Ar-Ar Geochronology in a gneiss dome within the Zagros Orogénic Belt     

Akram Alizadeh  Margarita López Martínez  Khalil Sarkarinejad 《Comptes Rendus Geoscience》2010,342(11):837-846

Exhumation of the Tutak mantled gneiss dome without significant cooling has taken place in a doubly plunging anticline within the Sanandaj-Sirjan HP-LT metamorphic belt in the Zagros Thrust System of Iran. Reconstruction of structural evolution of the Tutak gneiss dome at the contact between Arabian and Iranian plates by ⁴⁰Ar/³⁹Ar geochronology exhibits history of the closure of Neo-Tethyan Ocean. There are two granites of different ages in the core of dome; the oldest corresponds to the central Iranian continental crust and was deformed at about 180 Ma. The younger granite was emplaced in the NE–SW transpression system. The timing of strain-related fabrics and exhumation history of the region illustrates the closure of Neo-Tethys and beginning of continent-continent collision at about 77 Ma, as constrained by a well defined plateau ⁴⁰Ar/³⁹Ar age obtained on biotite. Then, the biotite age corresponds to the second stage of emplacement of the Bendenow granite-gneiss which illustrating repeated orogenic events. Continuing deformation without interruption that by now has been created at about 77 Ma, was largely restricted to the transpression and high proportion of simple shear components relative to the pure shear components along the NE–SW.  相似文献   

The Stellar Imager (SI) project: a deep space UV/Optical Interferometer (UVOI) to observe the Universe at 0.1 milli-arcsec angular resolution     

Kenneth G. Carpenter  Carolus J. Schrijver  Margarita Karovska 《Astrophysics and Space Science》2009,320(1-3):217-223

The Stellar Imager (SI) is a space-based, UV/Optical Interferometer (UVOI) designed to enable 0.1 milli-arcsecond (mas) spectral imaging of stellar surfaces and of the Universe in general. It will also probe via asteroseismology flows and structures in stellar interiors. SI’s science focuses on the role of magnetism in the Universe and will revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically controlled processes, such as accretion, in the Universe. The ultra-sharp images of SI will revolutionize our view of many dynamic astrophysical processes by transforming point sources into extended sources, and snapshots into evolving views. SI is a “Flagship and Landmark Discovery Mission” in the 2005 Heliophysics Roadmap and a potential implementation of the UVOI in the 2006 Science Program for NASA’s Astronomy and Physics Division. We present here the science goals of the SI Mission, a mission architecture that could meet those goals, and the technology development needed to enable this mission. Additional information on SI can be found at: http://hires.gsfc.nasa.gov/si/.  相似文献   

The Holocene record of Alberca de Tacámbaro,a tropical lake in western Mexico: evidence of orbital and millennial-scale climatic variability     

Beatriz Ortega-Guerrero  Margarita Caballero  Isabel Israde-AlcáNtara 《第四纪科学杂志》2021,36(4):649-663

Laminated sediments in a core from Alberca de Tacámbaro, western central Mexico, provide a high-resolution record of palaeoclimatic variability for most of the Holocene. Using compositional and textural characteristics we identified 14 facies classified in biogenic, clastic and volcaniclastic groups, in which diatoms and other algal remains are the most common components. In addition to facies analysis, high-resolution geochemical data from continuous core scanning XRF and the analysis of discrete samples for organic and inorganic carbon content, provide the basis for palaeoclimatic reconstruction. The age model indicates that the record spans from 9.4 cal ka bp toad 1760. Three main phases in the sequence are identified, controlled by millennial-scale variability. During the period between 9.4 and 5.7 cal kabp , the lake is dominated by siliceous organisms. Drier conditions between 8.2 and 6.3 cal kabp are linked to decreases in summer insolation and solar irradiance. By 5.7 cal kabp , the change in sedimentation is related to the increase in El Niño Southern Oscillation frequency. Evidence of the occurrence of dry conditions during the archaeological Late Classic period (ad 600–900) and historical droughts are also documented in the Alberca de Tacámbaro record. Unprecedented changes in the landscape are recorded afterad 1520.  相似文献   

