375 research outputs found
Oblique Convergence in the Himalayas of Western Nepal Deduced from Preliminary Results of GPS Measurements
A GPS network consisting of 29 sites was installed in central and western Nepal, with measurements taken in 1995 and partial remeasurements in 1997. Data suggest 15 +/−5 mm/yr of N180° convergence between the Higher Himalayas and India, a result that is consistent with N‐S shortening across the arcuate shape of the Nepalese Himalayas and an oblique underthrusting of the Indian crust below the High Himalayas of western Nepal. A 4 +/−3 mm/year E‐W extension and deviation of the principal shortening axes are inferred east of 83°E, where Quaternary faults (Darma‐Bari Gad fault system and Thakkhola graben) delineate a crustal wedge. This wedge is located on the SE projection of the Karakorum fault and may segment the Himalayan thrust belt. The convergence between the outer belt of western Nepal and India is less than 3 mm/yr, an attenuation consistent with creep on a dislocation locked beneath the Lesser Himalayas. A preliminary model suggests that this N 120°E striking dislocation is affected by a 19 mm/yr thrust component and a 7 mm/yr right lateral component
Properties of high-z galaxies as seen through lensing clusters
We discuss the first results obtained on the study of a sample of high-z
galaxies (2 < z < 7), using the gravitational amplification effect in the core
of lensing clusters. Sources are located close to the critical lines in
clusters with well constrained mass distributions, and selected through
photometric redshifts, computed on a large wavelength domain, and lens
inversion techniques.Comment: 5 pages, 3 figures, Conference Proceedings of the "Clustering at High
Redshift" Conference, June 29 to July 2, 1999, Marseille (France
Spectroscopic follow up of arclets in AC114 with the VLT
We present the first results on the VLT/FORS-1 spectroscopic survey of
amplified sources and multiple images in the lensing cluster AC114. Background
sources were selected in the cluster core, close to the critical lines, using
photometric redshifts combined with lensing inversion criteria. Spectroscopic
results are given, together with a brief summary of the properties of some of
these high-z galaxies.Comment: 4pages. To appear in the Proceedings of the XXth Moriond Astrophysics
Meeting "Cosmological Physics with Gravitational Lensing", eds. J.-P. Kneib,
Y. Mellier, M. Moniez and J. Tran Thanh Van, Les Arcs, France, March
11th-18th 200
Detection of correlated galaxy ellipticities on CFHT data: first evidence for gravitational lensing by large-scale structures
We report the detection of a significant (5.5 sigma) excess of correlations
between galaxy ellipticities at scales ranging from 0.5 to 3.5 arc-minutes.
This detection of a gravitational lensing signal by large-scale structure was
made using a composite high quality imaging survey of 6300 arcmin^2 obtained at
the Canada France Hawaii Telescope (CFHT) with the UH8K and CFH12K panoramic
CCD cameras. The amplitude of the excess correlation is 2.2\pm 0.2 % at 1
arcmin scale, in agreement with theoretical predictions of the lensing effect
induced by large-scale structure.We provide a quantitative analysis of
systematics which could contribute to the signal and show that the net effect
is small and can be corrected for. We show that the measured ellipticity
correlations behave as expected for a gravitational shear signal. The
relatively small size of our survey precludes tight constraints on cosmological
models. However the data are in favor of cluster normalized cosmological
models, and marginally reject Cold Dark Matter models with (Omega=0.3,
sigma_8<0.6) or (Omega=1, sigma_8=1). The detection of cosmic shear
demonstrates the technical feasibility of using weak lensing surveys to measure
dark matter clustering and the potential for cosmological parameter
measurements, in particular with upcoming wide field CCD cameras.Comment: 19 pages. 19 Figures. Revised version accepted in A&
Thermokinematic evolution of the Annapurna-Dhaulagiri Himalaya, central Nepal: The composite orogenic system
