Recent vertical crustal movements from precise leveling surveys in the Blue Ridge and Piedmont Provinces, North Carolina and Georgia     

Gary P. Citron  Larry D. Brown 《Tectonophysics》1979,52(1-4)

Examination of two lines of repeated leveling in North Carolina and Georgia reveals

1. (1) apparent uplift at the Blue Ridge-Piedmont physiographic boundary (the AtlanticGulf drainage divide) relative to the Atlantic Coastal Plain on the east and the Valley and Ridge province to the west; and

2. (2) large tilts over short baselines superimposed upon the regional pattern in the vicinity of the nearby Blue Ridge—Piedmont geologic boundary (the Brevard fault zone). In the North Carolina profile a very pronounced correlation between topography and movement suggests possible systematic leveling error, but the observed movements appear to be larger than those normally attributed to leveling error. Thus, either refraction or rod errors are larger than expected, or the movement is real and strongly correlates with topography along this portion of the leveling line.

Anomalously high stream-gradients over both resistant and nonresistant lithologies are found around the drainage divide in North Carolina, and may be associated with the relative uplift inferred from releveling. The drainage divide in Georgia, also characterized by relative uplift on the movement profile, approximately separates two different types of stream patterns. In both cases evidence presented here suggests that stream morphology may be responding to contemporary deformation as implied by the observed elevation changes. The relative uplift in North Carolina also correlates with a positive Bouguer gravity anomaly of 30–40 mGal in the midst of the regional Blue Ridge gravity low, although the significance of the correlation is unclear.The close spatial correspondence between the zone of maximum uplift and the drainage divide suggests that the vertical movements and geomorphic anomalies may result from the same mechanism, although the nature of such is unclear. One possible mechanism could be displacement at depth along the nearby Brevard zone. However, on the basis of dislocation modeling it appears that the geodetic observations cannot be adequately explained by surface deformation associated with any simple models of slip on the Brevard zone.  相似文献   

Origin of major element chemical trends in DSDP Leg 37 basalts, Mid-Atlantic Ridge     

Gary R. Byerly  Thomas L. Wright 《Journal of Volcanology and Geothermal Research》1978,3(3-4)

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Petrography of the Manu'a Islands,Samoa     

Gary D. Stice 《Contributions to Mineralogy and Petrology》1968,19(4):343-357

The rocks of the Manu'a Islands are predominantly olivine basalt with lesser amounts of picrite basalt (both ankaramite and oceanite), basalt, hawaiite, olivine gabbro, basaltic lapilli tuff, and ash. Alkali silica ratios obtained from chemical analyses of twenty widely selected samples place the rocks in the alkali basalt suite. All of the samples are also high in titanium. Plots of the chemical analyses, including samples from nearby Tutuila Island, show a progressive enrichment in alkalis. The occurrence of hawaiite and picrite basalt indicates that a primitive alkalic olivine basalt magma was undergoing differentiation. The most important factor in this process was crystal settling, especially of olivine. The dunite xenoliths in the late-stage rocks of Ta'u Island probably came from a residual olivine layer near the bottom of the magma chamber. The magma did not become sufficiently silicic to produce the trachytic end-member of the series, which probably would have contained normative and possibly some modal quartz, as on Tutuila Island. With increasing silica content, iron and titanium generally decrease slightly, whereas alkalis increase.Hawaii Institute of Geophysics Contribution No. 237.  相似文献   

Stress and shear fracture (fault) patterns resulting from a suite of complicated boundary conditions with applications to the Wind River Mountains     

Gary Couples 《Pure and Applied Geophysics》1977,115(1-2):113-133

Summary The Airy stress function is used, via the Principle of Superposition and the series summation concept, to obtain stress states in a static, self-gravitating elastic beam subjected to boundary stresses. The boundary conditions investigated are more complicated than those previously published and include cases with sawtooth-, step-, and sinusoidally-shaped lower-boundary loads, with and without additional tectonic end leads. Potential shear fracture (fault) patterns derived from the calculated stress fields indicate co-existing (simultaneous) regions of lateral shortening and extension. Application of one of the cases to the study of the structural geometry of the Wind River Mountains of Wyoming yields a good fit and forms a possible explanation for the observed rotations and zones of shortening and extension.Paper derived from MA Thesis submitted to Rice University.  相似文献   

