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101.
Silicon mono-crystals have been bent thanks to a series of parallel superficial indentations on one of the largest faces of the crystals. This technique relies on irreversible compression of the crystal beneath and beside the indentations. This latter causes deformation with no need for external device, resulting in a uniform self-standing curvature within the crystal. Indented Si crystals have been characterized at European Synchrotron Radiation Facility using a monochromatic beam ranging from 150 to 700 keV. Crystals exhibited very high diffraction efficiency over a broad range of energy, peaking 95% at 150 keV. Measured angular spread of the diffracted beam was always very close to the morphological curvature of the sample under investigation, proving that the energy passband of bent crystals can be controlled by simply imparting a selected curvature to the sample. The method of superficial indentations was found to offer high reproducibility and easy control of diffraction properties of the crystals. Moreover the method is cheap and simple, being based on mass production tools. A Laue lens made of crystals bent by superficial indentations can provide high-efficiency concentration of hard x-ray photons, leading significant improvement in many astrophysical applications.  相似文献   
102.
Strain caps are one of a series of microstructures that typically form during deformation of a softer matrix around hard objects. However??in contrast to other microstructures around porphyroblasts, for example pressure shadows??strain caps are rarely described in the literature. Here we describe strain caps with particular focus on strain caps associated with growth of a new phase, not elsewhere present in the paragenesis. Examples from foliated, amphibolite facies, metapelitic schists from Alaska, Sinai and Bhutan are discussed. All examples show chlorite growth exclusively in strain caps formed around porphyroblasts. Porphyroblasts around which the strain caps grow are muscovite, staurolite and garnet, respectively. In all of these examples strain caps formed synkinematically, but the chlorite grew statically at a later stage. Three mechanisms can explain the formation of new phases in the strain cap region: (a) the strain cap region may have experienced different P-T conditions from the matrix; (b) the strain cap region has a different effective bulk composition from the surrounding matrix; (c) fluid flow that is preferentially focused parallel to the foliation planes causing only local adjustment to retrograde metamorphism in the strain cap region. We show that the third hypothesis is the most preferable mechanism. Indeed, the absence of chlorite outside the strain cap region allows a quantification of the amount of fluid that infiltrated the rock. It is shown that for Bhutan sample about 8.5 mole% more water must have been added to the rock during fluid infiltration to cause the strain cap formation.  相似文献   
103.
The new mineral agricolaite, a potassium uranyl carbonate with ideal formula K4(UO2)(CO3)3, occurs in vugs of ankerite gangue in gneisses in the abandoned Giftkiesstollen adit at Jáchymov, Czech Republic. The name is after Georgius Agricola (1494?C1555), German scholar and scientist. Agricolaite occurs as isolated equant irregular translucent grains to 0.3?mm with yellow color, pale yellow streak, and vitreous luster. It is brittle with uneven fracture and displays neither cleavage nor parting. Agricolaite is non-fluorescent. Mohs hardness is ~4. It is associated with aragonite, brochantite, posnjakite, malachite, rutherfordine, and ??pseudo-voglite??. Experimental density is higher than 3.3?g.cm?3, Dcalc is 3.531?g.?cm?3. The mineral is monoclinic, space group C2/c, with a 10.2380(2), b 9.1930(2), c 12.2110(3) ?, ?? 95.108(2)°, V 1144.71(4) ?3, Z?=?4. The strongest lines in the powder X-ray diffraction pattern are d(I)(hkl): 6.061(55)(002), 5.087(57)(200), 3.740(100)(202), 3.393(43)(113), 2.281(52)(402). Average composition based on ten electron microprobe analyses corresponds to (in wt.%) UO3 48.53, K2O 31.49, CO2(calc) 22.04 which gives the empirical formula K3.98(UO2)1.01(CO3)3.00. The crystal structure was solved from single-crystal X-ray diffraction data and refined to R 1?=?0.0184 on the basis of the 1,308 unique reflections with F o?>?4??F o. The structure of agricolaite is identical to that of synthetic K4(UO2)(CO3)3 and consists of separate UO2(CO3)3 groups organized into layers parallel to (100) and two crystallographically non-equivalent sites occupied by K+ cations. Both the mineral and its name were approved by the IMA-CNMNC.  相似文献   
104.
