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宁强碳质球粒陨石的球粒和基质中出现大量圆形的不透明矿物集合体。其中的主要矿物为磁铁矿、富镍金属和硫化物，另有少量磷酸盐、硅酸盐及微量的铂族金属。离子探针测定显示：①磁铁矿的氧同位素组成服从质量分馏[斜率为0.51±0.04,Δ17O为（-2.8±0.4)‰],δ18O值在-15.3‰~-1.6‰的较大范围内变化；②球粒中的橄榄石(Δ17O为-5.0‰）与不透明矿物集合体处于氧同位素不平衡状态。不透明矿物集合体是由小行星母体中的蚀变反应产生的，金属铁被氧化为磁铁矿，同时使剩余的金属富集镍。 相似文献
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富钙长石-橄榄石包体与其他部分典型包体W-L边的成因 总被引：1，自引：1，他引：0
球粒陨石中的富Ca、Al包体(简称CAI)形成于星云演化的最初始阶段,保存了大量星云形成和演化的各种信息。研究认为,包体的成因主要包括星云直接凝聚和熔融结晶,少部分甚至经历过高温蒸发过程。部分CAI最外层具有由一种或几种矿物组成的Warking-Lovering边(简称为W-L边),CAI和其W-L边对于认识早期星云环境和界定CAI的形成时间等均具有重要意义。目前,对于W-L边的形成过程研究并不深入,且一直存在争议。本文主要介绍了三个典型包体:C#1(富钙长石-橄榄石包体)、GRV 022459-2RI5(A型包体)和GRV 021579-3RI5(富尖晶石球粒状包体)及其W-L边的矿物岩石学和氧同位素组成特征。C#1包体明显经历过熔融结晶过程,W-L边氧同位素组成具有与包体内部矿物相似的富~(16)O同位素特征,表明W-L边的成因与包体的形成过程密切相关,形成于同一富~(16)O同位素组成区域,且W-L边属于包体熔融结晶过程后期的产物。矿物岩石学特征表明,GRV 022459-2RI5属于星云直接凝聚形成,其W-L边为包体形成过程最晚期星云凝聚产物。GRV021579-3RI5经历过熔融结晶过程,其W-L边为包体结晶最后阶段的产物。 相似文献
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准确限定球粒陨石的Ca同位素组成对于研究太阳星云物质演化和行星形成都具有重要意义.选取7块典型的球粒陨石,包括3块CV3型陨石(Leoville、Allende和Vigarano)、1块CM2型陨石(Murchison)、1块CO3.2型陨石(Kainsaz)、1块EH4型陨石(Indarch)以及1块H4型陨石(LaPaz Icefield 03601),进行了Ca同位素组成的研究.其中,Kainsaz、Leoville和LaPaz Icefield 03601共3块陨石的Ca同位素组成是首次报道.结果显示:(1)在增大样品量以规避"样品量效应"的情况下,我们对CV群球粒陨石Ca同位素组成进行更加精确的制约,δ44/40Ca的平均值为0.45‰±0.04‰(n=3,2SE);(2)碳质球粒陨石的Ca同位素组成相对于硅酸盐地球偏轻,从CV群(0.45‰±0.04‰,2SE)、CM群(0.73‰±0.04‰,2SE)到CO群(0.78‰±0.03‰,2SE)逐渐变重,可能与不同化学群陨石中富钙铝难熔包体(CAIs)丰度的变化有关;(3)顽火辉石球粒陨石和普通球粒陨石的Ca同位素组成与硅酸盐地球(BSE)组成一致,证实它们可以作为地球初始的组建物质.本研究丰富了球粒陨石Ca同位素组成数据库,有利于正确认识球粒陨石的Ca同位素组成及变化原因. 相似文献
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本文研究了2个富钙长石-橄榄石型包体和2个富黄长石-尖晶石型和富尖晶石-辉石型包体（分别来自宁强和南极格罗夫山碳质球粒陨石）的矿物岩石学特征,并对它们进行了对比。富钙长石-橄榄石型包体的矿物模式组成具有富橄榄石和缺失黄长石的特征,其可能是球粒和典型难熔包体之间的中间产物,是认识它们之间相互关系的钥匙。矿物岩石学特征表明富黄长石-尖晶石型和富尖晶石-辉石型包体可能是星云直接凝聚的产物,而富钙长石-橄榄石型包体经历过熔融结晶过程。富钙长石-橄榄石型包体的初始物质可能是富Al的球粒或含难熔组分的蠕虫状橄榄石集合体。矿物化学组成对比研究发现,GRV 022459-RI6中的尖晶石具有最富FeO的特征,表明包体的蚀变可能发生在高氧逸度的星云环境。 相似文献
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陈永亨 《矿物岩石地球化学通报》1992,(3)
最新的陨石学资料证明,陨石中表征早期太阳星云同位素异常的证据普遍存在,尤其是碳质球粒陨石难熔包体中。近年在铁陨石和球粒陨石单矿物中也发现了同位素异常,看来在形成行星初始物质的早期太阳星云中,同位素不均匀性是一种非常普遍的现象。 1.氧同位素异常陨石中氧同位素的变化过去一直认为是由于质量分馏造成的。例如,Onuma等(1972)将其变化归结于原始尘埃和冷却的太阳星云气体之间的同位素交换。在3个含钙铝黄长石-尖晶石的阿伦德包体中,相对于SMOW,δ~(18)O为—9.7‰～—11.5‰,这样的组成是在与太阳星云的平衡温度低至800K产生的,或者在包体形成的太阳星云区有非常低的δ~(18)O,此温度较包体的矿物学和结构显示的温度低得多,这一明显差异难以得到合理解释。Clayton等(1973)首先证明了碳质球粒陨石中无水高温矿物强烈贫重氧同位素~(17)O和~(18)O,这种效应是核过程的结果,来自于几乎纯~(16)O组分的的混合,也许产生于太阳系,也许代表了与核合成历史分离的星际尘埃。Clayton等(1977)指出,C_2、C_3和C_4球粒陨石中,相对于地球丰度都存在~(18)O过剩,所有C_3、C_4陨石全岩和矿物分离相都落在与1％ 相似文献
