The behavior of apatite during crustal anatexis: Equilibrium and kinetic considerations   总被引：5，自引：0，他引：5  

T.Mark Harrison  E.Bruce Watson 《Geochimica et cosmochimica acta》1984,48(7):1467-1477

The solubility and dissolution kinetics of apatite in felsic melts at 850°–1500°C have been examined experimentally by allowing apatite crystals to partially dissolve into apatite-undersaturated melts containing 0–10 wt% water. Analysis of P and Ca gradients in the crystal/melt interfacial region enables determination of both the diffusivities and the saturation levels of these components in the melt. Phosphorus diffusion was identified as the rate-limiting factor in apatite dissolution. Results of four experiments at 8 kbar run in the virtual absence of water yield an activation energy (E) for P diffusion of 143.6 ± 2.8 kcal-mol^?1 and frequency factor (D₀) of 2.23^+2.88_?1.26 × 10⁹cm²-sec^?1. The addition of water causes dramatic and systematic reduction of both E and D₀ such that at 6 wt% H₂O the values are ~25 kcal-mol^?1 and 10^?5 cm²-sec^?1, respectively. At 1300°C, the diffusivity of P increases by a factor of 50 over the first 2% of water added to the melt, but rises by a factor of only two between 2 and 6%, perhaps reflecting the effect of a concentration-dependent mechanism of H₂O solution. Calcium diffusion gradients do not conform well to simple diffusion theory because the release of calcium at the dissolving crystal surface is linked to the transport rate of phosphorus in the melt, which is typically two orders of magnitude slower than Ca. Calcium chemical diffusion rates calculated from the observed gradients are about 50 times slower than calcium tracer diffusion.Apatite solubilities obtained from these experiments, together with previous results, can be described as a function of absolute temperature (T) and melt composition by the expression: In D^apatite/melt_P = [(8400 + ((SiO₂ ? 0.5)2.64 × 10⁴))/T] ? [3.1 + (12.4(SiO₂ ? 0.5))] where SiO₂ is the weight fraction of silica in the melt. This model appears to be valid between 45% and 75% SiO₂, 0 and 10% water, and for the range of pressures expected in the crust.The diffusivity information extracted from the experiments can be directly applied to several problems of geochemical interest, including I) dissolution times for apatite during crustal anatexis, and 2) pileup of P, and consequent local saturation in apatite, at the surfaces of growing major-mineral phases.  相似文献   

Petrological influence on differential weathering and inselberg development in the Kora area of central Kenya     

K. Pye  A. S. Goudie  A. Watson 《地球表面变化过程与地形》1986,11(1):41-52

In the Kora area of central Kenya domed inselbergs are well developed on outcrops of granitoid migmatite, while positive relief features are rare on the surrounding gneiss. Block-strewn, vegetated hills occur on restricted areas of granoblastite, gabbro, and metagabbro. Schmidt Hammer measurements have shown that the apparent differences in resistance to weathering and erosion are not due to variations in rock hardness, since all the rock types have similar ‘R’ values. The results of geochemical analyses have shown that the migmatites are significantly more potassic than the surrounding gneiss. Samples of migmatite from the inselbergs were also found to be slightly richer in potassium than migmatite samples from the inter-inselberg areas. The variations in potassium content probably reflect differences in protolith composition, chemical fractionation during partial melting, and the effects of metasomatism. These findings support earlier suggestions that, other things being equal, potassium-rich granitoid rocks weather more slowly than less potassic rocks.  相似文献   

Spatial variability in soil moisture as predicted from airborne thematic mapper (ATM) data     