Total trace metals (Cd, Co, Cu, Fe, Mn, Ni, Pb, Zn), Al, and pyrite- and reactive-associated metals were measured for the first time in a microbial mat and its underlying anoxic-sulfidic sediment collected in the saltern of Guerrero Negro (GN), Baja California Sur, Mexico. It is postulated that the formation of acid volatile sulfide (AVS) and pyrite in the area of GN could be limited by the availability of reactive Fe, as suggested by its limited abundance (mat and sediment combined average value of only 19 ± 10 ??mol g?1; n = 22) as well as the low pyrite (0.89?C7.9 ??mol g?1) and AVS (0.19?C21 ??mol g?1) concentrations (for anoxic-sulfidic sediments), intermediate degrees of pyritization (12?C50%), high degrees of sulfidization (14?C100%), generally low degrees of trace metal pyritization, and slight impoverishment in total Fe. This is a surprising result considering the large potential reservoir of available Fe in the surrounding desert. Our findings suggest that pyrite formation in the cycling of trace metals in the saltern of GN is not very important and that other sedimentary phases (e.g., organic matter, carbonates) may be more important reservoirs of trace elements. Enrichment factors [EFMe = (Me/Al)sample/(Me/Al)background] of Co, Pb, and Cd were high in the mat (EFMe = 2.2 ± 0.4, 2.8 ± 1.6 and 34.5 ± 9.8, respectively) and even higher in the underlying sediment (EFMe = 4.7 ± 1.5, 14.5 ± 6.2 and 89 ± 27, respectively), but Fe was slightly impoverished (average EFFe of 0.49 ± 0.13 and 0.50 ± 0.27 in both mat and sediment). Organic carbon to pyrite-sulfur (C/S) molar ratios measured in the mat (2.9 × 102?C27 × 102) and sediment (0.81 × 102?C6.6 × 102) were, on average, approximately 77 times higher than those typically found in marine sediments (7.5 ± 2.1). These results may indicate that ancient evaporation basins or hypersaline sedimentary environments could be identified on the basis of extremely high C/S ratios (e.g., >100) and low reactive Fe.  相似文献   
105.
The Punta del Este Terrane (eastern Uruguay) lies in a complex Neoproterozoic (Brasiliano/Pan-African) orogenic zone considered to contain a suture between South American terranes to the west of Major Gercino?CSierra Ballena Suture Zone and eastern African affinities terranes. Zircon cores from Punta del Este Terrane basement orthogneisses have U?CPb ages of ca. 1,000?Ma, which indicate an lineage with the Namaqua Belt in Southwestern Africa. U?CPb zircon ages also provide the following information on the Punta del Este terrane: the orthogneisses containing the ca. 1,000?Ma inheritance formed at ca. 750?Ma; in contrast to the related terranes now in Africa, reworking of the Punta del Este Terrane during Brasiliano/Pan-African orogenesis was very intense, reaching granulite facies at ca. 640?Ma. The termination of the Brasiliano/Pan-African orogeny is marked by formation of acid volcanic and volcanoclastic rocks at ca. 570?Ma (Sierra de Aguirre Formation), formation of late sedimentary basins (San Carlos Formation) and then intrusion at ca. 535?Ma of post-tectonic granitoids (Santa Teresa and José Ignacio batholiths). The Punta del Este Terrane and unrelated western terranes represented by the Dom Feliciano Belt and the Río de La Plata Craton were in their present positions by ca. 535?Ma.  相似文献   
106.
Geologically complex crystalline aquifers underlie large parts of the semi-arid Limpopo Province where some of the greatest groundwater needs in South Africa occur. It is important to identify potentially high-yielding zones that can be targeted for water supply. The study covered four distinct geologic and morpho-structural domains within Limpopo Province, together covering about 23,500?km2. Results from over 2,500 pumping test analyses indicate that bedrock type (e.g. pegmatite), lithological setting (e.g. aureole of granitoids), proximity and orientation of dykes and lineaments, topographic setting (e.g. slopes or valleys) and proximity of surface-water drainages may exert an influence on borehole productivity. No correlation between borehole productivity and weathering depth was found. Lineaments and dykes striking perpendicular to the current maximum horizontal stress seem to be more favourable targets, which is inconsistent with the predicted regime. Due to the complex geologic history, it is difficult to link open discontinuities to a distinct recent or past tectonic event. Regional stress-field data, as in this case, may not account for local, possibly highly significant, stress-field variations. The hydrogeologic importance of several factors related to groundwater occurrence, here presented, can be used as a working reference for future groundwater development programmes.  相似文献   
107.
