The formation of eclogite facies metatroctolites and a general petrogenetic grid in Na₂O–CaO–FeO–MgO–Al₂O₃–SiO₂–H₂O (NCFMASH)     

G. Rebay  R. Powell 《Journal of Metamorphic Geology》2002,20(9):813-826

Eclogite facies metatroctolites from a variety of Western Alps localities (Voltri, Monviso, Lanzo, Allalin, Zermat–Saas, etc.) that preserve textural evidence of their original form as bimineralic olivine‐plagioclase rocks are considered in terms of calculated mineral equilibria in the system Na₂O‐CaO‐FeO‐MgO‐Al₂O₃‐SiO₂‐H₂O (NCFMASH). Pseudosections, based on a new petrogenetic grid for NCFMASH presented here, are used to unravel the metamorphic history of the metatroctolites, considering the rocks to consist of different composition microdomains corresponding to the original olivine and plagioclase grains. On the basis that the preservation of the mineral assemblage in each microdomain will tend to be from where on a rock's P–T path the metamorphic fluid phase is used up via rehydration reactions, P–T pseudosections contoured for water content, and P–T path‐M_H2O (amount of water) pseudosections, are used to examine fluid behaviour in each microdomain. We show that the different microdomains are likely to preserve their mineral assemblages from different places on the P–T path. For the olivine microdomain, the diagnostic mineral assemblage is chloritoid + talc (+ garnet + omphacite). The preservation of this assemblage, in the light of the closed system P–T path‐M_H2O relationships, implies that the microdomain loses its metamorphic fluid as it starts to decompress, and, in the absence of subsequent hydration, the high pressure mineral assemblage is then preserved. In the plagioclase microdomain, the diagnostic assemblage is epidote (or zoisite) + kyanite + quartz suggesting a lower pressure (of about 2 GPa) than for the olivine microdomain. In the light of P–T path‐M_H2O relationships, development of this assemblage implies breakdown of lawsonite across the lawsonite breakdown reaction, regardless of the maximum pressure reached. It is likely that the plagioclase microdomain was mainly fluid‐absent prior to lawsonite breakdown, only becoming fluid‐present across the reaction, then immediately becoming fluid‐absent again.  相似文献   

Experimental studies on three potassium-rich ultramafic rocks from Damodar Valley, East India     

A. K. Gupta  B. Chattopadhyay  W. S. Fyfe  M. Powell 《Mineralogy and Petrology》2002,74(2-4):343-360

Summary An experimental study on the phase relationships of three potassium-rich ultramafic rocks from the Damodar Valley, Gondawana basins, has been performed under upper mantle P–T conditions (1.0–2.5 GPa, 700–1200 °C). The Mohanpur lamproite and Satyanarayanpur minette, both from the Raniganj basins, have been investigated with the addition of 15 wt% H₂O. No water was added in the experiments done on an olivine minette from the Jarangdih coal mine, Bokaro Basin, which originally contains 15 wt% CO₂ and 2.86 wt% H₂O. In all cases, olivine is the liquidus phase followed by phlogopite. The subsolidus assemblage for the three rocks is a phlogopite-bearing harzburgite, associated with apatite, Mg-ilmenite and carbonates for the Jarangdih rock; apatite, chromian spinel and carbonates and priderite (only between 1.0 and 1.2 GPa) in the case of the Mohanpur lamproite, and finally apatite, chromian spinel, rutile, and carbonate in the Satyanarayanpur sample. Although orthopyroxene is absent in the natural potassium-rich ultramafic rocks, its presence in the run products of the Jarangdih rock is possibly related to a reaction between olivine and a CO₂-bearing fluid phase. The presence of orthopyroxene in the run products of Mohanpur and Satyanarayanpur rocks may be due to a reaction between K-feldspar, olivine and a vapour phase to produce phlogopite and orthopyroxene. On the basis of present experimental investigation and isotopic studies made by previous investigators, it has been suggested that these K-rich rocks have crystallized from melts derived by vein-plus-wall-rock melting of a phlogopite-bearing harzburgite source rock. Received December 15, 1999; revised version accepted June 17, 2001  相似文献   

A macro-scale flood risk model for Jamaica with impact of climate variability     

Christopher P. Burgess  Michael A. Taylor  Tannecia Stephenson  Arpita Mandal  Leiska Powell 《Natural Hazards》2015,78(1):231-256

