岩浆脱气动力学研究进展

岩浆脱气动力学是地球动力学的一个重要方面,介绍H2O和CO2在岩浆中溶解,气泡成核,气泡生长与上升以及岩浆喷发等过程的研究成果。由前人的研究结果可知,压力降低使得气体在岩浆中过饱和是气泡形成的主要原因,气体过饱和度增大加速气体的释放和气泡的生长,进而导致岩浆的浮力增大,岩浆上升速度加快,气泡膨胀和加速作用发生在岩浆爆裂之前,并且是引起爆裂的真正原因,此外,CO2的溶解度较小和岩浆中CO2含量较高是所泡中CO2含量高的主要原因,同时也指出,文献中的模型与岩浆喷发的实际情况相比,体系成分过于简单,还有待进一步完善,对岩浆脱气动力学研究作了客观评价和展望。     

刻在46亿岁地球上的活历史

火山活动与岩石 ⊙岩浆、火山喷出物、火成岩 在地表深处,有些区域的岩石因地球内部的热量而熔化成黏稠的岩浆.在地表附近由岩浆房中岩浆喷发所形成的地形就是火山. 地下的岩浆中含有水和二氧化碳.随着岩浆上升,水和二氧化碳变成气泡开始膨胀.这些气泡爆炸般急剧膨胀的结果就是火山喷发.喷出地表的物质称为火山喷出物.     

延伸流场中的气熔两相流实验现象与分析

为研究气泡在熔体中的动力学,自行设计了圆柱形可视化流道,直接将CO2气体注入聚合物熔体中,观察CO2气泡在小孔延伸流场中不同位置区域时,其形态、大小、运动、变形等动力学现象.并从经典两相流理论的角度出发,分析了流场结构参数、加工条件对气泡在聚合物熔体中形态、分布、运动变化等的影响.实验结果表明:气相在熔体中是以泡状存在的,单一的大气泡经过延伸后,将发生破裂,成为许多细碎的小气泡,且破裂的小气泡的大小、分布、密度等与加工温度、速度、进气压力等有关;气泡经过小孔延伸后破裂,使气熔两相趋于混合,有利于CO2作为发泡剂在泡沫塑料制品生产中的应用.     

钢液/（N2、H2）过饱和体系中气泡生长的数值分析

采用水/CO2体系模拟研究钢液/( N2、H2)过饱和体系中气泡生长动力学行为，分别建立水溶液和钢液中气泡形核长大机理模型。基于三种不同的气泡生长数学模型，分别研究水/CO2和钢液/( N2、H2)体系数学模型中气泡生长动力学，并采用水模型实验数据对数学模型进行验证。分析钢液/( N2、H2)体系前期和后期处理压力以及钢液深度等因素对气泡生长的影响。研究表明：采用气泡浮选去除夹杂物技术时，前期处理压力对气泡生长有显著促进作用；后期处理压力对气泡生长有阻碍作用，随着后期处理压力的升高影响逐渐加强；钢液深度对气泡生长有阻碍作用，随着钢液深度的增加影响逐渐减弱；相比氮气，钢液中氢气气泡析出长大更快。     

集束射流火焰燃烧特性热态实验

通过实验室建立的小型实验炉,进行集束射流加热金属冷料的热态模拟实验,分析了集束射流火焰在不同冶炼阶段的成分变化.实验研究表明:集束射流火焰形态呈现多样性特点,燃烧产物成分不断变化.在金属冷料的存在作用下,少量CO2气体产生,O2增加,CO下降;熔化期中,O2逐渐升高,CO逐渐降低,CO2体积分数一直保持在1%～2%;脱碳期与熔化期相比,O2下降,而CO上升,CO2稍有增加;脱碳期中,钢水中C含量逐渐降低,CO2和O2有所增加,而CO含量剧烈降低.集束射流火焰燃烧产物中,各成分之间关系密切,CO的含量随着O2含量的升高而降低.在熔化期中,CO气体含量随着CO2气体含量的增加而增加;在脱碳期,CO气体含量随着CO2气体含量的增加而降低.     

