The ilmenite/titano-magnetite assemblage: kinetics of re-equilibration     

Patrick A. Hammond  Lawrence A. Taylor 《Earth and Planetary Science Letters》1982,61(1):143-150

Compositions of coexisting ilmenite and titano-magnetite commonly have been used to establish the conditions of formation for igneous and metamorphic rocks (Buddington-Lindsley geothermometer/oxybarometer). Temperatures so determined for some rocks are lower than might be expected for magmatic crystallization. These low temperatures are the result of re-equilibration of the Fe-Ti oxides during slow cooling. This process is one in which titano-magnetites are oxidized and ilmenites are reduced upon cooling along a buffer curve or in the presence of a fluid of constant composition. Textural studies indicate that the reduction of the ilmenite-hematite phase may be the slower reaction consequently, the rate-controlling step of the re-equilibration.The kinetics of the reduction reactions in the two-phase region between the joins for the ilmenite-hematite and magnetite-ulvöspinel solid solution series were studied by thermogravimetric analysis at controlledf_O2. With experiments conducted near the Ni/NiO and QFM buffers, annealed ilmenite(ss) synthetic charges were reduced isothermally. The temperature range for the experiments was 900–1250°C, with total gas-flow rates of 0.35 and 1.0 cm/s. Kinetic data were collected by measuring the weight change during each experiment as a function of time. Additionally, a cooling-rate (0.5°C/hr) experiment was conducted near the QFM buffer from 1150 to 985°C starting with an ilmenite-saturated spinel phase.At 1200°C and 0.35 cm/s flow rate, the reaction mechanism is an interfacial process where mass transport of the reacting gases is the rate-controlling step. In isothermal experiments at 1100°C and lower, diffusion of reactants through a solid product layer was the controlling mechanism. The activation energy for this diffusion process is 59±6 kcal/mole. Significant enhancement of diffusion occurs along grain boundaries.Although the individual phases may re-equilibrate internally upon cooling, the Fe-Ti contents must remain unchanged for proper use of this mineral indicator-i.e. no external re-equilibration. It is imperative that the kinetics of the situation be appreciated. These preliminary kinetic experiments indicate that extreme caution must be exercised when applying this ilmenite/titano-magnetite geothermometer/oxybarometer. These phases may only truly “quench” in the parameters of formation in the case of certain hypabyssal and extrusive occurrences  相似文献   

Exsolution in the mss-pentlandite system: Textural and genetic implications for Ni-sulfide ores     

A. Durazzo  L. A. Taylor 《Mineralium Deposita》1982,17(3):313-332

Experimentation in synthetic systems is essential for a correct interpretation of ore-mineral textures such as the pyrrhotite-pentlandite (po-pn) intergrowths of Ni-sulfide deposits. Within the Fe-Ni-S system, isothermal and cooling exsolution experiments were performed on monosulfide solid solution (mss) of various compositions using sealed, evacuated silica-glass tubes. The charges were annealed between 400° and 200°C for periods ranging from 20 minutes to 5 weeks; also, charges were cooled from 500° to 100°C at 1°C/h. Early-formed isothermal textures form by nucleation and growth, and depend on the initial degree of supersaturation and metal diffusivities; the final textures result from further growth and coarsening of the early forms and are particularly sensitive to the diffusivities, which are a function of temperature. The cooling-rate experiments indicate that massive pn develops by exsolution between 610° and about 250°C during slow cooling from temperatures above the mss-pn solvus; coarsened pn forms along basal planes in the mss matrix between about 250° and 150°C; pn "Flames" result at 150°C or slightly below. Crossing pn lamellae, obtained isothermally at high degrees of supersaturation and virtually unknown in ores, cannot form during slow cooling.  相似文献   

4333828 Automatic dump valve     

D.F. Taylor 《Marine pollution bulletin》1983,14(3):115-116

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The reproductive cycle of the bay scallop,Argopecten irradians irradians (Lamarck), in a small coastal embayment on Cape Cod,Massachusetts     

Rodman E. Taylor  Judith M. Capuzzo 《Estuaries and Coasts》1983,6(4):431-435

The spawning activity of the bay scallop Argopecten irradians irradians (Lamarck) was monitored from May through September in a small embayment on Cape Cod, Massachusetts and compared with changes in hydrographic conditions. Spawning activity of bay scallops began in May and continued through July with some minor activity occurring during August and September. Activity was most closely related to changes in ambient temperature and occurred predominantly before the summer maximum temperature was recorded. As temperatures declined in the late summer and early fall, increased gametogenic activity was evident. A longer period of spawning activity was observed than was previously reported for New England waters.  相似文献   

Geochemistry of Archean shales from the Pilbara Supergroup,Western Australia     

Scott M. McLennan  S.R. Taylor  K.A. Eriksson 《Geochimica et cosmochimica acta》1983,47(7):1211-1222

