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1.
Arnold Kadik 《Physics of the Earth and Planetary Interiors》1997,100(1-4):157-166
The oxygen fugacity (f(O2)) values recorded by diamondiferous peridotite and eclogite xenoliths from Siberia indicate that the redox state of the ancient lithosphere is heterogeneous on a scale of at least four log units, mainly in the range between the wüstite-magnetite (WM) and iron-wüstite (IW) oxygen buffers. Highly reduced peridotites can be interpreted as relict from earlier lower f(O2). The f(O2) values recorded by ‘fertile’ and less modified spinel peridotites from Mongolia, Baikal and Tien-Shan show that the redox state of the lithosphere beneath central Asia and Tien-Shan is heterogeneous on a scale of 2–3 log units, mainly in the range between the WM and IW + 1 oxygen buffers. These data provide evidence for the presence of a lower-f(O2) regime of carbon-bearing mantle beneath the Baikal rift zone and Tien-Shan, and the oxidation of diapirs ascending from the asthenosphere. The ‘dry’ xenoliths from Mongolia primarily reflect closed system behavior in the upper mantle, the f(O2) of which is buffered by ferric-ferrous redox equilibrium. The observed evolution of f(O2) values is closely linked to the distribution of volatile species in the mantle. H2O and CO2 are the dominant volatiles for the more depleted and oxidized part of peridotites, and CH4 for the more reduced and less modified part. It is proposed that the upper mantle was originally more reduced and has become progressively more oxidized, resulting perhaps largely from the preferential loss of hydrogen and carbon during melting. The oxygen budget of the upper mantle results from the opposing contributions of crustal recycling and transfer of carbon-bearing material from the deep mantle. 相似文献
2.
D.P. Mattey R.H. Carr I.P. Wright C.T. Pillinger 《Earth and Planetary Science Letters》1984,70(2):196-206
High-sensitivity stepped extraction reveals two isotopically distinct forms of carbon in submarine basalt glasses: an isotopically light carbon component released by combustion from 200 to 600°C and an isotopically heavy CO2 liberated from vesicles (magmatic carbon) from 600 to 1200°C. The δ13CPDB of the low release temperature carbon varies from −24 to −30‰ and is believed to be surficial organic contamination. A survey of various types of oceanic glasses demonstrates that the δ13C of magmatic CO2 varies from −4.2 to −7.5‰ in mid-ocean ridge basalt (MORB), from −2.8 to −6.7‰ in glasses from Hawaii and Explorer Seamount and from −7.7 to −16.3‰ in glasses from the Scotia Sea and Mariana Trough. Magmatic CO2 in back-arc basin basalts (BABB) is on average 5‰ lighter than equivalent CO2 in MORB and can be explained by the mixing in the source regions for BABB magmas of juvenile (MORB-like) CO2 with an organic carbon component from subducted pelagic sediments. It is inferred that significant amounts of pelagic carbonate carbon (δ13C 0‰) must be recycled into the mantle. 相似文献
3.
Gas is extracted from large (6–31 kg) Antarctic ice samples to obtain sufficient CO2 for14C measurements with small low-level proportional counters. The14C ages of Byrd core ice are in accord with glaciological estimates ranging from (2.2−1.1+1.4)×103 yr at 271 m depth to more than 8 × 103 yr at 1071 m depth. The CO2 abundances in gas extracted from Byrd core ice range from 0.0216 to 0.051%, with below present-day atmosphere CO2 abundances for ice from 1068 and 1469 m depths. The CO2 abundance in gas from Allan Hills surface ice samples ranges between four and six times the atmospheric value and the CO2 had a specific activity three times that of contemporary carbon. A possible explanation for the anomalously high specific activity is surface melting with the incorporation into CO2 of14C produced by cosmic ray spallation of oxygen in ice. The CO2 abundance in gas extracted from subsurface Allan Hills ice ranged from 0.030 to 0.065%, and the specific activities are below contemporary carbon, indicating ages greater than 5×103 yr. The18O/16O ratio of oxygen in the trapped gas is the same as that of atmospheric oxygen and differs markedly from the18O/16O ratio in the ice. The O2, N2, and Ar abundances and isotopic compositions are similar to those in contemporary air, except for positive15N/14N ratios in a few samples. 相似文献
4.
