排序方式： 共有26条查询结果，搜索用时 31 毫秒
1.
2.
3.
Constraining the composition of primitive kimberlite magma is not trivial. This study reconstructs a kimberlite melt composition using vesicular, quenched kimberlite found at the contact of a thin hypabyssal dyke. We examined the 4 mm selvage of the dyke where the most elongate shapes of the smallest calcite laths suggest the strongest undercooling. The analyzed bulk compositions of several 0.09-1.1 mm2 areas of the kimberlite free from macrocrysts were considered to be representative of the melt. The bulk analyses conducted with a new “chemical point-counting” technique were supplemented by modal estimates, studies of mineral compositions, and FTIR analysis of olivine phenocrysts. The melt was estimated to contain 26-29.5 wt% SiO2, ∼7 wt% of FeOT, 25.7-28.7 wt% MgO, 11.3-15 wt% CaO, 8.3-11.3 wt% CO2, and 7.6-9.4 wt% H2O. Like many other estimates of primitive kimberlite magma, the melt is too magnesian (Mg# = 0.87) to be in equilibrium with the mantle and thus cannot be primary. The observed dyke contact and the chemistry of the melt implies it is highly fluid (η = 101-103 Pa s at 1100-1000 °C) and depolymerized (NBO/T = 2.3-3.2), but entrains with 40-50% of olivine crystals increasing its viscosity. The olivine phenocrysts contain 190-350 ppm of water suggesting crystallization from a low SiO2 magma (aSiO2 below the olivine-orthopyroxene equilibrium) at 30-50 kb. Crystallization continued until the final emplacement at depths of few hundred meters which led to progressively more Ca- and CO2-rich residual liquids. The melt crystallised phlogopite (6-10%), monticellite (replaced by serpentine, ∼10%), calcite rich in Sr, Mg and Fe (19-27%), serpentine (29-31%) and minor amounts of apatite, ulvöspinel-magnetite, picroilmenite and perovskite. The observed content of H2O can be fully dissolved in the primitive melt at pressures greater than 0.8-1.2 kbar, whereas the amount of primary CO2 in the kimberlite exceeds CO2 soluble in the primitive kimberlite melt. A mechanism for retaining CO2 in the melt may require a separate fluid phase accompanying kimberlite ascent and later dissolution in residual carbonatitic melt. Deep fragmentation of the melt as a result of volatile supersaturation is not inevitable if kimberlite magma has an opportunity to evolve. 相似文献
4.
Stuart J. Mills Anthony R. Kampf Mati Raudsepp William D. Birch 《Mineralogy and Petrology》2010,100(3-4):249-253
Sr- and Ca-rich waylandite, $ {\left( {{\hbox{B}}{{\hbox{i}}_{0.{54}}}{\hbox{S}}{{\hbox{r}}_{0.{31}}}{\hbox{C}}{{\hbox{a}}_{0.{25}}}{{\hbox{K}}_{0.0{1}}}{\hbox{B}}{{\hbox{a}}_{0.0{1}}}} \right)_{\Sigma 1.12}}{{\hbox{H}}_{0.{18}}}{\left( {{\hbox{A}}{{\hbox{l}}_{{2}.{96}}}{\hbox{C}}{{\hbox{u}}_{0.0{2}}}} \right)_{\Sigma 2.98}}{\left[ {{{\left( {{{\hbox{P}}_{0.{97}}}{{\hbox{S}}_{0.0{3}}}{\hbox{S}}{{\hbox{i}}_{0.0{1}}}} \right)}_{\Sigma 1.00}}{{\hbox{O}}_4}} \right]_2}{\left( {\hbox{OH}} \right)_6} $ , from Wheal Remfry, Cornwall, United Kingdom has been investigated by single-crystal X-ray diffraction and electron microprobe analyses. Waylandite crystallises in space group R $ \overline 3 $ ? m, with the cell parameters: a?=?7.0059(7) Å, c?=?16.3431(12) Å and V?=?694.69(11) Å3. The crystal structure has been refined to R 1?=?3.76%. Waylandite has an alunite-type structure comprised of a rhombohedral stacking of (001) composite layers of corner-shared AlO6 octahedra and PO4 tetrahedra, with (Bi,Sr,Ca) atoms occupying icosahedrally coordinated sites between the layers. 相似文献
5.
Nenad Marić Sanja Mrazovac Kurilić Ivan Matić Stanko Sorajić Jelena Zarić 《Environmental Earth Sciences》2014,72(2):525-534
This paper provides insight into the quality of groundwater used for public water supply on the territory of Kikinda municipality (Vojvodina, Serbia) and main processes which control it. The following parameters were measured: color, turbidity, pH, KMnO4 consumption, TDS, EC, NH4 +, Cl?, NO2 ?, NO3 ?, Fe, Mn, total hardness, Ca2+, Mg2+, SO4 2+, HCO3 ?, K+, Na+, As. The correlations and ratios among parameters that define the chemical composition were determined aiming to identify main processes that control the formation of the chemical composition of the analyzed waters. Groundwater from 11 analyzed sources is Na–HCO3 type. Intense color and elevated organic matter content of these waters originate from humic substances. The importance of organic matter decay is assumed by positive correlation between organic matter content and TDS, HCO3 content. There is no evidence that groundwater chemistry is determined by the depth of captured aquifer interval. The main processes that control the chemistry of all analyzed water are cation exchange and feldspar weathering. 相似文献
6.
7.
Bancy M. Mati 《Journal of Arid Environments》2000,46(4):333
The effect of climate change on maize production in the semi-humid and semi-arid, agro-climatic zones III-IV of Kenya was evaluated using two General Circulation Models (GCMs): the Canadian Climate Center Model (CCCM) and the Geophysical Fluid Dynamics Laboratory (GFDL), as well as the CERES-Maize model. Long-term climate data was obtained from three meteorological stations situated in eastern, central and western regions of Kenya, while maize data was obtained from six sites within the regions. The climate scenarios were projected to the year 2030. Temperature increases of 2·29 and 2·89°C are predicted by the CCCM and GFDL, respectively. Rainfall levels are predicted to remain unchanged, but there are thought to be shifts in distribution. It is predicted that the short-rains season (October–January) will experience some increased rainfall, while the long-rains season (April–July) will show a decrease. Maize yields are predicted to decrease in zone III areas, while an increase is predicted in zone IV areas. However, the predicted changes in yields are low since they all fall below 500 kg ha−1, except the Homa Bay site. Thus, to counter the adverse effects of climate change on maize production, it may be necessary to use early maturing cultivars, practice early planting, and in eastern Kenya, shift to growing maize during the short-rains season. 相似文献
8.
9.
10.