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81.
Allan M. Findlay David Short Aileen Stockdale 《Applied geography (Sevenoaks, England)》2000,20(4):257
An economic audit of the labour-market impact of in-migration to rural Scotland provides evidence that migrants make rather than take jobs. A survey of 689 households in six study areas selected from across rural Scotland provides the basis for examining the scale and nature of job growth associated with in-migration. Job multipliers are calculated by migrant type and by economic sector. 相似文献
82.
1 Introduction The Gaojiacun intrusive complex is one of the numerous ultramafic-mafic intrusions in Sichuan Province of China. It was mapped during the 1970s and studied mainly by Chinese scientists (e.g. Geological Team 106, 1975; Shen et al., 1986, 1989; CGGJC, 1986; Yang et al., 1993; Li et al., 1995; Shen et al., 2003; Zhu et al., 2004a). Since the year 2000, China has become one of the largest PGE consumers. While the country can produce only less than 1 ton PGE/year, the Chin… 相似文献
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Mammalian fossils recently discovered near Fulbeck in Lincolnshire, include abundant hippopotamus, suggesting an Ipswichian date for the Fulbeck Sand and Gravel (new name). These deposits mark a former course of the River Witham; clasts indicate derivation from outcrops of Jurassic rocks and chalky till to the south and south-east. The relationship of the Fulbeck Sand and Gravel to the terrace deposits of the River Trent necessitates a revised chronology. The Balderton Sand and Gravel (new name), laid down by the Trent along its former course to the Lincoln Gap, is shown to be older than the Ipswichian Fulbeck Sand and Gravel, and was probably deposited during the Wolstonian Stage. The Eagle Moor Sand and Gravel (new name), probably glaciofluvial outwash from the chalky tills of the region, is considerably older than the Balderton Sand and Gravel and, together with the tills, is assigned to the early part of the Wolstonian, or the Anglian glacial Stage. It is suggested that the Balderton and Eagle Moor terraces equate with the lower and upper facets of the composite Hilton Terrace of the Middle Trent. 相似文献
86.
Over recent months the Ordnance Survey, Britain's national mapping agency, has changed the way in which it uses photogrammetry to update its large scales topographic database. The nature of the database itself has also changed during the same period, as the concept of a "Digital National Framework" has developed. This paper describes the Digital National Framework, the topographic data captured by Ordnance Survey within this framework and the capture methods currently used. The paper concentrates on the use of photogrammetry in the update process, describing the methods of the past, the methods currently in production, and the outlook for photogrammetry within the Ordnance Survey in future. 相似文献
87.
Joel Massmann R. Allan Freeze Leslie Smith Tony Sperling Bruce James 《Ground water》1991,29(4):536-548
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Hydrogeological Decision Analysis: 1. A Framework 总被引:6,自引:0,他引:6
R. Allan Freeze Joel Massmann Leslie Smith Tony Sperling Bruce James 《Ground water》1990,28(5):738-766
90.
Mixing of magmas from enriched and depleted mantle sources in the northeast Pacific: West Valley segment,Juan de Fuca Ridge 总被引:1,自引:0,他引:1
Brian L. Cousens James F. Allan Matthew I. Leybourne R. L. Chase Nancy Van Wagoner 《Contributions to Mineralogy and Petrology》1995,120(3-4):337-357
The 50 km-long West Valley segment of the northern Juan de Fuca Ridge is a young, extension-dominated spreading centre, with volcanic activity concentrated in its southern half. A suite of basalts dredged from the West Valley floor, the adjacent Heck Seamount chain, and a small near-axis cone here named Southwest Seamount, includes a spectrum of geochemical compositions ranging from highly depleted normal (N-) MORB to enriched (E-) MORB. Heck Seamount lavas have chondrite-normalized La/Smcn0.3, 87Sr/86Sr=0.70235–0.70242, and 206Pb/204Pb=18.22–18.44, requiring a source which is highly depleted in trace elements both at the time of melt generation and over geologic time. The E-MORB from Southwest Seamount have La/Smcn1.8, 87Sr/86Sr=0.70245–0.70260, and 206Pb/204Pb=18.73–19.15, indicating a more enriched source. Basalts from the West Valley floor have chemical compositions intermediate between these two end-members. As a group, West Valley basalts from a two-component mixing array in element-element and element-isotope plots which is best explained by magma mixing. Evidence for crustal-level magma mixing in some basalts includes mineral-melt chemical and isotopic disequilibrium, but mixing of melts at depth (within the mantle) may also occur. The mantle beneath the northern Juan de Fuca Ridge is modelled as a plum-pudding, with plums of enriched, amphibole-bearing peridotite floating in a depleted matrix (DM). Low degrees of melting preferentially melt the plums, initially removing only the amphibole component and producing alkaline to transitional E-MORB. Higher degrees of melting tap both the plums and the depleted matrix to yield N-MORB. The subtly different isotopic compositions of the E-MORBs compared to the N-MORBs require that any enriched component in the upper mantle was derived from a depleted source. If the enriched component crystallized from fluids with a DM source, the plums could evolve to their more evolved isotopic composition after a period of 1.5–2.0 Ga. Alternatively, the enriched component could have formed recently from fluids with a less-depleted source than DM, such as subducted oceanic crust. A third possibility is that enriched material might be dispersed as plums throughout the upper mantle, transported from depth by mantle plumes. 相似文献