Sources for the assessment of British woodland change in the twentieth century     

Charles Watkins 《Applied geography (Sevenoaks, England)》1985,5(2):151-166

After a discussion of the problems of defining woodland for the purpose of survey, the paper goes on to consider the sources available to geographers and others for the study of woodland change in Britain, particularly within the 20th century. The main sources considered are Ordnance Survey maps, aerial photographs and satellite remote sensing, Forestry Commission censuses. Forestry Commission and private estate records, land utilization surveys and agricultural statistics.  相似文献   

The fluid regime of high-temperature metamorphism during granitoid magma genesis   总被引：4，自引：4，他引：4  

J. Clemens  J. Watkins 《Contributions to Mineralogy and Petrology》2001,140(5):600-606

The strong negative correlation between the temperatures and melt H₂O contents of granitoid magmas implies that the crustal melting reactions that produced the magmas were strongly buffered, with T and aH₂O co-varying within a narrow band. This observation can only be explained if the partial melting reactions that created the magmas were either fluid-absent from the outset or evolved toward this condition as melting progressed. Since these melting reactions occur during upper amphibolite- to granulite-facies metamorphism, it is reasonable to conclude that metamorphic events responsible for the generation of granitoid magmas generally occur in the absence of excess pervasive fluid.  相似文献   

Comments on the interpretation of linear magnetic anomalies     

N. D. Watkins 《Pure and Applied Geophysics》1968,69(1):179-192

Summary In response to the recent interpretation of marine magnetic anomalies in terms of the crustal spreading hypothesis, a summary is made of other factors including structural, initial cooling, post cooling, and possible spontaneous processes which may cause at least some of the characters of linear magnetic anomalies. Arguments are developed by presentation ofQ values for 571 specimens from fourteen Icelandic lavas and six dikes, and by theQ value, stability factor, and oxidation variation between the cooling faces of one of these lavas. None of the processes described can alone readily account for the observed symmetry of magnetic anomalies with respect to mid-oceanic ridges, but are presented to encourage examination and development of mechanisms other than geomagnetic polarity changes superimposed on a crustal generating system, as the causes of at least some oceanic magnetic anomalies.  相似文献   

A geomagnetic field reversal time scale back to 13.0 million years before present     

C.G.A. Harrison  Ian McDougall  N.D. Watkins 《Earth and Planetary Science Letters》1979,42(2):143-152

The ages of reversals of the Earth's magnetic field have been dated accurately back to 3.4 m.y. ago. Between this time and the age of the Cretaceous-Tertiary boundary, dates for reversals have been calculated assuming a constant rate of sea-floor spreading in the South Atlantic Ocean. The presence of thick piles of lava flows in Iceland allows us to produce independent evidence for the ages of reversals back to 13.0 m.y. B.P. Because of the extreme regularity of extrusion of these lava flows, the measurement of their magnetic polarity allows us to correlate the lava flows which were extruded during the polarity intervals associated with sea-floor spreading anomalies. The measurement of many K-Ar ages on these lava flows also allows us to compare the ages of reversals assumed by the linear interpolation between the ages of 3.4 m.y. and the Cretaceous-Tertiary boundary at 66.5 m.y., with those suggested by the radiometric dates. We find that in general the assumption of constant spreading has been a good one, but suggest a small change in the ages of reversals, amounting to an increase of about 0.27 m.y. in ages of reversals between 8.5 and 13.0 m.y. ago.  相似文献   

Amsterdam Island,an isolated volcano in the southern Indian ocean     

B. M. Gunn  C. E. Abranson  J. Nougier  N. D. Watkins  A. Hajash 《Contributions to Mineralogy and Petrology》1971,32(2):79-92

Twelve lavas have been sampled on Amsterdam Island, which is an extinct shield volcano located on a transform fault crossing the south-eastern branch of the Indian Ocean rise. Chemical analyses show that the lavas have mainly tholeiitic affinities, ranging from olivine tholeiites to plagioclase basalts with accumulation of bytownite. The high alumina lavas are similar to bytownite cumulates dredged from the Indian Ocean rise, and the low alumina lavas resemble tholeiites of Hawaii. The volcano appears to be in an early stage of evolution from oceanic ridge basalt to an alkaline volcano.  相似文献   