Floods account for more than half of the global hydrometeorological risks. Severe floods cause significant economic shocks and loss of lives, particularly for developing countries such as Jamaica. There is need for more information on the present and projected flood risks to justify macro-scale planning for climate change adaptation and facilitate the decision-making processes. In this study, a catalogue of 198 flood events occurring between 1678 and 2010 is compiled for Jamaica and used to examine the climatology, occurrence, trends, causes and duration of the island’s severe events. The annual flood risk is estimated to be a loss of life rate of 4 persons and estimated annual damage of USD96.3 million per annum in 2010 values and approximately 0.84 % of GDP per annum. Macro-scale models for flood risks (deaths and damages) are also developed using data from the flood catalogue and maximum precipitation at the town and parish level. The models examine the relationship between flood risks (death and damages) and extreme rainfall depths and intensities. Future climate risks of loss of lives and damages are predicted to increase 11 and 9 %, respectively, to 4.4 persons and USD105.2 million per annum.  相似文献   

The Great God beyond the Sierras     

J.M. Powell 《The Australian geographer》2015,46(2):281-287

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Calculation of partial melting equilibria in the system Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O (NCKFMASH)     

R. W. White  R. Powell  T. J. B. Holland 《Journal of Metamorphic Geology》2001,19(2):139-153

A thermodynamic model for haplogranitic melts in the system Na₂O–CaO–K₂O–Al₂O₃–SiO₂–H₂O (NCKASH) is extended by the addition of FeO and MgO, with the data for the additional end‐members of the liquid incorporated in the Holland & Powell (1998) internally consistent thermodynamic dataset. The resulting dataset, with the software thermocalc , is then used to calculate melting relationships for metapelitic rock compositions. The main forms for this are P–T and T–X pseudosections calculated for particular rock compositions and composition ranges. The relationships in these full‐system pseudosections are controlled by the low‐variance equilibria in subsystems of NCKFMASH. In particular, the solidus relationships are controlled by the solidus relationships in NKASH, and the ferromagnesian mineral relationships are controlled by those in KFMASH. However, calculations in NCKFMASH allow the relationships between the common metapelitic minerals and silicate melt to be determined. In particular, the production of silicate melt and melt loss from such rocks allow observations to be made about the processes involved in producing granulite facies rocks, particularly relating to open‐system behaviour of rocks under high‐grade conditions.  相似文献   

Rapid delineation of subsurface petroleum contamination using the site characterization and analysis penetrometer system     

W. M. Davis  E. R. Cespedes  L. T. Lee  J. F. Powell  R. A. Goodson 《Environmental Geology》1997,29(3-4):228-237

 The Site Characterization and Analysis Penetrometer System (SCAPS) was used to investigate subsurface petroleum contamination at Aberdeen Proving Ground, Maryland. The SCAPS is a rapid site-screening tool developed by the Tri-Services (U.S. Army, Navy, and Air Force) to reduce the cost of installation restoration activities. The system, consisting of a geophysical cone penetrometer fitted with a laser-induced fluorescence petroleum sensor, is capable of simultaneous, real-time delineation of subsurface stratigraphy and petroleum contamination. Onsite processing of the SCAPS data allows three-dimensional visualization of both subsurface stratigraphy and petroleum contaminant distribution. The site investigation described herein successfully identified three distinct areas of subsurface petroleum contamination caused by leaking underground storage tanks containing No. 2 healing oil. The SCAPS petroleum sensor response was verified by obtaining 20 soil samples and performing onsite and conventional laboratory analyses for petroleum contaminants. Verification sample results indicate a strong correlation between the SCAPS fluorescence data and conventional measures of petroleum contamination. This investigation illustrates the capabilities of the SCAPS for rapid site characterization. Received: 27 November 1995 · Accepted: 11 December 1995  相似文献   

MULTIVARIATE RESPONSE SURFACE MODELLING BY PRINCIPAL COMPONENTS ANALYSIS     

N.BRATCHELL 《地理学报(英文版)》1989,(3)

Analysis of multivariate response data by modelling the principal components of the response has beenapplied to two sets of data. In both cases principal components analysis revealed the relationships amongthe response variables and exploited them to simplify the problem of modelling and optimizing themultivariate response. The models and optima obtained from the principal components comparedfavourably with the individual models and simultaneous optima.  相似文献   

