The geothermal regime of the northern Yukon and Mackenzie delta regions of northwest Canada — studies of two regional profiles     

F. W. Jones  J. A. Majorowicz  J. Dietrich 《Pure and Applied Geophysics》1988,127(4):641-658

Temperature data from deep petroleum exploration wells and thermal conductivity estimates based on net rock analysis data have been used to make terrestrial heat flow estimates along two profiles across the sedimentary strata of the Mackenzie Delta, northern Yukon, and offshore Beaufort Sea regions.Both profiles exhibit low heat flow values that range from 34 mWm^–2 to 58 mWm^–2, and little change occurs over large distances in the continental part of the area. Low heat flow values (<40 mWm^–2) occur in the Beaufort-Mackenzie Basin and Rapid Depression, both of which are areas of thick successions of Cretacecus and Tertiary clastic sedimentary strata. High heat flow values of almost 80 mWm^–2 occur to the south in the Taiga Nahoni Foldbelt and values as high as 60 mWm^–2 are indicated along the Aklavik Arch Complex, northeast of Aklavik.The regional variations of effective thermal conductivity are insufficient to account for the heat flow variations along the profiles, and so these may indicate deep radiogenic or other heat sources.  相似文献   

楚科奇海-加拿大海盆表层沉积物中的氨基酸     

王奎  陈建芳  金海燕  金明明  李宏亮  张海生 《沉积学报》2008,26(4):661-669

对2003年中国第二次北极科学考察所获得的部分表层沉积物样品进行了总水解氨基酸(THAA)、氨基糖(HA)的测定。不同区域氨基酸主要成分不同,楚科奇海站位的氨基酸主要成分为甘氨酸(Gly)、谷氨酸(Glu),位于加拿大海盆的B80、B11、P27站THAA的主要成分为丝氨酸(Ser)。沉积物的总有机碳(TOC)、总氮(TN)、THAA、HA含量等特征随区域不同有较大差别,白令海峡的BS11站TOC、HA含量最低,加拿大海盆的B80站THAA、TN含量最低。楚科奇海R03站TOC、TN为最高,THAA在R11含量达最大值,HA在楚科奇海台的P11站最高。初步讨论了楚科奇海—加拿大海盆表层沉积物中氨基酸的空间分布,根据氨基酸选择性降解和主成份分析结果引入DI”指标,并对七个站位表层沉积物有机质新鲜程度进行了比较,新鲜度由大至小顺序为C15>BS11>R11>S11>P11>R03>B80,这与表层沉积物来源、水动力条件等有关,由此推测楚科奇海陆架、白令海峡沉积物有机质较楚科奇海台、加拿大海盆较为新鲜。  相似文献   

Late Neoproterozoic A-type granites in the northernmost Arabian-Nubian Shield formed by fractionation of basaltic melts     

G.H. Jarrar  W.I. Manton  D. Zachmann 《Chemie der Erde / Geochemistry》2008,68(3):295-312

Geochemical, isotopic and age constraints support a comagmatic origin for Ghuweir Mafics and the Feinan A-type granites. The two rocks types, named collectively in this paper as the Feinan Ghuweir Magmatic Suite (FGMS), formed between 556 and 572 Ma ago according to Rb-Sr whole-rock dating. FGMS has low Sr initial ratios, which preclude a significant contribution of much older crust in the magma genesis.The FGMS has a wide range of silica contents, with a gap at 55-65 wt% SiO₂. It has a transalkaline to alkaline character; belongs to the medium to high K calc-alkaline series; it ranges from metaluminous to mildly peraluminous character and belongs to the alkali and alkali-calcic series. The Feinan granites and the Ghuweir rhyolites and rhyodacites are classified as A-type granites and belong to group A2 of Eby [Eby, N.G., 1992. Chemical subdivision of the A-type granitoids: petrogenetic and tectonic iplications. Geology 20, 641-644].According to geochemical modeling the Ghuweir Mafics were derived from a subduction modified lithospheric mantle by 10% batch modal partial melting of a phlogopite-bearing spinel lherzolite. The intra-suite geochemical variations can be ascribed to fractional crystallization of olivine, pyroxene, and plagioclase. The accumulation of apatite in the most evolved samples is responsible for the high concentrations of REE.The Feinan granites and the Ghuweir rhyolites and rhyodacites were derived from the mafic magma by the fractional crystallization of ≈78% of the original magma to the mineral assemblage olivine+pyroxene+plagioclase+magnetite. The intra-suite geochemical variations in the Feinan A-type granites are due to the fractional crystallization of the mineral phases: amphibole +Na and K-feldspar+apatite +magnetite+zircon+allanite.The FGMS correlates with time-equivalent rocks in many parts of the Arabian-Nubian Shield and the surrounding areas.  相似文献   