Experimental determination of U and Th partitioning between clinopyroxene and natural and synthetic basaltic liquid 总被引：2，自引：0，他引：2
Clinopyroxene-silicate liquid partition coefficients for U and Th have been determined by particle track radiography from 1 atm crystallization experiments at controlledfO2. Two natural basaltic and one synthetic composition were studied atfO2 values from the NiNiO oxygen buffer to 1 log unit more oxidizing than FeFeO (IW+ 1). Over the range offO2 values and compositions studied,DUcpx/liq = 0.0034–0.015,DThcpx/liq = 0.008–0.036, andDThDU= 3.4–1.1. With decreasingfO2,DThDU can decrease by up to a factor of 3 for a given composition, primarily from an increase inDUcpx/liq, which we interpret as resulting from an increase in the proportion of tetravalent U in the system with decreasingfO2. This demonstrates that crystal-liquid UTh fractionation isfO2 dependent and that U in terrestrial magmas is not entirely tetravalent.DThcpx/liq appears to decrease in the two basalts at the lowestfO2, possibly as a result of changes in composition withfO2.
Our data show the sense of UTh fractionation by clinopyroxene-liquid partitioning is consistent with previous experimental determinations, in thatDThcpxDUcpx> 1 in all cases. This indicates that, during partial melting, the liquid will have aTh/U ratio less than the clinopyroxene in the source. The observed238U230Th disequilibrium in MORB requires that the partial melt should have aTh/U ratio greater than the bulk source, and, therefore, cannot result from clinopyroxene-liquid partitioning. Further, the magnitudes of the measured partition coefficients are too small to generate significant UTh fractionation in either direction. Assuming that clinopyroxene contains the bulk of the U and Th in MORB source, our results indicate that238U230Th disequilibrium in MORB may not be caused by partial melting at all. 相似文献
5.
The concentrations of free dissolved carbon dioxide in lake water were measured with a newly developed CO2 sensor, which was installed in a through-flow measurement system. The results of measurements demonstrate the CO2 dynamics in lake Willersinnweiher. The CO2 concentrations showed a correlation with the oxidation of CH4 in the metalimnion and caused shifts in the carbonate system, thus affecting the autochthonous precipitation and dissolution of calcite.
From the results of measurement appears that the CO2 sensor is capable of very exact measurements of dissolved free CO2 in lake water. At the same time, the parameter is easily determined in the field without large expenditures. 相似文献
6.
2008年汶川地震导致了大量地下含碳气体释放. 本文基于卫星高光谱数据采用差值法获取了汶川地震前后川西地区含碳气体异常的时空分布特征. 结果显示汶川地震前后不同含碳气体异常的时空分布特征不同. 空间分布上,CH4,CO2和CO异常分布于震中附近且受断裂控制明显,与热红外异常特征类似;CO和CO2异常的范围较CH4大,CO除沿断裂带分布外,在四川盆地也大面积出现. 异常出现时间上,CO2异常最早,其次为CH4和CO. 气体来源上,CO2和CH4主要来源于地球内部沿断裂带释放,在地球内部还原条件下,CH4还可由CO2还原形成;CO异常除了沿断裂带释放和由断裂带释放的CH4氧化生成外,还由四川盆地渗漏的CH4氧化生成. 本文结果可用于地震监测预测研究,不仅提供了新的地震前兆观测参数,还为地震热红外异常机制“地球放气温室效应”提供了科学依据,同时对地震引起的地质碳排放研究也有重要意义. 相似文献
7.
