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1.
The microdistribution of U has been studied, using fission track techniques, in eleven mesosiderites, seven pallasites and four iron meteorites with silicate inclusions. When concentrated, U is usually found in phosphates: merrillite and/or chlorapatite. As in stony meteorites, the U concentrations in a given phosphate phase are highly variable from meteorite to meteorite and sometimes also exhibit variations in the same meteorite. Uranium is found to be concentrated in merrillite (0.25 to 1.43 ppm) in all the mesosiderites except Bondoc where none was observed. No U-rich phase was identified in six of the seven pallasites. In the seventh, Marjalahti, there are merrillite grains with concentrations ranging from 0.06 to 0.14 ppm. Where observed, the phosphates from silicate inclusions in the irons appear to have U concentrations similar to the mesosiderites.  相似文献   

2.
火星次生含水蚀变矿物是火星地质历史时期水环境和气候演变历史的真实记录,一直以来都是火星探测、火星陨石研究的重点,是认识火星环境特征和气候演化的重要研究对象。文中对比研究了表土角砾岩NWA7034、火成堆晶岩MIL03346等两块最富蚀变矿物火星陨石,以及Gale撞击坑出露的Sheepbed泥岩3种岩石类型的蚀变程度及其蚀变矿物类型和组合,分析了层状硅酸盐、铁氧化物/氢氧化物、钙硫酸盐等蚀变矿物的成因及环境指示意义。发现这3类岩石的蚀变作用各不相同。火星陨石NWA7034的蚀变作用以氧化和加热作用为主,无蒸发盐类矿物。火星陨石MIL03346的蚀变程度最低,为后期水溶液进入缝隙而引发的,蚀变作用以橄榄石的伊利石化、裂隙和缝隙中填充次生矿物细脉为主。而火星Sheepbed泥岩经历了后期的等化学风化过程(isochemical weathering),次生过程包括成岩蚀变和成岩后蚀变两个阶段。其中,成岩过程中的蚀变以橄榄石蚀变为铁氧化物和蒙皂石矿物为主,成岩后以形成蒸发盐类矿物硫酸钙为主。以上3种岩石蚀变矿物组成差异反映了火星上不同地质背景中、不同气候条件下蚀变过程的复杂性。文中对火星含水矿物及部分典型矿物的形成条件和过程进行系统总结,这对于理解未来火星探测任务、识别含水矿物的形成、揭示火星水环境和地质历史具有重要指导意义。  相似文献   

3.
Most magmas proposed as parental to the Martian SNC meteorites are high in iron and low in alumina. Yet, experiments at low pressures on such liquids have not produced the cumulate or melt-inclusion assemblages seen in the chassignite meteorites. Therefore, elevated pressure experiments under anhydrous and hydrous (water-undersaturated) conditions were conducted on a high-Fe, low-Al liquid proposed to be parental to the Chassigny meteorite. These experiments failed to produce the most magnesian cumulate phases, as well as the olivine hosted kaersutite-bearing melt-inclusion assemblage, of the chassignites. These results suggest that the parental liquid to the chassignite meteorites is both more magnesium and aluminum-rich than the previously considered composition (A∗; Johnson et al., 1991). The proposed composition is similar to the Martian Adirondack class Gusev basalt Humphrey and suggests a link between the Chassigny meteorite and rocks on the surface of Mars.  相似文献   

4.
In common with the remarkable variation in the bulk rock Zr content of distinct meteorite groups, ranging from <1 ppm to >800 ppm, the occurrence and abundance of accessory zircon is also highly diverse and limited to certain meteorite classes. A detailed literature study on the occurrence of meteoritic zircon, along with other Zr-bearing phases reveals that lunar rocks, eucrites and mesosiderites are the prime sources of meteoritic zircon. Rare zircon grains occur in chondrites, silicate-bearing iron meteorites and Martian meteorites, with grain sizes of >5 μm allowing chemical and chronological studies at high spatial resolution using secondary ion mass spectrometry (SIMS) technique. Grain sizes, crystal habits, structural and chemical characteristics of zircon grains derived from various meteorite types, including their REE abundances, minor element concentrations, and Zr/Hf values is diverse. Superchondritic Zr/Hf values (47 ± 8; s.d. with n = 97), i.e., typical for zircon in eucrites and mesosiderites, indicate crystallization from a fractionated, incompatible-element-rich (residual) melt. Differences in REE abundances, occurrence or absence of Ce- and Eu-anomalies, and overall REE patterns that are often fractionated with a depletion in LREE, might be primarily controlled by variable formation conditions of individual grains and/or differences in the residual melt compositions on a small, local scale within single samples. Subsequent fractionation/modification of the chemical fingerprint of meteoritic zircon can involve high-temperature annealing processes during thermal metamorphic reactions and/or impact events along with mixing of lithic fragments since many samples are breccias.  相似文献   

