Sr-isotopic studies of the origin of the Morin anorthosite complex,Quebec, Canada     

Jackson M. Barton Jr.  Ronald Doig 《Contributions to Mineralogy and Petrology》1977,61(3):219-230

Rb-Sr isotopic investigations of the rock-types within the Morin anorthosite complex, Quebec, suggest that: 1. both the mangerites and the leuconorites and anorthosites within this complex crystallized with a range of ⁸⁷Sr/⁸⁶Sr ratios, and 2. at least some of the mangerites crystallized approximately 100 m.y. after the anorthosites and leuconorites. From this evidence, it is argued that a number of magma sources gave rise to the melts that formed these rocks and that some local hybridization of these melts also took place by assimilation of other rock types. This same pattern is found in the Adirondack and Nain Complexes.  相似文献   

Hard Burst Emission from the Soft Gamma Repeater SGR 1900+14     

Woods PM  Kouveliotou C  van Paradijs J  Briggs MS  Hurley K  Göğüş E  Preece RD  Giblin TW  Thompson C  Duncan RC 《The Astrophysical journal》1999,527(1):L47-L50

We present evidence for burst emission from SGR 1900+14 with a power-law high-energy spectrum extending beyond 500 keV. Unlike previous detections of high-energy photons during bursts from soft gamma repeaters (SGRs), these emissions are not associated with extraordinarily bright flares. Not only is the emission hard, but the spectra are better fitted by D. Band's gamma-ray burst (GRB) function rather than by the traditional optically thin thermal bremsstrahlung model. We find that the spectral evolution within these hard events obeys a hardness/intensity anticorrelation. Temporally, these events are distinct from typical SGR burst emissions in that they are longer ( approximately 1 s) and have relatively smooth profiles. Despite a difference in peak luminosity of greater, similar1011 between these bursts from SGR 1900+14 and cosmological GRBs, there are striking temporal and spectral similarities between the two kinds of bursts, aside from spectral evolution. We outline an interpretation of these events in the context of the magnetar model.  相似文献   

Effects of pressure on the micromechanics of faulting in San Marcos gabbro     

Teng-Fong Wong  Ronald Biegel 《Journal of Structural Geology》1985,7(6):737-749

Samples of San Marcos gabbro were deformed to both pre- and post-failure stages at confining pressures of 100, 250 and 350 MPa. Scanning electron microscope observations were performed on the samples after ion-milling. The unstressed gabbro has insignificant crack porosity but a high volume fraction of healed and sealed cracks. Extensive stress-induced cracking at high angles to the maximum compressive stress is observed at the two higher pressures. Such high-angle cracks are mostly associated with the pre-existing healed cracks or cleavage planes, and they control the geometry and length scale of crack networks in plagioclase. Intensive kinking in biotite is widely observed at 350 MPa pressure, which together with the crack networks control the brittle fracture process. Stress-induced cracks in samples deformed at 100 MPa pressure are predominantly subparallel to the maximum compressive stress, and their coalescence leads to shear localization.Quantitative measurements of crack density as a function of differential stress indicate that crack interaction is appreciable beyond about 90% peak stress for all three pressures. The data also show significant decreases in stress-induced anisotropy as pressure increases, suggesting that there may be a threshold pressure beyond which stress-induced anisotropy vanishes with the onset of cataclasis.  相似文献   

Color display of well logs     

Briggs  Peter L. 《Mathematical Geosciences》1985,17(4):481-481

Mathematical Geosciences - Information displayed in image form is conventionally at least two-dimensional. One-dimensional data can also be displayed as imagery by “amplitude slicing” a...  相似文献   

Precise distance measurements in Iceland     

James L. Brander  Ronald G. Mason  Rodney W. Calvert   《Tectonophysics》1976,31(3-4)

Precise distance measurements made on four networks of permanent benchmarks situated on the active axes of Iceland during the four-year period 1968–1972 showed that a combination of left-lateral and extensional movement is occurring on the Reykjanes Peninsula in southwest Iceland at a rate of about 9 mm per year. Elsewhere in Iceland, the movements, if they exist, are too small to be detected. Measurements from a geothermal area in southwest Iceland showed also that large horizontal movements occur in the vicinity of producing geothermal wells.  相似文献   

