The solubility of CO2CO fluids in a mid-ocean ridge basalt (morb) has been measured at 1200°C, 500–1500 bar, and oxygen fugacities between NNO and NNO-4. High oxygen fugacities, and thus CO2-rich fluids, were produced by using a starting material equilibrated at NNO, and Ag2C2O4 as the fluid source. Low oxygen fugacities were achieved by using graphite capsules, and MgCO3 as the fluid source. These graphite-saturated fluids have the lowest possibleC/O2CO ratio for a given pressure and temperature.
Experiments were run in a rapid-quench internally heated pressure vessel. Fluid compositions were measured using a simple vacuum technique and by Raman spectroscopy of fluid inclusions. The two techniques yielded comparable results. Fourier transform micro-infrared spectroscopy was used to identify and measure concentrations of dissolved volatiles in double-polished wafers of the quenched glasses. Carbonate was the only carbon-bearing species identified. Raman spectroscopic analysis of inclusion-free areas of glass confirmed the absence of dissolved molecular CO2, CO and carbon. The measured concentrations of dissolved CO2 in the glasses were proportional to the fugacity of CO2 during the experiments, calculated from the measured fluid compositions. The data were fit to the equationXCO2melt(ppm)= 0.492 fCO2 (bar).
The insolubility of CO, compared to CO2, may be related to the fact that dissolution of CO requires reduction of another species in the melt, whereas dissolution of CO2 does not. Due to the fact that CO will be an important component of natural CO fluids at low pressures and low oxygen fugacities, equilibrium dissolved CO2 contents will be less than calculated assuming pure CO2 fluids, but as theC/O2CO ratio in a pure CO fluid at fixed pressure and temperature is a direct function of oxygen fugacity, measurement of the oxygen fugacity of quenched glasses or trapped fluids in natural samples should allow saturation concentrations to be calculated. Dissolved CO2 contents of somemorb are less than expected if they were in equilibrium with pure CO2. These samples must, therefore, have been more reduced than average if they were fluid-saturated. Together with results from other studies of CO2 and H2O solubilities in basalt, the results of this study provide a comprehensive framework for modelling CO2 solution inmorb. 相似文献
The ascendance of the Pacific Rim is an indisputable global happening. North American geography, a logical leader in the study of this high profile phenomenon, has lagged behind other disciplines in Rim-focused research. This article argues in favor of a heightened Rim awareness, surveys recent publications, suggests promising Pacific Rim research directions, and proposes how the Association of American Geographers can help promote Rim studies. 相似文献
With recent research indicating the importance of the rolling mechanism of deformation in granular systems consisting of perfectly round particles, it has become popular to use ellipse-shaped particles in the Discrete Element Method (DEM) numerical model. Inherent in this technique is the need for accurately computing ellipse to ellipse intersection, in order to properly detect contact formation and compute relative contact velocities. However, the commonly used algorithms for computing ellipse-ellipse intersection are generally poorly conditioned and can be inaccurate. An alternate method for computing ellipse-ellipse intersection is developed and presented which results in a well-conditioned, stable and accurate contact detection method. These modification are incorporated into the general DEM algorithm. 相似文献
The eastern Mediterranean has been the cradle of many great civilizations. The history of the area consisted of glorious battles, heroic acts, and the rise and fall of great civilizations. But, sometimes, natural hazards became the cause for a new classification of the political, as well as of the military status quo of the region. The enormous eruption of the submarine volcano at the Greek island of Thera (Santorini) during the Bronze Age, around 1500 BC, is such a natural hazard. The tsunami generated by the eruption, literally wiped out the peace-loving Minoan civilization who inhabited the island of Crete. After the sea subsided, the configuration of the area was altered, and the decline of the Minoan principality on the Archipelago began. The present paper introduces evidence concerning the tsunami and states some of the after-effects which were partly responsible for the decline of the Minoan empire. All the information is gathered from historical sources and from recent research works. An effort has been made to include many of the theories introduced by various researchers through time concerning the event. Finally, information has been included from all known research, as well as from the author's own conclusions, in order to make the paper useful to future researchers. 相似文献
Postcumulus trapped liquid shift in layered complexes produces cumulate minerals with more fractionated compositions than the original primary phases. This effect is shown by olivine compositions from the base of the Mount Ayliff Intrusion, where varying proportions of olivine to interstitial liquid produce a suite of rocks which define a tight linear trend on a binary whole-rock plot of MgO versus FeO. Extrapolation of this trend constrains the composition of the primary cumulus olivine to the range Fo84–86, whereas olivine actually present have compositions Fo77–83. The magnitude of the discrepancy between the theoretical and observed olivine compositions correlates directly with the weight fraction of interstitial liquid. These observations are quantitatively predicted by the trapped liquid shift model. They also argue against significant migration of residual liquid. Trapped liquid shift is documented over a vertical interval of 60 m. It occurred in rocks lying only 1 m above the basal contact of the intrusion and hence must be a comparatively rapid process. 相似文献
One of the most popular petrogenetic concepts is that of simultaneous assimilation and fractional crystallisation (AFC).
The equations governing these processes are well known and widely applied. The power and attraction of the model are that,
with the minimum of constraints, petrogenetic schemes can be erected for essentially any group of rocks. These models are
usually based on the observed variations in a small number of trace elements and/or isotopic systems. In this paper we have
generated well-constrained AFC models for the Variscan, calc-alkaline Quérigut complex in the French Pyrénées. Our models
are based on geological constraints on the identities of the parent magma and candidate assimilants, and the Sm-Nd and Rb-Sr
isotope systematics of the rocks. The modelling is successful in mimicking the isotope array for the actual rocks. However,
the results are massively inconsistent with those produced using the major- and trace-element concentrations. Our major conclusion
is that AFC modelling should be undertaken only with robust initial constraints on the compositions of the parent magma and
the proposed assimilant, with due respect for crystal-liquid partition coefficients, in so far as they are known. The results
should then be accepted only if the isotope-based model parameters are consistent with those derived from major- and trace-element
variations.
Received: 19 August 1994/Accepted: 23 March 1995 相似文献