Geochemistry of high H2 and CH4 vent fluids issuing from ultramafic rocks at the Rainbow hydrothermal field (36°14′N, MAR)

The Flores diving cruise was part of the MAST III-AMORES (1995-1998) program funded by the European Union. One of the major achievements of the Flores cruise was the discovery of the Rainbow hydrothermal field hosted in ultramafic rocks south of the Amar segment on the Mid-Atlantic ridge (MAR). The Rainbow hydrothermal fluids exhibit temperatures of 365 °C, pH of 2.8, high chlorinity (750 mmol/kg), and low silica (6.9 mmol/kg). The uniformity in endmember major, minor, trace element concentrations and gas contents suggests that all Rainbow fluids originate from the same deep source. Although H₂S content is relatively low (1.20 mmol/kg), all vent fluids show extraordinary high H₂ (16 mmol/kg), CH₄ (2.5 mmol/kg) and CO (5 μmol/kg) endmember concentrations compared to fluids collected from other vent sites along the MAR. Hydrogen represents more than 40% of the total gas volume extracted from the fluids. At Rainbow, H₂ production is likely associated with alteration of olivine and orthopyroxene minerals during serpentinization. Given that exposures of ultramafic rock may be common, particularly along slow-spreading ridges, the production of H₂ may have important implications for microbial activity at and beneath the seafloor.     

Retrograde processes in migmatites and granulites revisited

Many migmatites and granulites preserve evidence of a clockwise P–T evolution involving decompression (decrease in P) while close to the thermal peak. The extent of post‐thermal peak reaction is influenced by several factors, including: (1) the P–T path in relation to invariants in the system and the Clapeyron slopes of the equilibria; (2) the rate of cooling; and (3) the availability of fluid (H₂O‐rich volatile phase or melt) for fluid‐consuming reactions. Reaction may occur between products of a prograde (increasing T) fluid‐generating reaction as the same equilibrium is re‐crossed in the retrograde (decreasing T) sense. In general, reaction reversal or ‘back reaction’ requires the P–T path to approximate isobaric heating and cooling, without significant decompression, and evolved fluid to remain within the equilibration volume. The larger the decompression segment in the P–T evolution, the more chance there is of crossing different reactions along the retrograde segment from those crossed along the prograde segment. For common pelite compositions, we may generalize by considering three pressure regimes separated by the [Spl, Ms, H₂O] invariant in KFMASH (approximately 9 kbar) and the intersection of muscovite breakdown with the H₂O‐rich volatile phase‐saturated solidus (approximately 4 kbar). Reaction reversal cannot occur along P–T paths that traverse around one of these points, but may occur along P–T paths confined to one of the three regimes in between. Additionally, above the solidus, melt segregation and loss potentially change the composition of the equilibration volume; and, the size of the equilibration volume shrinks with decreasing T. Since the proportion of melt to residue in the equilibration volume may change with decreasing size, the composition of the equilibration volume may change throughout the supra‐solidus part of the retrograde segment of the P–T evolution. If melt has been lost from the equilibration volume, reaction reversal may not be possible or may be only partial; indeed, the common preservation of close‐to‐peak mineral assemblages in migmatite and granulite demonstrates that extensive reaction with melt is uncommon, which implies melt isolation or loss prior to crossing potential melt‐consuming reactions. Water dissolved in melt is transported through the crust to be exsolved on crystallization at the solidus appropriate to the intrinsic a(H₂O). This recycled water causes retrogression at subsolidus conditions. Consideration of the evidence for supra‐solidus decompression‐dehydration reactions, and review of microstructures that have proven controversial, such as corona and related microstructures, selvage microstructures and ‘late’ muscovite, leads to the conclusion that there is more than one way for these microstructures to form and reminds us that we should always consider multiple working hypotheses!     

成矿流体的流动-反应-输运耦合与金属成矿

中国著名的铜官山、冬瓜山、新桥等铜、金和硫化物矿床均赋存于上泥盆统五通组砂岩、石英砂岩和中、上石炭统的黄龙组碳酸盐岩不整合面或假整合面邻近。研究表明两个地质事件引发该区形成成因相同或相似的金属矿床。该区具有特定的岩性和地层组合 ;岩浆侵入到该地层组合的同时带进成矿物质和热能 ,热能又驱动成矿流体在岩体周边循环流动。文中对流体从含黄铁矿砂岩流到不整合面时产生的流体流动矿物溶解物质输运沉淀堆积的成矿过程进行了研究和分析 ,提出了一套用于描述热液成矿流动扩散反应过程耦合的偏微分方程组 ,并对此类矿床的成矿过程进行计算机模拟和动力学分析     

低温低压下水—岩反应动力学实验中一些主要元素的变化规律

作者根据北京小汤山一带热、矿泉水文地质特征，把９０％的白云岩和１０％的花岗岩作为试料，把二次蒸馏水作为反应溶液，将它们一起放在纯钛高压釜内，在５０—２００℃的温度和（２００—５００）×１０￣５Ｐａ的压力下进行水—岩反应动力学的实验。实验结果表明：水从岩石中萃取出的Ｋ￣（＋）、Ｎａ￣（＋）、Ｃａ￣（２＋）、Ｍｇ￣（２＋）、Ａｌ￣（３＋）、ＨＣＯ、ＮＯ、Ｆ￣（－）、Ｃｌ￣（－），ＳＯ、∑Ｆｅ和ＳｉＯ＿２等离子和氧化物的含量随着岩石的成分、温度、压力、水的ｐＨ值、岩石粒度、氧化—还原环境、时间和水的循环次数呈规律性变化。这些规律揭示了小汤山一带热、矿泉形成的机理。为热田的开发和人造温泉提供了理论上的依据。     

