Quantitative measures of textural anisotropy resulting from magmatic compaction illustrated by a sample from the Palisades sill, New Jersey     

Norman H. Gray  Anthony R. Philpotts  Loretta D. Dickson 《Journal of Volcanology and Geothermal Research》2003,121(3-4):293-312

Early in the crystallization of many tholeiitic basaltic magmas, plagioclase crystals cluster together into a 3-D cellular network, which forms a passive marker capable of recording the deformation that accompanies compaction of crystal mush. Although irregular in detail, the overall network is initially isotropic and only becomes anisotropic as a result of compaction. We have developed four independent methods to quantify the 3-D textural anisotropy of a basalt sample using at least three non-parallel thin sections. Three of the methods are based on the geometrical properties of digitized maps of the feldspar chain networks. One approach focuses on the angular variation of the mean intercept along parallel traverses through the network, another examines the orientation and size distribution of individual links, and the third considers the average shape of interstitial regions outlined by the plagioclase network. The fourth technique approximates the textural anisotropy by the variogram anisotropy of a scanned thin section image. We illustrate the methods using five oriented non-parallel thin sections from a sample of diabase 146 m above the base of the 300-m-thick Palisades sill of New Jersey. Compaction of crystal mush in this sill has previously been postulated on the basis of chemical evidence. The 3-D feldspar network anisotropy based on the first three approaches suggests nearly uniaxial compaction on the order of 8.6% in a direction within 3° of the intersection of the columnar joints at the sample site. A rigorous statistical test based on the statistics of elliptically contoured non-normal multivariate distributions documents that the link-vector distribution in vertical sections are statistically anisotropic at a 95% confidence level and that the overall compaction is 7.9±2.6%. The orientation and magnitude of the 3-D textural anisotropy determined by the image variogram of the non-opaque minerals is almost identical to the mean feldspar network anisotropy; 8.5% compaction in a direction 10° from the columnar joint intersections. The major silicate textural and feldspar network anisotropy axes both plunge almost directly down dip of the sill. On the other hand, the major axis of the variogram anisotropy of the opaque minerals is approximately parallel to the strike of the sill and to the major axis of the anisotropic magnetic susceptibility. The anisotropy of the silicate mineral fabric may reflect down-dip flow of a deformable melt-rich crystal mush, whereas the AMS and opaque textural anisotropy reflects the influence of gravitational stresses during the growth of magnetite in the final stages of melt crystallization. Evidently the Palisades sill was not originally horizontal but was intruded in an orientation close to its present attitude.  相似文献   

Empirical attenuation relationship for Arias Intensity   总被引：1，自引：0，他引：1  

Thaleia Travasarou  Jonathan D. Bray  Norman A. Abrahamson 《地震工程与结构动力学》2003,32(7):1133-1155

Arias Intensity is a ground motion parameter that captures the potential destructiveness of an earthquake as the integral of the square of the acceleration–time history. It correlates well with several commonly used demand measures of structural performance, liquefaction, and seismic slope stability. A new empirical relationship is developed to estimate Arias Intensity as a function of magnitude, distance, fault mechanism, and site category based on 1208 recorded ground motion data from 75 earthquakes in active plate‐margins. Its functional form is derived from the point‐source model, and the coefficients are determined through non‐linear regression analyses using a random‐effects model. The results show that for large magnitude earthquakes (M > 7) Arias Intensity was significantly overestimated by previous relationships while it was underestimated for smaller magnitude events (M ? 6). The average horizontal Arias Intensity is not significantly affected by forward rupture directivity in the near‐fault region. The aleatory variability associated with Arias Intensity is larger than that of most other ground motion parameters such as spectral acceleration. However, it may be useful in assessing the potential seismic performance of stiff engineering systems whose response is dominated by the short‐period characteristics of ground motions. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Lithosphere mapping beneath the North American plate   总被引：2，自引：0，他引：2  

W.L. Griffin  Suzanne Y. O''Reilly  B.J. Doyle  N.J. Pearson  H. Coopersmith  K. Kivi  V. Malkovets  N. Pokhilenko 《Lithos》2004,77(1-4):873-922

Major- and trace-element analyses of garnets from heavy-mineral concentrates have been used to derive the compositional and thermal structure of the subcontinental lithospheric mantle (SCLM) beneath 16 areas within the core of the ancient Laurentian continent and 11 areas in the craton margin and fringing mobile belts. Results are presented as stratigraphic sections showing variations in the relative proportions of different rock types and metasomatic styles, and the mean Fo content of olivine, with depth. Detailed comparisons with data from mantle xenoliths demonstrate the reliability of the sections.