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碳质球粒陨石中富斜长石包体有两种:(1)mm/cm级富Ca—Al包体(CAIs),具30～60Vol％钙长石和可达35％的Ti—Al辉石(Tpx)、黄长石(Mel),尖晶石(Sp)。(2)较小的CA球粒(<3mm),类似于普通球粒陨石的球粒,其中含较多的Na质斜长石、辉石。榄橄石和尖晶石。CAIs被正式命名为类型Ⅰ,把A型CAIs和B型CAIs之间具特殊化学和矿物成分的“过渡型”示为一独立的类型,命名为C型。C型CAIs具Ⅰ组成Ⅱ组的微量元素模式,28Al/27Al(初)比值低(5×10~(-6)),aK(Ca、Mg黄长石)35～55的典型黄长石,Tpx含2—12％的TiO_2,不透明颗粒小于10um。结构、结晶顺序和同心分带表明是由小的熔滴结晶而成。钙长石的结构变化,从粗板条状到细粒基质,反映成核作用后延增加。极少的CAIs具有低于液相线慢冷却的粗板条状钙长石,大多数是由完全熔融的物质快速冷却而来。C型的微量元素丰度受挥发份支配,这种熔体不是由行星(岩浆)作用形成的。蒸发残留和重熔固体凝聚也被排除,因为自然界产生的这种成分、实验产物和热力学计算的残留以及固体凝聚物与C型CAIs都不相同。C型CAIs的成分类似子在高太阳气压下或富尘埃的环境对液体凝聚计算的成分,少量由不完全熔融物质结晶的C型CAIs可能是被重新加热了的液体凝聚物或混合液体/固体凝聚物。 相似文献
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富Ca,Al包体、球粒和蠕虫状橄榄石集合体都是早期星云事件的产物。本文探讨了4个富橄榄石的富Ca,Al组分集合体的矿物岩石学特征,并对它们进行了对比。矿物岩石学特征表明含橄榄石边的富尖晶石-辉石型包体和富Ca,Al组分蠕虫状橄榄石集合体都属于星云直接凝聚的产物,而富钙长石-橄榄石型包体(POI)和富Ca,Al组分球粒经历过熔融结晶过程。矿物模式组成表明POI包体和富Ca,Al组分球粒可能是认识典型富Ca,Al包体与球粒之间相互关系的钥匙。蠕虫状橄榄石集合体GRV022459-2C1中尖晶石普遍具有高的FeO含量,表明其蚀变发生于高氧逸度的星云环境。球粒与粗粒富Ca,Al包体可能属于同一热事件的产物,粗粒富Ca,Al包体形成于富Ca,Al矿物富集的区域,Mg,Fe质硅酸盐球粒形成于富Ca,Al矿物缺失的区域,POI包体和富Ca,Al组分球粒可能形成于上述两个区域之间的过渡区域。 相似文献
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白云鄂博赋矿白云岩与微晶丘和碳酸岩墙的碳氧同位素对比研究 总被引：26，自引：7，他引：19
本文通过方解石和白云石的碳和氧同位素分析,对比研究了白云鄂博赋矿白云岩、黑脑包微晶丘、北京西山微晶丘、宽沟北正常沉积灰岩和白云鄂博碳酸岩墙,从而探讨了赋矿白云岩的成因及其与超大型Fe-Nb-REE矿床的成因关系。结果为:①黑脑包腮林忽洞群顶部微晶丘和北京西山寒武系顶部微晶丘碳酸盐的δ~(13)C值都在0±2‰左右,δ~(18)O值为18.3‰～25.1‰,均具有典型海相沉积碳酸盐岩的特点;②白云鄂博东矿采场δ~(13)C值为-7.9‰～-1.1‰,δ~(18)O值为9.1‰～20.9‰;矿区东西两端δ~(13)C值-7.9‰～-0.6‰,δ~(18)O值8.6‰～25.7‰;均介于地幔流体与典型沉积碳酸盐岩之间。部分赋矿白云岩样品中白云石与方解石之间的碳氧同位素分馏△~(13)C和△~(18)O值均小于0‰,表明其受到过次生蚀变作用,低δ~(18)O值白云石样品所对应的负△~(18)O值反映了地幔镁质流体对沉积碳酸盐岩的强烈交代作用;③矿区—富稀土碳酸岩墙的δ~(13)C值为-7.2‰～-4.7‰,δ~(18)O价值为11.9‰～16.4‰,表明其碳酸岩岩浆并非原始地幔来源,而可能与俯冲板块携带的沉积碳酸盐岩与地幔流体在深部的高温混合熔融有关。碳酸岩墙中白云石与方解石之间的碳和氧同位素分馏均小于0‰,说明该碳酸岩墙中的白云石与方解石并非同成因矿物,至少其中之一为 相似文献
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钾和其他中等挥发性元素亏损是类地行星普遍的全岩化学成分特征之一,能用来示踪不同的亏损过程.球粒陨石是组成行星的前体物质,研究球粒陨石中钾同位素的亏损和分异机制,对于太阳系物质或行星的起源、形成和演化具有十分重要的意义.本文利用近年来发展的高精度钾同位素分析技术,测试了 14 个中国南极陨石以及6 个目击型陨石(Murchison、Allende、Ningqiang、Tagish Lake、Xinyang 和Banma)的全岩钾同位素组成.结果显示,21 个碳质球粒陨石全岩δ41 K值分布范围为－0. 62‰±0. 05‰至0. 37‰±0. 08‰,平均值为－0. 32‰± 0. 24‰(2SD),比全岩硅酸盐地球(BSE)稍重.18 个普通球粒陨石全岩数据(如果异常值 GRV 021603 除外)的δ41 K值分布范围为－1. 02‰±0. 05‰到－0. 61‰±0. 02‰,平均δ41 K值为－0. 81‰±0. 15‰(2SD),比全岩硅酸盐地球稍轻.2 个目击型陨石 Murchison(CM2 型)和 Allende(CV3 型),呈现较大的内部钾同位素差异(分别为0. 22‰和0. 16‰),可能反映了水蚀变导致的钾同位素在100 mg球粒陨石全岩尺度上的不均一性.小行星母体过程(水蚀变、热变质和冲击变质)不能很好地解释球粒陨石的钾同位素分馏,母体作为一个封闭体系只是平衡均一化同一个化学群内的钾同位素成分.不同化学群球粒陨石之间的钾同位素与钾元素之间没有显示明确的相关性,这一趋势与最近国际上发表的数据在误差范围内基本一致,太阳星云的单阶段热过程如蒸发或冷凝均不能很好地解释.核合成异常是一种可能的解释,大质量恒星的星风或者超新星爆发注入可以增加一些41 K到太阳星云中,从而在原始球粒陨石中保存下来,然而这一观点需要更多研究支持. 相似文献
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Ilmenite, magnetite, and peraluminous Mesoproterozoic anorogenic granites of Laurentia and Baltica 总被引：5，自引：0，他引：5
Emplacement of 1.6 to 1.3 Ga Mesoproterozoic plutons in Baltica and Laurentia formed an immense belt of A-type granite batholiths that include (1) low-fO2, ilmenite-series granite intrusions from the Baltic region to Wyoming, (2) high-fO2, magnetite-series granite intrusions of the central to southwestern U.S., and (3) peraluminous, two-mica granite intrusions from Colorado to central Arizona. These mineralogic divisions are mirrored by substantial elemental and oxygen isotopic differences. The ilmenite-series granites, which often contain classic rapakivi textures, have the highest Fe/Mg ratios and are highest in LIL element enrichment. They also have the lowest whole-rock δ18O values at 5.7‰ to 7.7‰. The magnetite-series granites are less potassic, less LILE-enriched, and have higher whole-rock δ18O values, ranging from 7.6‰ to 10.8‰. Although they retain A-type characteristics, the peraluminous granites are the least LILE-enriched and have the lowest Fe/Mg ratios. They also have the highest whole-rock δ18O values ranging from 8.8‰ to 12.0‰. Feldspar, where strongly reddened, can exhibit elevated δ18O values, which is interpreted to indicate subsolidus exchange with surface-derived aqueous fluids. Quartz δ18O values are interpreted to generally retain their magmatic values. The transcontinental mineralogic, chemical, and oxygen isotopic variations are interpreted as indicative of broad changes in the composition of a lower crustal source, which is compatible with a reduced mantle-derived crustal source for the ilmenite-series granites and a more oxidized crustal source for the others, including a metasedimentary component in the source for the two-mica granite subprovince.
Widespread thermal metamorphism at 1.4 Ga is present throughout much of the magmatic province and is viewed as a consequence of this immense event. Compressional deformation associated with several western 1.4 Ga Laurentia granite batholiths, alternatively interpreted as the distal expressions of a presumed 1.4 Ga orogeny, have at least in part been shown to be localized on preexisting Paleoproterozoic zones of deformation. Thus, we do not find compelling evidence for a 1.4 Ga orogeny related to the formation of most of these granites. Renewed intrusions at 1.0–1.1 Ga between and immediately following phases of the Grenville orogeny indicate that situations leading to their formation need to be more broadly considered.
The origin of this red granite-forming event in Laurentia and Baltica is considered as part of a global magmatic event that was coeval with intrusion of massif anorthosites and associated charnockites. Most are viewed as anorogenic, but it is recognized that the same conditions leading to their formation may have occurred during extensional phases of orogens. The immense volumes of red granites produced are also essentially unique to the Mesoproterozoic and appear to be tied to the stabilization and eventual break up of supercontinents of both Paleoproterozoic and Mesoproterozoic age. 相似文献
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13.
A computational study of oxygen diffusion in olivine 总被引：1，自引：1，他引：0
Atomistic modelling techniques are used to study the rate-determining steps that limit diffusion of oxygen in forsterite. The activation energies for diffusion parallel to all three crystallographic axes by the vacancy and interstitial mechanisms are calculated. The activation energy for extrinsic vacancy diffusion is predicted to be isotropic with a barrier height of 119 kJ mol–1. Conversely, in the interstitial case it is found to be anisotropic, with extrinsic activation energies that range between 94 and 178 kJ mol–1. The effect of intrinsic defects and two typical impurities, iron and hydrogen, upon diffusion is also considered. We find that the migration energy is slightly higher in iron-rich fayalite compared with forsterite and that the presence of hydrogen defects will not affect the diffusion mechanism. These observations lead us to reinterpret existing experimental results on oxygen diffusion in natural olivine. We suggest that at low oxygen partial pressure the mechanism observed is a vacancy mechanism, while at high oxygen partial pressure the mechanism is interstitial. We believe that this change in mechanism is mediated by iron redox reactions. Taking this process into account, we derive activation energies in excellent agreement with those found experimentally in natural samples of olivine. The anisotropy of activation barriers and hence the change in diffusion rates with temperature could be used to distinguish between the two mechanisms in future experimental work. 相似文献
14.
Claudia I. Mora Lee R. Riciputi David R. Cole Karen D. Walker 《Contributions to Mineralogy and Petrology》2009,157(6):781-795
The Boehls Butte anorthosite consists predominantly of an unusual bimodal assemblage of andesine and bytownite–anorthite.
Oxygen isotope compositions of the anorthosite were profoundly altered by high temperature, retrograde interaction with meteoric-hydrothermal
fluids that varied in composition from isotopically evolved to nearly pristine meteoric water. Oxygen isotope ratios of bulk
plagioclase separates are in the range +7.0 to −6.2‰ V-SMOW, however, secondary ion mass spectrometry indicates spot-sized
isotope values as low as −16‰. Typical inter- and intra-plagioclase grain variability is 3–6‰, and extreme heterogeneity of
up to 20‰ is noted in a few samples. High-temperature hydrothermal alteration of intermediate plagioclase is proposed to explain
the origin of bytownite–anorthite in the anorthosite and creation of its unusual bimodal plagioclase assemblage. The anorthite-forming
reaction created retrograde reaction-enhanced permeability which, together with rapid decompression, extension, and unroofing
of the anorthosite complex, helped to accommodated influx of significant volumes of meteoric-hydrothermal fluids into the
anorthosite. 相似文献
15.
西秦岭寨上金矿床地球化学特征
及成因机制研究 总被引：4，自引：0，他引：4
寨上金矿床共发现金矿脉22条,金矿体19条.通过氢、氧同位素分析得出:该区成矿流体水具有多来源特征.δ34S的组成特点可能反映了硫源为岩浆硫和地层硫的混合.碳的来源主要由海相沉积碳酸盐岩经溶解作用和花岗岩岩浆热液提供.矿石稀土元素并没有完全继承围岩的特征.成矿流体具有以下特征:成矿流体为中低温、低盐度、低密度、多期次活动的流体.金矿成矿是在300Ma之后燕山晚期形成的.成矿热液中,金主要以硫化物配合物的形式迁移.成矿流体与围岩发生充分的物质交换后.运移到裂隙发育部位,并因为流体的混合和围压突然降低,成矿流体产生强烈的沸腾作用,使成矿物质沉淀富集成矿. 相似文献
16.
陨石氧同位素组成及其地学意义 总被引：1，自引：0，他引：1
介绍了各类陨石氧同位素组成的特点,对陨石氧同位素组成的主要成因观点进行了评述,结合地球的原始物质组成,讨论了陨石氧同位素组成的地球科学意义。 相似文献
17.
定量恢复高大地形的古高程是地质学家一直以来追求的目标，将自生矿物中氢氧同位素用作古高程计的历史不长，这种方法还有很大的应用潜力，可用到比新生代更古老的时期。根据与气团上升和水汽凝结的热动力学性质相关的瑞利平衡分馏原理，建立了这种古高程计的热动力模型，这个模型应用简便，适用于纬度小于35°的地区。区域性经验关系的方法误差较小，但也有计算繁琐、适用区域有限的不足。以上两种方法的计算精度均有待于提高。研究中使用方解石作为样品最普遍，在方解石、高岭石、蒙脱石和针铁石等矿物中,究竟使用哪种推算古高程产生的误差更小，还需进一步研究。 相似文献
18.
影响青藏高原的天气系统与降水中氧同位素的关系 总被引：13，自引：9，他引：13
青藏高原的天气系统对降水中氧同位素比率的大小有重要的影响，在西风槽的影响下，降水中δ＾１８Ｏ与温度呈正相关关系；在切变线和高原低涡系统的影响下，高原季风区降水δ＾１８Ｏ与降水量和温度呈负相关，非季风区降水中δ＾１８Ｏ与温度仍呈正相关。 相似文献
19.
A new protocol for oxygen isotope analysis of authigenic and biogenic fine silica grains using laser-extraction technique 总被引：1，自引：0，他引：1
J. Crespin A. Alexandre C. Sonzogni F. Sylvestre 《Journal of Geochemical Exploration》2006,88(1-3):423
We report here a 30 W CO2 laser heating protocol for analyzing oxygen isotope composition (δ18O in ‰ vs. V-SMOW) of quartz and amorphous silica grains lower than 50 and 2 μm with a good external precision (1σ < 0.15‰). This technique is used to investigate δ18O composition of macro-, micro- and crypto-crystalline quartz cements of quartzite levels occurring in a sand sequence from the South of France (Apt Series), after a physical separation of the quartz cements. δ18O data obtained from this technique are compared with δ18O data obtained from in situ ion microprobe analyses. This study also presents promising results on δ18O analysis of phytoliths obtained with the laser heating protocol (1σ < 0.1‰). 相似文献
20.
S. K. Simakov 《Contributions to Mineralogy and Petrology》2006,151(3):282-296
Pressure–Temperature-
conditions and fluid compositions estimated for mineral parageneses from inclusions in diamonds, diamond-bearing and diamond-free
xenoliths using a garnet–clinopyroxene–silica oxygen barometer data indicate that the upper mantle is zoned, with a relatively
oxidized lithosphere and a reduced asthenosphere. Calculations in the C–O–H system indicate that eclogite inclusions within
diamonds and xenoliths have formed mainly in equilibrium with water-rich fluids. 相似文献