Vegetation and associated environments during the past 14,000 years near Moulton Pond,Maine     

Ronald B. Davis  Theodore E. Bradstreet  Robert Stuckenrath  Harold W. Borns 《Quaternary Research》1975,5(3):435-465

Pollen influx and percentage diagrams were prepared from an 11.4 m core from Moulton Pond, Maine. The pond basin was deglaciated about 14,000 y. a., after which it was located on an island in a sea of subarctic character until about 12,400 y. a. when the surrounding area emerged from the sea. The terrestrial vegetation was tundra until about 10,000 y. a. A change in the tundra vegetation is synchronous with the emergence from the sea, but synchroneity with the Pineo Ridge glacial readvance, which reached its maximum 50 km to the east of the pond about 12,700 y. a., is also possible because of imprecision in the dating. Comparisons of the Moulton Pond results with late-glacial pollen sequences elsewhere in eastern United States and adjacent Canada reveal a lack of synchroneity in vegetational changes casting doubt on claims of major broad-scale climatic shifts over the entire area.The tundra period at Moulton Pond ended with a transition of a few hundred years to partly open, relatively xeric forests of low diversity dominated by white pine, oak, and birch trees. There was no intervening boreal forest. In the postglacial period the vegetation was continually changing, including in the early portion a series of immigrations of temperate tree taxa which later became important in the forests. The transient nature of these assemblages is further indicated by their differences from the closest modern analogs. From about 7100 y. a. until settlement by Europeans 200 y. a., the forests were closed. A major decline of conifers centering about 4700 y. a. was followed by maxima of mesic hardwoods about a thousand years later. In the most recent 2000 yr, the pollen record suggests greater environmental severity, evidenced by increasing spruce. But for the entire postglacial period, the closest modern vegetational analogs are all in the conifer-hardwood region. Much of the postglacial pollen sequence is inexplicable in climatic terms, as evidenced by nonsynchronous behavior of hemlock and beech.The pollen influx diagram is useful for distinguishing tundra from forest, but for the postglacial period it is difficult to interpret. Pollen influx data are strongly affected by shifts in the pattern of sedimentation in lakes. We propose that such shifts account for the major changes in influx in mid- and late-postglacial time at Moulton Pond and at Rogers Lake, Connecticut. This complicates the interpretation of influx data which otherwise are superior to percentage data.  相似文献   

Origin,depositional environment and age of the Cheltenham Sand and Gravel and related deposits     

D.J. Briggs 《Proceedings of the Geologists' Association. Geologists' Association》1975,86(3):333-348

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Nitrogen and phosphorus distribution and utilization bySpartina alterniflora in a Louisiana gulf coast marsh     

Roland J. Buresh  Ronald D. DeLaune  William H. Patrick 《Estuaries and Coasts》1980,3(2):111-121

Nitrogen and phosphorus content ofSpartina alterniflora Loisel and soil nitrogen were measured along a transect perpendicular to a stream in a Louisiana salt marsh in order to provide information on differences between the so-called streamside and inland regions. Total plant nitrogen and phosphorus levels in June and September tended to be greater at streamside than inland sites. Total soil nitrogen on a dry soil weight basis increased with distance inland from a natural stream toward an interdistributary basin in the marsh. Soil extractable ammonium-nitrogen levels measured in June were very low in vegetated streamside and inland areas, but they were much higher in inland areas devoid of plants. Nitrogen and phosphorus utilization byS. alterniflora was also investigated at an inland location in the salt marsh. Labelled ammonium-nitrogen and phosphate-phosphorus were added in May at a rate of 200 kg/ha to the soil of replicated plots. Added nitrogen significantly increased total above-ground plant biomass and plant height by 28 and 25%, respectively, 4 months after application. The ratio of belowground macro-organic matter to total aboveground biomass was decreased from 5.7 to 4.7 by the additional nitrogen. Added phosphorus did not significantly affect plant height and biomass. The use of¹⁵N-depleted nitrogen tracers showed that about half of the nitrogen in the aboveground portion ofS. alterniflora from 1 to 4 months after the nitrogen addition was derived from the added ammonium-nitrogen. After 4 months, 28 and 29% of the added labelled nitrogen was recovered in the aboverground and belowground biomass ofS. alterniflora, respectively. Recovery of added nitrogen was overestimated with a non-tracer method based on the difference in total nitrogen uptake between nitrogen-amended plots and untreated plots. Soil organic nitrogen comprised the majority of the nitrogen in the salt marsh. Nitrogen in the standing crop biomass ofS. alterniflora represented only about 2% of the total nitrogen in the plantsoil system of an inland marsh to a 20 cm soil depth.  相似文献   