In the Slave Province, the SCLM in most areas shows a two-layer structure with a boundary at 140–160 km depth. The upper layer shows pronounced lateral variations, whereas the lower layer, after accounting for different degrees of melt-related metasomatism, shows marked uniformity. The lower layer is interpreted as a subcreted plume head, added at ca. 3.2 Ga; this boundary between the layers rises to <100 km depth toward the northern and southern edges of the craton. Strongly layered SCLM suggests that plume subcretion may also have played a role in the construction of the lithosphere beneath Michigan and Saskatchewan.

Outside the Slave Province, most North American Archon SCLM sections are less depleted than similar sections in southern Africa and Siberia; this may reflect extensive metasomatic modification. In E. Canada, the degree of modification increases toward the craton margin, and the SCLM beneath the Kapuskasing Structural Zone is typical of that beneath Proterozoic to Phanerozoic mobile belts.

SCLM sections from several Proterozoic areas around the margin of the Laurentian continental core (W. Greenland, Colorado–Wyoming district, Arkansas) show discontinuities and gaps that are interpreted as the effects of lithosphere stacking during collisional orogeny. Some areas affected by Proterozoic orogenesis (Wyoming Craton, Alberta, W. Greenland) appear to retain buoyant, modified Archean SCLM. Possible juvenile Proterozoic SCLM beneath the Colorado Plateau is significantly less refractory. The SCLM beneath the Kansas kimberlite field is highly melt-metasomatised, reflecting its proximity to the Mid-Continent Rift System.

A traverse across the continent shows that the upper part of the cratonic SCLM is highly magnesian; the decrease in mg# with depth is interpreted as the cumulative effect of metasomatic modification through time. The relatively small variations in seismic velocity within the continental core largely reflect the thickness of this depleted layer. The larger drop in seismic velocity in the surrounding Proton and Tecton belts reflects the closely coupled changes in SCLM composition and geotherm.  相似文献   

Trace-metal content of the Pueblo Viejo precious-metal deposits and their relation to other high-sulfidation epithermal systems     

Stephen E. Kesler  Norman Russell  Karr McCurdy 《Mineralium Deposita》2003,38(6):668-682

We provide here information on the distribution of copper, zinc, lead, gold, silver, barium, arsenic, antimony, mercury, selenium and tellurium in the Moore and Monte Negro high-sulfidation epithermal deposits in the Pueblo Viejo district, Dominican Republic. Moore and Monte Negro are funnel-shaped zones of advanced argillic alteration and precious-metal mineralization which extend to depths of about 350 m below the present surface. The uppermost part of the Moore deposit has been removed by erosion, whereas the Monte Negro deposit is covered by rocks containing low, but still anomalous gold grades. At Moore, concentrations of all elements except copper increase upward through the deposit. At Monte Negro, all elements except barium and zinc show a similar upward increase in concentration to a point near the top of the deposit from which they decrease upward. This difference reflects the fact that the top of the Moore deposit has been removed by erosion. Because the deposits are funnel-shaped and average metal concentrations increase by almost an order of magnitude upward, most of the metals are concentrated in the upper parts of the deposits. The upward increase in concentration of most metals is gradual and similar in magnitude to the prograde temperature dependence in solubilities of many metal complexes, suggesting that the metals were deposited by cooling. By contrast, concentrations of mercury and, to a lesser extent, tellurium increase more abruptly in the upper part of the deposits. This change probably reflects boiling of the hydrothermal solutions and partitioning of mercury and tellurium into a rising vapor phase, and it suggests that host rocks overlying the deposits will be anomalous in mercury and tellurium. Comparison to the Broadlands, New Zealand, hydrothermal system supports these inferred depositional processes. It shows that the behavior of arsenic and antimony at Broadlands was different from that at Pueblo Viejo, possibly because the elements were complexed differently in the two ore fluids. Comparison of trace-element abundances at Pueblo Viejo to other high-sulfidation epithermal systems shows differences in base-metal, arsenic and mercury abundances which may be related to the depths at which the deposits formed. The results of this study highlight the application and need for quantitative trace-element data from epithermal deposits.  相似文献   

