变质橄榄岩中尖晶石的分形结构因子类型及其成因意义

利用沈步明（１９９３）提出的分形结构因子的新方法，计算了橄榄岩包体、方辉橄榄岩、纯橄榄岩和铬铁矿等六种尖晶石的分形结构因子。划分了四种尖晶石分形结构因子类型：Ａ１和Ｃｒ强变异型、Ａ１和Ｃｒ变异型、Ｍｇ和Ｆｅ２－变异型、Ｍｇ和Ｆｅ２－强变异型，结合尖晶石的地质产状讨论了这四种类型的成因意义。通过大量分形结构子的计算和图表．有力说明分形结构因子对于表征物质在空间分布的结构性和数据之间的相关性，是一种有效的定量化手段。在推测尖晶石和主岩的成因方面，尖晶石的Ｃｒ（Ａ１）和Ｍｇ（Ｆｅ２＋）的ＦＳＦ值图解更优于尖晶石的Ｃｒ／（Ｃｒ＋Ａ１）－Ｍｇ／（Ｍ＋Ｆｅ２－）图解。     

尖晶石型结构的晶体化学

在具有尖晶石型的晶体结构中，阳离子都处于特殊位置，O离子的坐标为（u，u，u），在成分或温度变化时，O离子的坐标发生变动，就牵动着整个结构的变化。本文在讨论了尖晶石型结构中各离子的几何关系之后，作了一些关系图，例如Y（B-0）对Y（O-A）／关系图。它按（A-O）／（B-O）数值的大小（或者u值的大小）将各点分成五个区，显然，它们受A、B阳离子大小的控制，在这基础上讨论了O离子的移动轨迹。最后讨论了尖晶石衍生体结构的空间群变化规律性。     

橄榄石的后尖晶石相变研究进展

橄榄石在高温高压条件下分解为钙钛矿和方镁石(后尖晶石相变),这是地幔中最为重要的相变之一,被认为是660KM地震波速间断面的成因。现今所取得的重要进展表现在3个方面:①MG_2SI O_4的后尖晶石相变的原位X射线高温高压实验研究;②水、AL_2O_3以及压力标尺对后尖晶石相变的影响效应;③下地幔条件下地幔岩组分中的后尖晶石相变。在对研究进展进行概述的基础上,对目前存在的问题进行了分析并提出未来可能的研究方向。     

伊通新生代玄武岩中辉石岩捕虏体的尖晶石成分分带

伊通新生代玄武岩中存在3种不同成因的捕虏体,其中上地幔岩浆分异结晶形成的辉石岩捕虏体中尖晶石具有独特的成分分带。电子探针分析显示在尖晶石矿物的边缘富Al,而贫Mg、Fe和Cr,矿物中心富Mg、Fe和Cr,而贫Al,从中心向两侧基本对称。从尖晶石成分分带的元素分布特征判断,其形成不是固溶体相平衡过程中的离子扩散,而可能是化学平衡过程中结晶矿物与熔浆之间化学成分平衡的结果,属于化学平衡导致的成分分带。从尖晶石矿物中心到边缘的温度变化不能反映矿物形成后所经历的温度变化状况,与尖晶石共生矿物的二辉石地质温度计所能代表的地质意义是矿物中心的温度(~1 006℃),反映矿物开始结晶时的温度状态。     

西藏普兰超镁铁岩体东部铬尖晶石矿物学特征及其地质意义

尖晶石是地幔橄榄岩中一种非常重要的矿物,虽然含量很低,却可以作为其寄主岩石——地幔橄榄岩——的成因指示剂.普兰岩体东部铬尖晶石分布广泛,几乎在所有岩石类型中都有出现.通过矿物学特征的研究,认为尖晶石可分为两类,一类较自形,颜色较深;另一类多呈不规则状和蠕虫状,颜色较浅.根据其化学特征,又可分为富铬型的尖晶石(Cr#＞60)和富铝型的尖晶石(Cr#＜60),富铬型尖晶石主要出现在纯橄岩、蛇纹岩和辉石岩中,富铝型尖晶石主要出现在二辉橄榄岩中.其中,方辉橄榄岩中的尖晶石形态、化学成分变化比较大,说明它经历了较为复杂的形成和变化过程.通过对尖晶石矿物学和化学特征的综合研究,认为该区尖晶石具有深海橄榄岩和上部俯冲板片(SSZ)构造环境橄榄岩特征,普兰岩体可能先后经历了MOR和SSZ两种构造环境.     

