吉林陨石中铁镍合金的磁学性质

铁镍合金是陨石中重要的磁性物质,其中铁纹石、镍纹石和四方镍纹石是球粒陨石中的主要铁镍合金.然而,迄今针对陨石中铁镍合金的磁学性质研究仍非常缺乏.本文研究了吉林陨石中的铁纹石、四方镍纹石、以及陨硫铁的磁学特征.实验表明,镍含量为6%~7%的铁纹石是该陨石中最主要的铁镍合金物质,它具有低矫顽力和高的热稳定性,居里温度~750 ℃.镍含量为~48%的四方镍纹石具有高矫顽力和高的热稳定性,居里温度~565 ℃,它是剩磁的主要载体.陨硫铁在室温为反铁磁性,不具有载剩磁能力,在60 K左右存在一个低温转换,在氩气中加热较稳定而在空气中加热被氧化转化为磁铁矿.这些研究结果为鉴定球粒陨石中的磁性物质提供了依据.     

岩石的磁学性质

岩石磁学是古地磁学和环境磁学的基础，正确认识岩石的磁学性质对获得可靠的古地磁学和环境磁学记录是至关重要的，本文较详细综述了自然界学了性矿物的晶体化学结构，主要磁学性质以及鉴定特征，并讨论了它们的磁学性质在古地磁学和环境磁学研究中的意义。     

南丹铁陨石 中国最早记载的目击陨石

<正>"正德丙子夏五月夜,西北有星陨,长六丈,蜿蜒如龙蛇,闪烁如电,须叟而灭"。——《庆远府志》这是我国第一次既有实物发现又有文献记载的一场陨石雨,文字记载在广西河池地区的《庆远府志》中,正德丙子为明朝末年,公元1516年。陨石降临南丹1516年农历5月的一个夜晚,广西河池地区,随着天空一片响亮,周边的人都为之惊骇,有人猜想可能是天塌了,随后,似乎什么也没发生。待天明以后,人们发现地面上散落着许多大小不一泛银色的硬     

世界陨石大观

正陨石与地球岩石一样,基本上都是由矿物组成。组成陨石的近100种化学元素与组成太阳、地球和月球等太阳系天体的化学元素是一样的。但由于陨石体长期处于高度真空的宇宙空间环境,未经历地球岩石所受的变质作用和风化作用。因此,陨石矿物种类和共生组合与地球矿物存在明显不同。陨石中矿物约117种,其中约34     

陨石状态方程形式的选择与参量的确定——以吉林球粒陨石和南丹铁陨石为例

在二级轻气炮动高压装置上用电探针技术测量了吉林球粒陨石(H5)和南丹铁陨石(ⅢCD)的冲击压缩线,然后分别选择几种可能适用于普通球粒陨石和铁陨石状态方程的数学表达式,并确定了状态方程中的有关参量值.从状态方程的P(V)关系曲线与实验数据的比较来看,吉林球粒陨石最适合采用普适状态方程形式,而南丹铁陨石则最适合采用三项式状态方程形式.吉林球粒陨石的普适状态方程参量K_(OS)=48.10GPa,K’_(OS)=4.13.南丹铁陨石的三项式状态方程参量Q=41.2353lGPa,q=12.27179,这是吉林球粒陨石和南丹铁陨石状态方程的首次报道.     

南丹铁陨石物态方程用于地核的研究

从南丹铁陨石的物态方程和地球的PREM模型出发,求得内外地核交界面处的物质密度为12.83-13.419/cm~3,温度为5440-5680K;地心处物质密度为13.12-13.73g/cm~3,温度为5660-5990K,推估内地核可能由铁镍合金组成.     

环境磁学视角下的北冰洋深海磁性地层：以罗蒙诺索夫脊ARC5-ICE4孔为例

近年来,北冰洋深海百万年尺度的磁性地层年代框架受到了来自诸如Mn旋回地层和钛磁赤铁矿“自反转”现象的强烈质疑,以致对该方法在北冰洋的适用性产生了巨大争议.鉴于此,本文对中国第五次北极科学考察在北冰洋罗蒙诺索夫海岭获得的ARC5-ICE4钻孔岩心(水深2860 m,进尺4.15 m)开展了深入的岩石磁学分析.结果证实岩心中的载磁组分以磁铁矿为主,部分颗粒表面发生轻微氧化作用,另含少量磁赤铁矿、赤铁矿、钛磁赤铁矿等;整体粒径呈现相对均一的准单畴(PSD：pseudo-single domain),且含量随深度变化不大.岩心1.15~2.04 m区间显示的负极性并非“自反转”所致,而是真实的古地磁场记录;结合相对古强度(RPI)曲线模式和S-ratio的旋回变化特征,将其对应于松山期(约2.58~0.78 Ma),钻孔底界年龄 < 3.58 Ma.另外,上述年代框架指示的沉积速率变化模式很好地吻合了北半球冰期加强(iNHG：intensification of Northern Hemisphere glaciation)和中更新世气候转型(MPT：mid-Pleistocene transition)等古气候事件,更加印证了其可靠性.因此,即使“自反转”现象在北冰洋深海地区真实存在,其影响范围也是局部的,即磁性地层对于建立该区新生代年代框架的重要性仍不容忽视.总之,目前北冰洋深海沉积物定年仍面临诸多难题和挑战,今后需加强多学科协作.