Hazards Risk Assessment Methodology for Emergency Managers: A Standardized Framework for Application   总被引：1，自引：3，他引：1  

Norman Ferrier  C. Emdad Haque 《Natural Hazards》2003,28(2-3):271-290

The public and the decision and policy makers who serve themtoo often have a view of community risks that is influenced and distorted significantlyby media exposure and common misconceptions. The regulators and managers, responsible forplanning and coordination of a community's mitigation, preparedness, response and recoveryefforts, are originated from a variety of disciplines and levels of education. Not only mustthese individuals deal with the misconceptions of their communities, but also frequently lacka basic methodology for the assessment of risks. The effective planning of mitigation andresponse are, however, directly dependent upon the understanding of the complexities, types,and nature of risks faced by the community, determining the susceptible areas, and conceptualizinghuman vulnerability.In this study, a review of the existing literature on both theconceptual underpinnings of risk and its assessment is attempted. A standardized framework is proposedfor use by all emergency managers, regardless of training or education. This frameworkconsists of the numerical ranking of the frequency of the event in the community, multiplied bya numerical ranking of the severity or magnitude of an event in a given community, based upon thepotential impact characteristics of a `worst-case' scenario. This figure is then multipliedby a numerical ranking indicating the Social Consequence; a combination of community perception ofrisk level and collective will to address the problem. The resulting score, which is notstrictly scientific, would permit emergency managers from a variety of backgrounds to comparelevels of community exposure to such disparate events as hazardous materials spills andtornadoes, and to set priorities for both mitigation efforts and for the acquisition of response needs,within the availability of community resources.  相似文献   

Sulphide inclusions in diamonds from the Koffiefontein kimberlite, S Africa: constraints on diamond ages and mantle Re–Os systematics     

D.G. Pearson  S.B. Shirey  J.W. Harris  R.W. Carlson 《Earth and Planetary Science Letters》1998,160(3-4):311-326

Re–Os isotope compositions of syngenetic sulphide inclusions in both eclogite suite (E-type) and peridotite suite (P-type) parageneses in diamonds from the Koffiefontein mine, South Africa have been analysed using a technique capable of analysing single inclusion grains, or, in some cases multiple inclusions from the same diamonds. Sulphide inclusion Ni contents broadly correlate with Os abundances in that low-Ni (6.8–8.7% Ni), E-type sulphides have 4.7 to 189 ppb Os whereas the two high-Ni (25%), P-type sulphides have 5986 and 6097 ppb Os. Two P-type sulphides from the same diamond define the first mineral isochron obtained for a single diamond which has an age of 69±30 Ma with chondritic initial ¹⁸⁷Os/¹⁸⁸Os. This indicates that the sulphides, and hence the host diamond, crystallised close to the time of kimberlite emplacement (90 Ma), in the Mesozoic. This is supported by Pb isotopic measurements of a fragment from one of the sulphides, together with the absence of significant Type IaB nitrogen aggregation in the host diamond lattice. E-type sulphide inclusions have radiogenic Os isotopic compositions, ¹⁸⁷Os/¹⁸⁸Os 0.346 to 2.28, and Re–Os model ages from 1.1 to 2.9 Ga. They define an array on a Re–Os isochron diagram that may be interpreted as defining a single period of E-type sulphide growth at 1.05±0.12 Ga, with an elevated initial ¹⁸⁷Os/¹⁸⁸Os. Alternatively, two episodes of sulphide crystallisation, from a chondritic reservoir, may be invoked in the Archaean and in the Proterozoic. The results for both P- and E-type diamonds point to a spectrum of diamond crystallisation ages. High contents of both Re and Os, and the similarity of Re/Os ratios of sulphide inclusions in diamonds to whole rock eclogite and peridotite xenoliths indicate that small amounts of sulphides can dominate the mantle budget of both these elements during melting. Recent addition to the lithospheric mantle of high-Os material similar to that from which the P-type sulphides crystallised may explain the variable, sometimes young Os model ages seen in whole rock xenolith Re–Os data.  相似文献   

Melting and metasomatism in the continental lithosphere: laser ablation ICPMS analysis of minerals in spinel lherzolites from eastern Australia   总被引：28，自引：0，他引：28  