Pierre Schiano Bernard Bourdon Robert Clocchiatti Dominique Massare Maria E. Varela Yan Bottinga 《Earth and Planetary Science Letters》1998,160(3-4):537-550
The study of glass inclusions inside mantle minerals provides direct information about the chemistry of naturally occurring mantle-derived melts and the fine-scale complexity of the melting process responsible for their genesis. Minerals in a spinel lherzolite nodule from Grande Comore island contain glass inclusions which, after homogenization by heating, exhibit a continuous suite of chemical compositions clearly distinct from that of the host basanitic lava. The compositions range from silicic, with nepheline–olivine normative, 64 wt% SiO2 and 11 wt% alkali oxides, to almost basaltic, with quartz normative, 50 wt% SiO2 and 1–2 wt% alkali oxides. Within a single mineral phase, olivine, the inferred primary melt composition varies from 54 to 64 wt% SiO2 for MgO content ranging from 8 to 0.8 wt%. An experimental study of the glass and fluid inclusions indicates that trapped melts represent liquids that are in equilibrium with their host phases at moderate temperature and pressure (T≈1230°C and P≈1.0 Gpa for melts trapped in olivine). Quantitative modelling of the compositional trends defined in the suite shows that all of the glasses are part of a cogenetic set of melts formed by fractional melting of spinel lherzolite, with F varying between 0.2 and 5%. The initial highly silicic, alkali-rich melts preserved in Mg-rich olivine become richer in FeO, MgO, CaO and Cr2O3 and poorer in SiO2, K2O, Na2O, Al2O3 and Cl with increasing melt fractions, evolving toward the basaltic melts found in clinopyroxene. These results confirm the connection between glass inclusions inside mantle minerals and partial mantle melts, and indicate that primary melts with SiO2 >60 wt%, alkali oxides >11%, FeO <1 wt% and MgO <1 wt% are generated during incipient melting of spinel peridotite. The composition of the primary melts is inferred to be dependent on pressure, and to reflect both the speciation of dissolved CO2 and the effect of alkali oxides on the silica activity coefficient in the melt. At pressures around 1 GPa, low-degree melts are characterized by alkali and silica-rich compositions, with a limited effect of dissolved CO2 and a decreased silica activity coefficient caused by the presence of alkali oxides, whereas at higher pressures alkali oxides form complexes with carbonates and, consequently, alkali-rich silica-poor melts will be generated. 相似文献
8.
Primary carbonaceous material has been identified in submarine basaltic glasses and mantle-derived peridotite nodules from alkali basalts using electron microprobe techniques. In the submarine rocks carbon occurs (1) in quench-produced microcracks in glasses and phenocrysts, (2) in vesicles, where it is preferentially concentrated on the sulfide spherules attached to vesicle walls, and (3) in microcracks and CO2-rich bubbles in inclusions of glass completely enclosed by phenocrysts. In peridotite nodules carbon exists in intergrain cracks, along grain boundaries, and on the walls of fluid inclusions disposed in two dimensional arrays. The carbonaceous material is believed to consist of a mixture of graphite, other forms of elemental carbon, and possibly small amounts of organic matter.It is suggested that carbon precipitates by disproportionation of CO according to the reaction 2 CO→C+CO2 and that this reaction is catalyzed by sulfide-oxide surfaces in vesicles. Once deposition has begun, the reaction continues on carbon surfaces as well. Based on the large amounts of condensed carbon observed in some vapor inclusions and the apparent lack of oxidation features associated with them, it is proposed that carbon condensed from a magmatic vapor in which CO was a significant constituent. This implies that oxygen fugacities of undegassed basaltic melts under confining pressures of the shallow crust are typically lower than those of the QFM buffer at equivalent temperatures. This is in agreement with some intrinsic oxygen fugacity measurements on similar undegassed materials.Regardless of the mechanism of its formation, the presence of carbon in CO2-rich vesicles and inclusions in basaltic glasses and mantle nodules adds uncertainty to estimates of minimum pressures of entrapment based on measurements of fluid densities. Condensed carbon also accounts for some of the carbon isotopic characteristics of these rocks. 相似文献
9.