辽宁瓦房店金伯利岩中铬尖晶石成分的两种分带趋势及其成…

首次报道金伯利岩中铬尖晶石的两种成分分带趋势，其中斑晶铬尖晶石以核部富Ｃｒ、边缘逐渐富Ａｌ和Ｆｅ＾３＋为特征，该铬尖晶石为金伯利岩岩浆上升过程中形成的；基质铬尖晶石则同上述变化趋势相反，它们是岩浆在温、压增大或母岩在熔融程度增加过程中形成的。根据Ｃｒ２Ｏ３含量，基质铬尖晶石可分为两类：一是岩浆演化晚期，岩管爆发前增压过程中结晶的低铬铁尖晶；二是来自深源捕虏体的高铬铁尖晶石，本文探讨了它们的形成机制     

缺位型铬尖晶石化学成分计算

缺位型铬尖晶石的存在是20世纪50年代才被认识的，因其高反射率并具磁性；长期以来被误认为磁铁矿，本文对比了它与正常型铬尖晶石化学结构式的差异；论证了其化学结构式的推导计算方法和鉴别特征，铬尖晶石的组成和结构是地质地球化学的重要信息。     

金伯利岩中铬尖晶石的特征及与其它岩类中铬尖晶石之对比

本文根据我国金伯利岩中铬尖晶石的a_0、比重、红外光谱分析、穆斯堡尔谱分析、湿法化学分析、探针分析和稀土元素分析资料及其它岩类中的铬尖晶石类的化学成分资料,研究了各金伯利岩区之间及其区内各岩体的铬尖晶石的差异,指出了作为粗晶、原生基质矿物、金刚石中的包体、金伯利岩深源包体中的矿物产出的铬尖晶石特征,将金伯利岩中的铬尖晶石与其它岩类中的铬尖晶石作了对比。研究表明,地球上,所有铬尖晶石中,以金刚石中铬尖晶石包体的Cr_2O_3组分最高。同时,随着金伯利岩中金刚石含量增加,岩石中粗晶铬尖晶石的Cr_2O_3组分增加,625—645cm~(-1)及500—525cm~(-1)红外吸收谱带向低频率方向移动,IS[Fe~(3+)(B)]穆斯堡尔参数增高,QS[Fe~(3+)(B)]及QS[Fe~(2+)(A)]穆斯堡尔参数降低。     

橄榄岩中尖晶石的O同位素继承性与晶体结构转换

应用增量法计算的矿物对O同位素分馏曲线，得到正尖晶石-矿物对O同位素温度高于尖晶石在地幔中的熔点，而用反尖晶石-矿物对计算的O同位素温度低于尖晶石的熔点，较为合理。因此，地幔橄榄岩中镁铝尖晶石的O同位素组成可能继承了其母体反尖晶石特征，即使反结构尖晶石在发生相变作用变成正结构尖晶石时未发生O同位素再平衡。     

尖晶石的矿物学特性及其在工业上的应用

尖晶石族矿物广泛地分布于自然界，它们是许多变质岩和岩浆岩的主要矿物成分。工业上应用较多的主要是镁铝尖晶和镁铬尖晶石。镁铝尖晶石耐火材料是目前冶金用耐火材料的重点发展方向之一，对这种材料的理论及应用研究也成为耐火材料研究的热点。尖晶石的其它应用，如尖晶石轴承及颜料等也取得了较大的发展。笔者根据尖晶石的矿物学特性，对尖晶石的生成以及工业生产的基本原理、基本工艺和基本过程操作一系统的概述，并对尖晶石原料     

地质记录中的微球粒

地质记录中的微球粒根据成因可以分为宇宙尘、地外物体撞击成因微球粒、火山成因微球粒、生物成因微球粒、沉积作用微球粒和现代微球形飞灰等。宇宙尘含有丰富的宇宙物质,出现Fe、Ni核心和方铁矿等,具有宇宙尖晶石和宇宙不丰富的元素的亏损是判断宇宙尘的关键特征。撞击事件可以产生近源区的撞击熔融玻璃球和远源区的撞击汽云凝结球两类微球粒,常与其他撞击成因矿物伴生。火山微球粒是在低粘稠度的岩浆岩喷发形成的玻璃质火山灰中,有球形、液滴形和哑铃形的微颗粒。这三种成因的微球粒在各种地层中的赋存对于地层对比和地史事件研究中有着非常重要的意义,为判断和研究不同的地质事件提供了一个很好的媒介,因此长期以来一直是微球粒研究的主要对象。另外,在现代工业生产过程中也可以产生大量微球形飞灰,这些飞灰经常包含非常复杂的表面纹饰和独特的化学组成,比如高的ZnO含量等。     

