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1.
We describe recent mechanical andeelectronic modifications to the Cambridge Ocean Bottom Hydrophone system, enabling it to record in addition three geophone channels from a deployed, disposable geophone package. Examples of data from seismic refraction experiments show good correspondence between records of ground motion detected by the hydrophone and the vertical geophone. Seismic signals are undistorted by noise from instrument related sources. Clear examples of P to S conversions just below the receiver are observed. Improved recording conditions are achieved by deploying the geophones in a small pressure vessel as far away as possible from the main instrument package. 相似文献
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Ten rare-earth elements (La, Ce, Nd, Sm, Eu, Gd, Tb, Tm, Yb and Lu) and Ta, Th and Hf contents in eight kimberlites and inclusions from Greenland and Zambia have been determined by instrumental neutron activation. All the samples have highly fractionated rare-earth (REE) distribution patterns. La/Yb ratios in the Greenland kimberlites (hypabyssal facies) vary from 111.8 to 188.4, and the total rare-earth contents range from 204.8 to 380.3 ppm. No europium anomaly is present. The Zambian kimberlites (diatreme facies) are altered and carbonated. Rare-earth patterns in these are also light REE-enriched. A significant difference is shown to exist between the diatreme and hypabyssal facies of kimberlites. 相似文献
4.
The occasional occurrence of brief but intense bursts of cosmic gamma-rays was disclosed through a systematic search of data acquired from the Vela satellites. Confirmation of the nature of the events and additional detail of their characteristics has subsequently been provided by 15 other groups of experimenters with instruments on 13 spacecraft. Thirty-nine such events have been identified from data spanning a period of four and a half years. The record of intensity as a function of time varies considerably for different events, with total durations ranging from 0.1 to 60s. Time-integrated flux density ranges from 10–6 to 10–3 erg cm–2. Spectral measurements have been accomplished by several groups of experimenters, showing a broad maximum in the energy distribution at about 150 keV. The distribution of source directions implies either near galactic or extragalactic locations. The existing data are not sufficient to distinguish between the various models proposed to explain the phenomenon; no model is completely consistent with all observed characteristics.Work performed under the auspices of the United States Energy Research and Development Administration.Paper presented at the COSPAR Symposium on Fast Transients in X-and Gamma-Rays, held at Varna, Bulgaria, 29–31 May, 1975. 相似文献
5.
Philip J. Potts Michael Thompson Stephen Wilson 《Geostandards and Geoanalytical Research》2002,26(2):197-235
Results are presented for round one of a new international proficiency testing programme designed for microprobe laboratories involved in the routine analysis of silicate minerals. The sample used for this round was TB-1, a basaltic glass fused and prepared by the USGS. Thirty nine laboratories contributed data to this round, the majority of major element results being undertaken by EPMA and the majority of trace elements by LA-ICP-MS. Assigned values were derived from the median of results produced by nine selected laboratories that analysed powdered material by conventional ICP-MS, INAA and XRF techniques using bulk powders of the sample. Submitted microprobe results were evaluated using a target precision calculated using the Horwitz function, adopting the same criteria as those used for "applied" geochemistry laboratories in the companion GeoPT proficiency testing programme for laboratories involved in the routine bulk analysis of silicate rocks. An evaluation of results from participating microprobe laboratories indicated that overall, data were compatible with this precision function. A comparison between the performance of bulk and microprobe techniques used in the analysis of the basaltic glass showed remarkably good agreement, with significant bias only observed for the major oxide MgO. 相似文献
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Rhabdosargus holubi is a small (maximum weight=2.4?kg) yet important fishery species in the estuaries of the south-east coast of South Africa. Little is known of its biology and specifically its growth rate, which is essential for sustainable management of the fishery. We examined and counted the opaque zones in the sectioned otoliths of 134 R. holubi to determine its age and growth parameters. The otoliths from two recaptured fish marked with oxytetracycline confirmed that one opaque zone was deposited annually. The species reached a maximum age of 18 years and growth was adequately described by a von Bertalanffy growth function of the form: Lt = 358.1 (1 – e?0.24(t+0.77)) mm fork length. There were no significant differences between any of the male and female growth parameters (likelihood ratio test: p = 0.3). The growth was slow (omega index: ω = 86.56); however, despite this, the unique life history of R. holubi may provide a degree of resilience to heavy fishing pressure in estuaries. 相似文献
9.
John Stamatakos Rob Van Der Voo Ben Van Der Pluijm Stephen Potts Trond Torsvik 《Geophysical Journal International》1994,119(3):1009-1013
10.
Petrogenesis of calc-alkaline,shoshonitic and associated ultrapotassic Oligocene volcanic rocks from the Northwestern Alps,Italy 总被引:1,自引:0,他引:1
G. Venturelli R. S. Thorpe G. V. Dal Piaz A. Del Moro P. J. Potts 《Contributions to Mineralogy and Petrology》1984,86(3):209-220
Along the Western Alps there is geological evidence of late-Alpine (Oligocene) magmatic activity which clearly postdates the
Lepontine (Eocene-early Oligocene) metamorphism and related deformation of the Alpine nappe pile. This magmatic activity was
notably delayed in relation to the most important convergent processes and may be related to buoyancy of lithosphere, tensional
tectonics and thermal updoming subsequent to the collision between the Eurasian and African plates. The geochemical features
of the rocks and the geophysical characteristics of the Alpine chain, suggest that: (a) shoshonitic and calcalkaline melts
may have been generated by partial melting of metasomatized peridotitic material and subsequent fractional crystallization
and crustal contamination; silicic andesites and latites, however, could have been also derived from metasomatized eclogite
or deep continental crust material; (b) the ultrapotassic lamprophyres with high K, P, LREE, Th, Zr, U and high 87Sr/86Sr ratios were generated by partial melting of strongly metasomatized mantle; the varied Sr-isotopic ratios may partially
also reflect additional radiogenic component from the continental crust following magma segregation from the source. 相似文献