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1.
The length (more than 300 km) and size of the St. Narcisse morainic system suggest that it represents an important glacial event, probably climatically controlled and not related to a surge. Dates on marine material (shells) both from within and external to the moraine suggest that its time of emplacement was roughly 11,000 years ago, well after the beginning of the Champlain Sea Episode, but still possibly correlative with the Valders event of the Lake Michigan area. 相似文献
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Phase equilibria modelling coupled with U–Pb zircon and monazite ages of garnet–cordierite gneiss from Vallikodu Kottayam in the Kerala Khondalite Belt,southern India are presented here.The results suggest that the area attained peak P–T conditions of^900C at 7.5–8 kbar,followed by decompression to 3.5–5 kbar and cooling to 450–480C,preserving signatures of the partial melting event in the field of high to ultra-high temperature metamorphism.Melt reintegration models suggest that up to 35%granitic melt could have been produced during metamorphism at^950C.The U–Pb age data from zircons(~1.0–~0.7 Ga)and chemical ages from monazites(~540 Ma and^941 Ma)reflect a complex tectonometamorphic evolution of the terrain.The^941 Ma age reported from these monazites indicate a Tonian ultra-high temperature event,linked to juvenile magmatism/deformation episodes reported from the Southern Granulite Terrane and associated fragments in Rodinia,which were subsequently overprinted by the Cambrian(~540 Ma)tectonothermal episode. 相似文献
3.
Lee S. Elson 《地球物理与天体物理流体动力学》2013,107(1):319-323
Abstract This work describes the development of a diagnostic model designed to deduce characteristics of the mean circulation of a portion of the upper atmosphere of Venus. The model will use remotely sensed, global scale temperatures and solves momentum and mass flux equations. The solutions are dependent on externally specified, and inexactly known parameters. 相似文献
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Rebecca A. W. Elson Steinn Sigurdsson Melvyn Davies Jarrod Hurley & Gerard Gilmore 《Monthly notices of the Royal Astronomical Society》1998,300(3):857-862
We determine the binary star fraction as a function of radius in NGC 1818, a young rich cluster in the Large Magellanic Cloud, using Hubble Space Telescope images in bands F336W (∼ U ) and F555W (∼ V ). Our sample includes binaries with M primary ∼ 2–5.5 M⊙ and M secondary ≳ 0.7 Mprimary . The binary fraction increases towards the cluster centre, from ∼ 20 ± 5 per cent in the outer parts, to ∼ 35 ± 5 per cent inside the core. This increase is consistent with dynamical mass segregation and need not be primordial. We compare our results with expectations from N -body models, and discuss the implications for the formation and early evolution of such clusters. 相似文献
6.
R. A. Johnson S. F. Beaulieu G. F. Gilmore J. Hurley B. X. Santiago N. R. Tanvir R. A. W. Elson † 《Monthly notices of the Royal Astronomical Society》2001,324(2):367-380
We present colour–magnitude diagrams for two rich (≈104 M⊙ ) Large Magellanic Cloud star clusters with ages ≈107 yr, constructed from optical and near-infrared data obtained with the Hubble Space Telescope . These data are part of an HST project to study LMC clusters with a range of ages. In this paper we investigate the massive star content of the young clusters, and determine the cluster ages and metallicities, paying particular attention to Be-star and blue-straggler populations and evidence of age spreads. We compare our data with detailed stellar-population simulations to investigate the turn-off structure of ≈25 Myr stellar systems, highlighting the complexity of the blue-straggler phenomenon. 相似文献
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Surendra P. Verma Sanjeet K. Verma Elson P. Oliveira 《International Geology Review》2015,57(11-12):1365-1388
Fifty-five new multi-dimensional diagrams, mostly based on log-ratio transformations, were used to decipher tectonic settings for 17 cases of Precambrian belts in Canada, the USA, Poland, Finland, Jordan, Democratic Republic of Congo and Zambia, China, and India. The results of different sets of diagrams for basic-ultrabasic, intermediate, and acid magmas were generally internally consistent. Possible reasons for some inconsistencies may be related to the use of a sample group of mixed ages because of their uncertainties, extreme element mobility caused by metamorphism especially of high-grade type, analytical data quality, different petrogenetic processes for basic to acid magmas such as mantle versus crustal origin, and some deficiencies that still exist in the multi-dimensional diagrams. To partly overcome the last problem, one new multi-dimensional diagram is proposed and used to discriminate mid-ocean ridge and oceanic plateau settings. 相似文献
8.