为了研究吉兰泰断陷盆地周缘断裂带气体排放及其对断层活动性的指示意义,在盆地周缘4条活动断裂上布设了5条土壤气测量剖面和1条电磁测量剖面,观测了土壤气中Rn,Hg和CO2的浓度、释放通量和地电阻率,对各测量剖面进行了土壤化学组分分析,计算得到了断层活动性相对指数KQ。研究结果显示:土壤气体CO2和Rn受渗透性较低的粉砂土阻挡,主要沿结构破碎的断层上盘逃逸,并形成浓度高峰;吉兰泰盆地南缘土壤气Rn,Hg和CO2的浓度和释放通量最高,可能与盆地西南缘花岗岩中U和Ra的运移以及盆地南缘碳酸盐岩的分解有一定的关系。各测量剖面的断层活动性相对指数KQ值的变化特征表明,正断层和逆断层的KQ值大于走滑断层,且巴彦乌拉山山前断裂上的KQ值最高,揭示其活动性最强,有可能是地震发生的潜在危险区。 相似文献
10.
L.V. Dmitriev A.V. Sobolev A.V. Uchanov T.V. Malysheva W.G. Melson 《Earth and Planetary Science Letters》1984,70(2):303-310
Most abyssal basalt can be divided into two groups based on major and minor element compositions of the glassy rinds of pillow lavas. Crystal differentiation models cannot relate one group to the other. Instead, depth of partial melting may exert the primary control. The first group (MORB-1) is characterized by low TiO2 and Na2O and higher MgO, and is derived from a primary melt originating from the spinel peridotite facies. The higher TiO2-NaO2 group (MORB-2) appears to have been derived from the lower-pressure (shallower depth) plagioclase peridotite facies. Mössbauer spectra show that MORB-1 is from a mantle source region with lower oxidation states (between the QFM and NNO buffers) than for MORB-2 (around the NNO buffer). 相似文献
11.
本文利用美国国家大气环境中心(NCAR)的二维化学、辐射和动力相互作用的模式(SOCRATES),模拟了大气中N2O增加对O3和温度的影响,并从化学、辐射和动力过程讨论了影响原因,此外还与大气甲烷和平流层水汽增加对大气环境的影响进行了对比.分析表明:大气中N2O浓度增加以后,将通过化学过程引起30 km以上O3损耗,30~40 km损耗较多;30 km以上降温明显,下平流层中低纬度地区以及对流层O3增加并有微弱升温;30~40 km附近,北半球中高纬地区O3减少以及降温幅度都大于南半球.对流层升温主要是N2O和O3增加所致,而平流层温度变化主要受O3控制.北半球中高纬地区动力过程对温度变化的反馈较其它地区明显,这种反馈对平流层中高层北半球中高纬地区温度和O3的变化都有明显影响.大气中甲烷增加引起的O3损耗在45 km以上,45 km以下O3增加.平流层水汽增加会引起40 km以上O3减少,20~40 km大部分地区O3增加.N2O增加造成的O3损耗正好位于臭氧层附近,其排放对未来O3层恢复至关重要.N2O增加引起下平流层15~25 km中低纬度地区有弱的升温,这与其它温室气体增加对该地区温度的影响不同,CO2,CH4和H2O等增加后下平流层通常是降温. 相似文献
12.
Tetsuya Komabayashi Kei Hirose Nagayoshi Sata Yasuo Ohishi Leonid S. Dubrovinsky 《Earth and Planetary Science Letters》2007,260(3-4):564-569
A phase transition in pure CaSiO3 perovskite was investigated at 27 to 72 GPa and 300 to 819 K by in-situ X-ray diffraction experiments in an externally-heated diamond-anvil cell. The results show that CaSiO3 perovskite takes a tetragonal form at 300 K and undergoes phase transition to a cubic structure above 490–580 K in a pressure range studied here. The transition boundary is strongly temperature-dependent with a slightly positive dT / dP slope of 1.1 (± 1.3) K/GPa. It is known that the transition temperature depends on Al2O3 content dissolved in CaSiO3 perovskite [Kurashina et al., Phys. Earth Planet. Inter. 145 (2004) 67–74]. The phase transition in CaSiO3(+ 3 wt.% Al2O3) perovskite therefore could occur in a cold subducted mid-oceanic ridge basalt (MORB) crust at about 1200 K in the upper- to mid-lower mantle. This phase transition is possibly ferroelastic-type and may cause large seismic anomalies in a wide depth range. 相似文献
13.
