Deep Fractionation of Clinopyroxene in the East Pacific Rise 13 degrees N: Evidence from High MgO MORB and Melt Inclusions

Mid-ocean ridge basalts (MORBs) from East Pacific Rise (EPR) 13 degrees N are analysed for major and trace elements, both of which show a continuous evolving trend. Positive MgO-Al2O3 and negative MgO-Sc relationships manifest the cotectic crystallization of plagioclase and olivine, which exist with the presence of plagioclase and olivine phenocrysts and the absence of clinopyroxene phenocrysts. However, the fractionation of clinopyroxene is proven by the positive correlation of MgO and CaO. Thus, MORB samples are believed to show a "clinopyroxene paradox". The highest magnesium-bearing MORB sample E13-3B (MgO = 9.52%) is modelled for isobaric crystallization with COMAGMAT at different pressures. Observed CaO/Al2O3 ratios can be derived from E13-3B only by fractional crystallization at pressure > 4 +/- 1 kbar, which necessitates clinopyroxene crystallization and is not consistent with cotectic crystallization of olivine plus plagioclase in the magma chamber (at pressure similar to 1 kbar). The initial compositions of the melt inclusions, which could represent potential parental magmas, are reconstructed by correcting for post-entrapment crystallization (PEC). The simulated crystallization of initial melt inclusions also produce observed CaO/Al2O3 ratios only at > 4 +/- 1 kbar, in which clinopyroxene takes part in crystallization. It is suggested that MORB magmas have experienced clinopyroxene fractionation in the lower crust, in and below the Moho transition zone. The MORB magmas have experienced transition from clinopyroxene+plagioclase+olivine crystallization at > 4 +/- 1 kbar to mainly olivine+plagioclase crystallization at < 1 kbar, which contributes to the explanation of the "clinopyroxene paradox".

Generation and evolution of magma beneath the East Pacific Rise: Constraints from U-series disequilibrium and plagioclase-hosted melt inclusions

Mid-ocean ridge basalt (MORB) samples from the East Pacific Rise (EPR 12 degrees 50'N) were analyzed for U-series isotopes and compositions of plagioclase-hosted melt inclusions. The Ra-226 and Th-230 excesses are negatively correlated; the Ra-226 excess is positively correlated with Mg# and Sm/Nd, and is negatively correlated with La/Sm and Fe-8; the Th-230 excess is positively correlated with Fe-8 and La/Sm and is negatively correlated with Mg# and Sm/Nd. Interpretation of these correlations is critical for understanding the magmatic process. There are two models (the dynamic model and the "two-porosity" model) for interpreting these correlations, however, some crucial parameters used in these models are not ascertained. We propose instead a model to explain the U-series isotopic compositions based on the control of melt density variation. For melting either peridotite or the "marble-cake" mantle, the FeOt content, Th-230 excess and La/Sm ratio increases and Sm/Nd decreases with increasing pressure. A deep melt will evolve to a higher density and lower Mg# than a shallow melt, the former corresponds to a long residence time, which lowers the Ra-226 excess significantly. This model is supported by the existence of low Ra-226 excesses and high Th-230 excesses in MORBs having a high Fe-8 content and high density. The positive correlation of Ra-226 excess and magma liquidus temperature implies that the shallow melt is cooled less than the deep melt due to its low density and short residence time. The correlations among Fe-8, Ti-8 and Ca-8/Al-8 in plagioclase-hosted melt inclusions further prove that MORBs are formed from melts having a negative correlation in melting depths and degrees. The negative correlation of Ra-226 excess vs. chemical diversity index (standard deviation of Fe-8, Ti-8 and Ca-8/Al-8) of the melt inclusions is in accordance with the influence of a density-controlled magma residence time. We conclude that the magma density variation exerts significant control on residence time and U-series isotopic compositions. (c) 2010 Elsevier B.V. All rights reserved.

基于模拟退火算法的挤出模参数优化

建立了塑料熔体在异型材挤出机头流道中的流动均匀性模型 ,阐明了模具结构参数与流动均匀性间的关系,确定了塑料挤出模优化设计的目标函数和设计变量 ,并将一种改进的模拟退火算法用于流线型塑料异型材挤出机头的优化设计。实例表明所用方法对挤出模优化设计的适用性,该方法在利用经验的同时 ,优化了模具结构参数 ,提高了模具设计的智能化

XRD and XPS studies on the ultra-uniform Raney-Ni catalyst prepared from the melt-quenching alloy

We present a novel method for preparing an ultra-uniform Raney-Ni catalyst, which includes melt-quenching, hydrogen treatment and leaching in an alkali solution. The resultant catalyst shows superior activity in the reaction of cyclohexanone hydrogenation. X-ray diffraction (XRD) and XPS have been employed to characterize the catalysts. As demonstrated, the pretreatment with hydrogen caused a distinct phase transfer of the Ni-Al alloys, forming more of the Ni2Al3 component. In the subsequent leaching process, the Ni2Al3 component shows high activity and the resultant catalyst exhibits high surface areas and small pores. Moreover, metallic Al in the hydrogen-pretreated alloy appeared to be leached more easily and thus the aluminium species remaining on the catalyst surface is aluminium oxide predominantly, which serves as a matrix to stabilize active Ni species on the surface. Copyright (C) 2001 John Wiley & Sons, Ltd.