Sanjeet K. Verma Elson P. Oliveira Surendra P. Verma 《International Geology Review》2015,57(11-12):1566-1581
Multidimensional discrimination diagrams (2006–2011) for basic and ultrabasic igneous rocks were applied to Precambrian rock suites from the Amazonian and São Francisco cratons, and the Tocantins Province, Brazil, to infer their possible tectonic settings. The chosen study cases in the Amazonian craton include the ca. 3.0 Ga metabasalts of the Identidade greenstone belt, 1.87–1.80 Ga Parauapebas anorogenic basalt-rhyolite dikes, 1.86–1.82 Ga Rio Branco anorogenic gabbro-basalt association, ca. 1.76–1.74 Ga Aripuanã and Teles Pires intracratonic basalt-felsic volcanic associations, and 1.76–1.74 Ga Jamari and 1.60–1.53 Ga Serra da Providência arc-related gabbroic rocks. In the São Francisco craton, we selected 1.48 Ga arc-related amphibolites of the Rio Capim greenstone belt, continental mafic dikes of Uauá (2.6 Ga), Curaçá and Chapada Diamantina (1.5 Ga), and Espinhaço (ca. 1.0 Ga). In the Tocantins Province, ca. 3.0 Ga komatiites associated with oceanic basalts of the Crixás and Guarinos greenstone belts were studied. The application of the diagrams generally provided consistent results with the authors’ proposed tectonic settings based on field relationships and geochemical data. The exceptions are some within-plate (continental) mafic dikes and basalts for which our diagrams do not work well. For comparison, we also used two ternary and two bivariate traditional discrimination diagrams for the data from the Amazonian craton, whose results were poorer than the newer multidimensional diagrams. 相似文献
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Juliana Finoto Bueno Elson Paiva Oliveira Neal J. McNaughton Jorge Henrique Laux 《Gondwana Research》2009,15(1):86-97
The Sergipano Belt is the outcome of collision between the Pernambuco–Alagoas Massif and the São Francisco Craton during Neoproterozoic assembly of West Gondwana. Field relationships and U–Pb geochronology of granites intruded in garnet micaschists of the Macururé Domain are used to constrain the main collisional event (D2) in the belt. The granites are divided into two groups, the pre-collisional granites (pre- to early-D2) and the syn-collisional granites (syn- to tardi-D2), the latter were emplaced as sheets along the S2 axial plane foliation or they were collected at the hinge zones of F2 folds. A U–Pb SHRIMP zircon age of 628 ± 12 Ma was obtained for the pre-collisional Camará tonalite. Two U–Pb TIMS titanite ages were obtained for the syn-collisional granites, 584 ± 10 Ma for the Angico granite and 571 ± 9 Ma for the Pedra Furada granite, and these ages are close to the garnet-whole rock Sm–Nd isochron of 570 Ma found for the peak of metamorphism in the Sergipano Belt. The ages of the Camará tonalite (628 Ma) and the Pedra Furada granite (571 Ma) mark respectively the maximum age for beginning of the D2 event and minimum age for the end in the Macururé Domain. Using these ages, the main Neoproterozoic D2 collisional event has been in operation in the Sergipano Belt for at least 57 million years. Correlation with coeval granitoids farther north in the Borborema Province indicate that while in the Sergipano Belt the syn-D2 granites (ca. 590–570 Ma) were emplaced under compression, in the Borborema Province they emplaced under extensional conditions related to regional strike-slip shear zones. These contrasting emplacement settings for contemporaneous Neoproterozoic granitoids are explained by a combination of continent–continent collision and extrusion tectonics. 相似文献
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Comparisons are made between observations of spatial variations in the thermal emission from Venus obtained with ground-based telescopes and those from spacecraft. In particular, we concentrate on measurements of solar-related structure at low and mid-latitudes, limb-darkening, and on the high-contrast polar structure. We conclude that (1) the solar-related emission is predominantly wavenumber 2, although it contains a significant diurnal component; (2) the relative amplitudes of the semidiurnal and diurnal components vary with latitude; (3) thermally excited temperature waves or, alternatively, solar-driven vertical motions of the cloud top are better able to account for the magnitude of the solar-locked emission than brightness temperature contrasts resulting from variations in aerosol microphysical properties; (4) the equatorial limb-darkening shows the top of the main cloud to be diffuse and approximately uniformly mixed with the gas; (5) polar collars are persistent at least for several months but disappear on occasion; and (6) collars have been observed at both poles simultaneously, but whether simultaneous appearance is the exception or the rule is still in question. 相似文献