed, involving the creation of  900 m of bathymetry within the Gulf and the uplift by many hundreds of metres of the part of the PGCB, south of the modern Gulf, which forms the Gulf's main sediment supply. It is assumed that, as a result of climate change around 0.9 Ma, erosion of this sediment source region and re-deposition of this material within the Gulf began, both processes occurring at spatial average rates of  0.2 mm a^− 1. Modelling of the resulting isostatic response indicates that the local effective viscosity of the lower crust is  4 × 10¹⁹ Pa s, indicating a Moho temperature of  560 °C. It predicts that the  10 mm a^− 1 of extension across this  70 km wide model region, at an extensional strain rate of  0.15 Ma^− 1, is partitioned with  3 mm a^− 1 across the sediment source,  2 mm a^− 1 across the depocentre, and  5 mm a^− 1 across the ‘hinge zone’ in between, the latter value being an estimate of the extension rate on normal faults forming the major topographic escarpment at the southern margin of the Gulf. This modelling confirms the view, suggested previously, that coupling between this depocentre and sediment source by lower-crustal flow can explain the dramatic development in local relief since the late Early Pleistocene. The effective viscosity of the lower crust in this region is not particularly low; the strong coupling interpreted between the sediment source and depocentre results instead from their close proximity. In detail, the effective viscosity of the lower crust is expected to decrease northward across this model region, due to the northward increase in exposure of the base of the continental lithosphere to the asthenosphere; in the south the two are separated by the subducting Hellenic slab. The isostatic consequences of such a lateral variation in viscosity provide a natural explanation for why, since  0.9 Ma, the modern Gulf has developed asymmetrically over the northern part of the PGCB, leaving the rest of the PGCB to act as its sediment source.  相似文献   

Consistent estimation of geodetic parameters from SLR satellite constellation measurements     

Mathis Bloßfeld  Sergei Rudenko  Alexander Kehm  Natalia Panafidina  Horst Müller  Detlef Angermann  Urs Hugentobler  Manuela Seitz 《Journal of Geodesy》2018,92(9):1003-1021

In this paper, we consistently estimate geodetic parameters such as weekly 3-D station coordinates, Earth orientation parameters (EOP) including daily x/y-pole coordinates and the excess length of day \(\Delta \hbox {LOD}\), and selected weekly Earth’s gravitational field (Stokes) coefficients up to degree and order 6 from Satellite Laser Ranging measurements to up to 11 geodetic satellites. The SLR constellation consists of LAGEOS-1/2, Etalon-1/2, Stella, Starlette, Ajisai, Larets, LARES, BLITS and WESTPAC, and its observations cover a time span of 38 years ranging from February 16, 1979, to April 30, 2017. If multiple satellites with various altitudes and orbit inclinations are combined, correlations between estimated parameters are significantly reduced. This allows us (i) to investigate the ability of satellite constellations to reduce existing correlations and (ii) to estimate reliable parameters with higher precision compared to the standard 4-satellite constellation (LAGEOS-1/2, Etalon-1/2) which is currently used by the International Laser Ranging Service for the determination of the Terrestrial Reference Frame (TRF) and EOP products. In particular, the Stokes coefficients, EOP and TRF datum parameters (three translations, three rotations, one scale factor), which are highly correlated with satellite-specific orbit parameters, are improved. From our investigations, we found for an 11-satellite solution compared to the above-mentioned 4-satellite solution a decrease in the scatter of the TRF datum parameters of up to 37%, the transformation residuals are decreased by up to 22%, the scatter of the EOP is decreased by up to 22%, and their mean values are decreased by up to 84% w.r.t. the reference solutions. The largest improvement is obtained for the Stokes coefficients which significantly benefit from a combination of multiple satellites (inclinations and orbit altitudes). In total, single coefficients are improved by up to 93% and the overall improvement is up to 74%. Moreover, it could be clearly identified that Ajisai significantly disturbs the TRF solution due to an erroneous center-of-mass correction. We further quantify the impact of specific satellites on the determination of different geodetic parameters and finally evaluate the potential of the existing SLR-tracked spherical satellite constellation to support the goals of GGOS.  相似文献   

Thermal behavior of ferric selenite hydrates (Fe₂(SeO₃)₃·3H₂O,Fe₂(SeO₃)₃·5H₂O) and the water content in the natural ferric selenite mandarinoite     

Astrid Holzheid  Marina V. Charykova  Vladimir G. Krivovichev  Brendan Ledwig  Elena L. Fokina  Ksenia L. Poroshina  Natalia V. Platonova  Vladislav V. Gurzhiy 《Chemie der Erde / Geochemistry》2018,78(2):228-240