5.
干旱沙漠地区与南极冰盖均有利于陨石样品保存。2013年4-5月,通过首次新疆哈密沙漠陨石考察,回收了陨石样品47块。文中报导其中6块样品的矿物岩石学特征,并划分它们的化学岩石类型。Arlatager004、006、0014、0022和TuzLeik001等5块样品主要由橄榄石、辉石、长石、铁镍金属和陨硫铁组成,具有典型的普通球粒陨石岩石结构特征,其球粒结构不明显,表明经历过较强的热变质,岩石类型划分为5型;根据样品中橄榄石Fa值,低钙辉石Fs值和样品的金属含量等,将Arlatager004、006、0014、0022划分为L5型普通球粒陨石;TuzLeik001划分为H5型普通球粒陨石。Kumtag005具有典型的球粒结构,结合橄榄石Fa值和低钙辉石Fs值以及岩石学特征,将其划分为L3型普通球粒陨石。根据橄榄石Fa值与其百分标准平均方差(PMD)之间的关系,将Kumtag005的岩石类型亚型划分为L 3.4。这6块样品代表了3个化学群,结合该地区回收到的其他陨石分析结果,表明新疆哈密沙漠是一个新的陨石富集区,这些沙漠陨石的发现和研究,必将极大促进中国陨石学和天体化学的发展。  相似文献   

6.
We report the results of textural and mineralogical investigations of fragment #d(3–8)B of the Kaidun meteorite. The fragment is represented by six polished thin sections obtained by sequential sawing of a meteorite sample. Its main mineral is magnesian olivine; pyroxenes, augite and enstatite, are less abundant. The minor minerals are Fe-Ni sulfides, and the accessory minerals are chromian magnetite and apatite. The minerals show highly variable compositions. Several lithological types of material were distinguished on the basis of texture and composition. A characteristic feature is the presence of fractures, whose walls are enriched in olivine and, occasionally, sulfides. Some fractures contain relatively large euhedral crystals of zoned olivine. Olivines occurring on the walls of fractures and within fractures show a negative correlation between Mg# values and nickel content. The fragment has been subjected to multiple impact events. The material of the fragment bears evidence for intense multistage metasomatic alteration with the influx of olivine material and formation of pegmatoid-type segregations. This process has never previously been observed in meteorites, but is quite common in terrestrial massifs. The results of this study are in good agreement with our hypothesis that Phobos is the parent body of the Kaidun meteorite and indicate a possible Martian origin for Kaidun fragment #d(3–8)B.  相似文献   

7.
Electron microprobe analyses have been performed on 300 olivine grains found in 11 howardites. The olivine compositions almost continuously range from Fa 8 to Fa 89 with two prominent populations at Fa 13 and Fa 30. The tail of the fayalite contents distribution may correspond to the succession of several small clusters of Fe-rich olivine grains. Most howardites have olivine populations in common that would result from the fragmentation of different rocks of the howardites parent body. The distribution of the olivine grains between several groups of different FeOMnO ratios indicates olivine crystallization from distinct magmas. The chemical characteristics of the olivines of the pallasites, diogenites and mesosiderites are found among the olivines of the howardites and suggests a common parent body for these different types of meteorites. The differentiation model of the eucrites parent body proposed by Stolper (1977) is extended to the partial fusion of distinct assemblages silicates + metal which could proceed from recrystallizations, under different oxidation-reduction conditions, of a primordial chondritic material depleted in volatile elements.  相似文献   

