Hf-Fe同位素分析方法及其在腾冲火山岩研究中的应用

发布时间：2018-01-17 16:33

  本文关键词：Hf-Fe同位素分析方法及其在腾冲火山岩研究中的应用　出处：《中国科学技术大学》2016年博士论文　论文类型：学位论文

  更多相关文章： 放射成因同位素Hf 金属稳定同位素Fe 化学分离 MC-ICP-MS 同位素标准物质 同位素示踪 腾冲火山岩 大陆岩石圈地幔

【摘要】：近年来,随着同位素测试技术的革新以及现代分析仪器的开发和推广,同位素分析方法(包括放射成因同位素分析和稳定同位素分析)迅速发展,已成为地学研究中一门重要的分析技术。壳-幔体系中,放射成因同位素铪(Hf)在示踪源区特征及演化过程方面,能比传统锶-钕-铅(Sr-Nd-Pb)同位素提供更好的观察视角：金属稳定同位素铁(Fe)依据同位素分馏规律,在示踪岩石成因上具有显著优势,现已成为一种新的地球化学示踪剂。基于同位素分析方法蓬勃发展的大背景下,并结合放射成因同位素和金属稳定同位素的独特示踪优势,我们在Hf-Fe同位素联合分析方法及地质应用方面开展了一系列工作,以期更精确地揭示岩石的源区特征和壳-幔相互作用,为同位素地球化学领域开辟一条新的研究思路。本论文主要从以下四个方面展开：(1)Hf、Fe同位素分析方法研究进展随着多接收电感耦合等离子体质谱(MC-ICP-MS)的发展,同位素分析方法出现重大突破。本部分综述了Hf、Fe同位素分析技术的发展历程,Hf、Fe化学分离方法的研究进展以及质谱测定的影响因素。纵观前人研究,Hf和Fe独立的化学分离方法已经日趋成熟,并被广泛应用于国内、外各大实验室。此外,MC-ICP-MS已成为当前Hf、Fe同位素组成测定的主流方法。(2)建立“同一岩样Hf-Fe化学分离方法”前人研究表明,主量元素Fe对Hf同位素分析会产生巨大的干扰(如聚合物干扰、基质效应等),如何从Hf待测溶液中彻底去除Fe是一个亟待解决的问题。然而,近年来Hf-Fe同位素联合分析在高温地质应用中的潜在价值逐渐被发现。由此,我们提出一个设想：是否能从同一份地质样品中分离、纯化出Hf和Fe?如此,不但能消除Fe对Hf的干扰,还能就一份岩样同时获得它们的Hf、Fe同位素信息,进而达到Hf-Fe同位素联合分析的目的。基于前人独立的Hf、Fe分离理念,我们设计出一套简单且高效的Hf-Fe多元素化学分离流程。这是一套离子交换色谱法和提取色谱法相结合的两阶段分离流程,先通过Bio-Rad AG-MP-1M阴离子交换树脂从充分溶解的岩液中分离获得Fe元素,再将所接收到的含Hf基质溶液经Eichrom LN-Spec树脂进一步分离纯化出Hf元素。值得一提的是,本流程除了能彻底分离Hf和Fe之外,还可以根据需要,进一步分离纯化出Lu、Rb、Sr、Sm、Nd、Pb等多种元素,能够就同一份样品提供更多的同位素信息。(3)确立“合适的Hf、Fe同位素标准物质”准确可靠的同位素标准物质是支撑同位素分析技术发展的一个重要保证。然而,就Hf、Fe同位素分析而言,国际标准物质的供不应求很大程度上阻碍了该技术的推广。同时,一种新Hf、Fe国际标准的建立,不仅难度大且耗时长。因此,人们尝试从现有的元素标准物质中寻找适合用于同位素分析的“内部标准”,来协助国际标准一起完成常规测试。基于此,我们首次对三种国家火成岩一级标准物质(GSR-1花岗岩：GSR-2安山岩;GSR-3玄武岩)进行了系统的Hf、Fe同位素分析,判定它们是否适合用作Hf、Fe同位素分析的“内部标准”。分析结果表明,GSR-2和GSR-3均适合用作Hf同位素分析的内部标准,相应的同位素组成推荐值分别为176Hf/177Hf=0.282641±6 (MSWD=1.5,2σ, n=10)和176Hf/177Hf=0.282985±4 (MSWD=0.48,2σ, n=10)。但是,GSR-1花岗岩可能因继承锆石而表现出同位素组成上的不均一,由此,它不适合用作Hf同位素标准物质。此外,GSR-1, GSR-2和GSR-3均适合用作Fe同位素分析的内部标准,它们的同位素推荐值657Fe分别为+0.35±0.02‰,+0.22±0.05‰,+0.43±0.02‰(相对于IRMM-014,2σ,n=3)。(4)晚新生代腾冲火山岩Hf-Fe-(Sr-Nd-Pb)同位素示踪中国西南部腾冲火山区分布着众多新生代镁铁质大陆板内火山岩,该区共有68座具有明显火山锥山体的火山,熔岩的分布面积约为800平方公里。结合前人已有的报道,我们对该区18个新鲜的火山岩样品进行了主、微量元素和Hf-Fe-Sr-Nd-Pb多种同位素的综合分析,旨在深入探究腾冲火山岩的源区特征以及岩浆演化过程。