Fluid inclusions in diamonds from the Diavik mine, Canada and the evolution of diamond-forming fluids   总被引：3，自引：0，他引：3  

Ofra Klein-BenDavid  Elad S. Izraeli  Oded Navon 《Geochimica et cosmochimica acta》2007,71(3):723-744

The analysis of micro-inclusions in fibrous diamonds from the Diavik mine, Canada revealed the presence of high density fluids (HDFs) that span a continuous compositional range between carbonatitic and saline end-members. The carbonatitic end-member is rich in Na, Ca, Mg, Fe, Ba and carbonate; the saline one is rich in K, Cl and water. In molar proportions, the composition of the saline end-member is: K₃₈Na_7.7Ca_1.8Mg_1.6Fe_1.5Ba_1.9SiO_3.1Cl₄₆(CO₃)_5.5(H₂O)₅₆ and that of the carbonatitic end member is: K₁₅Na₂₁Ca_6.7Mg_8.1Fe_6.2Ba_5.7Si_4.8Ti_1.4Al_1.9O₁₇Cl₂₉(CO₃)₂₉(H₂O)₂₉. The micro-inclusions in one diamond span a narrow range between a silicic end-member (rich in Si, K and water) and a carbonatitic one (rich in Mg, Ca, Fe and carbonate). Its average composition is: K₂₆Na_5.5Ca_13.8Mg_8.3Fe_9.6Ba_0.9P_2.5Si₂₅Ti_1.6Al_3.8Cl_2.5O₈₁(CO₃)₂₉(H₂O)₇₈. Thus, the Diavik diamonds span most of the known compositional range for fluids trapped in diamonds. Based on these data and previous analyses of fluids trapped in diamonds, we discuss possible models for the evolution of diamond-forming fluids. The most plausible model is where carbonatitic-HDFs are parental to all the other compositions. They evolve by fractionation of divalentions- and alkali-carbonates and by immiscible separation into saline- and silicic-HDFs. Each phase continues to evolve separately, crystallizing carbonates, diamond, and accessory silicates, phosphates, halides and more of the immiscible phase. Other processes, like the mixing of evolved fluids with fresh parental carbonatitic fluids, or metasomatic interactions with the wallrock also play a role in the evolution of the HDFs. We also propose that the parental carbonatitic-HDF evolves through fractional crystallization of an alkali-rich, low degree melt that is similar to the high pressure parental melts of kimberlites or lamproites.  相似文献   

Surface properties of stabilizing coastal dunes: combining spectral and field analyses     

NOAM LEVIN  GIORA J. KIDRON†  EYAL BEN-DOR 《Sedimentology》2007,54(4):771-788

The coastal dunes of Israel have been undergoing a process of stabilization since 1948. One of the major features of this process is a change in the surface properties of the dunes – the development of a biological soil crust (BSC), and a change in the properties of the sand grains themselves. In Ashdod, at the southern coastal plain of Israel, sand properties that include the BSC, their fines (silt and clay) content and free iron-oxide (indicating their degree of rubification) have been analysed in detail using field and lab spectroscopy methods. In addition, sand erosion and deposition were measured using erosion pins to determine their effect on the presence of the above-mentioned factors. It was found that the BSC over these dunes is comprised of green algae that differs in its reflectance spectra from cyanobacterial crust, especially in the blue band. The crust was found to be particularly developed in the stable areas (mainly the interdunes) and on the north-facing slopes rather than on the south-facing slopes. A positive correlation was found between the crust fines and chlorophyll content, with stable areas showing more developed BSC. The stable areas showed also a lower albedo and slightly more developed reddish colour, indicating a slightly higher rate of rubification. This study demonstrates that the intensity of sand erosion/deposition rates affects soil properties, with the BSC being the fastest to react to the stabilization process (months to several years), followed by the content of fine particles (several years to a decade), whereas the rubification process is a much weaker marker and may need much longer time periods to develop (decades to centuries).  相似文献   

A thin orogenic wedge upon thick foreland lithosphere and the missing foreland basin     

