| 地外物质中铂族等亲铁元素的分析及应用 | |
| Alternative Title | Analysis and application of PGEs and other siderophile elements in extraterrestrial materials |
| 徐琳 | |
| 2008-05-30 | |
| Degree Grantor | 中国科学院地球化学研究所 |
| Place of Conferral | 地球化学研究所 |
| Degree Name | 博士 |
| Keyword | 铂族等亲铁元素 陨石金属相 Icp-ms 生物灭绝 P/t 界线 地外撞击 火山喷发玄武岩 |
| Abstract | 长久以来，对于陨石金属相的全岩研究主要使用中子活化分析方法（INAA），该方法具有灵敏度高、无损样品及制样简单等优点，但它无法测定所有铂族元素（PGEs）。随着分析技术的发展，电感耦合等离子质谱（ICP-MS）越来越广泛地应用于地质学领域，但在地外物质的应用中研究较少。 本论文在分析方法上，首先在国内开展了球粒陨石金属相和铁陨石的主、微量元素的ICP-AES和ICP-MS实验分析方法研究，对四块球粒陨石的金属相以及四块铁陨石进行了分析，初步讨论了星云凝聚和小行星热变质中亲铁元素的变化特征，进一步揭示了星云的凝聚过程、以及铁陨石的结晶过程。对新发现的乌拉斯台铁陨石所做的研究表明，该陨石和新疆陨石可能为成对陨石。并将研究延伸到地外撞击事件的研究中，通过对浙江煤山P/T界线层的样品进行分析，对当时的生物大灭绝事件给出了合理解释。 乌拉斯台铁陨石是在我国新疆新发现的一块铁陨石，其发现地点距离新疆铁陨石（Armanty）约130公里。我们应用ICP-MS分析了乌拉斯台铁陨石（IIIE），以及新疆铁陨石（IIIE）、南丹铁陨石（IIICD）和Mundrabilla铁陨石（IIICD）的全岩组成，结果显示和参考文献有很好的一致性，证明了该分析方法的可行性。我们对乌拉斯台铁陨石进行了系统的岩石学、矿物学、以及微量元素分析，该陨石的岩石结构属于粗粒八面体，铁纹石带宽为1.2 0.2 mm。合纹石以各种微观结构大量存在于该陨石中。陨磷镍铁矿以富镍（30.5-55.5%）的形式出现在合纹石中，或者与陨硫铁，陨硫铬铁矿等共生。并通过计算获知该陨石的冷却速率约为20℃/Myr。其岩石矿物学特征和全岩组成和新疆铁陨石相似，二者都落在IIIE化学群的范围，因此，我们将乌拉斯台铁陨石划分为IIIE化学群，并初步认为和新疆铁陨石是成对陨石。同时，对吉林球粒陨石（H5）、安龙球粒陨石（H5）、以及南极陨石GRV 9919（L3）和GRV 021603（H3）四块球粒陨石金属相进行的研究显示，球粒陨石金属相的亲铁元素配分模式主要与元素的挥发性相关，具有难熔元素基本上平坦分布，而中等和强挥发性元素随其挥性的增高而趋于贫化的特征。 铂族元素的研究不仅在讨论星云凝聚过程中亲铁元素的分异、金属-硅酸盐分异与核-幔的形成，以及金属熔体的结晶分异方面有着重要的意义，对于讨论地外物质的示踪也有着重要的作用。铂族元素在地壳中高度亏损，但在大部分地外物质中富集，因此通常将Ir的异常已否作为是否有地外物质加入的重要依据之一。距今2.51亿年前的二叠纪-三叠纪（P/T界线）时期，发生了地质历史上最大规模的生物灭绝事件，然而对于该事件的诱因却一直存有争议，主要存在两种观点：“地外撞击”和“火山喷发”。我们使用锍镍火试金和同位素稀释法，结合Te共沉淀， 应用ICP-MS分析技术，对我国煤山二叠纪-三叠纪界线层的样品进行了Ir、Ru、Rh、Pt和Pd的测定。火试金方法结果显示Ir的含量为0.053 ng/g，而同位素稀释法对P/T界线事件层样品的分析结果显示，Ir的含量在0.005-0.028 ng/g，两种分析方法的结果均显示没有Ir的正异常。将PGE使用碳质球粒陨石标准化后，整个配分模式呈现出高度分异，Ir/Pd的比值为0.02-0.03CI，明显不同于各类陨石。相反，该界线层样品的PGE配分模式和西伯利亚玄武岩（甚至也可能和峨眉山玄武岩）相似，证明了该界线层样品中的PGE可能来源于玄武岩。P/T界线层样品中PGE的含量从富含黄铁矿的壳层24f向26层呈上升趋势，且在26层为最大值，然后在28层回落，这种趋势可能暗示了玄武岩最大规模的喷发可能出现在26层。该结果有力地证明了P/T界线时期的生物灭绝事件与火山喷发的相关性，给一直存有争议的二叠纪-三叠纪生物灭绝事件提供了新的证据。 |
| Other Abstract | In the long past the instrumental neutron activation analysis (INAA) has been mainly employed in the study of whole-rock metal phases in meteorites since this technique has the advantages of high sensitivity, no sample damage and simple sample preparation. Unfortunately, this method is not powerful enough to determine all the platinum-group elements (PGEs). With the development of analytical techniques, inductively coupled plasma mass spectrometry (ICP-MS) has found wider and wider applications in the geological field, but less in the study of extraterrestrial materials. In this paper, on the basis of this analysis method, the methodological studies of ICP-AES and ICP-MS have been carried out for the first time in China to analyze the major and trace elements of metal phases in meteorites. We employed both the methods to analyze metal phases in four chondrites and four iron meteorites, preliminarily explore the variation characteristics of siderophile elements in the processes of nebular condensation and asteroid thermal metamorphism, and further disclose the process of nebular condensation and that of crystallization of iron meteorites. Research done on the newly found Ulasitai iron meteorite has revealed that this meteorite may pair to the Armanty meteorite. Moreover, our research has been expanded to the study of extraterrestrial impact event. On the basis of the results of analysis of the P/T boundary samples at Meishan, Zhejiang Province, reasonable explanations have been proposed for the mass extinction event at that time. The Ulasitai iron meteorite is a piece of iron meteorite which has been newly found in Beitashan, Qinghe County, Xinjiang, whose find site is about 130 km to that of the Armanty (Xinjiang, IIIE) meteorite. We employed ICP-MS to analyze the bulk samples of Ulasitai, together with the Armanty（IIIE）, Nandan (IIICD) and