Marc D. Norman 《Contributions to Mineralogy and Petrology》1998,130(3-4):240-255

Olivine, low-Ca pyroxene, diopside, and spinel from a suite of protogranular lherzolite xenoliths from southeastern Australia have been analysed for their major and trace element compositions using electron microprobe and laser ablation ICPMS. Bulk compositions of the lherzolites range from fertile (12–13% modal diopside) to depleted (2–3% modal diopside), with equilibration temperatures of 850–900 °C indicating entrainment of these lherzolites from relatively shallow depths (probably ≤ 35 km) within the lithosphere. Mineral compositions and abundances indicate a primary control by partial melting, with decreasing abundance of modal diopside accompanied by increasing Mg# of olivine and pyroxene, decreasing Al and Ti contents of diopside, increasing Ni contents of olivine, and increasing Cr/Al of spinel. HREE, Y, and Ga in diopside also follow melting trends, decreasing in concentration with increasing Mg#. In contrast, highly incompatible elements such as LREE, Nb, and Th reveal divergent behaviour that cannot be ascribed entirely to partial melting. Diopsides from the fertile lherzolites have mantle-normalized patterns that are depleted in Th, Nb, and the LREE relative to Y and the HREE, whereas, diopsides from the cpx-poor samples are strongly enriched in Th, Nb and the LREE, and have elevated Sm/Hf and Zr/Hf, and low Ti/Nb. All diopsides have strongly negative Nb anomalies relative to Th and the LREE. Trace element patterns of diopside in the fertile lherzolites can be reproduced by ≤ 5% batch melting of a primitive source. The negative Nb anomalies are a consequence of this melting, and do not require special conditions or tectonic environments. The low concentrations of Y and HREE in diopside from the cpx-poor lherzolites cannot be produced by realistic degrees of batch melting, but can be accomplished by up to ∼20% fractional melting, suggesting multiple episodes of melt depletion. Os isotopic compositions of these lherzolites show that the melt depletion events occurred in the middle and late Proterozoic, demonstrating the long-term stability of lithospheric mantle beneath regions of eastern Australia. The LREE-enriched diopsides are well equilibrated and record metasomatic enrichment events that pre-date the magmatism that entrained these xenoliths. Trace element patterns of these pyroxenes suggest a carbonatitic melt as the metasomatic agent. Received: 24 September 1996 / Accepted: 12 August 1997  相似文献   

Volume estimation of the 1998 flank collapse at Casita volcano,Nicaragua: a comparison of photogrammetric and conventional techniques     

Norman Kerle 《地球表面变化过程与地形》2002,27(7):759-772

In October 1998 a precipitation‐triggered flank collapse occurred at Casita volcano, Nicaragua, leading to a devastating lahar. In this paper the failure volume was calculated using a range of methods. Several pre‐ and post‐failure digital elevation models (DEMs) were created, based on photogrammetric, cartometric and surveying data. The wide range in resulting volumes prompted an assessment of the accuracies and potential problems associated with each of the datasets and techniques used. The best estimate for the failure volume is 1·6 × 10⁶ m³. It is based on a vegetation‐corrected pre‐failure DEM, generated using automated digital photogrammetry, and a post‐failure surface based on a field survey carried out with a Total Station. The volume figure is approximately an order of magnitude higher than values reported in previous publications, all of which are based solely on field estimates. This demonstrates that values reported in the literature, if they are not based on rigorous quantitative analysis, must be regarded with caution. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Comment on “the use of the minimum-dissipation principle in tectonophysics” by P. Bird and D.A. Yuen     

Norman H. Sleep  Seth Stein  Robert J. Geller  Richard G. Gordon 《Earth and Planetary Science Letters》1979,45(1):218-220

  相似文献   

The abundance of volatiles in Hawaiian tholeiitic submarine basalts     

David W. Muenow  Diana G. Graham  Norman W.K. Liu  John R. Delaney 《Earth and Planetary Science Letters》1979,42(1):71-76

High-temperature mass spectrometric studies have been made to determine the distribution of volatiles within glassy rims of submarine pillow basalts dredged from the east rift zone of Kilauea volcano, Hawaii. The CO₂/H₂O mole ratio for glass-vapor inclusions within olivine phenocrysts in the glassy rims is greater than 30 : 1 compared to 0.06 for matrix glasses. Enclosing matrix glasses contain 0.53–0.74 wt.% H₂O, 0.02–0.04 wt.% carbon, 0.08–0.12 wt.% sulfur, 0.012–0.028 wt.% chlorine and 0.012–0.077 wt.% fluorine.  相似文献