8.
Silicate from two unusual iron-rich meteorites were analyzed by the I-Xe and 40Ar-39Ar techniques, Enon, an anomalous iron meteorite with chondritic silicate, shows no loss of radiogenic 40Ar at low temperature, and gives a plateau age of 4.59 ± 0.03 Ga. Although the Xe data fail to define an I-Xe correlation (possibly due to a very low iodine content), the inferred PuU ratio is more than 2σ above the chondritic value, and the Pu abundance derived from the concentration of Pu-fission Xe is 6 times greater than the abundance inferred for Cl meteorites. These findings for Enon, coupled with data for IAB iron meteorites, suggest that presence of chondritic silicate in an iron-rich meteorite is diagnostic of an old radiometric age with little subsequent thermal disturbance. The Eagle Station pallasite, the most 16O-rich meteorite known, gives a complex 40Ar-39Ar age pattern which suggests a recent (?0.85 Ga) severe thermal disturbance. The absence of excess 129Xe, and the low trapped Ar and Xe contents, are consistent with this interpretation. The similarity between 40Ar-39Ar data for Eagle Station and for the olivine-rich meteorite Chassigny lends credence to the previous suggestion of a connection between Chassigny and pallasites, in the sense that similar processes operating at similar times on different parent bodies may have been involved in the formation of olivine in both types of meteorites.  相似文献   

9.
Total N has been measured in a number of meteorites by neutron activation analysis using the reaction N14(n, p)C14. From each meteorite a number of chips have been analysed to investigate the variation of N contents in a sample. Many meteorites are found to contain a heterogeneous distribution of N. Eighteen chondrites, mostly of the classes C3, H4, H5, L4, L5, L6 and LL6, and six achondrites are found to have average N contents of 10–45 ppm. These do not show any clear-cut dependence of N on petrological group. However, the inherent heterogeneity or the fact that from most meteorite classes only single falls were studied might be responsible for this lack of correlation. In Cold Bokkeveld (C2) N is high (420 ppm). Unlike C, N content of ureilites is low (26 ppm). Nitrogen is enriched in the non-magnetic as compared to the magnetic fractions in H-group chondrites. Analyses of sieved Bjurböle phases show no enrichment of N in finer matrix material, nor any depletion in chondrules. In two gas-rich meteorites, Kapoeta and Assam, there is no excess N in the dark phases. Nine iron meteorites and three mesosiderites were analysed. Twenty analyses of Canyon Diablo and seven of Odessa establish a very heterogeneous N distribution in these meteorites.  相似文献   

10.
本文对南丹IIICD铁陨石的矿物学特征进行了研究,并与同为铁陨石但化学分类不同的阿根廷IAB铁陨石和西伯利亚IIB铁陨石进行了对比,重点探讨了风化作用对铁陨石矿物学特征的影响.首先用偏光显微镜、静水称重、扫描电镜观察了样品的基本矿物学特征和微形貌特征,然后用振动式样品磁强计、X射线衍射与电子探针能谱半定量测试研究了样品的磁学性质、物相和化学组成.研究结果表明,南丹铁陨石在较强的自然风化作用下,光泽变弱为土状光泽,相对密度降低;风化产生的反铁磁性物质会使陨石的磁性下降;另外,样品表面物相组成也发生较大变化,以针铁矿(FeOOH)和磁铁矿(Fe3O4)等铁的次生矿物为主;但风化壳以下的矿物物相及化学成分均未发生明显变化,以Fe、Ni为主的铁纹石、镍纹石物相存在.  相似文献   

11.
The history of the solar system is locked within the planets, asteroids and other objects that orbit the Sun. While remote observations of these celestial bodies are essential for understanding planetary processes, much of the geological and geochemical information regarding solar system heritage comes directly from the study of rocks and other materials originating from them. The diversity of materials available for study from planetary bodies largely comes from meteorites; fragments of rock that fall through Earth's atmosphere after impact‐extraction from their parent planet or asteroid. These extra‐terrestrial objects are fundamental scientific materials, providing information on past conditions within planets, and on their surfaces, and revealing the timing of key events that affected a planet's evolution. Meteorites can be sub‐divided into four main groups: (1) chondrites, which are unmelted and variably metamorphosed ‘cosmic sediments’ composed of particles that made up the early solar nebula; (2) achondrites, which represent predominantly silicate materials from asteroids and planets that have partially to fully melted, from a broadly chondritic initial composition; (3) iron meteorites, which represent Fe‐Ni samples from the cores of asteroids and planetesimals; and (4) stony‐iron meteorites such as pallasites and mesosiderites, which are mixtures of metal and dominantly basaltic materials. Meteorite studies are rapidly expanding our understanding of how the solar system formed and when and how key events such as planetary accretion and differentiation occurred. Together with a burgeoning collection of classified meteorites, these scientific advances herald an unprecedented period of further scientific challenges and discoveries, an exciting prospect for understanding our origins.  相似文献   