大吉山花岗岩中宇宙尘的初步研究

大吉山花岗岩人工重砂中的宇宙尘呈黑色,具强磁性,平均粒径为0.206mm,按形态可分为球状、椭球状和不规则状,按成分可分为铁质和硅酸质两种类型。主要矿物有方铁矿、α-Fe、自然铜、钠长石和钾长石。主要组构类型有瘤状突起构造、喷气孔构造、“毛刺”构造、壳层构造、空腔构造、花边构造和脑纹状构造。通过研究得出如下结论:(1)大吉山宇宙尘是低氧逸度条件下高温淬火形成的非平衡结晶产物;(2)宇宙尘的来源与大吉山花岗岩的成因有密切联系,是花岗岩岩源层的残留物;(3)宇宙尘可以作为花岗岩成因指示物。     

Mechanical transport of metallogenic materials in endogenic hydrothermal solutions: evidence from the microspherules in micro-disseminated gold deposits,northwestern Sichuan,China

Numerous steel-gray microspherules were recently unexpectedly discovered in ore and rock samples from several disseminated gold deposits hosted in Middle–Upper Triassic turbidites in northwestern Sichuan Province, China. Both nature surfaces and part sections of 227 microspherules have been observed by reflected light microscope, scanning electron microscope (SEM), electron microprobe analyses, X-ray energy spectra, X-ray powder patterns, the results reveal them to be cosmic dust. It is the first discovery of cosmic dust in this kind of deposits in China.The size of the microspherules ranges from 25 to 185 μm and generally is less than 100 μm. According to their composition, they belong to chromium-rich iron cosmic dust. The microspherules have complex, diverse and diagnostic microscope structures and textures, and such as very distinct airprint structure that are compatible with extraterrestrial material. Variation of geochemical content of the microspherules in the gold deposits in generally positively correlates with both the Ir content of the enclosing strata and the intensity of mineralization and hydrothermal alteration. The abnormally high content of Ir is important evidence for an extraterrestrial source for the microspherules. The fact that a geological body with strong alteration and mineralization is rich in microspherules may raise a new concept: Under endogenic conditions, it is not only possible but also realistic for mineralized material to be transported mechanically, in addition to the generally accepted chemical transport of ore constituents in hydrothermal solution because it is obviously impossible for cosmic spherules to fall directly from space into cemented hydrothermal ore veins more than 1 km deep in the earth.     

Factors controlling compositions of cosmic spinels: application to atmospheric entry conditions of meteoritic materials

During their deceleration through the Earth's atmosphere, meteoritic materials, i.e., interplanetary dust particles, micrometeorites and meteorites, experience thermal shocks which may alter their pristine mineralogy, texture or chemical characteristics. Among these changes, one of the most ubiquitous is the formation of spinels resulting from partial melting and subsequent crystallization of the meteoritic material. These “cosmic spinels” differ from terrestrial spinels by their high Ni and Fe³⁺ contents and show large variations in composition. In order to better understand the factors controlling their chemistry, pulse-heating experiments simulating atmospheric entry of extraterrestrial objects were carried out using Orgueil samples as proxies of meteoritic material. Covering a large range of experimental conditions (temperature 500°C < T <1500°C, duration: 5 s < t < 120 s, and oxygen fugacity: −0.68 < log fO₂ < −8), this work shows (1) that the whole range of composition of cosmic spinels analyzed so far at the micrometer scale in fine-grained and scoriaceous micrometeorites, in cosmic spherules or in the fusion crust of several stony meteorites can be reproduced, and (2) that these compositional changes can be expressed as a function of temperature, time and oxygen fugacity.We also show that, due to their fast crystallization kinetics, cosmic spinels can record through their composition, i.e., Al₂O₃ contents and FeO/Fe₂O₃ ratio, the diverse conditions of the atmosphere crossed by the extraterrestrial object during its fall towards the Earth's surface. Chemistry of cosmic spinels is thus a powerful tool for constraining the entry conditions in the Earth's atmosphere of any extraterrestrial object, including altitude of deceleration, entry angle and incident velocity. These in turn, may provide valuable information on the origin of the extraterrestrial material.     