Z. Garfunkel  R. O. Greiling 《International Journal of Earth Sciences》1998,87(3):314-325

Along the Caledonian front in central Scandinavia, the expected peripheral or pro-foreland basin is neither physically present nor are there any significant traces in the sedimentary record. In order to explain and quantify this situation, the authors assess the major geometric and mechanical constraints on the Caledonian orogenic wedge and model the orogenic load and its influence on the foreland lithosphere of Baltica. Geologic and geophysical data show a strong foreland lithosphere with a flexural parameter (α) of approximately 100 km. The shape of the orogenic wedge and its critical taper angle are dependent mainly on basal friction and wedge strength. In the external part organic-rich black shales provide a low-friction horizon both at the basal detachment surface and within the wedge itself. The more internal part of the wedge is composed of metamorphic and crystalline rocks, which cooled and strengthened prior to thrusting. As a result, the external part of the wedge had a lower strength and a smaller critical taper angle than its internal part, so the orogenic load is upward concave. Modelling of the effect of such a load on the Baltica lithosphere shows a very small depression in front of the load (2 km). The flexural depression produced by the main part of the orogenic load is filled up by the thickening thrust-and-fold belt, so that there is little space left for a foreland basin. These results imply that the missing foreland basin in front of the central Scandinavian Caledonides is not due to subsequent erosion, but is a primary feature.  相似文献   

Post-cultivation recovery of biological soil crusts in semi-arid native grasslands,southern Australia     

《Journal of Arid Environments》2012

Biological soil crusts take a long time to recover after soil disturbance but data on the rate and trajectory of crust recovery are lacking. Using a space-for-time chronosequence of time-since-cultivation, we assessed the recovery of crust diversity and cover in semi-arid grasslands in southern Australia. Using sites that spanned from recently-cultivated to never-cultivated, we show that the recovery of soil crust cover is highly variable with time-since-cultivation; recently-cultivated sites generally had the lowest total cover of biological soil crusts and morphological type diversity relative to sites allowed to recover for ≥60 yrs. Moss, liverworts, squamulose and crustose lichens return to grasslands quickly after cultivation, but cover returned at highly variable rates; this might reflect that other factors (stock grazing, microtopography, soils) also affect crust cover recovery. Our results suggest that soil crusts are initially slow to recover after soil disturbance. However, post-cultivation recovery does occur but this is in the context of historical and spatial contingencies. The patterns of cover and diversity that we observed provide a useful way to interpret effects of disturbance on semi-arid grasslands in Australia and may be useful indicators of grassland condition where cultivation history is not known.  相似文献   

γ-ray burst ultraviolet/optical afterglow polarimetry as a probe of quantum gravity     

Yi-Zhong Fan †  Da-Ming Wei  Dong Xu 《Monthly notices of the Royal Astronomical Society》2007,376(4):1857-1860

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Constrained simulations of the local universe – I. Mass and motion in the local volume     

Luis A. Martinez-Vaquero  Gustavo Yepes  Yehuda Hoffman 《Monthly notices of the Royal Astronomical Society》2007,378(4):1601-1608

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Extrasolar planets and planet formation     

《Planetary and Space Science》2007,55(5):535

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Estimating ground water recharge using flow models of perched karstic aquifers   总被引：3，自引：0，他引：3  

Weiss M  Gvirtzman H 《Ground water》2007,45(6):761-773

The fraction of rain that is annually recharged to ground water is a function of the transient quantities of precipitation (wet vs. dry years) as well as other meteorological and geologic factors, and thus it is very difficult to estimate. In this study, we have used long records (20 to 30 years) of precipitation and spring discharge to reconstruct the transient character of yearly recharge. These data sets were used to calibrate numerical ground water flow models on the less than 3 km(2) scale for four separate perched karstic aquifers in the Judean and Samarian Mountains of Israel. The stratification and karstic character of the local carbonate rock aquifers cause ground water to flow through discrete dissolution channels and to discharge at isolated springs. An innovative, dual-porosity approach was used where a finite-difference solution simulates flow in the rock matrix, while the karstic channels are simulated using computationally simple drains. Perched conditions are also simulated innovatively using MODFLOW by treating the bottom unsaturated layer as if it is saturated, but by assuming zero pressure head throughout the "unsaturated" layer. Best fitting between measured and computed spring hydrograph data has allowed us to develop a set of empirical functions relating measured precipitation to recharge to the aquifer. The generic methodology presented gives insight into the suspected changes in aquifer recharge rates between particularly wet or dry years.  相似文献   

Variations of O/O and O/O in meteoric waters     

Boaz Luz  Eugeni Barkan 《Geochimica et cosmochimica acta》2010,74(22):6276-6286

The variations of δ¹⁷O and δ¹⁸O in recent meteoric waters and in ice cores have proven to be an important tool for investigating the present and past hydrologic cycle. In order to close significant information gaps in the present distribution of δ¹⁷O and δ¹⁸O of meteoric water, we have run precise measurements, with respect to VSMOW, on samples distributed globally from low to high latitudes. Based on the new and existing data, we present the Global Meteoric Water Line (GMWL) for δ¹⁷O and δ¹⁸O as: