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在一般石陨石中，球粒陨石硅酸盐相约占其化学组成的三分之二，而橄榄石(Mg、Fe)，SiO4和斜方辉石(Mg、Fe)SiO3又是组成硅酸盐相的主要矿物。较详细地研究橄榄石和辉石的化学组成对石陨石各化学群的划分及球粒陨石岩石类型的划分都是十分重要的。 相似文献
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用微束矿物学和激光拉曼光谱等分析测试技术,并结合人工高压实验结果,研究了我国随州陨石冲击熔脉中的白磷钙石高压相变形成涂氏磷钙石的必要条件,并对寺巷口陨石冲击熔脉中的白磷钙石虽与林伍德石、镁铁榴石和玲根石等高压矿物共生,但仅表现为结构损伤而未相变成涂氏磷钙石的原因进行了探讨.研究结果发现,随州陨石中白磷钙石或氯磷灰石的存在是涂氏磷钙石得以形成的物质前提,陨石熔脉中高达24 GPa和2000℃以上的高压高温环境是涂氏磷钙石能够形成的条件保障,而压力释放后熔脉极快的冷却速率是涂氏磷钙石得以淬火并稳定保存的关键.研究还查明,寺巷口陨石冲击熔脉比随州陨石的熔脉要宽1至2个量级,其冷却速率比随州陨石慢得多,因此,熔脉中早先形成的涂氏磷钙石,可能在脉内较高的冲击后温度影响下,慢慢退变质成白磷钙矿. 相似文献
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橄榄石高压多形林伍德石被认为是地幔过渡带的主要矿物。天然产状林伍德石主要在发生强烈冲击变质的球粒陨石冲击脉体中出现。目前还没有在地球岩石中发现林伍德石的报告。陨石冲击脉体的温度压力历史和矿物组合特征研究表明,林伍德石形成后,高压下淬火是使林伍德石不发生退变作用的重要条件。陨石中有利于林伍德石保存的淬火时间仅为数秒到十多秒。在地球上任何地质事件中,均难以实现在如此短的时问内使位于地幔过渡带的林伍德石被带往地球表层。寻找地球产状的林伍德石,关键是要在岩石和矿物中存在有利于林伍德石保存的条件,特别是当这些岩石和矿物仍处于高温的环境时。 相似文献
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据统计,我国现已收集27次石陨石及24次铁陨石(图1)。如图1所示我国陨石的分布与人口密度出现正比关系。石陨石多为普通球粒陨石,其中最大的为吉林陨石雨,共收集到约2500公斤样品。铁陨石中最大的是新疆铁陨石,重约30吨,按其重量居世界第三位。 本文的主要目的是根据已发表的部分资料和笔者的室内工作,对我国部分球粒陨石的物质成分、化学-岩石类型及其形成和演化历史进行初步探讨。 相似文献
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玻璃陨石(tektite)或称熔融石是一种天然玻璃,它的成因是目前陨石学研究中激烈争论的问题。雷公墨是玻璃陨石的一种,发现于海南岛及雷州半岛等地。 相似文献
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据四川省隆昌县志卷十二记载,隆昌铁陨石于明代(1368—1644)时陨落到隆昌县城西北郊约五华里的道观坪,清乾隆二十五年(1761)掘出,被人们精心保存。对隆昌铁陨石的性质、隆昌县志有“紫色,似石非石,似铁非铁,叩之有声”的描述。1972年,成都地质学院陈列馆将该陨石运到该馆陈列,尚无前人进行过研究。本文是对隆昌铁陨石的初步研究报告。 相似文献
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《地球化学》1978,(3):197-201
大量石陨石的K-Ar年龄测定表明其年龄值一般要低于陨石母体的形成年龄，它反映了陨石的气体保留年龄。因此根据K—Ar年龄可以研究陨石母体与陨石的受热历史。陨石中Ar^38含量的测定可以提供陨石受宇宙射线辐射的时间标度。吉林陨石是目前世界上发现的最大的球粒陨石，因而通过对气体保留年龄和宇宙射线暴露年龄研究将为进一步了解球粒陨石的成因与演化史提供重要的资料。本文除对吉林陨石雨的Ⅴ号、Ⅱ号、Ⅰ号陨石进行测定研究外，还对其他三块在我国降落的球粒陨石进行了对比研究。根据球粒陨石的有关资料，我们对吉林陨石的受热历史和母体环境作了分析，并讨论了宇宙空间球粒陨石的形成与消失过程。 相似文献
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40Ar/39Ar年龄谱是研究陨石冲击事件的重要资料。根据对55块陨石40Ar/39Ar冲击年龄和陨石暴露年龄的分析,发现陨石的冲击年龄与陨石类型之间存在对应关系。据此,将陨石冲击事件划分为九期。其中3900-4000Ma、470-540Ma和小于65Ma是陨石母体的三个重要演化阶段。阶段Ⅰ、Ⅱ和Ⅲ(冲击年龄大于30亿年)主要涉及高钙型无球粒陨石。所有球粒陨石的冲击年龄均小于30亿年。陨石暴露年龄因类型而异,铁陨石最大,石铁陨石次之,石陨石最小。 相似文献
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1997年降落在山东省鄄城县的陨石雨,是橄榄石-古铜辉石球粒陨石。该陨石中的金属矿物主要为铁纹石和陨硫铁,其次为镍纹石,金属矿物呈填隙状分布于以橄榄石和古铜辉石为主的硅酸盐矿物粒间及球粒周围。陨石中可见由铁纹石和镍纹石组成的显微蠕虫状连晶,是陨石中金属矿物在降温冷却过程中发生固溶体分离作用而成。陨石中金属矿物的分布特征表明,金属Fe-Ni和硫化物（FeS）应该是星云凝聚不同阶段的产物。陨石中金属矿物的成分和组构特征及陨石中出现的球粒结构、橄榄石的炉条结构等特征表明,该球粒陨石是星云物质快速冷却的产物。 相似文献
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Edward R.D. Scott 《Geochimica et cosmochimica acta》1973,37(10):2283-2294
Taenite fields when etched develop a cloudy brown rim with approximate compositional limits of 25 and 40 per cent Ni. In iron meteorites this cloudy zone is only a few microns wide, with a sharp, high-Ni edge about 1 μm from the kamaciteinterface and a diffuse edge several microns from the central plessite. It is always present in irons unless the meteorite has been cosmically or terrestrially reheated.X-Ray and electron diffraction of grains scratched from exceptionally large areas of cloudy taenite in the mesosiderite Estherville show that this etching zone contains a fine exsolution of kamacite. Electron microscopy reveals a cellular structure with kamacite walls surrounding taenite volumes about 1000 Å in diameter; about one-third of the total volume is kamacite. Electron diffraction from a thin foil of Tazewell indicates that for several microns the cloudy border consists of a single crystal of kamacite interpenetrating a single crystal of taenite.Detailed electron-probe investigations of taenite in Estherville show that there is a step in the M-shaped Ni profile at the