上倾管道充气排液过程两相流动特性

在直径为40 mm、倾斜角为20°的管道内,以空气、水为试验介质,利用高速摄影仪和数据采集仪对上倾管道充气排液过程气液两相流动特性进行研究。建立跟随气泡和领先气泡速度比与气泡距离的关系,对比不同入口气体流速下管道内部压力、流量、气泡变化特性。结果表明,充气排液过程分为4个阶段,气体侵入和气液喷发阶段是气液混合物产生阶段,此阶段上倾管内流型以段塞流为主。管道底部压力和出口流量随气体流速的增大而增大,排空时间随气体流速的增大而减小。气体侵入过程气泡呈合并趋势,入口气速越大气泡越长,形状越不规则,领先气泡的速度和液体速度呈线性关系。Hout公式与本文中拟合公式最为接近。     

林业废弃物氧气-水蒸气气化的Aspen Plus模拟

基于Aspen Plus软件对林业废弃物氧气-水蒸气气化进行模拟计算,并对比模拟结果与试验结果以验证模型的可靠性,研究了气化温度、气化压力、当量比及水蒸气与废弃物的质量配比(S/F)对气化特性的影响.结果表明:随着温度升高气体产物中H2和CO含量增加,同时气化效率也相应增加,800℃时气化效率达到最高值为87.38%;压力增大时气体产物中H2,CO含量减少,但干气体产物的CH4含量及气体热值迅速增大;气化的最佳当量比约为0.22,过高或过低均会导致可燃组分和气化效率的下降;S/F增大时,气体产物中CO2,H2含量增多,CO含量减少,当S/F≥0.5时气化效率达到最大值并保持不变.     

CO_2水合物生成的影响因素研究

在体积350 m L的恒容反应釜中研究了CO2水合物的生成过程,实验考察了搅拌速率、温度和压力等因素对CO2水合物生成过程的影响。实验结果表明,相对静止条件下机械搅拌可以通过促进传质传热,加速CO2水合物生成过程。随着搅拌速率的增大,CO2水合物的平均生长速率从0.283 mmol/min增大到1.132 mmol/min,且搅拌速率为800 rpm时实验条件下的水合物的诱导期最短;不同实验温度(273.65 K,274.15 K,275.15 K,276.15 K)下,CO2水合物生成过程中的溶解速率、诱导期及反应速率变化不大,即受温度影响不明显;CO2水合物的生长受压力影响明显,增压可显著缩短诱导期、加快反应速率。水合物生长过程主要受客体分子浓度的影响,是动力学控制过程。3 MPa时CO2水合物的平均生长速率高达1.1 mmol/min,是2 MPa时的5倍。     

电弧炉炉气成分的影响因素

为进一步完善对电弧炉炉气成分变化规律的研究,本文分别对电弧炉炉气中CO、CO2、O2和N2间的相互关系,以及电弧炉供氧流量、电弧炉熔池碳含量对电弧炉炉气成分的影响进行实验研究.结果表明,炉气中CO在有大量CO2气体存在下开始出现,并随着CO2含量的增加而增加;O2与CO2、N2含量呈线性关系;O2与CO与呈指数关系;随着供氧流量的提高,炉气中CO和CO2的含量逐上升,O2和N2的含量降低,氧气的利用率提高;当钢水中碳质量分数为1.3%左右时,炉气中CO、CO2含量达到最大.     

微藻工程固定二氧化碳减缓温室效应

由于工业污染,大气中CO2和其它气体(如N2O9H4)的含量持续上升,引起了水储备、农业、海岸保护、城市建设等方面的全球性变化,CO2含量的上升主要是由人类过度的燃烧木材、煤、石油以及对森林的破坏引起的.CO2等气体含量的增加会导致全球平均气温上升,而全球逐渐的变暖则引起全球海平面的上升.为了防止海平面的上升,必须降低CO2的含量.因此,利用植物,特别是微藻来固定CO2就是惟一的方法.     

Breaking of Henry's law for noble gas and CO2 solubility in silicate melt under pressure

Degassing of the Earth is still poorly understood, as is the large scatter in He/Ar ratios observed in mid-ocean ridge basalts. A possible explanation for such observations is that vesiculation occurs at great depths with noble-gas solubilities different from those measured at 1 bar (ref. 1). Here we develop a hard-sphere model for noble-gas solubility and find that, owing to melt compaction, solubility may decrease by several orders of magnitude when pressure increases, an effect subtly overbalanced by the compression of the fluid phase. Our results satisfactorily explain recent experimental data on argon solubility in silicate melts, where argon concentration increases almost linearly with pressure, then levels off at pressures of 50-100 kbar (refs 2-5). We also model vesiculation during magma ascent at ridges and find that noble-gas partitioning between melt and CO2 vesicles at depth differs significantly from that at low pressure. Starting at 10 kbar (approximately 35 km depth), several stages of vesiculation occur followed by vesicle loss, which explains the broad variability of He-Ar concentration data in mid-ocean ridge basalts. 'Popping rocks', exceptional samples with high vesicularity, may represent fully vesiculated ridge magma, whereas common samples would simply have lost such vesicles.     

