L‐chondrite asteroid breakup tied to Ordovician meteorite shower by multiple isochron 40Ar‐39 Ar dating     

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   

Interannual variability of Mars global dust storms: an example of self-organized criticality?     

Alexey A Pankine  Andrew P Ingersoll 《Icarus》2004,170(2):514-518

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   

Network geoinformation technology for seismic hazard research     

Valeri Gitis  Alexander Derendyaev  Pavel Metrikov  Alexey Shogin 《Natural Hazards》2012,62(3):1021-1036

In this paper, we present two network geoinformation technologies. Their common major features are (1) network access to geographical information, which may be distributed over network servers or reside on the user PC, (2) modern methods of knowledge acquisition from spatial and spatio-temporal data and (3) high interactivity and clarity of visualization boosting the decision-making efficiency. The technologies are incorporated into web-GIS GeoProcessor 2.0 and GeoTime 2.0. By means of analyzing several case studies, we argue that the proposed applications are effective tools for seismic hazard research.  相似文献   

Test results of railway ballast for bearing capacity calculations     

Alexey F. Kolos  Anastasia A. Konon 《寒旱区科学》2017,9(3):312-316

This paper presents the results of field and laboratory tests of railway ballast.Field tests were aimed to study vibrational acceleration of ballast particles and ballast layer stressed state in terms of train traffic with heavy axle loads.The test results are vibrational acceleration and stress values distribution in ballast layer and experimental relationships of vertical and horizontal vibroaccelerations damping in terms of train operation with axle load up to 300 kN.Laboratory stabilometer tests were directed to study the change of ballast strength properties due to vibrodynamic impact and shows that for dynamic loading with 10,25,55 Hz frequencies vibrodynamic impact influences strength properties insignificantly and coincides with the accuracy of test equipment.Stated test results provide references for calculation of ballast and sub-ballast bearing capacity.  相似文献   

Global coherence of GPS-measured high-frequency surface tremor motions     

Alexey Lyubushin 《GPS Solutions》2018,22(4):116

The traditional approach of GPS investigations is determining trends which are connected with the motion of tectonic plates. At the same time, a global GPS network provides the possibility of investigating statistical properties of high-frequency earth surface tremor in different parts of the world. Based on the results of coherence and correlation analysis of noise components of daily three-component GPS time series, representing measurements of earth surface displacements at 1097 stations, we have found that, during 2010–2011, there was a significant increase in the average level of noise coherence or correlation with dominant periods 7–9 days of surface tremor in nine regions of the earth, and in some of these regions, the average level of coherence or correlation is still high and does not return to the previous level. The increase of the average level of coherence and correlation could be detected on the graphs purely visually, while the middle time point of the time interval in which the ascending occurred is detected more precisely by a formal method based on the use of the Fisher’s ratio.  相似文献   

A Global Perspective on Crustal Structure and Evolution based on A New Crustal Classification     

Irina M. ARTEMIEVA  Alexey SHULGIN 《《地质学报》英文版》2021,95(Z1):48-50

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The Fe–C–O–H–N system at 6.3–7.8 GPa and 1200–1400 °C: implications for deep carbon and nitrogen cycles     

Alexander?G.?SokolEmail authorView author&#;s OrcID profile  Anatoly?A.?Tomilenko  Taras?A.?Bul’bak  Alexey?N.?Kruk  Pavel?A.?Zaikin  Ivan?A.?Sokol  Yurii?V.?Seryotkin  Yury?N.?Palyanov 《Contributions to Mineralogy and Petrology》2018,173(6):47

Interactions in a Fe–C–O–H–N system that controls the mobility of siderophile nitrogen and carbon in the Fe⁰-saturated upper mantle are investigated in experiments at 6.3–7.8 GPa and 1200–1400 °C. The results show that the γ-Fe and metal melt phases equilibrated with the fluid in a system unsaturated with carbon and nitrogen are stable at 1300 °C. The interactions of Fe₃C with an N-rich fluid in a graphite-saturated system produce the ε-Fe₃N phase (space group P6₃/mmc or P6₃22) at subsolidus conditions of 1200–1300 °C, while N-rich melts form at 1400 °C. At IW- and MMO-buffered hydrogen fugacity (fH₂), fluids vary from NH₃- to H₂O-rich compositions (NH₃/N₂?>?1 in all cases) with relatively high contents of alkanes. The fluid derived from N-poor samples contains less H₂O and more carbon which mainly reside in oxygenated hydrocarbons, i.e., alcohols and esters at MMO-buffered fH₂ and carboxylic acids at unbuffered fH₂ conditions. In unbuffered conditions, N₂ is the principal nitrogen host (NH₃/N₂?≤?0.1) in the fluid equilibrated with the metal phase. Relatively C- and N-rich fluids in equilibrium with the metal phase (γ-Fe, melt, or Fe₃N) are stable at the upper mantle pressures and temperatures. According to our estimates, the metal/fluid partition coefficient of nitrogen is higher than that of carbon. Thus, nitrogen has a greater affinity for iron than carbon. The general inference is that reduced fluids can successfully transport volatiles from the metal-saturated mantle to metal-free shallow mantle domains. However, nitrogen has a higher affinity for iron and selectively accumulates in the metal phase, while highly mobile carbon resides in the fluid phase. This may be a controlling mechanism of the deep carbon and nitrogen cycles.  相似文献   

From Craton to Shelf: example from the Barents Sea     

Alexey Shulgin  Rolf Mjelde  Jan Inge Faleide 《《地质学报》英文版》2018,92(Z1):105-105

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Low‐frequency wave propagation in periodically layered media     

Yuriy Roganov  Alexey Stovas 《Geophysical Prospecting》2012,60(5):825-837

In this paper, we consider wave propagation in a layered medium. Using the Baker‐Campbell‐Hausdorff series, we expand the logarithm of a propagator matrix in series of frequency. The series coefficients allow us to extend the effective Backus medium for low frequencies. The proposed technique is applied to vertical propagation in a periodically layered and binary medium as well as for a gradient medium. The velocity dispersion equations are derived for these media. We also consider the layered medium with monoclinic anisotropy. We illustrate the accuracy of the proposed method on synthetic and well‐log data.  相似文献   

Slowness surface approximations for qSV-waves in transversely isotropic media     

Alexey Stovas  Yuriy Roganov 《Geophysical Prospecting》2009,57(1):1-11

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