The CO2 content, air saturation and calcite equilibrium of the River Ilm and some of its tributaries were analysed. CO2 content was measured by degasing the CO2 from water. The CO2 level is a very sensitive indicator for a low pollution in oxygen saturated waters. Clean running waters have a CO2 content close to the air saturation of 0.1–0.3 mg C l−1. Ground water and springs are rich in CO2. Polluted waters are characterised by higher CO2 contents, also organic pollution can result in high values of CO2. Carbon dioxide concentration of streams and brooks is limited by re-aeration.
The headwater region (softwater) of the River Ilm is unsaturated, the hard water in the middle- and underflow is oversaturated. In summer and autumn high saturation could be found, but without autochthonous calcite precipitation like in hard water lakes. 相似文献
14.
We use sulfur (S) isotope signatures within ancient sediments and a photochemical model of sulfur dioxide (SO2) photolysis to interpret the evolution of the atmosphere over the first half of Earth's history. A decrease in mass-independent sulfur isotope fractionation has been reported in Archean rocks deposited between ~ 2.7 Ga and ~ 3.2 Ga, and is reinforced by new S isotope data that we report here. This pattern has been interpreted by some as evidence that atmospheric oxygen (O2) was elevated during this time. In this paper, we argue against that conclusion, and show that it is inconsistent with other geochemical data. In its place, we propose a new model that can explain the sulfur isotope record that can also avoid conflicts with independent constraints on O2 and account for concurrent glacial deposits. Specifically, we suggest that prior to the rise of O2 excursions in the sulfur isotope record were modulated by the thickness of an organic haze. This haze would have blocked the lower atmosphere from the UV fluxes responsible for the anomalous sulfur photochemistry and would have caused an anti-greenhouse effect that triggered the glaciations. We used a photochemical model to verify that a haze could have affected the isotopic signal in this manner, and to examine how changes in atmospheric methane (CH4) and carbon dioxide (CO2) concentrations could have controlled haze thickness. Finally, we combined the resulting relationships with climate models and sulfur isotope and glacial records to deduce a new evolutionary sequence for Archean climate, surface chemistry, and biology. 相似文献
15.
An Aleutian high-alumina basalt from the island of Atka at one atmosphere crystallizes plagioclase (1275°C) followed by olivine (1170°C) and clinopyroxene (1115°C). At oxygen fugacities along NNO, magnetite crystallizes below 1070°C, but its liquidus increases to at least 1175°C at an oxygen fugacity two log units above NNO. Phase relations at two kilobars pressure of melts containing small amounts of water are similar, although orthopyroxene and magnetite are observed to follow clinopyroxene. Amphibole crystallizes at near-liquidus temperatures only at water contents of melts approaching 4.5%. Amphibole assumes the liquidus in melts containing 5% water.Anhydrous melts crystallize plagioclase to 19 kbar, where garnet and clinopyroxene assume the liquidus. Olivine yields to clinopyroxene as the highest-temperature subliquidus phase at about 9 kbar.The array of compositions of basaltic Atka rocks, as displayed on appropriate pseudoternary projections, can be interpreted as a crystal fractionation path at moderate pressure (8 kbar) and small melt-water contents. The interpreted fractionating minerals are olivine, clinopyroxene, plagioclase, and (probably) magnetite. (The actual phenocrysts in Atka basalts like AT-1, which lacks phenocrystic clinopyroxene, must have crystallized at pressure less than 8 kbar, however.) The compositions of two-pyroxene andesites from Atka can be interpreted to lie on a lower-pressure fractionation trend at melt water contents of 2–3%. Such water contents are consistent with the complete absence of amphibole in any Atka rocks and are suggestive that water contents of the basaltic magmas, if the basalts are parental to the andesites, were 1–2%. 相似文献
16.