     

环境磁学研究的简介

本文概述了环境磁学研究方法的基本问题，原理和应用，提出了环境磁学存在的问题和发展的方向。     

我国两个南极陨石及光明山和庄河球粒陨石宇宙射线暴露历史

在岩石矿物学研究的基础上, 测定了我国两个南极陨石、以及光明山和庄河球粒陨石的稀有气体同位素丰度, 并根据宇宙成因核素的产率, 获得了这4个普通球粒陨石的宇宙射线暴露年龄和气体保存年龄. 两个南极陨石的暴露年龄分别为17.0±2.5 Ma(GRV 98002)和0.052±0.008 Ma(GRV 98004), 光明山球粒陨石为68.9±10 Ma, 庄河球粒陨石为3.8±0.6 Ma. GRV 98004(H5)的暴露年龄是目前南极陨石中已知最低的, 而光明山球粒陨石的暴露年龄高于我国其他H群球粒陨石. GRV 98002和庄河球粒陨石在宇宙射线暴露期间可能受到冲击事件或由于小的近日距轨道导致加热, 造成低的4He含量, 而GRV 98002和光明山球粒陨石的宇宙成因核素³He和⁴He则基本上同步丢失.     

环境磁学研究现状和进展

环境磁学是八十年代逐步发展起来的具有学科交叉特点的边缘学科。它主要应用岩石和矿磁学研究磁性颗粒的搬运、沉积以及转化受大气圈、水圈和岩石圈环境变化影响的过程。近年来，环境磁学已提供了大量有关全球变化过程以及人类活动对环境影响等重要资料，其研究范畴迅速扩展，已成为当今地学的前沿学科之一。     

A classification of meteorites based on oxygen isotopes

On the basis of¹⁸O/¹⁶O and¹⁷O/¹⁶O ratios, meteorites and planets can be grouped into at least six categories, as follows: (1) the terrestrial group, consisting of the earth, moon, differentiated meteorites and enstatite chondrites; (2) types L and LL ordinary chondrites; (3) type H ordinary chondrites; (4) anhydrous minerals of C2, C3, C4 carbonaceous chondrites; (5) hydrous matrix minerals of C2 carbonaceous chondrites; (6) the ureilites. Objects of one category cannot be derived by fractionation or differentiation from the source materials of any other category.     

A continuous thermal demagnetizer for rock magnetism

Summary A new instrument for measuring the magnetic vector of rock specimens while they are being heated is described and the performance and advantages of the instrument are discussed.     

The pre-terrestrial history of group IV A iron meteorites

A number of group IVA iron meteorites show metallographic features suggesting that a shock annealing event intervened during the formation of the Widmanstatten structure. This could complicate the estimation of cooling rates based on diffusion profile methods but would have less influence on methods based upon macroscopic measurements of kamacite band widths.     

Lithification of gas-rich meteorites

High-voltage electron microscopy has been used to study the fine structure of four gas-rich meteorites, with particular reference to the cementation and compaction processes that have affected the fine-grained matrix. The observed features are compared with similar effects in lunar breccias. Lithification is attributed to the passage of shock waves through porous aggregates, causing deformation whose intensity varied spatially on a small scale, the most intense deformation and heating effects being concentrated at the edges of large grains and in the matrix between them. It is inferred that relatively mild shocks have produced amorphous cement between matrix grains in the achondrite Khor Temiki and the chondrite Weston. Relatively intense shock is inferred for specimens of the chondrites St. Mesmin and Pantar. These have non-porous, completely crystalline matrices, and fine-grained black veins which fill cracks in relatively large deformed grains. Recrystallization of some deformed material is attributed to shock-heating, which was not sustained long enough to erase the irradiation record from all the relatively large grains. Matrix recrystallization without extensive melting constitutes a metamorphic event, and the observations indicate that shock was responsible for the metamorphism experienced by these chondrites at relatively late stages of the evolution of their parent bodies.     

