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31.
Summary The granites of the Sistema Central Espanol are richer in ammonium than those of most other regions, and have a mean NH4
+ content of 84 ppm (range = 1–243 ppm). Among the possible causes for the high level of ammonium, a high proportion of organic-rich pelitic protolith and reducing conditions during anatexis are considered to be the most significant. The behaviour of the ammonium ion during magmatic differentiation is discussed by reference to its distribution in the Pedrobernardo layered intrusion: ammonium is depleted in the final liquid fraction, but there is no relative fractionation of NH4
+ and K+. The depletion of the melt in NH4
+ during crystallization is attributed to its removal by biotite and to a lesser extent by K-feldspar. The behaviour of the ammonium ion during anatexis is discussed with reference to the Peña Negra migmatite complex. It is shown that large amounts of NH4
+ are present in these high grade metamorphic rocks, and that NH4
+ is preferentially partitioned into the restite fraction during partial melting. These relationships are attributed to the preferential incorporation of NH4
+ into potassic host minerals in the order: biotite > muscovite > K-feldspar.
With 5 Figures 相似文献
Ammonium in Zentralspanischen Graniten, und das Verhalten des Ammonium-Ions während Anatexis und fraktionierter Kristallisation
Zusammenfassung Die Granite des Sistema Central Espanol sind reicher an Ammonium als die der meisten anderen Regionen, und haben einen durchschnittlichen NH4 + Gehalt von 84 ppm (von 1-243 ppm). Der hohe Ammoniumgehalt könme auf einen hohen Anteil peiitischer Ausgangsgesteine, die reich an organischen Material sind, and auf reduzierende Bedingungen während der Anatexis zurückgehen. Das Verhalten des Ammonium-Ions während magmatischer Differentiation wind in Hinblick seiner Verteilung in der geschichteten Intrusion von Pedrobernardo diskutiert: Ammonium ist in der finalen Schmelzfraktion angereichert, aber es gibt keine relative Fraktionierung von NH4 + and K+. Die Verarmung der Schmelze an NH4 + wahrend der Kristallisation geht darauf zurück, daß NH4 + von Biotit and in einem geringen Ausmaß von K-Feldspat aufgenommen wird. Das Verhalten des Ammonium-Ions während der Anatexis wird am Peña Negra Migmatit-Komplex diskutiert. Es zeigt rich, daß große Mengen von NH4 + in diesen hochgradig metamorphen Gesteinen vorkommen, and das NH4 + während teilweiser Aufschmelzung vorzugsweise in der Restit-Fraktion angereichert wird. Diese Beziehungen gehen auf die vorzugsweise Aufnahme von NH4 + in Kali-führenden Gastmineralen zurück, and zwar in folgender Ordnung: Biotit > Muskovit > K-Feldspat.
With 5 Figures 相似文献
32.
M.A. Maslin M.A. Hall N.J. Shackleton E. Thomas 《Geochimica et cosmochimica acta》1996,60(24):5089-5100
The δ13C of organic matter bound within the crystal lattice of foraminiferal calcite tests may provide a potential tracer of the isotopic composition of the surface water primary photosynthate. Using δ13C of the organic matter extracted from the crystal lattice and the calcite test, it is theoretically possible to estimate the paleo-surface water pCO2. We have tailored this technique initially for the subpolar planktonic foraminifera species Globigerina bulloides. Initial surface water pCO2 estimates from deep-sea core BOFS 5K (50°41.3′N, 21°51.9′W, water depth 3547 m) indicate that the northeast Atlantic Ocean may have been a greater sink for CO2 during the last glacial than during the Holocene. Greatly reduced benthic foraminifera abundances, especially phytodetritus feeders, in BOFS 5K during the last glacial indicates low surface productivity. This rules out a productivity-driven CO2 sink. The enhanced glacial CO2 sink must, therefore, have results from a southwards shift of the centre of deep water formation. 相似文献
33.
Kevin Hall 《地球表面变化过程与地形》2004,29(1):43-57
Discussions regarding weathering in cold environments generally centre on mechanical processes and on the freeze–thaw mechanism in particular. Despite the almost ubiquitous assumption of freeze–thaw weathering, unequivocal proof of interstitial rock water actually freezing and thawing is singularly lacking. Equally, many studies have used the crossing of 0 °C, or values close to that, as the basis for determining the number of ‘freeze–thaw events’. In order to assess the weathering regime at a site in northern Canada, temperatures were collected at the surface, 1 cm and 3 cm depth for sets of paving bricks, with exposures both vertical and at 45°, orientated to the four cardinal directions. Temperature data were collected at 1 min intervals for 1 year. These data provide unequivocal proof for the occurrence of the freezing and thawing of water on and within the rock (freeze–thaw events). The freeze event is evidenced by the exotherm associated with the release of latent heat as the water actually freezes. This is thought to be the ?rst record of such events from a ?eld situation. More signi?cantly, it was found that the temperature at which freezing occurred varied signi?cantly through the year and that on occasion the 1 cm depth froze prior to the rock surface. The change in freeze temperature is thought to be due to the chemical weathering of the material (coupled with on‐going salt inputs via the melting of snowfall), which, it is shown, could occur throughout the winter despite air temperatures down to ?30 °C. This ?nding regarding chemical weathering is also considered to be highly signi?cant. A number of thermal stress events were also recorded, suggesting that rock weathering in cold regions is a synergistic combination of various chemical and mechanical weathering mechanisms. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
34.