Vapour undersaturation in primitive mid-ocean-ridge basalt and the volatile content of Earth's upper mantle

The analysis of volatiles in magmatic systems can be used to constrain the volatile content of the Earth's mantle and the influence that magmatic degassing has on the chemistry of the oceans and the atmosphere. But most volatile elements have very low solubilities in magmas at atmospheric pressure, and therefore virtually all erupted lavas are degassed and do not retain their primary volatile signatures. Here we report the undersaturated pre-eruptive volatile content for a suite of mid-ocean-ridge basalts from the Siqueiros intra-transform spreading centre. The undersaturation leads to correlations between volatiles and refractory trace elements that provide new constraints on volatile abundances and their behaviour in the upper mantle. Our data generate improved limits on the abundances of carbon dioxide, water, fluorine, sulphur and chlorine in the source of normal mid-ocean-ridge basalt. The incompatible behaviour of carbon dioxide, together with the CO(2)/Nb and CO(2)/Cl ratios, permit estimates of primitive carbon dioxide and chlorine to be made for degassed and chlorine-contaminated mid-ocean-ridge basalt magmas, and hence constrain degassing and contamination histories of mid-ocean ridges.     

Kimberlite ascent by assimilation-fuelled buoyancy

Kimberlite magmas have the deepest origin of all terrestrial magmas and are exclusively associated with cratons. During ascent, they travel through about 150 kilometres of cratonic mantle lithosphere and entrain seemingly prohibitive loads (more than 25 per cent by volume) of mantle-derived xenoliths and xenocrysts (including diamond). Kimberlite magmas also reputedly have higher ascent rates than other xenolith-bearing magmas. Exsolution of dissolved volatiles (carbon dioxide and water) is thought to be essential to provide sufficient buoyancy for the rapid ascent of these dense, crystal-rich magmas. The cause and nature of such exsolution, however, remains elusive and is rarely specified. Here we use a series of high-temperature experiments to demonstrate a mechanism for the spontaneous, efficient and continuous production of this volatile phase. This mechanism requires parental melts of kimberlite to originate as carbonatite-like melts. In transit through the mantle lithosphere, these silica-undersaturated melts assimilate mantle minerals, especially orthopyroxene, driving the melt to more silicic compositions, and causing a marked drop in carbon dioxide solubility. The solubility drop manifests itself immediately in a continuous and vigorous exsolution of a fluid phase, thereby reducing magma density, increasing buoyancy, and driving the rapid and accelerating ascent of the increasingly kimberlitic magma. Our model provides an explanation for continuous ascent of magmas laden with high volumes of dense mantle cargo, an explanation for the chemical diversity of kimberlite, and a connection between kimberlites and cratons.     

Aluminium control of argon solubility in silicate melts under pressure

Understanding of the crystal chemistry of the Earth's deep mantle has evolved rapidly recently with the gradual acceptance of the importance of the effect of minor elements such as aluminium on the properties of major phases such as perovskite. In the early Earth, during its formation and segregation into rocky mantle and iron-rich core, it is likely that silicate liquids played a large part in the transport of volatiles to or from the deep interior. The importance of aluminium on solubility mechanisms at high pressure has so far received little attention, even though aluminium has long been recognized as exerting strong control on liquid structures at ambient conditions. Here we present constraints on the solubility of argon in aluminosilicate melt compositions up to 25 GPa and 3,000 K, using a laser-heated diamond-anvil cell. The argon contents reach a maximum that persists to pressures as high as 17 GPa (up to 500 km deep in an early magma ocean), well above that expected on the basis of Al-free melt experiments. A distinct drop in argon solubility observed over a narrow pressure range correlates well with the expected void loss in the melt structure predicted by recent molecular dynamics simulations. These results provide a process for noble gas sequestration in the mantle at various depths in a cooling magma ocean. The concept of shallow partial melting as a unique process for extracting noble gases from the early Earth, thereby defining the initial atmospheric abundance, may therefore be oversimplified.     

