Edge-driven convection   总被引：23，自引：0，他引：23  

Scott D King  Don L Anderson 《Earth and Planetary Science Letters》1998,160(3-4):289-296

We consider a series of simple calculations with a step-function change in thickness of the lithosphere and imposed, far-field boundary conditions to illustrate the influence of the lithosphere on mantle flow. We consider the effect of aspect ratio and far-field boundary conditions on the small-scale flow driven by a discontinuity in the thickness of the lithosphere. In an isothermal mantle, with no other outside influences, the basic small-scale flow aligns with the lithosphere such that there is a downwelling at the lithospheric discontinuity (edge-driven flow); however, the pattern of the small-scale flow is strongly dependent on the large-scale thermal structure of a much broader area of the upper mantle. Long-wavelength temperature anomalies in the upper mantle can overwhelm edge-driven flow on a short timescale; however, convective motions work to homogenize these anomalies on the order of 100 million years while cratonic roots can remain stable for longer time periods. A systematic study of the effect of the boundary conditions and aspect ratio of the domain shows that small-scale, and large-scale flows are driven by the lithosphere. Edge-driven flow produces velocities on the order of 20 mm/yr. This is comparable to calculations by others and we can expect an increase in this rate as the mantle viscosity is decreased.  相似文献   

有源带通滤波器的设计、调试与应用     

豆耀华  张素萍 《地震工程学报》1996,18(1):77-82

所述的有源带通滤波器是采用现代网络理论，通过查图表反复计算数值调试并利用多项式综合滤波器的设计理论得到的设计结果，从频率响应特性曲线和电路结构可见，它完全满足了设计时所提供的各项技术指标的要求。文中详细地讨论了由单元电路到全极点多反馈滤波网络电路设计时的理论根据，各支路参数实际的计算和调试方法。这种电路结构简单合理，调试和维修十分方便，代替了无源滤波器中的大型电感和电容，有利于设备小型化。  相似文献   

Measuring Rates of Biodegradation in a Contaminated Aquifer Using Field and Laboratory Methods   总被引：5，自引：0，他引：5  

Francis H. Chapelle  Paul M. Bradley  Derek R. Lovley  Don A. Vroblesky 《Ground water》1996,34(4):691-698

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油气形成的构造动力学理论和油气藏勘探的地球动力学方法综述   总被引：3，自引：1，他引：3  

史斗  刘文汇 《地球科学进展》1996,11(5):460-468

综述了石油和天然气形成构造动力学理论，其中包括构造挤压是有机质演化所需能量的重要来源、构造挤压的最重要伴生效应－力化学作用促进了有机质演化、构造挤压对烃类运移和 烃类资源分布有重要影响等观点。还综述了油气藏勘探的地球动力方法，其中包括这一方法的理论基础，可行性和具体任务以及应用前景等。  相似文献   

DISCUSSION OF "Hydrochemical Characterization of Brines and Identification of Brine Contamination in Aquifers," by Stephanie A. Novak and Yoram Eckstein, May-June 1988 issue, v. 26, no. 3, pp. 317–324     

Don Clabaugh  Project Manager 《Ground water》1989,27(2):248-248

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Petrology of a leucogabbroic interval within basal layered gabbros at North Arm Mountain,Bay of Islands ophiolite     

Stephen C. Komor  Don Elthon  John F. Casey 《Contributions to Mineralogy and Petrology》1987,95(3):278-300

Data from detailed sample traverses in the layered gabbro unit of the North Arm Mauntain massif, Bay of Islands ophiolite, allow meter-scale resolution of magmatic processes in spreading ridge magma chambers. One suite of 46 samples from a 195 m interval near the base of the layered gabbro unit contains cumulus plagioclase (An_73.7–87.5; average modal abundance=75%), clinopyroxene (Mg#=80.3–86.0; 18%), and olivine (Fo_76.6–82.1; 6%), with intergranular orthopyroxene (Mg#=78.0–83.3; 1%), and accessory Cr-Al spinel (Cr#=32.3–41.4). Ilmenite rims spinel in one sample. Whole rock Zr contents range from <6 to 15 ppm. Plots of stratigraphic height in the traverse versus petrogenetic indicators (e.g. Mg#'s of mafic phases and An in plagioclase) reveal both normal and reverse cryptic variation patterns; the patterns for all indices are generally correlated. The normal portions of the patterns formed during fractional crystallization of basalt batches. Ranges of mineral compositions in the normal trends suggest that 29–38% crystallization of each batch of basalt occurred before magmatic replenishment. The reverse cryptic trends formed by crystallization of hybrid magmas produced during periods of magma mixing. Other evidence for magma mixing is the systematic association of spinel and reversely zoned plagioclase with the reverse trends. Experiments and observations of natural assemblages indicate that 55% modal plagioclase crystallizes from basalts at the olivine+plagioclase+clinopyroxene+liquid piercing point. The average plagioclase content of this suite of leucogabbros from North Arm Mountain is too high to have formed from simple crystallization at the piercing point. Petrologic modeling indicates the leucogabbros may have formed from basalts into which a small amount (<10%) of plagioclase was resorbed during mixing; the initial compositions of these hybrid basalts lie in the plagioclase primary phase volume. Other suites of layered gabbros from North Arm Mountain are not so plagioclase-rich as the leucogabbros described above. Crystallization of basalts in the plagioclase primary phase volume and the consequent formation of plagioclaserich gabbros may occur in restricted portions of zoned magma chambers underlying oceanic spreading centers, or may occur episodically in the overall lifetimes of the magma chambers.  相似文献   