Antimony in iron meteorites

Antimony concentrations determined by radiochemical neutron activation analysis in 60 iron meteorites range from 0.2 ng/g to 36 μg/g. The meteorites with the highest Sb concentrations are those of the non-magmatic groups IAB and IIICD, while the lowest Sb concentrations are found in groups IVA and IVB, the groups with the lowest concentrations of the other most volatile siderophiles Ge and Ga. In all groups Sb is positively correlated with Ni. In each of the magmatic groups slopes on log Sb vs. log Ni plots decrease with increasing Ni. This decrease may reflect an increasing tendency to avoid schreibersite during the analysis of high-Ni meteorites because Sb partitions strongly into schreibersite.Schreibersite from New Westville is enriched in Cr, Ni, Ge, As, Sb and Au and depleted in Fe, Co and Ir; the content of Sb in schreibersite is 540 × higher than the bulk metal value.The Sb abundances of the iron meteorite groups are as expected from volatility trends with the exception of IAB and IIAB in which abundances appear depleted. The most likely explanation for this and the decreasing slope in the magmatic groups is that one or more Sb-rich phases were not sampled during metal analyses.     

Tungsten in iron meteorites

Tungsten concentrations have been determined by instrumental neutron activation in 104 iron meteorites, and range from 0.07 to 5 μg/g. In individual groups, concentrations vary by factors of between 1.5 and 8, but there are negative W-Ni correlations in 8 groups: IAB, IC, IIAB, IID, IIE, IIIAB, IIICD, and IIIF. The lowest W concentrations are found in groups IAB and IIICD, which also have the smallest slopes on a W-Ni plot. Eighteen anomalous irons have W concentrations between 5 μg/g (Butler) and 0.11 μg/g (Rafrüti). The distribution of W in irons shows similarities to that of other refractory siderophilic elements (except Mo), but is closest to the distribution of Ru and Pt.Assuming that chemical trends in group IIIAB were produced by fractional crystallization, a value of 1.6 can be deduced for the distribution coefficient of W between solid and liquid metal, cf. 0.89 for Mo. Experimental evidence in support of these values is tenuous.     

Al survey of Antarctic meteorites

An²⁶Al survey by non-destructive gamma ray spectrometry was conducted as part of the preliminary examination effort for Antarctic meteorites. A total of 220 samples were studied. The majority of the samples were from the Allan Hills area; however, samples from several other sites, including the Yamato Mountains, were studied. Compared to worldwide falls and finds, the Antarctic group shows a clear trend toward lower²⁶Al levels. At leasr 10% of the samples studied were clearly undersaturated in²⁶Al. The frequency of undersaturated samples suggests that terrestrial ages of several hundred thousand years are common among the Antarctic meteorite collection. The absence of samples with extremely low²⁶Al implies that the upper limit for terrestrial ages in the Antarctic is on the order of 1 million years.     

The petrophysical classification of meteorites

Summary Petrophysical properties (susceptibility, intensity of the Natural Remanent Magnetisation (NRM) and bulk density) of 489 meteorite samples from 368 meteorites are discussed. The samples, obtained from Finnish meteorite collections, represent all chemical-petrological meteorite classes and their groups. This meteorite petrophysical database has many potential applications in the geophysical studies of extraterrestrial bodies (planets and their moons, asteroids, meteorite parent bodies, etc.). Here we use the database to classify meteorites rapidly and non-destructively by applying the petrophysical classification scheme developed by Kukkonen and Pesonen [10]. For example, the main classes and many groups form distinct clusters in petrophysical relation diagrams such as susceptibility vs. density or NRM vs. susceptibility. The petrophysical classification method was tested on 24 meteorites from Czechoslovak, 3 from Swedish and one from Australian collections. The chemical-mineralogical classifications of these meteorites were previously known. The subjective classification method was also compared with a mathematical cluster analysis. The subjective classification technique was successful in 64% to 93% of the cases whereas the mathematical analysis was successful in 57% to 82% of the cases. The failures can be attributed to (i) non-uniqueness problems (cluster plots overlap) and (ii) effects of porosity, self-demagnetisation, electrical conductivity and frequency on measured values, or to biasing caused by small sample size.     

Textural remanence: A new model of lunar rock magnetism

In reexamining the accumulated magnetic data on lunar rocks, several common patterns of magnetic behavior are recognized. Their joint occurrence strongly suggests a new model of lunar rock magnetism, which appeals only to partial preferred textural alignment of the spontaneous moments of magnetic grains, without requiring the existence of ancient lunar magnetic fields. This magnetic fabric, mimetic to locally oriented petrofabric, gives rise to an apparent “textural remanent magnetization” (TXRM). In order to account for the observed intensity of “stable remanence” in lunar rocks, only a minute fraction (10^?3 to 10^?5) of the single-domain iron grains present need be preferentially aligned. Several mechanisms operating on the lunar surface, including shock and diurnal thermal cycling, appear adequate for producing the required type and degree of magnetic alignment in all lunar rock classes. The model is supported by a wide variety of direct and indirect evidence and its predictions (e.g. regarding anisotropic susceptibility and remanence acquisition) can be experimentally tested.