Magnetic field configuration of active region NOAA 6555 at the time of a long-duration flare on 23 March 1991 – An Exception to Standard Flare Reconnection Model     

Choudhary  Debi Prasad  Gary  G. Allen 《Solar physics》1999,188(2):345-364

The high-resolution H images observed during the decay phase of a long-duration flare on 23 March 1991 are used to study the three-dimensional magnetic field configuration of the active region NOAA 6555. Whereas all the large flares in NOAA 6555 occurred at the location of high magnetic shear and flux emergence, this long-duration flare was observed in the region of low magnetic shear at the photosphere. The H loops activity started soon after the maximum phase of the flare. There were a few long loop at the initial phase of the activity. Some of these were sheared in the chromosphere at an angle of about 45° to the east-west axis. Gradually, an increasing number of shorter loops, oriented along the east-west axis, started appearing. The chromospheric Dopplergrams show blue shifts at the end points of the loops. By using different magnetic field models, we have extrapolated the photospheric magnetograms to chromospheric heights. The magnetic field lines computed by using the potential field model correspond to most of the observed H loops. The height of the H loops were derived by comparing them with the computed field lines. From the temporal evolution of the H loop activity, we derive the negative rate of appearance of H features as a function of height. It is found that the field lines oriented along one of the neutral lines were sheared and low lying. The higher field lines were mostly potential. The paper also outlines a possible scenario for describing the post-flare stage of the observed long-duration flare.  相似文献   

Ground-Water Flow in the Coastal Plain Aquifers of South Carolina     

Walter R. Aucott  Gary K. Speiran 《Ground water》1985,23(6):736-745

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Sedimentary basin formation with finite extension rates   总被引：4，自引：0，他引：4  

Gary T. Jarvis  Dan P. McKenzie 《Earth and Planetary Science Letters》1980,48(1):42-52

Thinning of continental crust by rapid stretching of the lithosphere produces an initial subsidence and thermal anomaly. When stretching ceases, slow decay of the thermal anomaly produces subsidence (due to thermal contraction) on a time scale of approximately 60 Ma. The dependence of the heat flow and subsidence histories on the rate of extension is determined here using a time-dependent analytical model. Results are compared with the predictions of a simpler instantaneous stretching model and constraints on the use of the latter are provided in terms of the duration and amount of stretching. For most basins the simple model gives reasonably accurate results provided the duration of stretching is less than 20 Ma.  相似文献   

Nedagolla,a remelted iron meteorite     

Gary T Miyake  Joseph I Goldstein 《Geochimica et cosmochimica acta》1974,38(5):747-755

The Nedagolla meteorite was recognized by Axon to be a rare example of an iron which has been preterrestrially reheated to the point of melting. The dendrite secondary arms are spaced 200 μm apart, implying that Nedagolla solidified and cooled at ~0·02°C/sec. The presence of (Fe, Cr)_1-xS inclusions precipitated during cooling in the interdendritic regions and evidence of solute redistribution of Ni, Cr, Co, Si and P are consistent with this cooling rate. Such a rate indicates that Nedagolla cooled very near the surface of its parent ‘body’. Secondary microstructural features including the presence of isothermal taenite and minute phosphide precipitates, which have formed from the dissolution of primary phosphide material, indicate a later reheating to about 750°C for a period of several hours.  相似文献   

A technique for the molecular genetic analysis of Daphnia resting eggs from sub-recent lake sediments     

Vicky A. Reid  Gary R. Carvalho  D. Glen George  Huw I. Griffiths 《Journal of Paleolimnology》2002,27(4):481-486

The Polymerase Chain Reaction (PCR) was employed to facilitategenetic analyses of Daphnia ephippial egg banks fromsediment sequences from lakes Windermere and Esthwaite in the English LakeDistrict, UK. We present a robust DNA extraction technique for resting eggs andan account of genetic characterisation of dated resting eggs from sedimentcores using both mitochondrial and nuclear DNA markers. We also providepreliminary results from genetic analysis of egg banks preserved in shortsediment cores. PCR was employed to facilitategenetic analyses of Daphnia ephippial egg banks collected from both lakes. Thelong-term environmental data available from lake records can provide a backdropagainst which molecular genetic-environmental interactions over time can beexamined, providing a technique for direct assessments of population responseto environmental change in paleolimnological studies of biodiversityhistory.  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