A transitional alkalic dolerite dike suite of Mesozoic age in Southeastern New England     

O. Don Hermes  J. M. Rao  M. P. Dickenson  T. A. Pierce 《Contributions to Mineralogy and Petrology》1984,86(4):386-397

Dike rocks from the New England platform of Rhode Island and adjacent Massachusetts consist of premetamorphic and post-metamorphic suites. The older group includes metamorphosed dolerite, minette, and schistose dioritic rocks. Post-metamorphic dikes consist of dolerite and sparse monchiquite. The post-metamorphic dolerites are of comparable age to the Eastern North American dolerite suite associated with the Mesozoic basins along the eastern seaboard of North America. However, the southeastern New England dolerites exhibit mineralogy and chemistry more typical of a transitional alkalic suite compared to the more subalkalic tholeiitic dolerites of the Eastern North American suite. Both suites are compatible with a rift tectonic setting, but the more alkalic dolerites may represent a deeper source of small volume melts compared to the Eastern North American dolerites. These more alkaline melts may have concentrated at local centers, or they may be typical of flank dolerites as opposed to the less alkalic varieties that occur within the central axial rift.  相似文献   

Multichannel analysis of surface wave method with the autojuggie   总被引：2，自引：0，他引：2  

Gang Tian  Don W. Steeples  Jianghai Xia  Richard D. Miller  Kyle T. Spikes  Matthew D. Ralston 《Soil Dynamics and Earthquake Engineering》2003,23(3):61-65

The shear (S)-wave velocity of near-surface materials and its effect on seismic-wave propagation are of fundamental interest in many engineering, environmental, and groundwater studies. The multichannel analysis of surface wave (MASW) method provides a robust, efficient, and accurate tool to observe near-surface S-wave velocity. A recently developed device used to place large numbers of closely spaced geophones simultaneously and automatically (the ‘autojuggie’) is shown here to be applicable to the collection of MASW data. In order to demonstrate the use of the autojuggie in the MASW method, we compared high-frequency surface-wave data acquired from conventionally planted geophones (control line) to data collected in parallel with the automatically planted geophones attached to steel bars (test line). The results demonstrate that the autojuggie can be applied in the MASW method. Implementation of the autojuggie in very shallow MASW surveys could drastically reduce the time required and costs incurred in such surveys.  相似文献   

Hg and As Minerals in Fluid Inclusions from the Williams Mine,Hemlo,and Their Genetic Implications   总被引：1，自引：0，他引：1  

卢焕章 《中国地球化学学报》2002,21(1):1-18

The Hemlo mineralization is enigmatic compared to general Archean lode gold deposits based on the fact that is characterized by an exotic mineralogy containing elements such as As,Hg,Sb,Ba,V and Mo.The genetic concepts range from syngenetc to epigenetic types of mineralization.This reconnaissance study was designed to examine the relationshp of Hg-As minerals with respect of fluid inclusions in the Williams mine(formerly known as the Page Williams mine)covering the A and C ore zones.  相似文献   

Conflicting rights to the city in New York's community gardens   总被引：1，自引：0，他引：1  

Lynn A. Staeheli  Don Mitchell  Kristina Gibson 《GeoJournal》2002,58(2-3):197-205

In the mid-1990s, New York City initiated what would prove to be a long, highly visible struggle involving rights claims related to property, housing, and public space in the form of community gardens. The competing discourses of rights were part of a struggle over the kind of city that New York was to become, and more specifically, whether it would be one in which difference is accepted and in which access to the city and the public realm would be guaranteed. Using interviews with participants in the conflict over community gardens, we evaluate how the resolution to the gardens crisis, which in part occurred through the privatization of what are often taken to be public or community rights to land, transform not only the legal status of the gardens but also, potentially, their role as places where different `publics' can both exercise their right to the city and solidify that right in the landscape.  相似文献