Quaternary vegetation history of the Mississippi embayment     

Paul A. Delcourt  Hazel R. Delcourt  Ronald C. Brister  Laurence E. Lackey 《Quaternary Research》1980,13(1):111-132

Nonconnah Creek, located in the loess-mantled Blufflands along the eastern wall of the Lower Mississippi Alluvial Valley in Tennessee displays a sedimentary sequence representing the Altonian Substage through the Woodfordian Substage of the Wisconsinan Stage. The site has a biostratigraphic record for the Altonian and Farmdalian Substages that documents warm-temperate upland oak-pine forest, prairie, and bottomland forest. At 23,000 yr B.P., white spruce and larch migrated into the Nonconnah Creek watershed and along braided-stream surfaces in the Mississippi Valley as far as southeastern Louisiana. The pollen and plant-macrofossil record from Nonconnah Creek provides the first documentation of a full-glacial locality in eastern North America for beech, yellow poplar, oak, history, black walnut, and other mesic deciduous forest taxa. During the full and late glacial, the Mississippi Valley was a barrier to the migration of pine species, while the adjacent Blufflands provided a refuge for mesic deciduous forest taxa. Regional climatic amelioration, beginning about 16,500 yr B.P., is reflected by increases in pollen percentages of cooltemperate deciduous trees at Nonconnah Creek. The demise of spruce and jack pine occurred 12,500 yr B.P. between 34° and 37° N in eastern North America in response to postglacial warming.  相似文献   

Final results of the CONDORS convective diffusion experiment     

Gary A. Briggs 《Boundary-Layer Meteorology》1993,62(1-4):315-328

TheConvectiveDiffusionObserved byRemoteSensors (CONDORS) field experiment conducted at the Boulder Atmospheric Observatory used innovative techniques to obtain three-dimensional mappings of plume concentration fields, /Q, of oil fog detected by lidar and chaff detected by Doppler radar. It included extensive meteorological measurements and, in 1983, tracer gases measured at a single sampling arc. Final results from ten hours of elevated and surface release data are summarized here. Many intercomparisons were made. Oil fog /Q measured 40m above the arc are mostly in good agreement withSF ₆ values, except in a few instances with large spacial inhomogeneities over short distances. After a correction scheme was applied to compensate for the effect of its settling speed, chaff dy/Q agreed well with those of oil except in two cases of oil fog hot spots. Mass or frequency distribution vs. azimuth or elevation angle comparisons were made for chaff, oil, and wind, with mostly good agreements. Spacial standard deviations, _y and _z, of chaff and oil agree overall and are consistent at short range with velocity standard deviations _vand _w 0.6w^* (the convective scale velocity), as measured atz>100m. Surface release _y is enhanced up to 60% at smallx, consistent with the Prairie Grass measurements and with larger _v and reduced wind speed measured near the surface. Decreased _y at small dimensionless average times is also noted. Finally, convectively scaled dy, C _y, were plotted versus dimensionlessx andz for oil, chaff, and corrected chaff for each 30–60 min period. Aggregated CONDORSC _y fields compare well with laboratory tank and LES numerical simulations; surface-released oil fog compares expecially well with the tank experiments. However, large deviations from the norm occurred in individual averaging periods; these deviations correlated strongly with anomalies in measured distributions.On assignment to the US Environmental Protection Agency, Atmospheric Research and Exposure Assessment Laboratory, RTP, NC.  相似文献