Evolution of the Miocene Tejeda magmatic system,Gran Canaria,Canary Islands     

Stephen C. L. Clark  Frank J. Spera 《Contributions to Mineralogy and Petrology》1990,104(6):681-699

This paper is a companion to Clark (1988; hereafter Part I) which described the evolution of the Tejeda Magmatic System (TMS), a Miocene caldera complex, Gran Canaria, Spain, based on geochronologic, paleomagnetic and field data. In this study, petrochemical data are used to corroborate the history out-lined in Part I. Geochemical discriminant analysis shows that whereas the Extra-Caldera (EC) Mogan/Fataga volcanics are separated by a composition gap, no composition gap exists within the Intra-Caldera (IC) sequence. IC ignimbrites change rapidly but progressively from pantellerites and comendites to comenditic trachytes and finally to trachytes in a 0.47 Ma time interval. Significantly, the lower pantelleritic part of the IC series is similar to the EC pantellerites (units B, C and D) as expected based on results from Part I. The appearance of a compositional gap in the EC sequence is the result of flows having been trapped within the caldera during the 0.47 Ma Mogan-Fataga transition interval. The transitional IC sequence may be geochemically modelled by mixing of Mogan comendites and Fataga trachytes. The mixing was most probably induced by the high discharge of magma from the compositionally-zoned Tejeda magma body. The rate of change in erupted composition is best explained by imagining a continuous influx of Fataga or parental Fataga magma into a chamber whose previous silicic component (Mogan composition) was no longer being replenished and that the two magmas did not convectively mix prior to eruption. Repose times between successive eruptions in the lower to middle Mogan (from P1/T1 to A) were of order 30 000 a; the upper Mogan pantellerites and comendites/comenditic trachytes (B to F?) erupted once every 125 000 years or so. The longer repose time for the upper units is consistent with their more differentiated character.  相似文献   

Hydro-chemical evolution of groundwater in a sequence of Tertiary Formations in Northwest Oman     

Osman Abdalla  Rashid Al-Abri  Khadija Semhi  Talal Al-Hosni  Saif Al-Yaroubi  Ian Clark  Mansour Amerjeed 《Environmental Earth Sciences》2016,75(21):1410

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Estimating spatial variations of total evaporation using multispectral sensors within the uMngeni catchment,South Africa     

C. Shoko  D.J. Clark  M.G. Mengistu  H. Bulcock  T. Dube 《国际地球制图》2016,31(3):256-277

Total evaporation is of importance in assessing and managing long-term water use, especially in water-limited environments. Therefore, there is need to account for water utilisation by different land uses for well-informed water resources management and future planning. This study investigated the feasibility of using multispectral Landsat 8 and moderate resolution imaging spectroradiometer (MODIS) remote sensing data to estimate total evaporation within the uMngeni catchment in South Africa, using surface energy balance system. The results indicated that Landsat 8 at 30 m resolution has a better spatial representation of total evaporation, when compared to the 1000 m MODIS. Specifically, Landsat 8 yielded significantly different mean total evaporation estimates for all land cover types (one-way ANOVA; F_4.964?=?87.011, p < 0.05), whereas MODIS failed to differentiate (one-way ANOVA; F_2.853?=?0.125, p = 0.998) mean total evaporation estimates for the different land cover types across the catchment. The findings of this study underscore the utility of the Landsat 8 spatial resolution and land cover characteristics in deriving accurate and reliable spatial variations of total evaporation at a catchment scale.  相似文献   

ORTHOPHOTOGRAPHY APPLIED TO THE PLANNING OF STONEHOUSE NEW TOWN     

W. A. S. Clark  F. A. B. Richardson  D. Draffan 《The Photogrammetric Record》1974,8(44):154-166

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THE MEASUREMENT AND COMPARISON OF TOOTH SHAPE USING PHOTOGRAMMETRY     

C. E. Clark  R. M. Flinn  K. B. Atkinson  E. H. Wickens 《The Photogrammetric Record》1974,8(44):217-221

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A low resolution map of Europa from four occultations by Io     

James R. Vermilion  Roger N. Clark  Thomas F. Greene  Jon F. Seamans  William F. Yantis 《Icarus》1974,23(1):89-96

Analysis of three occultations of JII (Europa) by JI (Io) has resulted in a preliminary reflectivity map of JII for the hemisphere centered on longitude 324°, a measurement of 1483±20 km for the radius of JII, estimates of the event impact parameters, determination of the mid event times, and a visual geometric albedo, p_ν = 0.74, for JII. A fourth occultation light curve was used after derivation of the results to confirm their validity.  相似文献   

Cloud Fields Over Irrigated Areas In Southwestern Kansas—Data And Speculations     

G. A. Marotz  J. Clark  J. Henry  R. Standfast 《The Professional geographer》1975,27(4):457-461

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The Galilean satellites: New near-infrared spectral reflectance measurements (0.65–2.5 μm) and a 0.325–5 μm summary     

Roger N. Clark  Thomas B. Mc Cord 《Icarus》1980,41(3):323-339

New near-infrared (0.65–2.5 μm) reflectance spectra of the Galilean satellites with 1.5% spectral resolution and ≈2% intensity precision are presented. These spectra more precisely define the water ice absorption features previously identified on Europa, Ganymede, and Callisto at 1.55 and 2.0 μm. In addition, previously unreported spectral features due to water ice are seen at 1.25, 1.06, 0.90, and 0.81 μm on Europa, and at 1.25, 1.04, and possibly 0.71 μm on Ganymede. Unreported absorption features in Callisto's spectrum occur at 1.2 μm, probably due to H₂O, and a weak, broad band extending from 0.75 to 0.95 μm, due possibly to other minerals. The spectrum of Io has only weak absorption features at 1.15 μm and between 0.8 and 1.0 μm. No water absorptions are positively identified in the Io spectra, indicating an upper limit of areal water frost coverage of 2% (leading and trailing sides). It is found for Callisto, Ganymede, and Europa that the water ice absorption features are due to free water and not to water bound or absorbed onto minerals. The areal coverage of water frost is ≈ 100% on Europa (trailing side), ≈65% on Ganymede (leading side), and 20–30% on Callisto (leading side). An upper limit of ≈5% bound water (in addition to the 20–30% ice) may be present on Callisto, based on the strong 3-μm band seen by other investigators. A summary of spectra of the satellites from 0.325 to about 5 μm to aid in laboratory and interpretation studies is also presented.  相似文献   

Possible effects of schooling on the dynamics of exploited fish populations     

Clark  Colin W. 《ICES Journal of Marine Science》1974,36(1):7-14

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Toxicity assessment of sediment cores from Santa Monica Bay,California     

Greenstein D  Bay S  Jirik A  Brown J  Alexander C 《Marine environmental research》2003,56(1-2):277-297

During the summer of 1997, sediment core samples were taken at 25 stations in Santa Monica Bay. Toxicity testing was performed on 4-cm sections of the entire length of each core using purple sea urchin fertilization and amphipod survival tests. The sea urchin test identified sections as being toxic at six stations, all located near current or former Hyperion Treatment Plant (HTP) wastewater outfall locations. The amphipod test identified sections from 17 stations as having toxic sediments. The stations having toxic sediments were scattered throughout the bay and toxicity was identified at numerous core depths. Spatial and temporal patterns indicated that toxicity was most strongly associated with the historical disposal of municipal wastewater sludge. Many of the sections toxic to the amphipods did not have chemical levels expected to cause toxicity and were in locations where a source of toxicity was not apparent.  相似文献