Donald A. Davidson  Alistair I. Watson 《地球表面变化过程与地形》1995,20(3):219-230

In the first part of this project, the extent to which moisture content of alluvial soils could be predicted from imagery derived from an airborne thematic mapper (ATM) was investigated. From sampling done on the same day as the flight, it was found that digital numbers derived from the thermal channel (waveband 11) were strongly correlated with gravimetric moisture content. From sampling three fields of contrasting land cover, the relationship between waveband 11 values and moisture content was found to be independent of land cover type. Spatial variation in waveband 11 values and thus moisture content were related to palaeochannel patterns on the alluvial land. This was investigated by deriving variograms for long transects from each of the three investigated fields. The range and sills of the variograms are shown to express the nature and pattern of palaeochannels. By the application of such geostatistical techniques, high resolution imagery can thus be used to quantify palaeochannel characteristics on alluvial land.  相似文献   

An open letter to G. Matheron     

G. M. Philip  D. F. Watson 《Mathematical Geosciences》1987,19(5):453-454

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Diffusion of dissolved carbonate in magmas: Experimental results and applications     

E. Bruce Watson  Mark A. Sneeringer  Alan Ross 《Earth and Planetary Science Letters》1982,61(2):346-358

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Basalt contamination by continental crust: Some experiments and models   总被引：1，自引：1，他引：1  

E. Bruce Watson 《Contributions to Mineralogy and Petrology》1982,80(1):73-87

Chemical interaction between molten basalt and felsic minerals of the continental crust (quartz, K-feldspar, and oligoclase) was examined in static and dynamic experiments at 1,200°–1,400° C. Under circumstances of continuous stirring at 1,400°, -quartz dissolves in tholeiite melt at a rate of 3.3×10^–6 g/s per cm² of contact area; at 1,300°, the solution rate is 1.5×10^–6 g/cm{cm2}s. The feldspars are molten at the experimental conditions, and interact with contacting basalt melt by diffusion in the liquid state. This is a complex process characterized by rapid initial diffusion of alkalies to establish a distribution between felsic melt and basalt similar to that observed in cases of actual two-liquid equilibrium (both alkalies reach concentrations in the felsic melt 1.5–3 times those in the basalt). Alkali diffusion may be uphill or downhill, depending on which direction of net flux is required to produce a two-liquid type distribution. Once this distribution is attained, subsequent diffusion of all melt species is slow and apparently limited by the diffusivity of SiO₂, which is 10^–9-l0^–10 cm²/s at 1,200° C. Interdiffusion experiments involving molten basalt and synthetic granite confirm the behavior illustrated by the feldspar/basalt results, and give similar SiO₂ diffusivities.The solution rates and interdiffusion data can be used to model basalt contamination processes likely to occur in the continental crust. For the restricted case of solid quartzitic xenoliths, the uptake of SiO₂ in a well-mixed basalt magma is quite fast: appreciable SiO₂ contamination may occur over exposure times of only days to years. If basalt magma induces local melting of crustal rocks, the assimilation process becomes one of liquid-state interdiffusion. In this case, the varying diffusivities of ions and their differing preferences for silicic relative to basaltic melts can produce marked selective contamination effects. Selective contamination of ascending basaltic magmas is particularly likely in the case of K₂O, which may be introduced in substantial amounts even when other elements remain unaffected. The Na₂O content of mantle-derived magmas is buffered against contamination by crustal materials, and K₂O is buffered against further increases once it reaches a level of 1–1.5 wt.%.  相似文献   

A direct measurement of the distribution in depth of 26Al in the Estacado meteorite     

J.C. Barton  A.H. Watson  A.G. Wright 《Geochimica et cosmochimica acta》1982,46(10):1963-1967

The two-dimensional distribution of ²⁶Al across a slice of the Estacado meteorite was measured using non-destructive γ-γ coincidence counting. The maximum activity was found to be 60 ± 2 dpm kg^?1 and the variation across the slice rather small. The intensity and distribution are in moderate agreement with existing theoretical models if the pre-atmospheric shape of the meteorite had been a sphere of radius 0.35 ± 0.05 m, but it was more likely to have been slightly non-spherical.  相似文献   

Zircon saturation revisited: temperature and composition effects in a variety of crustal magma types   总被引：38，自引：0，他引：38  