Geochemistry of an oceanite-ankaramite-basalt suite from East Island,Crozet Archipelago   总被引：1，自引：0，他引：1  

Bernard M. Gunn  Ramon Coy-Yll  Norman D. Watkins  Christian E. Abranson  Jacques Nougier 《Contributions to Mineralogy and Petrology》1970,28(4):319-339

The petrology and geochemistry of East Island have been investigated for the first time. The island is a deeply dissected remnant of a Pleistocene shield volcano, one of several emerging from an oceanic rise forming part of the southwest branch of the Indian Ocean ridge system. The lavas form a flat-lying sequence of oceanites, ankaramites, olivine basalts and feldsparphyric basalts, the ankaramites containing 1 cm phenocrysts of diopsidic clinopyroxene. X-Ray fluorescence analyses were made of 43 lavas for the major elements plus Cr, Ni, Rb, Sr, Ba, Pb, and Th and the minerals were analysed by electron microprobe. The elements Mg, Cr, and Ni are strongly concentrated in spinel, olivine and clinopyroxene phases and in the ankaramites and oceanite lavas with maximum concentrations of 18% MgO, 1,000 ppm Cr, 380 ppm Ni, while Al, Ti, K, Rb, Ba, Th, Na, P, Sr concentrate in the groundmass and in the feldspathic and aphyric basalts. The elements Si, Ca, Fe and Mn remain virtually constant throughout the series.Correlations of +0.95 or better exist between the concentrations of elements within the two groups given above, and negative correlations between elements in different groups. The fractionation trends are unique with respect to the constant Al/Ti ratio and K/Sr ratio, but all trends may be reproduced by calculating the effect of subtraction of suitable amounts of chromite, olivine and low Ti clinopyroxene from an alkaline olivine basalt parent. Either fractionation has taken place involving these three phases under low pressure conditions or it is the result of different degrees of partial melting of mantle material.A complex magnesian chrome spinel is found in the ankaramites and is often jacketed by a chromian titanomagnetite. A complete series of intermediate compositions appears to exist between the two end members.  相似文献   

On the structure of geometric positioning information in GPS measurements     

D. Kuang  B. E. Schutz  M. M. Watkins 《Journal of Geodesy》1996,71(1):35-43

The geometric information from observables of the Global Positioning System is analyzed through the eigenvectors of the normal matrix in the positioning estimation problem. The relationship among observability, bias absorption and loss of information in differencing measurements is addressed. Some general conclusions for point positioning and relative positioning problems are drawn from analytic inference and supported by numerical simulations. Received 10 August 1995; Accepted 17 July 1996  相似文献   

Looking back and moving forward: Health geography in Aotearoa and beyond          下载免费PDF全文

Christina R. Ergler  Sarah Lovell  Alison Watkins  Christine Milligan  Lee Thompson  Daniel J. Exeter  Robin Kearns 《New Zealand geographer》2017,73(3):205-217

Health geography in Aotearoa New Zealand (NZ) has had a major impact on international sub‐disciplinary debates. It is timely to celebrate our domestic health geography achievements and alert ourselves to the challenges ahead. This reflection article provides a brief overview of Aotearoa NZ's maturing health geography community and includes the reflections of a panel discussion held during the bi‐annual NZ Geographical Society conference in 2016. We argue that the eclectism of health geography in NZ and beyond is both the sub‐discipline's major strength and challenge.  相似文献   

A visualization-based post-processing system for analysis of acoustic data     

Socha  David G.; Watkins  Jonathan L.; Brierley  Andrew S. 《ICES Journal of Marine Science》1996,53(2):335-338

  相似文献   

A post-processing technique to remove background noise from echo integration data   总被引：1，自引：1，他引：1  

Watkins  Jonathan L.; Brierley  Andrew S. 《ICES Journal of Marine Science》1996,53(2):339-344

  相似文献