Stuck in transition? Exploring the spaces of employment training for youth with intellectual disability     

Stephanie Butcher 《Geoforum》2008,39(2):1079-1092

This paper is concerned with the experiences of young adults with intellectual disabilities as they transition from high school in search of paid employment. The experiences of people with intellectual disability remain under-researched within geography. We use qualitative techniques to examine the experiences of six young adults with intellectual disabilities. Data are drawn from interviews with the youth themselves, their parents, and employers, as well as from participant observation at an employment training program for the intellectually disabled. While the primary goal of the youth and their parents was to make a transition to competitive paid work, a lack of transition planning, a shortage of appropriate opportunities and other factors meant the youth spent considerable time in ‘transitional spaces’ such as the vocational training centre, sheltered workshop, and supported employment placements. While these spaces are organized around an explicitly economic goal of augmenting the youth’s employability, they can play a critical role as spaces for social interaction and meaningful activity outside the home. Study findings point to the importance of moving beyond paid employment as the core of a successful transition to consider a broader goal of ‘meaningful activity’.  相似文献   

Analysis of snow-vegetation interactions in the low Arctic-Subarctic transition zone (northeastern Canada)     

Bruno-Charles Busseau  Alain Royer  Alexandre Roy  Alexandre Langlois  Florent Domine 《自然地理学》2017,38(2):159-175

Abstract

Recent studies have shown that northern vegetation has been growing in relation to a warming climate over the last four decades, especially across the transition zone between tundra and taiga. Shrub growth affects snow properties and the surface energy budget, which must be better studied to quantify shrub-snow-climate feedbacks. The objective of this research is to improve the characterization of the impact of shrubs on snow evolution, from its accumulation to its melt, using in-situ and satellite measurements. The research is presented for the Umiujaq site, Nunavik, representative of the low Arctic–Subarctic transition zone. Snow depth, measured along numerous transects spanning different land cover types is found to increase by a factor 2.5–3 between tundra and forest, while snow density decreases. This illustrates the trapping effect of vegetation well. Complementary, continuous snow depth measurements using weather stations from two sites (tundra with low shrubs and a small clearing with shrubs within the forest) show different site-dependent behaviors. Spatial analysis from high-resolution Pleiades images combined with Landsat (Normalized Difference Snow Index) and MODIS (Fractional Snow Cover) images suggest a slight delay in melt over open and dense forest areas compared to tundra and dense high shrubs.  相似文献   

Ten best practices to strengthen stewardship and sharing of water science data in Canada     

Bhaleka D. Persaud  Krysha A. Dukacz  Gopal C. Saha  Amber Peterson  Laleh Moradi  Stephen O'Hearn  Erin Clary  Juliane Mai  Michael Steeleworthy  Jason J. Venkiteswaran  Homa Kheyrollah Pour  Brent B. Wolfe  Sean K. Carey  John W. Pomeroy  Chris M. DeBeer  James M. Waddington  Philippe Van Cappellen  Jimmy Lin 《水文研究》2021,35(11):e14385

Water science data are a valuable asset that both underpins the original research project and bolsters new research questions, particularly in view of the increasingly complex water issues facing Canada and the world. Whilst there is general support for making data more broadly accessible, and a number of water science journals and funding agencies have adopted policies that require researchers to share data in accordance with the findable, accessible, interoperable, reusable (FAIR) principles, there are still questions about effective management of data to protect their usefulness over time. Incorporating data management practices and standards at the outset of a water science research project will enable researchers to efficiently locate, analyse and use data throughout the project lifecycle, and will ensure the data maintain their value after the project has ended. Here, some common misconceptions about data management are highlighted, along with insights and practical advice to assist established and early career water science researchers as they integrate data management best practices and tools into their research. Freely available tools and training opportunities made available in Canada through Global Water Futures, The Gordon Foundation DataStream, the Digital Research Alliance of Canada Portage Network, Compute Canada, and university libraries, among others are compiled. These include webinars, training videos, and individual support for the water science community that together enable researchers to protect their data assets and meet the expectations of journals and funders. The perspectives shared here have been developed as part of the Global Water Futures programme's efforts to improve data management and promote the use of common data practices and standards in the context of water science in Canada. Ten best practices are proposed that may be broadly applicable to other disciplines in the natural sciences and can be adopted and adapted globally.  相似文献   

Paleoproterozoic granitoids from the northern limit of the Archean Amapá block (Brazil), southeastern Guyana Shield: Pb–Pb evaporation in zircons and Sm–Nd geochronology     