脱气对致密油藏流体渗流规律影响研究进展

 致密油藏大多含有溶解气，开采压力低于泡点压力时溶解气析出，产生渗流阻力，影响产能。从致密储层孔喉结构特征入手，阐述了脱气后致密油藏流体渗流特征形成的内因，分析了油藏脱气后流体的流动特征和影响因素，对比了致密油藏和常规油藏在脱气后流体渗流特征的差异，概述了现有的研究手段及相关数学模型的研究现状，展望了脱气后致密油藏流体渗流规律研究趋势。     

制冷剂在毛细管内闪蒸流动的特性

针对制冷剂在毛细管中闪蒸流动过程出现的热力学不平衡现象,基于毛细管内的“综合成核”理论,建立了气泡密度模型和气泡成长模型以及闪蒸流动数学模型,计算出反映毛细管内制冷剂闪蒸流动过程特性的重要参数－气化欠压,并对计算结果进行了理论分析。结果表明：随着质量流量的增加和入口温度的降低,气化欠压增大。     

Carbon isotopic composition of mantle xenoliths in alkali basalt from Damaping, Hebei

The carbon isotopic composition of CO-2, CO and CH-4 extracted by pyrolysis from spinel lherzolite and black pyroxenolite xenoliths in alkali basalt from Damaping has been measured with GC_MS. The results show that, at heating temperatures from 400 to 1 140℃, the δ 13C of CO-2 and CO is -22‰--27‰, and that of CH-4 -30‰--50‰. The data imply that the magma which was generated in the upper mantle by partial melting in the area has experienced the multistage degassing process, and the δ 13C values represent the carbon isotopic composition of CO-2, CO and CH-4 remaining in it, respectively.     

Spectroscopic evidence for a lava fountain driven by previously accumulated magmatic gas

Lava fountains are spectacular continuous gas jets, propelling lava fragments to heights of several hundred metres, which occasionally occur during eruptions of low-viscosity magmas. Whether they are generated by the effervescent disruption of fast-rising bubbly melt or by the separate ascent of a bubble foam layer accumulated at depth still remains a matter of debate. No field measurement has yet allowed firm discrimination between these two models. A key insight into the origin of lava fountains may be gained by measuring the chemical composition of the driving gas phase. This composition should differ markedly depending on whether the magma degassing occurs before or during eruption. Here we report the analysis of magmatic gas during a powerful (250-600 m high) lava fountain, measured with Fourier transform infrared spectroscopy on Mount Etna, Sicily. The abundances of volcanic gas species, determined from absorption spectra of lava radiation, reveal a fountain gas having higher CO2/S and S/Cl ratios than other etnean emissions, and which cannot derive from syn-eruptive bulk degassing of Etna basalt. Instead, its composition suggests violent emptying of a gas bubble layer previously accumulated at about 1.5 km depth below the erupting crater.     

Explosive volcanism may not be an inevitable consequence of magma fragmentation

The fragmentation of magma, containing abundant gas bubbles, is thought to be the defining characteristic of explosive eruptions. When viscous stresses associated with the growth of bubbles and the flow of the ascending magma exceed the strength of the melt, the magma breaks into disconnected fragments suspended within an expanding gas phase. Although repeated effusive and explosive eruptions for individual volcanoes are common, the dynamics governing the transition between explosive and effusive eruptions remain unclear. Magmas for both types of eruptions originate from sources with similar volatile content, yet effusive lavas erupt considerably more degassed than their explosive counterparts. One mechanism for degassing during magma ascent, consistent with observations, is the generation of intermittent permeable fracture networks generated by non-explosive fragmentation near the conduit walls. Here we show that such fragmentation can occur by viscous shear in both effusive and explosive eruptions. Moreover, we suggest that such fragmentation may be important for magma degassing and the inhibition of explosive behaviour. This implies that, contrary to conventional views, explosive volcanism is not an inevitable consequence of magma fragmentation.     

相山矿田斑岩型铀矿床地球化学特征及成矿机制探讨

相山矿田北部多数铀矿床在时空和成因上与超浅成侵入相的花岗斑岩密切相关,可归属为斑岩型铀矿床.以横涧—岗上英、沙洲矿床为例,通过稀土元素、微量元素及C,O同位素地球化学特征研究,探讨铀成矿物质来源、成矿流体演化及成矿机制.研究表明,相山矿田火山岩系具同源性,是陆壳物质熔融的产物,火山岩浆在通向地表途中受到高度分馏的结晶作...