12.
The basaltic Martian meteorite Yamato 980459 consists of large olivine phenocrysts and often prismatic pyroxenes set into a fine-grained groundmass of smaller more Fe-rich olivine, chromite, and an interstitial residual material displaying quenching textures of dendritic olivine, chain-like augite and sulfide droplets in a glassy matrix. Yamato 980459 is, thus, the only Martian meteorite without plagioclase/maskelynite. Olivine is compositionally zoned from a Mg-rich core to a Fe-rich rim with the outer few micrometers being especially rich in iron. With Fo84 the cores are the most magnesian olivines found in Martian meteorites so far. Pyroxenes are also mostly composite crystals of large orthopyroxene cores and thin Ca-rich overgrowths. Separate pigeonite and augites are rare. On basis of the mineral compositions, the cooling rates determined from crystal morphologies, and crystal grain size distributions it is deduced that the parent magma of Yamato 980459 initially cooled under near equilibrium conditions e.g., in a magma chamber allowing chromite and the Mg-rich silicates to form as cumulus phases. Fractional crystallization at higher cooling rates and a low degree of undercooling let to the formation of the Ca-, Al-, and Fe-rich overgrowths on olivine and orthopyroxene while the magma was ascending towards the Martian surface. Finally and before plagioclase and also phosphates could precipitate, the magma was very quickly erupted quenching the remaining melt to glass, dendritic silicates and sulfide droplets. The shape preferred orientation of olivine and pyroxene suggests a quick, thin outflow of lava. According to the shock effects found in the minerals of Yamato 980459, the meteorite experienced an equilibration shock pressure of about 20-25 GPa. Its near surface position allowed the ejection from the planet’s surface already by a single impact event and at relatively low shock pressures.  相似文献   

13.
近40年来陨石分类学经历了3个发展阶段，60－70年代，由根据陨石的矿物结构的分类方法发展为球粒陨石的化学一岩石学分类法和铁陨石的化学群分类法；70－80年代，提出了分异型陨石和未分异型陨石的概念，球粒陨石被认为是未分异型陨石，而其它陨石（铁陨石，石铁陨石和无球粒陨石）大多被划入分异型陨石，80－90年代以来，陨石氧同位素组成成为了陨石成因分类的一个主要依据，使陨石分类学进入了一个新的成因分类阶段，作者对80－90年代以来新确立的R群，K小群，CR群和CK群球粒陨石，以及根据氧同位素划分出的原始型无球粒陨石系列：A－L无球粒陨石，Winonaites无球粒陨石和Brachinites无球粒陨石进行了介绍，笔者对陨石研究和陨石分类学的发展在估算地球整体成分，探讨地球成因和早期演化历史方面的重要意义进行了说明，并建议地球科学家应对陨石学和陨石分类的发展现状给以关注。  相似文献   

14.
We review the crystallization of the iron meteorite chemical groups, the thermal history of the irons as revealed by the metallographic cooling rates, the ages of the iron meteorites and their relationships with other meteorite types, and the formation of the iron meteorite parent bodies. Within most iron meteorite groups, chemical trends are broadly consistent with fractional crystallization, implying that each group formed from a single molten metallic pool or core. However, these pools or cores differed considerably in their S concentrations, which affect partition coefficients and crystallization conditions significantly. The silicate-bearing iron meteorite groups, IAB and IIE, have textures and poorly defined elemental trends suggesting that impacts mixed molten metal and silicates and that neither group formed from a single isolated metallic melt. Advances in the understanding of the generation of the Widmanstätten pattern, and especially the importance of P during the nucleation and growth of kamacite, have led to improved measurements of the cooling rates of iron meteorites. Typical cooling rates from fractionally crystallized iron meteorite groups at 500–700 °C are about 100–10,000 °C/Myr, with total cooling times of 10 Myr or less. The measured cooling rates vary from 60 to 300 °C/Myr for the IIIAB group and 100–6600 °C/Myr for the IVA group. The wide range of cooling rates for IVA irons and their inverse correlation with bulk Ni concentration show that they crystallized and cooled not in a mantled core but in a large metallic body of radius 150±50 km with scarcely any silicate insulation. This body may have formed in a grazing protoplanetary impact. The fractionally crystallized groups, according to Hf–W isotopic systematics, are derived originally from bodies that accreted and melted to form cores early in the history of the solar system, <1 Myr after CAI formation. The ungrouped irons likely come from at least 50 distinct parent bodies that formed in analogous ways to the fractionally crystallized groups. Contrary to traditional views about their origin, iron meteorites may have been derived originally from bodies as large as 1000 km or more in size. Most iron meteorites come directly or indirectly from bodies that accreted before the chondrites, possibly at 1–2 AU rather than in the asteroid belt. Many of these bodies may have been disrupted by impacts soon after they formed and their fragments were scattered into the asteroid belt by protoplanets.  相似文献   