sharp, high-Ni edge of the cloudy region, the Ni dropping suddenly from approximately 45 to 42 per cent. It is proposed that exsolution in the cloudy region effectively froze in the Ni profile at that temperature. On subsequent cooling only the clear outer taenite continued to equilibrate with the kamacite matrix producing the kink in the M profile.Cloudy taenite is therefore a variety of plessite differing from the usual varieties in that it forms at lower temperatures in areas much richer in Ni, and the morphology is not crystallographically oriented. Its absence can provide a sensitive indication of reheating. 相似文献
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The metallic phases in six bronzite and six hypersthene chondrites were studied metallographically and by electron microprobe. All of the chondrites studied contain zoned taenite. In bronzite chondrites, only about 5 per cent of the zoned taenite abuts on kamacite (the rest being apparently isolated from it) whereas in hypersthene chondrites an average of over 20 per cent abuts on kamacite. The compositions of the centers of zoned taenite can be used to obtain cooling rates by Wood's method. Including Wood's results, 14 out of 18 ordinary chondrites have cooling rates between 1 and 10°C/m.y. 相似文献
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Bevan and Axon (1980) proposed that polycrystalline γ (taenite) in the unequilibrated (H3) chondrite Tieschitz is a relic of rapid, non-equilibrium solidification of Fe-Ni-S melts during chondrule formation. Scott and Rajan (1980) dismissed our observations and conclusions. Here we defend and clarify our position. Grain boundaries as observed in polycrystalline γ(taenite) could not have been established either during slow, sub-solidus cooling of homogeneous γ(taenite), or, in the absence of γ/γ grain-boundary α precipitates, by deformation and annealing (hot working). 相似文献
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L.K. Ives M.B. Kasen R.E. Schramm A.W. Ruff R.P. Reed 《Geochimica et cosmochimica acta》1978,42(7):1051-1066
Metallography, electron microscopy and X-ray diffraction techniques were employed to study a fragment of the Tishomingo iron meteorite. The results suggest the following thermal-mechanical history: The fragment was originally a large crystal of taenite (γ). Cooling through the α + γ phase boundary did not result in accompanying precipitation of kamacite (α). Transformation to a martensitic structure initiated between ? 25 and ?65°C. Transformation continued as the temperature fell to ? 75 to ? 115°C, resulting in approx 80% martensite (α′). Subsequent shock deformation and thermal aging processes substantially modified the taenite and martensite microstructures. Twins in the retained taenite phase are attributed to shock deformation at a pressure estimated for a single event at ~170 kbar. The existing complex, altered martensite structure containing both taenite and kamacite (3–15% Ni) particles was apparently the product of both shock deformation and thermal aging processes. The maximum temperature reached during thermal aging is estimated to be less than 400°C, and perhaps below 310°C. 相似文献
