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951.
Trace Element Determination of Single Fluid Inclusions in Quartz by Laser Ablation ICP-MS 总被引:4,自引:0,他引:4
Tom E. McCandless David J. Lajack Joaquin Ruiz A. Mohammad Ghazi 《Geostandards and Geoanalytical Research》1997,21(2):279-287
Single fluid inclusions in quartz from a Pb-Zn-Ag carbonate replacement deposit were selected for trace element determination by laser ablation ICP-MS. Spikes in element intensities were noted between first breached fluids versus subsequent analyses, suggesting that accurate element concentrations may not be determined in smaller fluid inclusions when only one analysis is obtained before the fluid is exhausted. Elemental concentrations in the fluid inclusions were determined by external standardisation using solutions sealed in microcapillary tubes. Standards and single natural inclusion analyses give repeatabilities (%RSD) of ˜ 20% for Rb and Sr. Rubidium and strontium concentrations range from 0.56-5.07 μg ml-1 and 1.12-27.4 μg ml-1 , respectively, whereas Zn and Ag are below detection limits (< 10 ng ml-1 ). The results suggest that nearly all Zn and Ag are removed by the time hydrothermal fluids precipitate gangue minerals. 相似文献
952.
Maria Luce Frezzotti Tom Andersen Else-Ragnhild Neumann Siri Lene Simonsen 《Lithos》2002,64(3-4):77-96
Three types of fluid inclusions have been identified in olivine porphyroclasts in the spinel harzburgite and lherzolite xenoliths from Tenerife: pure CO2 (Type A); carbonate-rich CO2–SO2 mixtures (Type B); and polyphase inclusions dominated by silicate glass±fluid±sp±silicate±sulfide±carbonate (Type C). Type A inclusions commonly exhibit a “coating” (a few microns thick) consisting of an aggregate of a platy, hydrous Mg–Fe–Si phase, most likely talc, together with very small amounts of halite, dolomite and other phases. Larger crystals (e.g. (Na,K)Cl, dolomite, spinel, sulfide and phlogopite) may be found on either side of the “coating”, towards the wall of the host mineral or towards the inclusion center. These different fluids were formed through the immiscible separations and fluid–wall-rock reactions from a common, volatile-rich, siliceous, alkaline carbonatite melt infiltrating the upper mantle beneath the Tenerife. First, the original siliceous carbonatite melt is separated from a mixed CO2–H2O–NaCl fluid and a silicate/silicocarbonatite melt (preserved in Type A inclusions). The reaction of the carbonaceous silicate melt with the wall-rock minerals gave rise to large poikilitic orthopyroxene and clinopyroxene grains, and smaller neoblasts. During the metasomatic processes, the consumption of the silicate part of the melt produced carbonate-enriched Type B CO2–SO2 fluids which were trapped in exsolved orthopyroxene porphyroclasts. At the later stages, the interstitial silicate/silicocarbonatite fluids were trapped as Type C inclusions. At a temperature above 650 °C, the mixed CO2–H2O–NaCl fluid inside the Type A inclusions were separated into CO2-rich fluid and H2O–NaCl brine. At T<650 °C, the residual silicate melt reacted with the host olivine, forming a reaction rim or “coating” along the inclusion walls consisting of talc (or possibly serpentine) together with minute crystals of NaCl, KCl, carbonates and sulfides, leaving a residual CO2 fluid. The homogenization temperatures of +2 to +25 °C obtained from the Type A CO2 inclusions reflect the densities of the residual CO2 after its reactions with the olivine host, and are unrelated to the initial fluid density or the external pressure at the time of trapping. The latter are restricted by the estimated crystallization temperatures of 1000–1200 °C, and the spinel lherzolite phase assemblage of the xenolith, which is 0.7–1.7 GPa. 相似文献
953.
An approach for predicting swelling pressure of bentonites based on thermodynamic relationships between swelling pressure and suction is presented in this paper. The proposed method requires sorption isotherm data of the bentonites. A series of swelling pressure tests were performed on compacted specimens of bentonite-sand mixtures with different bentonite contents, water contents, and dry densities. The sorption isotherm of the pure bentonite was measured using a chilled-mirror hygrometer. It is found that the method works well for the bentonite-sand mixtures tested. Several published data on bentonites that have been proposed to be used as buffer and sealing material for nuclear waste repository were collected and used to verify the method. The proposed method is found to be also applicable for other bentonites of different types and therefore, can be used to predict swelling pressure of bentonites. 相似文献
954.
正1. Introduction One of the major challenges in Geoscience is to understand how the formation and evolution of the Earth System are governed by timescales e that is, how the various geological processes that continue to contribute to its present-day structure and composition operated in the deep past. The traditional view of such processes refers to events that occur at immense spatial scales and over hundreds of millions of years, constrained in most cases by the ages of rocks determined using isotopic dating methods or the fossil record. However, the modern view of geological processes has increasingly acknowledged that their durations can be significantly shorter than previously thought possible, or indeed detectable 相似文献