《Journal of South American Earth Sciences》2013

Central Amapá, northern Brazil is located at the boundary between: (a) a northern Paleoproterozoic domain, consisting mainly of granite-greenstones terrains and (b) a southern Archean continental block (Amapá block), including an Archean basement reworked during the Transamazonian orogeny (2.26–1.95 Ga). Field investigations, Pb–Pb zircon and Sm–Nd whole rock geochronology supported by geochemical data on granitoids brought further constraints on Paleoproterozoic crustal growth in the southeastern Guyana Shield. A first magmatic episode, dated at 2.26 Ga, is marked by the crystallization of metaluminous low-K tholeiitic tonalites and quartz-diorites, which geochemical affinity with volcanic arc and association with T-MORB amphibolites suggest that they formed in a back-arc basin – island arc system. This event is coeval to the oceanic stage registered in French Guyana during the Eorhyacian (2.26–2.02 Ga). A second magmatic episode is represented by peraluminous, medium- to high-K calc-alkaline tonalite and granodiorite, which revealed some similarities with Mesorhyacian TTG rocks of French Guyana. For granitoids of both episodes, T_DM and ε_Nd values indicate the contribution of some Archean crustal component, probably by assimilation or contamination. This second magmatic episode occurred at 2.10 Ga, indicating that the period of successive calc-alkaline magmatic arcs formation may have extended until the Neorhyacian. Meanwhile, during this time, tectonic accretion by collision of the newly formed continental landmass was the prevailing process in French Guyana. The latter magmatic episode, even though poorly constrained, was registered around 2.08–2.02 Ga in central Amapá. It corresponds to the emplacement and solidification of high-K collisional granitoids, produced by partial melting of the Archean continental crust, as testified by the Archean T_DM, inherited Pb–Pb zircon ages and strongly negative ε_Nd values. Our results point toward the existence of a protracted episode of crustal growth during the Neorhyacian in the southeastern Guyana Shield. This episode has been predominantly driven by magmatic arc accretion during, at least, 160 My, along the period of 2.26–2.10 Ga. This cycle ended with diachronic closure of the oceanic basins and arc–continent collision.  相似文献   

Microstructural analyses of a Middle Pliocene till from the James Bay Lowlands,Canada—evidence of “potential” fast ice streaming     

John Menzies  Cunhai Gao  Charles Kodors 《Proceedings of the Geologists' Association. Geologists' Association》2013

Sediment from the Attawapiskat area near James Bay, Northern Ontario was sampled for micromorphological analyses. The sediment is a glacial diamicton (till) of subglacial origin. The till contains entrained and scavenged sediments of proglacial and/or subglacial glaciofluvial/glaciolacustrine origin from a subglacial deforming layer that was emplaced due to both stress reduction and/or porewater dissipation. Evidence of porewater escape, clay translocation and other microstructures all point to emplacement under active subglacial bed deformation. The limited number of edge to edge (ee) grain crushing events, however, point to lower stress levels than might anticipated under a thin fast ice lobe of the James Bay during the Middle Pliocene. Microstructures of Pleistocene tills were quantitatively compared with the Attawapiskat till and the limited number of ee events at Attawapiskat further highlighted that grain to grain contact was curtailed possibly due to high till porosity, high porewater pressures and low strain rates or alternatively due to a high clay matrix component reducing grain crushing contact events. It is suggested that this Middle Pliocene till may be indicative of sediments emplaced under ice lobe surging conditions or fast ice stream subglacial environments. This proposal has significant implications for the glaciodynamics of this part of the Middle Pliocene James Bay lobe. This research highlights a crucial link between subglacial conditions, till microstructural analyses and glaciodynamics.  相似文献   

Evolution of Population Densities: Five Canadian Cities, 1971-20011     

《Urban geography》2013,34(7):616-638

This article presents new methods for comparative analysis of patterns of gross population density, and employs them in five Canadian metropolitan areas. By comparing changes in levels and patterns in the 1971-2001 period, assessments are made of the macro-level impacts of policies relating to densification and re-densification, and of how such impacts vary by city size. Three comparative techniques are employed. The first uses location quotients to map densities for census tracts in urbanized areas. A second approach defines central and peripheral density clusters, and analyzes their mapped patterns. The third method employs local indices of spatial autocorrelation (LISA) to detect locally significant "hotspots," particularly suburban outliers of higher density. Results suggest that in the suburbs homogenously low-density areas are in decline, while both high-density and heterogeneous areas are increasingly evident.  相似文献   

BEFOLKMNGS- OG ERHVERVSUDVIKLINGEN PÅ RØMØ 1950–70     

BODIL ENGELL M.Sc. 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(1):63-67

Engell. Bodil, 1977: Befolknings- og erhvervsudviklingen på Rømø 1950–70. Geografisk Tidsskrift 76: 63–67. København juni 1, 1977.

The general trend of unequal development between rural and urban intensifies on small islands. The development on the island of Rømø has further a special trend because of its intermediate position caused by the construction of the road-dam to Rømø, opened 1949. Furthermore, the recreational potential of the island and the special location close to the Danish-German border is of importance.  相似文献