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For most iron meteorites studied, the carbon isotopic composition of nodular graphite falls in the range ?4.8 to ?8.2%. vs PDB and shows a mode between ?5 and ?6%.. Fourteen cohenite analyses from the Magura meteorite fall between ?18.1 and ?19.2%. with a pronounced clustering around ?18.5%.. Carbon of a taenite separate from the same meteorite has an isotopic composition of ?18.8%.; compositions between ?19.7 and ?22.1%. were found for taenite carbon in five other octahedrites. It is suggested that the 12C enrichment in cohenite and taenite relative to the nodular graphite is a general phenomenon in iron meteorites, and that the study of 13C abundances in iron meteorites may aid in the elucidation of their history. To this end an experimental study of carbon isotope fractionations in the system Fe-Ni-C is essential. The 13C content of carbon from several silicate inclusions in the Four Corners and ‘El Taco’ (Campo del Cielo) meteorites is generally similar to the nodular graphite, the 12C enrichment (?13%.) in one specimen may be interpreted in terms of a mixing model involving an original inclusion carbon and carbon exsolved from the taenite upon cooling. 相似文献
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Optical and electron optical (SEM, TEM, AEM) techniques were employed to investigate the fine structure of eight ataxite-iron meteorites. Structural studies indicated that the ataxites can be divided into two groups; a Widmanstätten decomposition group and a martensite decomposition group. The Widmanstätten decomposition group has a Type I plessite microstructure and the central taenite regions contain highly dislocated lath martensite. The steep M shaped Ni gradients in the taenite are consistent with the fast cooling rates, ≥500°C/my, observed for this group. The martensite decomposition group has a Type III plessite microstructure and contains all the chemical group IVB ataxites. The maximum taenite Ni contents vary from 47.5 to 52.7 wt% and are consistent with slow cooling to low temperatures ≤350°C at cooling rates ≤25°C/my. Ordered FeNi and the cloudy border structure were not observed in any of the ataxites. Modest reheating to ≤350°C may have been responsible for the lack of these structures. 相似文献
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Yu. V. Erokhin V. A. Koroteev V. V. Khiller E. V. Burlakov K. S. Ivanov D. A. Kleimenov 《Doklady Earth Sciences》2016,471(2):1273-1276
New data on the mineral composition of the Ozernoye meteorite, found in the Kurgan region in 1983, are presented. It has been found that that the meteorite’s matter is composed of olivine (chrysolite), orthopyroxene (bronzite), clinopyroxene (augite), maskelynite, chromite, ilmenite, metals Fe and Ni (kamasite, taenite), sulfides (troilite, pentlandite), chlorapatite, and merrillite. Augite, taenite, pentlandite, and merrillite were identified in the Ozernoye meteorite for the first time. The chemical compositions are given for all these minerals. The meteorite itself is an ordinary chondrite stone belonging to petrological type L5. 相似文献
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In this study kamacite was experimentally grown in taenite grains of Fe-Ni-P alloys containing between 5 and 10 wt% Ni and 0 and 1.0 wt% P. Both isothermal heat treatments and non-isothermal heat treatments at cooling rates of 2 to 5°C/day were carried out. Analytical electron microscopy was used to examine the orientation and chemical composition of the kamacite and the surrounding taenite matrix. The kamacite so produced is spindle or rod shaped and has a Widmanstätten pattern orientation. The presence of heterogeneous sites such as phosphides is necessary for the nucleation of the intergranular kamacite. During kamacite growth both Ni and P partition between kamacite and taenite with chemical equilibrium at the two phase interface. The growth kinetics are limited by the diffusion of Ni in taenite. Additional diffusion experiments showed that the volume diffusion coefficient of Ni in taenite is raised by a factor of 10 at 750°C in the presence of only 0.15 wt% P.A numerical model to simulate the growth of kamacite in