Extraterrestrial microspherules from Bajada del Diablo,Chubut, Argentina

The Quaternary infilling of a circular structure located in Bajada del Diablo, Chubut Province, Argentina has been proposed as a crater strewn field in previous studies. Here we report the finding of about 65 microspherules collected in a trench excavated in the center of the structure. The majority of hand-picked specimens are single, but some of them exhibit compound forms. The single specimens are spherical with a mean size of 137 μm, whereas the more complex samples show peduncles and drop shapes. Dendritic crystal growth is recognized in the internal structure of some broken microspherules. Preliminary chemical composition from the surface and center of microspherules was determined by energy dispersive spectrometry employing EDS. Quantitative EMPA and XRD analysis indicate that the microspherules are mainly composed of Fe and O with magnetite, Fe0 with subordinate wüstite. Following consideration of possible anthropogenic and volcanic origins, these spherulites are ascribed to an extraterrestrial input. An accumulation rate of 47 microspherules per m²/yr is estimated for the studied sediments. This value is two orders of magnitude higher than the reference flux for cosmic dust estimated for the last 1 Ma in the Transantarctic Mountains. The microspherules might have been generated as a byproduct of asteroid entry in the atmosphere.     

宇宙尘似文象结构的图像分析和成因探讨

宇宙尘较广泛地分布于各地质时代和各种岩石中,它形成在不同的物理化学环境下,因此具有比较复杂的结构构造。本文对产于不同时代、不同岩性岩石中具有似文象结构的宇宙尘进行了广泛的研究,一方面研究Si、Al等元素的赋存状态,另一方面研究这些元素与似文象结构的关系,进一步为它们的成因提供信息。     

Spherules from the Tunguska event site: Could they originate from the Tunguska Cosmic Body?

Soil layers at the Tunguska event site may have accumulated infalling extraterrestrial matter derived from the Tunguska Cosmic Body (TCB). Using mineralogical, textural, and chemical criteria, a set of metal and silicate spherules of probably cosmic origin was identified in the collection of spherules and rounded particles recovered from sites with high concentrations of magnetic spherules on a terrace above the floodplain of the Chunya River. The metal spherules consist of Ni(Cr)-bearing wüstite and magnetite with Ni-rich metal inclusions. The silicate spherules are glassy, cryptocrystalline, barred, and porphyritic melted micrometeorites, some of which contain metal droplets. The number of spherules counted in our samples is higher than the background level, indicating the possible presence of the TCB material.     

A Preliminary Study on Dust Grains in the Stratosphere

Collected by means of a high-altitude scientific balloon and a self-made automatic sample collector,a total of 276 dust grains were selected for the study of shape,grain size and optical property.Some of the grains were examined by X-ray diffraction and electrom microprobe techniques,The stratospheric dust grains can be classified as 6 types:cosmic dusts,cosmic dusts(?),microtektite,natural pollutants,artificial pollutants and the unknown substances.The different types of dust grains have different characters and distinguishing symbols.Widespread in the space of the solar system,cosmic dusts are the initial substances of the solar system and ,to some degree,have recorded a great wealth of information on the early history of the solar system.So they have become one of the important objects in the field of cosmochemistry at present time,Since the 1960‘s,scholars of many countries have collected cosmic dusts both in the space near the earth(using rock ets,space probes and space shuttles)and in the stratosphere (using high-altitude balloons or U-2air planes).According to the shape(the scanning electron microimage),element composition(the energy-dispersive X-ray spectrum)and optical properties of dust grains,the substances in the stratosphere can be classified as 5 types:cosmic dusts,alumina spheroids,terrestrial artificial pollutants,terrestrial natural pollutants and unknown substances(CDPET,1982).     

Discovery of Cosmic Spherules from the Mesoproterozoic Strata and its Significance—in Case of the Ming Tombs Area, Beijing

This study covers cosmic spherules derived from the Mesoproterozoic Dahongyu Formation in the Ming Tombs area, Beijing. The cosmic spherules include iron oxide cosmic spherules, carbonaceous chondrites, and atomic iron “steely bead”-shaped cosmic spherules. The mineral assemblage of silicon carbide, forsterite, zircon, and glass spherules and fragments were picked from melt-silicified carbonate of the Mesoproterozoic Dahongyu Formation (ca. 1625 Ma). Cosmic spherule assemblages are solely discovered from sedimentary rocks in China. Platinum group elements (PGE) were determined for the first time in cosmic spherules and associated minerals. PGE comparative observation between meteorite and cosmic spherules is presented in this study. It is recognized that an extraterrestrial meteorite impact event might have occurred in the Dahongyu Stage. The main evidence is a large number of iron cosmic spherules in silicified oncolitic limestone, and associated cosmic silicon carbide, glass spherules, and fragments, as well as the presence of forsterite. The impact-volcanic crater is characteristic of a big black shale block dropped into the bended silicified limestone.