High-temperature order–disorder phase transition in nacaphite,Na2CaPO4F     

Margarita S. Avdontceva  Maria G. Krzhizhanovskaya  Sergey V. Krivovichev  Viktor N. Yakovenchuk 《Physics and Chemistry of Minerals》2015,42(8):671-676

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The MIKHNEVO small aperture array enhances the resolution property of seismological observations on the East European Platform     

Irina Alfatovna Sanina  Irina P. Gabsatarova  Oleg A. Chernykh  Oxana Y. Riznichenko  Sergey G. Volosov  Margarita A. Nesterkina  Natalya L. Konstantinovskaya 《Journal of Seismology》2011,15(3):545-556

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Dark matter haloes in interacting isolated galaxy pairs: The Importance of the Hα rotation curve     

Isaura Fuentes-Carrera  Philippe Amram  Margarita Rosado 《Astrophysics and Space Science》2002,281(1-2):411-414

We present Hα scanning Fabry-Perot observations of the interacting galaxy pair NGC 3893/96 (Kar 302), an M51-type galaxy pair. The velocity field and rotation curve of the main galaxy (NGC 3893) were derived. These show the galaxy follows a rather axisymmetric behaviour. Together with HI observations, several mass models were adjusted in order to study the nature of the dark halo as well as the mass-to-light ratio of the galaxy. We find that in order to constrain these models, it is important to have a high resolution Hα rotation curve for the inner parts of the galaxy. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

Distances on Cosmological Scales with VLTI     

Margarita Karovska  Martin Elvis  Massimo Marengo 《Astrophysics and Space Science》2003,286(1-2):261-266

We present here a new method using interferometric measurements of quasars, that allows the determination of direct geometrical distances on cosmic scales. Quasar Broad Emission Line Regions sizes provide a `meter rule' with which to measure the metric of the Universe. This method is less dependent of model assumptions, and even of variations in the fundamental constants (other than c).We discuss the spectral and spatial requirements on the VLTI observations needed to carry out these measurements. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

New Radial Velocities for Dwarf Galaxies in the Local Volume     

I. D. Karachentsev  M. E. Sharina  D. I. Makarov  Yu. A. Perepelitsyna  E. S. Safonova 《Astrophysics》2015,58(3):309-317

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The origin of presolar nova grains     

Jordi JOs  Margarita Hernanz 《Meteoritics & planetary science》2007,42(7-8):1135-1143

Abstract— Infrared observations reveal that classical novae often form dust in their expanding shells ejected into the interstellar medium as a consequence of violent outbursts. Recent experimental efforts have led to the identification of presolar nova candidate grains from the Acfer 094 and Murchison meteorites. Recently, however, concerns have been raised about the stellar paternity of these grains by new measurements on another sample of SiC grains: these grains are characterized by ¹²C/¹³C and ¹⁴N/¹⁵N ratios similar to the ones reported for the nova grains, but a number of different imprints suggest that a possible supernova origin cannot be excluded. Here we review the predicted nucleosynthetic imprints accompanying nova explosions and discuss the chances to synthesize heavier species, such as titanium, in nova‐like events.  相似文献   

Estimation of pore‐pressure change in a compacting reservoir from time‐lapse seismic data     

Margarita Corzo  Colin MacBeth  Olav Barkved 《Geophysical Prospecting》2013,61(5):1022-1034

An approach is developed to estimate pore‐pressure changes in a compacting chalk reservoir directly from time‐lapse seismic attributes. It is applied to data from the south‐east flank of the Valhall field. The time‐lapse seismic signal of the reservoir in this area is complex, despite the fact that saturation changes do not have an influence. This complexity reflects a combination of pressure depletion, compaction and stress re‐distribution throughout the reservoir and into the surrounding rocks. A simple relation is found to link the time‐lapse amplitude and time‐shift attributes to variations in the key controlling parameter of initial porosity. This relation is sufficient for an accurate estimation of pore‐pressure change in the inter‐well space. Although the time‐lapse seismic estimates mostly agree with reservoir simulation, unexplained mismatches are apparent at a small number of locations with lower porosities (less than 38%). The areas of difference between the observations and predictions suggest possibilities for simulation model updating or a better understanding of the physics of the reservoir.  相似文献