Any progress in our understanding of low-temperature mineral assemblages and of quantitative physico-chemical modeling of stability conditions of mineral phases, especially those containing toxic elements like selenium, strongly depends on the knowledge of structural and thermodynamic properties of coexisting mineral phases. Interrelation of crystal chemistry/structure and thermodynamic properties of selenium-containing minerals is not systematically studied so far and thus any essential generalization might be difficult, inaccurate or even impossible and erroneous. Disagreement even exists regarding the crystal chemistry of some natural and synthetic selenium-containing phases. Hence, a systematic study was performed by synthesizing ferric selenite hydrates and subsequent thermal analysis to examine the thermal stability of synthetic analogues of the natural hydrous ferric selenite mandarinoite and its dehydration and dissociation to unravel controversial issues regarding the crystal chemistry. Dehydration of synthesized analogues of mandarinoite starts at 56–87?°C and ends at 226–237?°C. The dehydration happens in two stages and two possible schemes of dehydration exist: (a) mandarinoite loses three molecules of water in the first stage of the dehydration (up to 180?°C) and the remaining two molecules of water will be lost in the second stage (>180?°C) or (b) four molecules of water will be lost in the first stage up to 180?°C and the last molecule of water will be lost at a temperature above 180?°C. Based on XRD measurements and thermal analyses we were able to deduce Fe₂(SeO₃)₃·(6-x)H₂O (x?=?0.0–1.0) as formula of the hydrous ferric selenite mandarinoite. The total amount of water apparently affects the crystallinity, and possibly the stability of crystals: the less the x value, the higher crystallinity could be expected.  相似文献   

Disperse megaspores in the Lower Visean deposits of the Kaluga oblast (1P/A Aleksandrovskaya borehole)     

O. A. Orlova  D. A. Mamontov  A. L. Kholopova 《Moscow University Geology Bulletin》2013,68(6):360-367

Disperse megaspores were first found in the Lower Visean deposits of the Kaluga region (1P/A borehole). A layered distribution of the megaspores in the studied section is shown. A large number of megaspores were established in the lower part of the section of the Bobrikovskian deposits. Higher along the section, there is a trend to a decrease in the number of megaspores until they disappear completely in the Tula deposits. Two megaspore assemblages were identified. A great variety of species was observed in the lower assemblage; the dominant megaspores are Zonalesporites brasserti and Aphanozonatisporites triglobatus. The only dominant species was recorded in the upper assemblage, Zonalesporites brasserti, with a low species diversity of the entire assemblage. The miospore and megaspore assemblages that are typical of the Lower Visean in the section of the analyzed borehole are compared.  相似文献   

Observations and box model analysis of radon-222 in the atmospheric surface layer at L’Aquila,Italy: March 2009 case study   总被引：1，自引：1，他引：0  

Giovanni Pitari  Eleonora Coppari  Natalia De Luca  Piero Di Carlo 《Environmental Earth Sciences》2014,71(5):2353-2359

Two years of radon-222 observations collected at L’Aquila (Italy) in the atmospheric surface layer during 2004–2006 were analyzed in correlation with meteorological data and other atmospheric tracers. A box model was developed to better understand the mechanisms of diurnal and seasonal variability of the tracer and to indirectly assess the magnitude of the monthly averaged radon soil flux in the L’Aquila measurement site. The model was successfully validated with measurements, with a 0.8 average correlation coefficient between hourly values for the whole period of radon observations. Measurements taken during March 2009 were analyzed to find possible signs of perturbation due to the ongoing seismic activity that would have reached its peak on the 6 April 2009 destructive earthquake. Contrary to the professed (and unpublished) dramatic increases of radon activity unofficially announced to the inhabitants at that time, the study presented here shows that no radon activity increase took place in L’Aquila with respect to a previous ‘seismically unperturbed’ year (same month with similar meteorological conditions), but that an average 30 % decrease was experienced. This conclusion is reached from a direct comparison of observed data and also as a result of the previously validated radon box model constrained by actual meteorological data, from which an indirect estimate of a 17 % reduction of the radon soil flux is obtained.  相似文献   

Chemical Composition of Some Saline Lakes in the Tuva Region(Russia)   总被引：1，自引：0，他引：1  

Yulia KOPYLOVA  Natalia GUSEVA  Choyganmaa OYDUP  Anastasia SHESTAKOVA 《《地质学报》英文版》2014,88(Z1):82-83

正1 Introduction Salt lakes are very interesting natural objects which can be found in different places in the world.Russia is not an exception.Climate conditions are various in Russia,but the climate is not very hot.In Russia there are a lot of places where salt lakes are spread.One of them is the Tuva region where lakes with different compositions are  相似文献   