基于AQUA AIRS传感器提取了2014年2月12日新疆于田MS7.3地震前后CO和O3数据, 讨论了数据变化与地震活动的关系。 差值法和异常指数法结果表明, 于田地震后CO和O3在3月份达到最大异常, 且气体柱浓度异常沿NE向发震构造呈线性分布; 不同高度的CO和O3的VMR值变化与差值法和异常指数法得到的结果相吻合; 地震前后短时间内CO和O3气体柱浓度出现下降, 且地震当月最低。 初步推断可能是阿尔金断裂尾部在SW向运动过程中使得震区断裂带在弹性挤压状态下出现闭锁, 气体不流通导致; CO和O3异常更多的可能是由于田地震引起地下气体大量释放, 其次可能是与地下气体逸散在大气圈中发生的一系列化学反应有关。 研究表明, 卫星高光谱遥感数据获得的CO和O3的地球化学信息与地震有密切联系, 在地震监测及预测领域具有重要的应用价值。 相似文献
17.
Shape analysis of Pacific seamounts 总被引：2，自引：0，他引：2
Deborah K. Smith 《Earth and Planetary Science Letters》1988,90(4):457-466
Shape statistics have been compiled from 85 profiles of well-surveyed Pacific seamounts in the height range 140–3800 m. A flat-topped cone was fit to each seamount's cross-sectional profile maintaining the slopes of the sides as closely as possible. On each profile a basal widthdb, a summit widthdt, and a maximum heighth, were measured. The height-to-basal-radius ratio isξh is estimated by the ratio2hdb and flatnessf by the ratiodtdb. Slope angleφ = arctan(ε) is estimated fromε =2h(db − dt). Summit height and basal radius are found to be highly correlated (r = 0.93). The 85-point sample mean of the height-to-basal-radius ratio isξh = 0.21 ± 0.08 implying that a seamount's summit height is typically one fifth its basal radius. Despite the high correlation, individual points show some scatter, and there may be groupings into different morphological types. For example, all but one of the seamounts with summit heights above 1000 m have values ofξh that are larger than the sample mean. The 85-point sample mean of flatness isf = 0.31 ± 0.18. Data points show a large scatter with values off varying between 0 (a pointy cone) and 0.69 (a flat-topped cone). A histogram representation of flatness, however, indicates that certain values off may be more common than others: the histogram shows a bimodal distribution with maxima occurring at values off in the ranges 0.10–0.20 and 0.35–0.50. Moreover, there is some evidence that the mean flatness decreases with summit height so that the preferred shape of a large-sized seamount may be a pointy cone. Slope angle has an 85-point sample mean ofφ = 18 ± 6°; individual values ofφ vary between 5° and 36°. In addition to having a lower than average mean flatness seamounts with heights above 2600 m also have a lower than average mean slope angle (15°). To determine which variables account for most of the observed variation in the seamount shapes, a multivariate principal component analysis was performed on the data using five shape variables (summit height, basal radius, summit radius, flatness, and slope). The analysis indicates that most of the variation is described by two variables: flatness and summit height. 相似文献
18.
致密油是重要的非常规石油资源,但由于其一次采收率低,需要开展提高采收率研究。由于致密油储层孔隙结构复杂,不同孔隙对产量的贡献差异很大,需要深入研究不同孔隙中原油的动用情况进而优化开发方式。本文采用核磁共振测试与驱替实验相结合的方法开展研究,直观反映不同注入条件下注入介质与原油的驱替过程,明确了注水和注CO2两种开发方式不同孔隙中原油的动用规律。结果表明:水驱和CO2驱不同孔隙区间原油动用程度随着驱替压差逐渐增大而增大;水驱和CO2驱大孔隙中的原油绝大部分被动用,随着孔隙半径逐渐减小,原油动用的比例逐渐降低;小于0.01μm微小孔隙中CO2驱动用效果明显好于水驱,致密油藏中CO2更易进入小孔隙提高致密油采收率。 相似文献
19.