麻山群孔兹岩系中的堇青片麻岩

黑龙江省东部麻山群中堇青片麻岩的主要矿物组合有石榴石＋夕线石＋堇青石＋石英＋钾长石＋黑云母；石榴石＋夕线石＋堇青石＋钾长石＋尖晶石；堇青石＋夕线石＋斜长石；柱晶石＋堇青石＋斜长石＋夕线石＋石榴石＋电气石；堇青石＋紫苏辉石＋石榴石＋斜长石＋黑云母＋石英。这些含堇青石组合是在麻粒岩相条件下已存石榴石＋夕线石＋石英矿物组合分解反应的产物，其形成压力（０．４５－０．５ＧＰａ＿比麻粒岩相“高峰”压力明显低，     

物种的溶液状态及其对分析反应性能的影响

收集了1986～1991年间参考文献,评述了物种的溶液状态及其对分析反应性能的影响,并论述其进展及代表性工作。内容包括概述、研究溶液状态的方法(其中含测定缔合数、缔合度的新方法)及其在分析化学中的应用(包括新型掩蔽剂、液相化学发光、氧化态和还原态的转换、溶剂效应、吸附与解吸、物种缔合的应用)。引用文献79篇。     

Flow reactor and triple quadrupole mass spectrometer investigations of negative ion reactions involving nitric acid: Implications for atmospheric HNO3 detection by chemical ionization mass spectrometry

Atmospheric nitric acid measurements by ACIMS (Active Chemical Ionization Mass Spectrometry) are based on ion-molecule reactions of CO₃ ^-(H₂O) _n and NO₃ ^-(H₂O) _n with HNO₃. We have studied these reactions in the laboratory using a flow tube apparatus with mass spectrometric detection of reactant and product ions. Both product ion distributions and rate coefficients were measured. All reactions were investigated in an N₂-buffer (1–3 hPa) at room temperature. The reaction rate coefficients of OH^-, O₂ ^-, O₃ ^-, CO₄ ^-, CO₃ ^-, CO₃ ^-H₂O, NO₃ ^-, and NO₃ ^-H₂O were measured relative to the known rate k=3.0×10^-9 cm³ s^-1 for the reaction of O^- with HNO₃. The main product ion of the reaction of CO₃ ^-H₂O with HNO₃ was found to be (CO₃HNO₃)^- supporting a previous suggestion made on the basis of balloon-borne ACIMS measurements. For the reaction of bare CO₃ ^- with HNO₃ three product ions were observed, namely NO₃ ^-, (NO₃OH)^-, and (CO₃HNO₃)^-. The reaction rate coefficients for CO₃ ^-H₂O (1.7×10^-9 cm³ s^-1) and NO₃ ^-H₂O (1.6×10^-9 cm³ s^-1) were found to be close to the collision rate. The measured k values for bare CO₃ ^- (1.3×10^-9 cm³ s^-1) and NO₃ ^- (0.7×10^-9 cm³ s^-1) are somewhat smaller. The collisional dissociations of CO₃ ^-(H₂O) _n , NO₃ ^-(H₂O) _n (n=1, 2), (CO₃HNO₃)^- and (NO₃HNO₃)^-, occasionally influencing ACIMS measurements, were also studied. Fragment ion distributions were measured using a triple quadrupole mass spectrometer. The results showed that previous stratospheric nitric acid measurements were unimpaired from collisional dissociation processes whereas these processes played a major role during previous tropospheric measurements leading to an underestimation of nitric acid concentrations. Previous ACIMS HNO₃ detection was also affected by the conversion of CO₃ ^-(H₂O) _n to NO₃ ^-(H₂O) _n due to ion source-produced neutral radicals. A novel ACIMS ion source was developed in order to avoid these problems and to improve the ACIMS method.     

Kinetics and thermodynamics of U reduction by natural and simple organic matter

The hypothesized reaction mechanisms for U reduction by the dehydrogenation of hydroxyl groups and aliphatic hydrocarbonaceous moieties of lignite were verified by kinetic U reduction experiments using simple alcohols (1-octadecanol and 2-propanol) and aliphatic hydrocarbons (n-octacosane). The rate constants and activation energies for U reduction by these alcohols are similar to those obtained for U reduction by lignite. The rate-determining step for U reduction by both simple and natural organic matter is hypothesized to be controlled by oxygen diffusion through U oxides. The equilibria of the system lignite-aqueous uranyl have been used to calculate standard free energy changes ΔG° for lignite dehydrogenation. Their comparison with those for the dehydrogenation of simple organic molecules supports the proposed reactions thermodynamically.     

On modelling stratospheric positive ions

There has been a considerable improvement in the knowledge of stratospheric positive ion chemistry during the last decade. Results of several in-situ measurements of ion composition have been reported. Total ion density has also been measured with greater accuracy. In this work, theoretical study has been made to reproduce the main features of the above observations. Difficulties encountered in such studies are discussed. Finally models of total ion density and ion composition are given.     

直流电弧放电中的高温化学反应

本文对近年来国内外关于直流电弧放电中的高温化学反应的应用进展进行了综述。附参考文献72篇。