A sample of 6C radio sources designed to find objects at redshift z > 4 — I. The radio data     

Katherine M.Blundell  SteveRawlings  Stephen A.Eales  Gregory B.Taylor  Alistair D.Bradley 《Monthly notices of the Royal Astronomical Society》1998,295(2):265-279

We describe the selection of a sample of 34 radio sources from the 6C survey from a region of sky covering 0.133 sr. The selection criteria for this sample, hereafter called 6C*, were chosen to optimize the chances of finding radio galaxies at redshift z  > 4. Optical follow-up observations have already led to the discovery of the most distant known radio galaxy at z  = 4.41. We present VLA radio maps and derive radio spectra for all the 6C* objects.  相似文献   

A radio-jet–galaxy interaction in 3C 441     

Mark Lacy  Steve Rawlings  Katherine M. Blundell  & Susan E. Ridgway 《Monthly notices of the Royal Astronomical Society》1998,298(4):966-976

Multiwavelength imaging and spectroscopy of the z =0.708 radio galaxy 3C 441 and a red aligned optical/infrared component are used to show that the most striking aspect of the radio–optical 'alignment effect' in this object is due to the interaction of the radio jet with a companion galaxy in the same group or cluster. The stellar population of the red aligned continuum component is predominantly old, but with a small post-starburst population superposed, and it is surrounded by a low-surface-brightness halo, possibly a face-on spiral disc. The [O iii ] 500.7/[O ii ] 372.7 emission-line ratio changes dramatically from one side of the component to the other, with the low-ionization material apparently having passed through the bow shock of the radio source and been compressed. A simple model for the interaction is used to explain the velocity shifts in the emission-line gas, and to predict that the ISM of the interacting galaxy is likely to escape once the radio source bow shock has passed through. We also discuss another, much fainter, aligned component, and the subarcsecond-scale alignment of the radio source host galaxy. Finally, we comment on the implications of our explanation of 3C 441 on theories for the alignment effect.  相似文献   

Assessing Ar transport paths and mechanisms in the McClure Mountains hornblende     

I. M. Villa  B. Grobéty  S. P. Kelley  R. Trigila  R. Wieler 《Contributions to Mineralogy and Petrology》1996,126(1-2):67-80

 We have investigated the mechanisms and pathways by which Ar diffuses through the McClure Mountains hornblende (ferroan pargasite), selected as a good example of material normally dated during Ar-Ar studies. A coarse-grained hornblende separated from the same hand specimen as the MMhb-1 age standard was subjected to a hydrothermal cold-seal bomb experiment and characterized by TEM. Heated and unheated crystals were subjected to four different ³⁹Ar/⁴⁰Ar dating extraction techniques: conventional stepwise heating, infra-red laser spot, ultra-violet laser depth profiling, and closed-system stepwise etching. The stepwise heating age spectrum reproduces the features often interpreted as resulting from a concentric diffusive zonation, but the other three techniques yield results that are not compatible with such a simple picture. The IR laser data indicate that the dependence of laboratory Ar loss on grain size, predicted by Fickian diffusion, is at best poor and instead is related mainly to mineralogical variations. The depth profiles show the importance of planar zones (spaced between <1 and >150 μm from TEM evidence) in providing fast pathways for inward diffusion of atmospheric Ar from the capsule, but showed no evidence of diffusive profiles in the bulk of the hornblende lattice. The data from closed system stepwise etching underscore the role of zones rich in planar defects both for Ar loss and for nucleation of etching. The age spectra obtained by stepwise heating suffer from the differential breakdown of impurity phases, whose presence can be diagnosed with several isotope correlation plots; particularly revealing are Cl-Ca-K trends. In addition to the problems of mineral decomposition during in-vacuo laboratory degassing, an equally important decomposition occurs during many hydrothermal experiments which, combined with problems of mineral purity, have led to an overestimation of the rate of argon diffusion in hornblende. The response of hornblende to thermal disturbance in a hydrothermal environment can be every bit as complex as breakdown in vacuo. Laboratory experiments on bulk samples have not succeeded in quantitatively constraining volume diffusion. Received: 12 October 1995 / Accepted: 11 July 1996  相似文献   

Heavy metals in Chukchi Sea sediments as compared to selected circum-arctic shelves   总被引：7，自引：0，他引：7  

A. S. Naidu  A. Blanchard  J. J. Kelley  J. J. Goering  M. J. Hameedi  M. Baskaran 《Marine pollution bulletin》1997,35(7-12):260-269

Surficial sediments from 31 stations on the northeastern Chukchi Sea, Alaskan Arctic were analysed by AAS and ICP-AES for Si, Al, Fe, Mn, Cu, Cr, Co, Zn, Ni and V. The metal concentrations are related to the sediment granulometry and show no correlations with organic carbon. Presumably all the heavy metals, except Cr and Co, are either adsorbed on clays and/or coprecipitated with ferrimanganic hydroxide. Cobalt is partitioned in an unknown mineral phase within the sand fraction.