Kiyoshi Kuramoto 《Physics of the Earth and Planetary Interiors》1997,100(1-4):3-20
Recent understandings of planetary accretion have suggested that accumulation of a small number of large planetesimals dominates intermediate to final growth stages of the terrestrial planets, with impact velocity high enough to induce extensive melting of the planetesimal and target materials, resulting in formation of a large molten region in which gravitational segregation of silicate and metal, that is, core formation proceeds. In case of homogeneous accretion, volatiles contained in each planetesimal are likely subjected to partitioning among gas, silicate melt, and molten metallic iron at significantly high temperatures and pressures in such a massive molten region. Each phase would subsequently form the proto-atmosphere, -mantle, or-core, respectively. Such chemical reprocessing of H and C associated with core formation, which is followed by both degassing from mantle and atmospheric escape, may result in a diverse range of H2O/CO2 in planetary surface environments, which mainly depends on the H and C content relative to metallic iron in planetary building stones. This may explain inferred difference in volatile distribution between the Earth's (relatively H2O-rich, CO2-poor) and the martian (H2O-poor, CO2-rich) surface environments. Such volatile redistribution may be systematically described by using the retentivity of H2O, ξ, defined as follows: ξ = 1 − ([CO]0 + 2[CH4]0 + 2[C(gr)]0)/[H2O]0, where [i]0 represents mol number of species i partitioned into non-metallic phases, that is, gas and silicate melt in impact-induced molten region. When ξ > 0.5, relatively H2O-rich and CO2-poor surface environment may eventually evolve, although a small portion of H2O partitioned into the NON=metallic phases are possibly consumed by subsequent chemical reactions with reduced C-species with producing CO2 and H2. When ξ< 0.5, on the contrary, H2O consumption by the above reactions and selective loss of H2 to space may result in relative H2O-depleted and CO2-rich surface environment. Given the building stone composition by the two-component model by Ringwood (1977) and Wänke (1981), ξ is found to decrease with increasing the mixing fraction of the volatile-rich component: ξ > 0.5 for the mixing fraction smaller than about 15–20% and ξ < 0 for the mixing fraction larger than about 20–30%. This is not significantly dependent on temperature and pressure in molten region and H/C ratio in the building stone. The estimated mixing fraction of the volatile-rich component, about 10% for the Earth and 35% for Mars, is consistent with the observed difference in volatile distribution between the surfaces of both planets. 相似文献
20.
K. Righter M. J. Drake G. Yaxley 《Physics of the Earth and Planetary Interiors》1997,100(1-4):115-134
We report new metal-silicate partition coefficients for Ni, Co and P at 7.0 GPa (1650–1750°C), and Ni, Co, Mo, W and P at 0.8, 1.0 and 1.5 GPa (1300–1400°C). Guided by thermodynamics, all available metal-silicate partition coefficients, D(i), where i is Ni, Co, P, Mo and W, are regressed against 1/T, P/T, lnf(O2), ln(1 − Xs) (XS is mole fraction of S in metallic liquid) and nbo/t (non-bridging oxygen/tetrahedral cation ratio, a silicate melt compositional-structural parameter) to derive equations of the following form: ln D(i) = aln f(O2) + (b/T) + (cP/T) + d(nbo/t) + eln(1 − XS) + f. Expressions for solid metal-liquid silicate and liquid metal-liquid silicate partition coefficients are derived for S-free and S-bearing systems.
We investigate whether Earth's upper-mantle siderophile element abundances can be reconciled with simple metal-silicate equilibrium. Sulfur-free metallic compositions do not allow a good fit. However, Ni, Co, Mo, W and P abundances in the upper mantle are consistent with simple metal-silicate equilibrium at mantle pressures and temperatures (27 GPa, 2200 K, ΔIW(iron-wüstite) = −0.15, nbo/t = 2.7; XS = 0.15). Although these conditions are near the anhydrous peridotite solidus, they are well above the hydrous solidus and probably closer to the liquidus. A hydrous magma ocean and early mantle are consistent with predicted planetary accretion models. These results suggest that siderophile element abundances in Earth's upper mantle were established by liquid metal-liquid silicate equilibrium near the upper-mantle-lower-mantle boundary. 相似文献