The Himalayan orogen represents a ‘‘Composite Orogenic System’’ in which channel flow, wedge extrusion, and thrust stacking operate in separate ‘‘Orogenic Domains’’ with distinct rheologies and crustal positions. We analyze 104 samples from the metamorphic core (Greater Himalayan Sequence, GHS) and bounding units of the Annapurna-Dhaulagiri Himalaya, central Nepal. Optical microscopy and electron backscatter diffraction (EBSD) analyses provide a record of deformation microstructures and an indication of active crystal slip systems, strain geometries, and deformation temperatures. These data, combined with existing thermobarometry and geochronology data are used to construct detailed deformation temperature profiles for the GHS. The profiles define a three-stage thermokinematic evolution from midcrustal channel flow (Stage 1, >7008C to 550–6508C), to rigid wedge extrusion (Stage 2, 400–6008C) and duplexing (Stage 3, <280–4008C). These tectonic processes are not mutually exclusive, but are confined to separate rheologically distinct Orogenic Domains that form the modular components of a Composite Orogenic System. These Orogenic Domains may be active at the same time at different depths/positions within the orogen. The thermokinematic evolution of the Annapurna-Dhaulagiri Himalaya describes the migration of the GHS through these Orogenic Domains and reflects the spatial and temporal variability in rheological boundary conditions that govern orogenic systems
Geology of the Dhaulagiri-Annapurna-Manaslu Himalaya, Western Region, Nepal. 1:200,000
Geological mapping of mountains belts is fundamental to understanding their structure and evolution. Here, a 1:200,000 scale geological map of the central Himalaya of Western Region, Nepal is presented. This map represents a compilation of previously published maps, integrated with new geological field data. The wide spatial coverage of the map and the accompanying cross sections reveal the detailed structure of the Dhaulagiri-Annapurna-Manaslu Himalaya. The addition of modern topographic and infrastructure data makes this map suitable for navigation through the region
Orogen-parallel deformation of the Himalayan mid-crust: Insights from structural and magnetic fabric analyses of the Greater Himalayan Sequence, Annapurna-Dhaulagiri Himalaya, central Nepal
The metamorphic core of the Himalaya (Greater Himalayan Sequence, GHS), in the Annapurna-Dhaulagiri region, central Nepal, recorded orogen-parallel stretching during midcrustal evolution. Anisotropy of magnetic susceptibility and field-based structural analyses suggest that midcrustal deformation of the amphibolite facies core of the GHS occurred under an oblate/suboblate strain regime with associated formation of low-angle northward dipping foliation. Magnetic and mineral stretching lineations lying within this foliation from the top of the GHS record right-lateral orogen-parallel stretching. We propose that oblate strain within a midcrustal flow accommodated oblique convergence between India and the arcuate orogenic front without the need for strain partitioning in the upper crust. Oblate flattening may have also promoted orogen-parallel melt migration and development of melt-depleted regions between km3 scale leucogranite culminations at ~50–100 km intervals along orogen strike. Following the cessation of flow, continued oblique convergence led to upper crustal strain partitioning between orogen-perpendicular convergence on thrust faults and orogen-parallel extension on normal and strike-slip faults. In the Annapurna-Dhaulagiri Himalaya, orogen-parallel stretching lineations are interpreted as a record of transition from midcrustal orogen-perpendicular extrusion to upper crustal orogen-parallel stretching. Our findings suggest that midcrustal flow and upper crustal extension could not be maintained simultaneously and support other studies from across the Himalaya, which propose an orogen-wide transition from midcrustal orogen-perpendicular extrusion to upper crustal orogen-parallel extension during the mid-Miocene. The 3-D nature of oblate strain and orogen-parallel stretching cannot be replicated by 2-D numerical simulations of the Himalayan orogen
Історія радянської України в бібліографічних покажчиках англомовних праць другої половини ХХ століття
У статті проаналізовано бібліографічні покажчики англомовної
слов’янознавчої та радянознавчої літератури, видрукувані в англомовних
країнах протягом другої половини ХХ ст. Зроблено спробу визначити
місце, яке у них займали праці з історії України, зокрема ті, що
стосуватися пізньосталінського та хрущовського періодів.В статье анализируются библиографические указатели англоязычной славяноведческой и советологической литературы, опубликованные в англоязычных странах во
второй половине ХХ века. Сделана попытка охарактеризовать положение, которое в
них занимала история Советской Украины, особенно ее позднесталинский и хрущевский
периоды.In the article, the bibliographic guides to the English-language publications in Slavic, East
European and Soviet Studies that were published in the second half of the 20th century are
analyzed. The special attention is given to history of Ukraine from the second half of the 1940s
till the mid-1960s as a particular subject in those guides
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