Phylogenetic Diversity of Microorganisms from Chemocline of the Meromictic Soda Lake Doroninskoe(Zabaikalie,Russia)     

Evgeniya MATYUGINA  Natalia BELKOVA 《《地质学报》英文版》2014,88(Z1):153-154

正1 Introduction Many soda and salt lakes are characterized by the formation of the meromictic conditions under which a part of the water column is not involved in the annual process of mixing(Mac Intyre,Melack,1982).This creates an  相似文献   

Correction to: Evaluation of a multi-model approach to estimate leaf wetness duration: an essential input for disease alert systems     

Gama  Andre B.  Perondi  Daniel  Dewdney  Megan M.  Fraisse  Clyde W.  Small  Ian M.  Peres  Natalia A. 《Theoretical and Applied Climatology》2022,149(1-2):101-101

Theoretical and Applied Climatology -  相似文献   

The Canyon Diablo impact event: 2. Projectile fate and target melting upon impact     

Natalia ARTEMIEVA  Elisabetta PIERAZZO 《Meteoritics & planetary science》2011,46(6):805-829

Abstract– Despite its centennial exploration history, there are still unresolved questions about Meteor Crater, the first recognized impact crater on Earth. This theoretical study addresses some of these questions by comparing model results with field and laboratory studies of Meteor Crater. Our results indicate that Meteor Crater was formed by a high‐velocity impact of a fragmented projectile, ruling out a highly dispersed swarm as well as a very low impact velocity. Projectile fragmentation caused many fragments to fall separately from the main body of the impactor, making up the bulk of the Canyon Diablo meteorites; most of these fragments were engulfed in the expansion plume as they approached the surface without suffering high shock compression, and were redistributed randomly around the crater. Thus, the distribution of Canyon Diablo meteorites is not representative of projectile trajectory, as is usual for impactor fragments in smaller strewn fields. At least 50% of the main impactor was ejected from the crater during crater excavation and was dispersed mostly downrange of the crater as molten particles (spheroids) and highly shocked solid fragments (shrapnel). When compared with the known distribution, model results suggest an impactor from the SW. Overall, every model case produced much higher amounts of pure projectile material than observed. The projectile‐target mixing was not considered in the models; however, this process could be the main sink of projectile melt, as all analyzed melt particles have high concentrations of projectile material. The fate of the solid projectile fragments is still not completely resolved. Model results suggest that the depth of melting in the target can reach the Coconino sandstone formation. However, most of the ejected melt originates from 30–40 m depth and, thus, is limited to Moenkopi and upper Kaibab material. Some melt remains in the target; based on the estimated volume of the breccia lens at Meteor Crater, our models suggest at most a 2% content of melt in the breccia. Finally, a high water table at the time of impact could have aided strong dispersion of target and projectile melt.  相似文献   

Radiocarbon chronology of Holocene glacial and climatic events in southeastern Altai (Central Asia)     

A.R. Agatova  A.N. Nazarov  R.K. Nepop  L.A. Orlova 《Russian Geology and Geophysics》2012,53(6):546-565

The geomorphological studies and radiocarbon dating of moraine complexes and the tree line within the North Chuya Ridge, along with active slope processes, soil formation, and peat formation in southeastern Gorny Altai, constrain the age of the main glacial and climatic events in this area at 7 ka to the first half of the 19th century. It is for the first time in the history of Altai studies that 57 absolute dates were obtained for glaciation in a vast but climatically and neotectonically homogeneous area. The new data refute the conventional idea that the Holocene glaciation in this mountain land comprised eight stages of the gradual retreat of the Late Würm (Sartan) glaciation. Also, they evidence that glaciation in the upper parts of the troughs retreated almost completely no later than 7 ka and valley glaciers in southeastern Altai were activated many times in the second half of the Holocene. Data are given on the morphology and age of three moraine generations reflected in the topography. A combination of temperature minima and humidity maxima led to a catastrophically rapid and the largest (up to 5–6 km) ice advance at the Akkem Stage (4.9–4.2 ka). In addition to the radiocarbon data, the time limits of the Historical stage (2.3–1.7 ka) were defined more precisely using dendrochronological and archaeological data from Scythian burials of Pazyryk culture in SE Altai. The moraines closest to the present-day glaciers formed at the Aktru Stage (late 13th–middle 19th century). During warm interglacials, the glaciers waned considerably or retreated completely and the zone of recent glaciation was reforested. As a result of progressive aridization in the Holocene, the glaciers in southeastern Altai waned at each successive stage, and their mass balance was not positive during the greatest temperature minimum of the last millennium (middle 19th century).  相似文献