Li/Ca ratios were measured in planktonic and benthic foraminifera from a variety of hydrographic settings to investigate the factors influencing lithium incorporation into foraminiferal tests including temperature, dissolution, pressure, and interspecies differences. Down-core measurements of planktonic (Orbulina universa, Globigerinoides ruber, and Globigerinoides sacculifer) and benthic foraminifera (calcitic Cibicides wuellerstorfi and aragonitic Hoeglandina elegans) show a systematic variation in Li/Ca with δ18O through the last glacial-interglacial transition. All species examined exhibit an increase in Li/Ca between 14 to 50% from the Holocene to the last glacial maximum. Li/Ca generally increases with decreasing temperature as seen in a latitudinal transect of planktonic O. universa and down-slope benthic species along the Bahama Bank margins. Postdepositional dissolution possibly causes a decrease in planktonic foraminiferal Li/Ca along the Sierra Leone Rise, and increased water depth causes a decrease in benthic foraminiferal Li/Ca in the deep Caribbean. However, none of these effects are sufficient to account for the observed glacial-interglacial changes. Physiological factors such as calcification rate may affect the Li/Ca content of foraminiferal calcite. The calcification rate in turn may be a function of carbonate ion concentration of ambient ocean water. This work shows that incorporation of lithium by foraminifera appears to be influenced by factors other than seawater composition and does not appear to be dominated by changes in temperature, dissolution, or pressure. We hypothesize that the consistent increase in foraminiferal Li/Ca during the last glacial maximum may be linked to changes in seawater carbonate ion concentration. Important parameters to be tested include calcification rate and foraminiferal test size and weight. If foraminiferal Li/Ca is dominantly controlled by calcification rate as a function of seawater carbonate ion concentration, then Li/Ca may act as a proxy of past atmospheric CO2. 相似文献
35.
36.
Seasonal and inter-annual relationships between vegetation and climate in central New Mexico, USA 总被引:8,自引:0,他引:8
Jeremy L. Weiss David S. Gutzler Julia E. Allred Coonrod Clifford N. Dahm 《Journal of Arid Environments》2004,57(4):507-534
Linear correlations between seasonal and inter-annual measures of meteorological variables and normalized difference vegetation index (NDVI) are calculated at six nearby yet distinct vegetation communities in semi-arid New Mexico, USA Monsoon season (June–September) precipitation shows considerable positive correlation with NDVI values from the contemporaneous summer, following spring, and following summer. Non-monsoon precipitation (October–May), temperature, and wind display both positive and negative correlations with NDVI values. These meteorological variables influence NDVI variability at different seasons and time lags. Thus vegetation responds to short-term climate variability in complex ways and serves as a source of memory for the climate system. 相似文献
37.
Detailed echo‐sounder and acoustic Doppler velocimeter measurements are used to assess the temporal and spatial structure of turbulent flow over a mobile dune in a wide, low‐gradient, alluvial reach of the Green River. Based on the geometric position of the sensor over the bedforms, measurements were taken in the wake, in transitional flow at the bedform crest, and in the internal boundary layer. Spatial distributions of Reynolds shear stress, turbulent kinetic energy, turbulence intensity, and correlation coefficient are qualitatively consistent with those over fixed, two‐dimensional bedforms in laboratory flows. Spectral and cospectral analysis demonstrates that energy levels in the lee of the crest (i.e. wake) are two to four times greater than over the crest itself, with minima over the stoss slope (within the developing internal boundary layer). The frequency structure in the wake is sharply defined with single, dominant peaks. Peak and total spectral and cross‐spectral energies vary over the bedform in a manner consistent with wave‐like perturbations that ‘break’ or ‘roll up’ into vortices that amalgamate, grow in size, and eventually diffuse as they are advected downstream. Fluid oscillations in the lee of the dune demonstrate Strouhal similarity between laboratory and field environments, and correspondence between the peak frequencies of these oscillations and the periodicity of surface boils was observed in the field. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
38.
Broadly speaking, there is, at least within geomorphic circles, a general acceptance that rocks with low albedos will warm both faster and to higher temperatures than rocks with high albedos, reflectivity influencing radiative warming. Upon this foundation are built notions of weathering in respect of the resulting thermal differences, both at the grain scale and at the scale of rock masses. Here, a series of paving bricks painted in 20 per cent reflectivity intervals from black through to white were used to monitor albedo‐influenced temperatures at a site in northern Canada in an attempt to test this premise. Temperatures were collected, for five months, for the rock surface and the base of the rock, the blocks being set within a mass of local sediment. Resulting thermal data did indeed show that the dark bricks were warmer than the white but only when their temperatures were equal to or cooler than the air temperature. As brick temperature exceeded that of the air, so the dark and light bricks moved to parity; indeed, the white bricks frequently became warmer than the dark. It is argued that this ‘negating’ of the albedo influence on heating is a result of the necessity of the bricks, both white and black, to convect heat away to the surrounding cooler air; the darker brick, being hotter, initially convects faster than the white as a product of the temperature difference between the two media. Thus, where the bricks become significantly hotter than the air, they lose energy to that air and so their respective temperatures become closer, the albedo influence being superceded by the requirement to equilibrate with the surrounding air. It is argued that this finding will have importance to our understanding of weathering in general and to our perceptions of weathering differences between different lithologies. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
39.
Jeremy P. Richards 《Resource Geology》2005,55(2):131-137
Abstract. The modern minerals industry is more environmentally responsible and socially aware than at any time in the past, and yet faces increasing challenges to improve its performance in these areas still further. Some of these expectations are reasonable and achievable, but others are unrealistic (e.g., “zero impact”) if real development is to continue. Moreover, because society is the ultimate beneficiary of the industry's products, it should be prepared to pay for the improvements it demands. Currently externalized costs, such as many environmental and social impacts, should be internalized into prices, and higher royalties should be charged on gross revenue to ensure effective capture of value of non‐renewable resources by host countries. Such costs to consumers could be offset by higher recycling value, leasing, or deposit‐return schemes. NGOs have an important role to play in working with industry to convince society to accept such changes. 相似文献
40.