Comparison of the heavy metal concentrations in muds of the Chukchi Sea with those of the high arctic shelves of Russia, East Greenland and the Beaufort Sea shows relatively lower levels of most metals in the Chukchi. Presumably these disparities are related to regional differences in sediment chemistries inherited from natural terrigenous sources rather than to any enhanced pollution in the non-Chukchi areas.

It is suggested that the concentrations and accumulation rates of the heavy metals reported here can serve as reliable baselines to monitor metal pollution in the Chukchi Sea.  相似文献   

Post-collision magmatism and tectonics in northwest Anatolia   总被引：1，自引：0，他引：1  

Nigel B. W. Harris  Simon Kelley  Aral I. Okay 《Contributions to Mineralogy and Petrology》1994,117(3):241-252

A suite of biotite-hornblende granodiorite intrusions has been emplaced into blueschist-facies metasediments in northwest Anatolia, following collision between two continental margins, now represented by the Tavanli and Sakarya zones. The ⁴⁰Ar/³⁹Ar ages of phengites and glaucophanes from the blueschists, metamorphosed under unusually high P-low T conditions (P=20±2 kbar, T=430±30° C), suggest that metamorphism apparently occurred over a period spanning at least 20 Ma from 108 to 88 Ma. Post-tectonic granodiorites were emplaced during the Eocene (53 to 48 Ma) resulting in a cordierite and andalusite-bearing thermal aureole, indicative of pressures of 3 kbar. Trace-element systematics of the granodiorites are consistent with a derivation either from mantle-derived magmas by fractional crystallisation in shallow magma chambers, or from anatexis of crustal lithologies of internediate composition at pressures <10 kbar. The preservation of high P-low T assemblages in the blueschists together with the range of ages determined for blueschist-facies metamorphism are indicative of rapid exhumation of delaminated fragments from a subducted continental margin. However decompression melting of the crust is unlikely to have been a significant cause of magmatism, both because exhumation of the blueschists from deep crustal levels predated magmatism by at least 25 Ma, and because of the small melt fraction (<0.1) that may be generated in crustal lithologies by this process. Melting in the mantle wedge is required either to generate a primary melt for the derivation of magmas of intermediate composition or to provide an advective heat source for crustal melting. The cause of melt formation in the upper mantle may be related to the termination of subduction following collision during the Mid-Eocene.  相似文献   

Syngenetic inclusions of yimengite in diamond from Sese kimberlite (Zimbabwe) — evidence for metasomatic conditions of growth     

G.P. Bulanova  E. Muchemwa  D.G. Pearson  B.J. Griffin  S.P. Kelley  S. Klemme  C.B. Smith 《Lithos》2004,77(1-4):181-192

Syngenetic inclusions of yimengite K (Cr, Ti, Mg, Fe, Al)₁₂O₁₉, a potassium member of the magnetoplumbite mineral group, have been recorded in an octahedral macrodiamond from the Sese kimberlite (50 km south of Masvingo, Zimbabwe). One yimengite inclusion carries lamellae of chromite suggesting peridotitic diamond paragenesis. The diamond and inclusions were studied in situ in a plate polished parallel to (011). Cathodoluminescence (CL) imaging has shown blue colour and octahedral zonation of the diamond, lack of cracks and the location of five yimengites in different growth zones. Nitrogen (N) contents (at. ppm) in the diamond determined by Fourier transform infrared spectroscopy (FTIR) steadily decrease from 576 (core) to 146 (rim). N aggregation (%1aB) is correspondingly 40% in the core and 30% in the rim. Hydrogen (H) content is high in the core, moderate in the intermediate and very high in the rim zones. Four yimengites were dated using the laser ⁴⁰Ar/³⁹Ar method. Three inclusions yielded total gas ages that agree with, or are younger than, or within error of, the Sese kimberlite eruption age (538±11 Ma) but may be compromised by gas loss. One inclusion, with the highest tapped interface gas yield, gave a total gas age of 892±21 Ma that is a likely minimum yimengite age. Time–T °C constraints from N aggregation systematics give a range of possible ages from kimberlite eruption date back to Archean and do not resolve the variable results of the ⁴⁰Ar/³⁹Ar dating. Compared with the published chemistry of yimengite from kimberlites, inclusions from the Sese diamond contain higher Al, Mg, and Sr and have lower concentration of Fe³⁺. The chondrite-normalised REE pattern of the yimengite shows enrichment in LREE and depletion in HREE, but LREE/HREE fractionations are lower than for lindsleyite–mathiasite series mantle titanates and rather similar to the REE concentrations in kimberlite and lamproite rocks. It is suggested that Sese yimengite formed in the lithospheric mantle from metasomatism of chrome spinel by a fluid rich in Ti, K, Ba and LREE.  相似文献   