South Peak is a 7-Mm3 potentially unstable rock mass located adjacent to the 1903 Frank Slide on Turtle Mountain, Alberta. This paper presents three-dimensional numerical rock slope stability models and compares them with a previous conceptual slope instability model based on discontinuity surfaces identified using an airborne LiDAR digital elevation model (DEM). Rock mass conditions at South Peak are described using the Geological Strength Index and point load tests, whilst the mean discontinuity set orientations and characteristics are based on approximately 500 field measurements. A kinematic analysis was first conducted to evaluate probable simple discontinuity-controlled failure modes. The potential for wedge failure was further assessed by considering the orientation of wedge intersections over the airborne LiDAR DEM and through a limit equilibrium combination analysis. Block theory was used to evaluate the finiteness and removability of blocks in the rock mass. Finally, the complex interaction between discontinuity sets and the topography within South Peak was investigated through three-dimensional distinct element models using the code 3DEC. The influence of individual discontinuity sets, scale effects, friction angle and the persistence along the discontinuity surfaces on the slope stability conditions were all investigated using this code.  相似文献   
108.
A large deep-seated landslide, triggered by a heavy rainfall, activated early in the morning on May 19, 2010 along the SW slope of Gírová Mt., NE Czech Republic. The landslide occurred within a zone of pre-existing deep-seated gravitational deformation, and it was accompanied with pronounced ground liquefying in the central and lower portion of the sliding mass. The precipitation that triggered the landslide was about 244.6 mm that fell between May 15th and 18th with an average of 61 mm/day. No properties or lives were lost. However, the landslide provided a good case study on triggering factors and process of liquefaction at mountain slopes in the E Czech Republic and adjacent areas.  相似文献   
109.
Tritium?Chelium groundwater dating was carried out in a trichloroethylene (TCE)-contaminated valley-fill aquifer system in Quebec, Canada, where a numerical groundwater flow model was developed. Forty seven discrete groundwater and dissolved gas samples were obtained along two flow paths originating from known TCE source zones whose related plumes converge down gradient to form a single plume. Sampling points in monitoring wells were projected onto vertical sections showing particle tracks along the two flow paths. At these points, simulated advective ages obtained from particle tracking were matched to tritium?Chelium ages using different porosity values; the best match was 0.35. Ages were also obtained above and below a prodeltaic silty aquitard in a portion of the aquifer where some source zones are located, which provide groundwater and TCE transit times through the aquitard as well as a mean vertical hydraulic conductivity that agrees with previous estimates used in the model. In certain locations, anomalously old ages associated with high terrigenic 4He indicate areas where groundwater from the underlying proglacial unit flows upward into the deltaic sand aquifer through aquitard windows. Upflow locations correspond with increased TCE concentrations, suggesting significant TCE provenance through the proglacial unit originating from a previously unrecognized TCE source zone.  相似文献   
110.
In the present paper, we propose a new method for the estimation of the variogram, which combines robustness with efficiency under intrinsic stationary geostatistical processes. The method starts by using a robust estimator to obtain discrete estimates of the variogram and control atypical observations that may exist. When the number of points used in the fit of a model is the same as the number of parameters, ordinary least squares and generalized least squares are asymptotically equivalent. Therefore, the next step is to fit the variogram by ordinary least squares, using just a few discrete estimates. The procedure is then repeated several times with different subsets of points and this produces a sequence of variogram estimates. The final estimate is the median of the multiple estimates of the variogram parameters. The suggested estimator will be called multiple variograms estimator. This procedure assures a global robust estimator, which is more efficient than other robust proposals. Under the assumed dependence structure, we prove that the multiple variograms estimator is consistent and asymptotically normally distributed. A simulation study confirms that the new method has several advantages when compared with other current methods.  相似文献   
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