15.
The angrites are a small and heterogeneous group of achondritic meteorites with highly unusual chemical and mineralogical features. The abundant presence of glasses in D'Orbigny makes this rock a unique member of the angrite group. Glasses fill open spaces, form pockets, and occur as inclusions in olivines. Their physical settings exclude an incorporation from an external source. Major and trace element (rare earth elements [REE], Li, B, Be, transition elements, N and C) contents of these glasses and host olivines were measured combining laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), secondary-ion mass spectrometry (SIMS), Nuclear Reaction Analysis (NRA), and EMP techniques. Based on the major element composition, glasses filling voids could represent either a melt formed by melting an angritic rock or a melt from which angrites could have crystallized. Trace element contents of these glasses strongly indicate a direct link to the D'Orbigny bulk meteorite. They are incompatible with the formation of the glasses by partial melting of a chondritic source rock or by shock melting. The refractory elements (e.g., Al, Ti, Ca) have about 10 × CI abundances with CaO/TiO2 and FeO/MnO ratios being approximately chondritic. Trace element abundances in the glasses appear to be governed by volatility and suggest that the refractory elements in the source had chondritic relative abundances. Although the glasses (and the whole rock) lack volatile elements such as Na and K, they are rich in some moderately volatile elements such as B, V, Mn, Fe (all with close to CI abundances), and Li (about 3-5 × CI). These elements likely were added to the glass in a sub-solidus metasomatic elemental exchange event. We have identified a novel mechanism for alteration of glass and rock compositions based on an exchange of Al and Sc for Fe and other moderately volatile elements in addition to the well-known metasomatic exchange reactions (e.g., Ca-Na and Mg-Fe).Because glass inclusions in olivine were partly shielded from the metasomatic events by the host crystal, their chemical composition is believed to be closer to the original composition than that of any other glasses. The relative trace element abundances in glasses of glass inclusions in olivine and glass pockets are also unfractionated and at the 10 to 20 × CI level. These glasses are chemically similar to the common void-filling glasses but show a much wider compositional variation. Inclusion glasses demonstrate that at least olivine grew with the help of a liquid. In analogy to olivines in carbonaceous chondrites, initial formation could also have been a vapor-liquid-solid condensation process. At that time, the glass had a purely refractory composition. This composition, however, was severely altered by the metasomatic addition of large amounts of FeO and other moderately volatile elements. The presence of volatile elements such as carbon and nitrogen in glasses of glass inclusions is another feature that appears to give these glasses a link with those hosted by olivines of carbonaceous chondrites. All these features point to an origin from a vapor with relative abundances of condensable elements similar to those in the solar nebula.  相似文献   

16.
A fast procedure for chemical analysis of different meteorites is presented, based on LIBS (Laser Induced Breakdown Spectroscopy). The technique is applied to several test cases (Dhofar 019, Dhofar 461, Sahara 98222, Toluca, Sikhote Alin and Campo del Cielo) and can be useful for rapid meteorite identification providing geologists with specific chemical information for meteorite classification. Concentration profiles of Fe, Ni and Co are simultaneously detected across the Widmanstätten structure of the iron meteorite Toluca with a view to determining cooling rates. The LIBS analysis of meteorites is also used as a laboratory test for analogous studies on the respective parent bodies (Mars, asteroids) in space exploration missions where one clear advantage of the proposed technique is that no direct contact with the sample is required.  相似文献   