植被和气候对阿拉斯加和加拿大北部北极苔原地区多年冻土活动层厚度的影响   总被引：2，自引：4，他引：2  

Alexia M. Kelley  Howard E. Epstein  Donald A. Walker 《冰川冻土》2004,26(Z1):269-274

The active layer is the top layer of permafrost soils that thaws during the summer season due to increased ambient temperatures and solar radiation inputs. This layer is important because almost all biological activity takes place there luring the summer. The depth of active layer thaw is influenced by climatic conditions. Vegetation has also been found to have a strong impact on active layer thaw, because it can intercept incoming radiation, thereby insulating the soil from ambient conditions. In order to look at the role of vegetation and climate on active layer thaw, we measured thaw depth and the Normalized Difference Vegetation Index (NDVI; a proxy for aboveground plant biomass) along a latitudinal temperature gradient in arctic Alaska and Canada. At each site several measurements of thaw and NDVI were taken in areas with high amounts of vegetation and areas with little to no vegetation. Results show that the warmest regions, which had the greatest levels of NDVI, had relatively shallow thaw depths, and the coldest regions, which had the lowest levels of NDVI, also had relatively shallow thaw depths. The intermediate regions, which had moderate levels of NDVI and air temperature, had the greatest depth of thaw. These results indicate that temperature and vegetation interact to control the depth of the active layer across a range of arctic ecosystems. By developing a relationship to explain thaw depth through NDVI and temperature or latitude, the possibility exists to extrapolate thaw depth over large scales via remote sensing applications.  相似文献   

新疆叶城晚新生代山前盆地演化与青藏高原北缘的隆升--Ⅱ沉积相与沉积盆地演化   总被引：15，自引：0，他引：15  

郑洪波  Chris Powell 《沉积学报》2003,21(1):46-51

叶城盆地属于塔里木盆地的西南坳陷 ,在晚新生代沉积了巨厚的磨拉石建造。盆地的演化具有阶段性 ,反映了西昆仑山不断的隆升。中新世 ,盆地的沉积环境为曲流河和辨状河等河湖相环境 ,到上新世早期变为冲积扇的远端。晚上新世 (～ 3.6 Ma)开始 ,盆地的沉积环境发生了质的变化 ,沉积物以粗颗粒砾岩为主 ,沉积环境为干旱气候条件下的冲 -洪积扇近端。沉积相的变化 ,反映了昆仑山在晚上新世有强烈的隆升。  相似文献   

Late Neogene loess deposition in southern Tarim Basin: tectonic and palaeoenvironmental implications   总被引：2，自引：0，他引：2  

Hongbo Zheng  Chris McA Powell  Katherine Butcher  Junji Cao 《Tectonophysics》2003,375(1-4):49

Uplift of the Tibetan Plateau during the late Cainozoic resulted in a thick apron of molassic sediments along the northern piedmonts of the Kunlun and Altyn Mountains in the southern Tarim Basin. Early Neogene sediments are characterised by sandstone, siltstone and red mudstone, representing floodplain to distal alluvial fan environments. The Early Pliocene Artux Formation consists of medium-grained sandstone and sandy mudstone with thin layers of fine pebbly gritstone. The Late Pliocene to Early Pleistocene Xiyu Formation is dominated by pebble to boulder conglomerate typical of alluvial fan debris flow deposits. Sedimentological investigation, together with grain size and chemical analyses of siltstone bands intercalated with sandstone and conglomerate in the Xiyu and Artux Formations, point to an aeolian origin, suggesting desertic conditions in the Tarim Basin by the Early Pliocene. The onset of aeolian sedimentation in the southern Tarim Basin coincided with uplift of the northern Tibetan Plateau inferred from the lithofacies change from fine-grained mudstone and sandstone to coarse clasts. Tibetan Plateau uplift resulted in the shift of sedimentary environments northwards into the southern Tarim Basin, and could well have triggered the onset of full aridity in the Taklimakan region as a whole.  相似文献   

The chemical composition of fogs and intercepted clouds in the United States     

Jeffrey L. Collett  Jr.  Aaron Bator  D. Eli Sherman  Katharine F. Moore  Katherine J. Hoag  Belay B. Demoz  Xin Rao  Jill E. Reilly 《Atmospheric Research》2002,64(1-4)

Over the past decade, the chemical compositions of fogs and intercepted clouds have been investigated at more than a dozen locations across the United States. Sampling sites have been located in the northeast, southeast, Rocky Mountain, and west coast regions of the US. They include both pristine and heavily polluted locations. Frontal/orographic clouds (warm and supercooled), intercepted coastal stratiform clouds, and radiation fogs have all been examined. Sample pH values range from below 3 to above 7. Major ions also exhibit a wide concentration range, with clouds at some locations exhibiting high sea salt concentrations, while composition at other locations is dominated by ammonium and sulfate or nitrate.  相似文献