Fe-Ni-P alloys, based on our experimental results, was developed and applied to estimate the cooling rates of the iron meteorites. The cooling rates predicted by the new model are two orders of magnitude greater than those of previous studies. For example the cooling rates of chemical groups I, IIIAB and IVA are 400–4000°C/106years, 150–1400°C/ 106 years and 750–6000°C/106years respectively. Previous models gave 1–4°C/106 years, 1–10°C/106 years and 3–200°C/106 years. Such fast cooling rates can be interpreted to indicate that meteorite parent bodies need only be a few kilometers in diameter or that iron meteorites can be formed near the surface of larger asteroidal bodies. 相似文献
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Electron optical techniques were employed to investigate the plessite structure and composition of four IIICD fine octahedrites. These meteorites have a similar thermal history and differences in plessite structure can be ascribed to varying bulk Ni content and/or localized differences in carbon content. Microdiffraction patterns from regions as small as 20 nm dia. were obtained for the first time from plessite structures. It was established that transformation twins in clear taenite I have the conventional fcc twin relationship, individual kamacite and taenite cells in the cloudy zone have the Kurdjumov-Sachs orientation and fine γ rods in the decomposed martensite zone display both the Nishiyama and Kurdjumov-Sachs relation with the matrix-α. All the IIICD irons contain cloudy zone and martensitic plessite. Except for Dayton, martensitic plessite shows further decomposition into α + λ at low temperatures. Using STEM X-ray microanalysis with a spatial resolution of ~ 50 nm, Ni composition profiles in taenite from all the IIICD irons showed a maximum of ~48 wt% Ni. The structural and compositional data indicate that plessite formation occurs at quite low temperatures (~ 200–300°C) during the cooling history of the IIICD irons. 相似文献
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Andrew J. Campbell 《Geochimica et cosmochimica acta》2003,67(13):2481-2495
Siderophile element abundances in individual metal grains in the ungrouped chondrite Grosvenor Mountains (GRO) 95551 and in the ordinary chondrites Tieschitz H3.6, Soko-Banja LL4, and Allegan H5 were measured with laser ablation-inductively coupled plasma mass spectrometry. Matrix metal in GRO 95551 falls into two distinct compositional groups, a high-Ni group with 7.2 ± 0.4 wt% Ni and a low-Ni group with 3.7 ± 0.1 wt% Ni, indicating that kamacite/taenite equilibration at ∼1020 K was followed by rapid cooling. The nonrefractory siderophile elements P, Co, Cu, Ga, Ge, As, Pd, and Au also partition between the high-Ni and low-Ni metal in a manner consistent with kamacite/taenite fractionation, but the refractory siderophiles Ru, Re, Os, Ir, and Pt show correlated variations that are unrelated to kamacite/taenite partitioning and indicate that variations in refractory components of the metal were not completely erased during equilibration at ∼1020 K. The Ni-normalized bulk metal composition of GRO 95551 is refractory depleted and volatile rich relative to Bencubbin and related metal-rich chondrites but bears strong similarities to equilibrated ordinary chondrite metal. GRO 95551 represents a new chondrite type with chemical affinity to the ordinary chondrites. Individual metal grains in unequlibrated ordinary chondrites also have correlated variations in refractory siderophile contents that cannot be produced by redox processes alone; these variations span three orders of magnitude and diminish with increasing metamorphic grade of the ordinary chondrites. 相似文献