Mundrabilla (IIICD). The results are in agreement with literature data for the same meteorites, indicating that this method is highly feasible. Systematic petrological, mineralogical and trace element analyses were conducted of the Ulastai iron meteorite, indicating that this meteorite is a coarse octahedrite, with a kamacite bandwidth of 1.2±0.2 (0.9-1.8) mm. Plessite is abundant with various micro-structures. Schreibersite is Ni-rich (30.5-55.5 wt%) in plessite or coexisting with troilite and daubreelite. Through calculation it is known that this meteorite has a cooling rate of ~20 C/Ma. The Ulasitai is similar in petrography and mineral chemistry to the Armanty, both plotting within the IIIE field. Therefore, the Ulasitai is classified as a new IIIE iron meteorite, suggesting that it pairs with the Armanty. At the same time, studies of the metal phases in the Jilin chondrite (H5), the Anlong chondrite (H5), and Antarctic meteorites GRV 9919（L3）and GRV 021603（H3）have shown that the distribution patterns of siderophile elements in the metal phases of the chondrites are mainly related to the volatility of the elements, i.e., the refractory elements generally show a smooth distribution pattern, while the moderately and strongly volatile elements tend to be depleted with increasing volatility. Research on the platinum-group elements (PGEs) is of great significance not only in dealing with the differentiation of siderophile elements, metal-silicate differentiation and core-mantle formation as well as the crystallization-fractionation of metal melt, but also has plaid a very important role in exploring the tracing of extraterrestrial materials. The platinum-group elements (PGEs) are enriched in most extraterrestrial materials, but highly depleted in the terrestrial crust materials. Therefore, Ir anomaly can be regarded as one important piece of evidence for the existence of extraterrestrial materials. The Permian-Triassic boundary sections (25.1 Ma B.P.) have recorded the most severe mass extinction event in the geological history. However, there is a long-standing controversy on whether bolide impact and/or basaltic flood volcanism triggered the mass extinction. We analyzed Ir, Ru, Rh, Pt and Pd in a set of samples from the global stratotype section and point (GSSP) of the Permian-Triassic boundary at Meishan, China, using isotope dilution inductively coupled plasma mass spectrometry (ID-ICP-MS) and nickel sulfide fire assay (NiS-FA) combined with Te coprecipitation. Results of fire assay showed that the content of Ir is 0.053 ng/g. The results of isotope dilution analysis for P/T boundary samples demonstrated that the contents of Ir are within the range of 0.005-0.028 ng/g. The analytical results obtained by the two methods both show no Ir anomaly and their PGE patterns normalized to chondrites are highly fractionated with Ir/Pd ratios of 0.02-0.03 CI, distinct from most meteorites. In contrast, the PGE distribution patterns of the P/T boundary samples are closely parallel to those of the Siberian and probably Emeishan flood basalts, suggestive of possible sources of PGEs from the basalts. The abundances of PGEs increase in order of the pyrite laminae at the top of bed 24, bed 25 and bed 26, and then decrease toward bed 28, probably indicative of a maximum eruption of flood basalts during deposition of bed 26. The results provide strong evidence in favor of massive volcanism, instead of extraterrestrial impact, as a major cause of the Permian-Triassic boundary mass extinction. |
| Pages | 106 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.gyig.ac.cn/handle/352002/3374 |
| Collection | 研究生_研究生_学位论文 |
| Recommended Citation GB/T 7714 | 徐琳. 地外物质中铂族等亲铁元素的分析及应用[D]. 地球化学研究所. 中国科学院地球化学研究所,2008. |
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