Archean clastic sedimentary rocks are well exposed in the Pilbara Block of Western Australia. Shales from turbidites in the Gorge Creek Group (ca. 3.4 Ae) and shales from the Whim Creek Group (ca. 2.7 Ae) have been examined. The Gorge Creek Group samples, characterized by muscovite-quartzchlorite mineralogy, are enriched in incompatible elements (K, Th, U, LREE) by factors of about two, when compared to younger Archean shales from the Yilgarn Block. Alkali and alkaline earth elements are depleted in a systematic fashion, according to size, when compared with an estimate of Archean upper crust abundances. This depletion is less notable in the Whim Creek Group. Such a pattern indicates the source of these rocks underwent a rather severe episode of weathering. The Gorge Creek Group also has fairly high B content (85 ± 29 ppm) which may indicate normal marine conditions during deposition.Rare earth element (REE) patterns for the Pilbara samples are characterized by light REE enrichment ($\text{La}{}_{\mathrm{N}}\text{Yb}{}_{\mathrm{N}}\text{≥ 7.5}$) and no or very slight Eu depletion ($\text{Eu}\text{Eu}{}^1\text{= 0.82 – 0.99}$). A source comprised of about 80% felsic igneous rocks without large negative Eu-anomalies (felsic volcanics, tonalites, trondhjemites) and 20% mafic-ultramafic volcanics is indicated by the trace element data. Very high abundances of Cr and Ni cannot be explained by any reasonable provenance model and a secondary enrichment process is called for.  相似文献   

Improved magnetic anomalies of the Antarctic lithosphere from satellite and near-surface data     

Hyung Rae Kim  Ralph R. B. von Frese  Patrick T. Taylor  Alexander V. Golynsky  Luis R. Gaya-Piqué  Fausto Ferraccioli 《Geophysical Journal International》2007,171(1):119-126

The Antarctic magnetic anomaly map compiled marine and airborne surveys collected south of 60°S through 1999 and used Magsat data to help fill in the regional gaps between the surveys. Ørsted and CHAMP satellite magnetic observations with greatly improved measurement accuracies and temporal and spatial coverage of the Antarctic, have now supplanted the Magsat data. We combined the new satellite observations with the near-surface survey data for an improved magnetic anomaly map of the Antarctic lithosphere. Specifically, we separated the crustal from the core and external field components in the satellite data using crustal thickness variations estimated from the terrain and the satellite-derived free-air gravity observations. Regional gaps in the near-surface surveys were then filled with predictions from crustal magnetization models that jointly satisfied the near-surface and satellite crustal anomalies. Comparisons in some of the regional gaps that also considered newly acquired aeromagnetic data demonstrated the enhanced anomaly estimation capabilities of the predictions over those from conventional minimum curvature and spherical harmonic geomagnetic field models. We also noted that the growing number of regional and world magnetic survey compilations involve coverage gaps where these procedures can contribute effective near-surface crustal anomaly estimates.  相似文献   

Emplacement, growth, and gravitational deformation of serpentinite seamounts on the Mariana forearc     

A. J. Oakley  B. Taylor  P. Fryer  G. F. Moore  A. M. Goodliffe  J. K. Morgan 《Geophysical Journal International》2007,170(2):615-634

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A User-Oriented Perspective of Error-sensitive GIS Development     

Matt Duckham 《Transactions in GIS》2002,6(2):179-193

The current lack of error-sensitive functionality found in commercial GIS is at odds with the research focus error-sensitive GIS development has enjoyed over recent years. In an attempt to address this undesirable situation, this paper explores the development of error handling capabilities within GIS from the perspective of GIS users. Increasingly, GIS users need to fulfil a variety of different roles, from database designers and data capture personnel through to decision makers, each of which may require an awareness of data quality issues. The user-oriented approach taken here contrasts with the predominately developer-oriented perspective in the literature. The paper concludes that from a user's perspective it is possible to identify a number of simple reformulations of current research that would help bring about the desired increase in availability and use of error-sensitive functionality within commercial GIS technology and applications.  相似文献   

Road Reduction Filtering for GPS-GIS Navigation   总被引：2，自引：0，他引：2  

George Taylor  Geoffrey Blewitt  Doerte Steup  Simon Corbett  & Adrijana Car 《Transactions in GIS》2001,5(3):193-207

A novel method of map matching using the Global Positioning System (GPS) has been developed for civilian use, which uses digital mapping data to infer the systematic position errors of less than 100m which result largely from 'selective availability' (S/A) imposed by the US military. Selective availability was switched off on the 2nd of May 2000, and is to be replaced with 'regional denial capabilities in lieu of global degradation'. The system tracks a vehicle on all possible roads (road centre-lines) in a computed error region, then uses a method of rapidly detecting inappropriate road centre-lines from the set of all those possible. This is called the Road Reduction Filter (RRF) algorithm. Point positioning is computed using C/A code pseudorange measurements direct from a GPS receiver. The least squares estimation is performed in the software developed for the experiment described in this paper. Virtual differential GPS (VDGPS) corrections are computed and used from a vehicle's previous positions, thus providing an autonomous alternative to DGPS for in-car navigation and fleet management. Height aiding is used to augment the solution and reduce the number of satellites required for a position solution. Ordnance Survey (OS) digital map data was used for the experiment, i.e. OSCAR 1 m resolution road centre-line geometry and Land Form PANORAMA 1:50,000, 50 m-grid digital terrain model (DTM). Testing of the algorithm is reported and results are analysed. Vehicle positions provided by RRF are compared with the 'true' position determined using high precision (cm) GPS carrier phase techniques. It is shown that height aiding using a DTM and the RRF significantly improve the accuracy of position provided by inexpensive single frequency GPS receivers.  相似文献   

Yaping Shao. Physics and Modelling of Wind Erosion     

Peter A. Taylor 《Boundary-Layer Meteorology》2001,101(1):127-128

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