A programmable microcomputer-based sonar echo processor for real-time processing     

Lee Powell Stanton  T. 《Oceanic Engineering, IEEE Journal of》1983,8(4):280-287

A programmable microcomputer-based sonar echo processor has been developed and field tested to process echo data in real time. The device was designed for use in fisheries acoustics and to analyze echoes from the sea floor. The instrument simultaneously performs the functions "echo integration" and "echo peak detection' on the sonar signal. The "echo integration" circuitry measures the relative acoustic energy of the echo while the "echo peak detection' electronics measure the probability density function (PDF) of the peak of the echo envelope. Each process is gated so the echoes may be processed in many short time intervals. In fisheries applications, estimates can be made of fish density (fish per unit volume), average backscattering cross section, and a combination of fish size and behavior. When using the device to analyze bottom echoes, it is possible to measure both the returned energy from the bottom sediment interfaces and the microrelief characteristics. The durability, flexibility, computer link, and floppy-disk data-storage features of the system are discussed. Data are presented of the processed echoes from biological organisms and the ocean bottom from a recent research cruise on the Atlantic Ocean near Cape Hatteras, NC. The biological results illustrated the organisms to be clearly divided into two separate spatial distributions-an observation not obvious from a standard echogram which was simultaneously used. The results from the bottom showed both 1) the difference in sub-bottom structure between two locations and 2) changes in microrelief of the water-bottom interface between another pair of locations.  相似文献   

NEW APPROACH TO ESTIMATING SOLAR RADIATION FROM SATELLITE IMAGERY*   总被引：1，自引：1，他引：0  

Gary L. Powell  Anthony J. Brazel  Martin J. Pasqualetti 《The Professional geographer》1984,36(2):227-233

A significantly less expensive but comparatively accurate means of estimating solar radiation from satellite imagery is demonstrated. Opaque cloud cover is visually extracted from nondigitized, photographic forms of GOES satellite imagery and solar radiation is estimated using this information as input into a relatively simple solar model. Daily root mean square, mean absolute and mean bias errors were 13.2, 8.6 and 1.1 percent, respectively. Maps of the spatial distribution of solar radiation for Arizona are included.  相似文献   

Uncertainty estimation of the global temperature trends for multiple radiosondes, reanalyses, and CMIP3/IPCC climate model simulations     

Jianjun Xu  Alfred M. Powell Jr 《Theoretical and Applied Climatology》2012,108(3-4):505-518

Based on three groups of datasets that include radiosondes, reanalyses, and climate model simulations (e.g., Coupled Model Intercomparison Project, CMIP3) from 1979 to 2008, the interannual variability, global temperature trends, and their uncertainty using ensemble spread among intra-group and inter-group datasets have been discussed. The results show that the interannual temperature variability increased from the troposphere to stratosphere, and the maximum occurs around 50?hPa. The CMIP3 climate models have the largest discrepancy in the stratosphere. The intra-group correlations at 500?hPa generally show high similarity within each data group while the inter-group correlations between reanalyses and the CMIP3 climate model simulations indicate lesser similarity. In contrast, the inter-group correlation at 50?hPa is improved except with the Japanese 25-year Reanalysis Project (JRA-25) dataset, and the Twentieth Century Reanalysis (20CR) reanalysis shows a weak cross correlation. The global temperature trends are highly dependent on the individual data sources. Compared to the radiosondes, the reanalyses show a large ensemble spread of trends in the stratosphere, and the CMIP3 climate model simulations have a large ensemble spread in the height of the crossover point where tropospheric warming changes into stratospheric cooling. The largest ensemble spread among the reanalyses in the stratosphere is mainly from the large discrepancy in the JRA-25 reanalysis after 1998 and a relatively weak anomaly in the 20CR before 1986. The largest ensemble spread among the CMIP3 climate models in the troposphere is related to the influence of both volcanic eruptions and El Ni?o/La Ni?a–Southern Oscillation events. The strong anomalies corresponding to the volcanic eruptions of El Chichon in 1982 and Mt Pinatubo in 1991 are clearly identified in the stratosphere. These volcanic eruptions reduced the warming in the troposphere and strengthened the cooling in the stratosphere during the most recent 30?years.  相似文献