E. Bruce Watson  T. Mark Harrison 《Earth and Planetary Science Letters》1983,64(2):295-304

Hydrothermal experiments in the temperature range 750–1020°C have defined the saturation behavior of zircon in crustal anatectic melts as a function of both temperature and composition. The results provide a model of zircon solubility given by: In D_Zr^zircon/melt= ?3.80?[0.85(M?1)]+12900/T where D_Zr^zircon/melt is the concentration ratio of Zr in the stoichiometric zircon to that in the melt, T is the absolute temperature, and M is the cation ratio (Na + K + 2Ca)/(Al · Si). This solubility model is based principally upon experiments at 860°, 930°, and 1020°C, but has also been confirmed at temperatures up to 1500°C for M = 1.3. The lowest temperature experiments (750° and 800°C) yielded relatively imprecise, low solubilities, but the measured values (with assigned errors) are nevertheless in agreement with the predictions of the model.For M = 1.3 (a normal peraluminous granite), these results predict zircon solubilities ranging from ～ 100 ppm dissolved Zr at 750°C to 1330 ppm at 1020°C. Thus, in view of the substantial range of bulk Zr concentrations observed in crustal granitoids (～ 50–350 ppm), it is clear that anatectic magmas can show contrasting behavior toward zircon in the source rock. Those melts containing insufficient Zr for saturation in zircon during melting can have achieved that condition only by consuming all zircon in the source. On the other hand, melts with higher Zr contents (appropriate to saturation in zircon) must be regarded as incapable of dissolving additional zircon, whether it be located in the residual rocks or as crystals entrained in the departing melt fraction. This latter possibility is particularly interesting, inasmuch as the inability of a melt to consume zircon means that critical geochemical “indicators” contained in the undissolved zircon (e.g. heavy rare earths, Hf, U, Th, and radiogenic Pb) can equilibrate with the contacting melt only by solid-state diffusion, which may be slow relative to the time scale of the melting event.  相似文献   

Efficient updating of kriging estimates and variances   总被引：2，自引：0，他引：2  

R. J. Barnes  A. G. Watson 《Mathematical Geology》1992,24(1):129-133

This short note presents a method for efficiently updating ordinary kriging estimates and variances when one or more additional samples are incorporated into the kriging system. First, the foundation linear algebra result is presented. Then the update equations are derived. Finally, an illustrative application of updating is briefly discussed.  相似文献   

Winners, losers and curate's eggs: Urban and regional outcomes of Australian economic restructuring 1971–1991     

Peter A. Murphy  Sophie Watson 《Geoforum》1995,26(4):337-349

Since the early 1970s the Australian economy has undergone major transformations common to other western industrialised countries. Jobs in manufacturing declined precipitately whilst the service economy grew, most significantly in producer services but also in lower skilled jobs. Tourism and services exports began to rival traditional agricultural and mining staples. Social outcomes, also typical of international trends, included rising unemployment and polarisation of incomes. Australia's changing global context, especially the nation's increasing orientation towards Asian growth economies, have underpinned restructuring. A political climate of economic rationalism has facilitated and accentuated restructuring. The economic shifts of the past quarter century have meant that everywhere the basis for economic growth has changed. Overlaying and reinforcing the re-definition of competitive advantage has been a shift in the pattern of agglomeration economies and diseconomies. New growth regions have emerged, others have had their prospects reinforced, and still others have had their outlook diminished in absolute or, more commonly, relative terms. The paper traces the regional outcomes of national economic restructuring and shifts in the balance of agglomeration economies and diseconomies over the period from 1971 to 1991. The focus is on the top end of the urban hierarchy, on specialised industrial cities where job loss from manufacturing has hit hard, amenity regions where international and domestic tourism have been major factors in growth, and non-metropolitan balances where growth has been uneven but generally low. Demographic, economic sectoral and welfare indicators are woven into a tableau of change expressed at national, intra-state and intrametropolitan scales.  相似文献