17.
Petrographic, mineralogical and chemical analysis of naturally weathered equilibrated ordinary chondrites collected from ‘ hot’ deserts and Antarctica has revealed striking similarities and also pronounced differences in weathering between the two environments. Terrestrial weathering in all meteorites studied is dominated by oxidation and hydration of Fe,Ni metal, producing Fe-oxides and oxyhydroxides that have partially replaced the metal grains and have also occluded primary intergranular pores to form veins. Troilite weathers readily in ‘ hot’ desert environments but undergoes very little alteration under Antarctic conditions. Most of the primary porosity of ordinary chondrites has been occluded by the time that ∼ 15 to 25% of the initial Fe0 and Fe2+ has been oxidised to Fe3+ in both environments. Results from modelling the volume changes upon alteration of primary minerals to a range of weathering products demonstrates that the primary porosity of most meteorites is sufficient to accommodate weathering products. Dilation of primary pores and brecciation, which has been observed in parts of some meteorites, will only occur if the meteorite is especially metal-rich, or has a low primary porosity. These weathering products are absent from recent falls but have formed in a fall after ∼ 100 yr of museum storage.Cl-bearing akaganéite and hibbingite are common weathering products in Antarctic finds but occur in abundance in only one ‘ hot’ desert meteorite, Daraj 014. The majority of Fe-rich weathering products in meteorites from both environments contain low, but variable concentrations of Si, Mg and Ca. In most meteorites a proportion of these elements are inferred to be present as a very finely crystalline mineral with a ∼ 1.0-nm lattice fringe spacing; where seen within intragranular fractures this mineral has a topotactic relationship with olivine and orthopyroxene. In the heavily-weathered Antarctic finds ALHA 78045 and 77002, Si is concentrated in cronstedtite, a Fe-rich phyllosilicate. An unidentified hydrous Si-Fe-Ni-Mg mineral or gel has also partially replaced taenite in ALHA 78045. In addition to Fe-rich weathering products, ‘ hot’ desert meteorites contain sulphates, Ca-carbonate and silica, whereas such minerals are largely absent from Antarctic finds. The abundance of silicate weathering products in Antarctic meteorites is unexpected and indicates that olivine and pyroxene undergo significant chemical weathering in these environments. As preterrestrial cronstedtite is abundant in CM2 carbonaceous chondrites, the Antarctic environment may be a powerful analog for aqueous alteration in the asteroidal parent bodies of primitive meteorites.  相似文献   

18.
Very precise silver (Ag) isotopic compositions have been determined for a number of terrestrial rocks, and high and low Pd/Ag meteorites by utilizing multicollector inductively coupled plasma mass spectrometry (MC-ICPMS). The meteorites include primitive chondrites, the Group IAB iron meteorites Canyon Diablo and Toluca, and the Group IIIAB iron meteorite Grant. Silver isotopic measurements are primarily of interest because 107Ag was produced by decay of the short-lived radionuclide 107Pd during the formation of the solar system and hence the Pd-Ag chronometer has set constraints on the timing of early planetesimal formation. A 2σ precision of ±0.05‰ can be obtained for analyses of standard solutions when Ag isotopic ratios are normalized to Pd, to correct for instrumental mass discrimination, and to bracketing standards. Caution must be exercised when making Ag isotopic measurements because isotopic artifacts can be generated in the laboratory and during mass spectrometry. The external reproducibility for geological samples based on replicate analyses of rocks is ±0.2‰ (2σ).All chondrites analyzed have similar Ag isotopic compositions that do not differ significantly (>0.3‰) from the ‘terrestrial’ value of the NIST SRM 978a Ag isotope standard. Hence, they show no evidence of excess 107Ag derived from 107Pd decay or, of stable Ag isotope fractionation associated with volatile element depletion within the accretion disk or from parent body metamorphism. The Group IAB iron meteorite samples analyzed show evidence of complex behavior and disturbance of Ag isotope systematics. Therefore, care must be taken when using this group of iron meteorites to obtain chronological information based on the Pd-Ag decay scheme.  相似文献   

19.
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   

20.
Recent work on fission track studies of meteorite samples to obtain cooling rates of metetorite parent bodies is reviewed. The cooling rates of chondrites are in excess of 1oK/106 yr. Fission track studies of phosphate grains in mesosiderites do not support the extremely slow cooling rates of 0°1oK/108 yr for these meteorites, inferred from metallographic studies. The accumulating evidence from fission track studies indicates a gross underestimation of the cooling rates of meteorites as determined by the metallographic techniques.  相似文献   

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