研究表明,这批火山岩中大部分样品均经历过分离结晶-同化混染作用(AFC)。其中,一些混染较为明显的样品,表现出极异常的轻Fe同位素特征,推测代表了混染的大陆地壳特征。依据主、微量元素、AFC演化趋势以及Hf-Nd同位素特征等多方证据,我们识别出三个样品具有初始岩浆特征,可能直接来源于地幔源区,它们的Hf-Fe-Sr-Nd-Pb同位素组成(176Hf/177Hf=0.282962, δ56Fe=0.13‰,87Sr/86Sr=0.705861,143Nd/144Nd=0.512675,206Pb/204Pb=18.305, 207Pb/204Pb=15.642,208Pb/204Pb=38.948)能够代表中国西南部腾冲地幔源区的特征。通过“熔融模拟”实验,我们认为腾冲火山的最佳成因模型可以表示为：受到过交代的地幔源区(由95-99%的原始亏损地幔(DMM)和1-5%的全球俯冲沉积物(GLOSS)构成)经历1-4%的部分熔融后形成腾冲原始岩浆。这些具有富集地幔特征的原始岩浆可能来自俯冲相关的交代岩石圈地幔。因此,腾冲火山岩的地幔源区与前人提出的富集地幔端员(如EM1,EM2)或DUPAUL地幔没有直接的联系,它们只是具有相似的同位素特征。此外该区缺少地幔柱存在的证据,我们推测腾冲火山作用是在“与印度次大陆反向应力有关”的伸展背景下,热的富集大陆岩石圈地幔被动上涌所触发的。由于受交代的富集地幔组分容易发生熔融,腾冲火山岩即是该区大陆岩石圈地幔富集组分减压熔融后的产物。
[Abstract]:In recent years, with the development and popularization of isotope test innovative technology and modern analytical instruments, methods of isotope analysis (including analysis of radiogenic isotope analysis and stable isotope) rapid development, has become an important research in the analysis. The crust mantle system, radiogenic isotope characteristics in HF (Hf) and the evolution of tracer source region process, energy than conventional SR nd Pb (Sr-Nd-Pb) provides a better perspective: metal isotope stable isotope of iron (Fe) on the basis of isotopic fractionation law, has a significant advantage in tracing the petrogenesis, has become a new geochemical tracer. Based on the background of rapid isotope analysis method the development, combined with the unique advantages of radiogenic isotope tracer and metal isotope, Hf-Fe isotope in our joint analysis method and geological application aspects carried out a series of Out of work, in order to more accurately reveal the feature of source rock and crust mantle interaction, open up a new way for the research of isotope geochemical field. This thesis mainly from the following four aspects: (1) Hf, with the research method of receiving power inductively coupled plasma mass spectrometry (Fe isotope analysis MC-ICP-MS) the development of methods to breakthrough isotopic analysis. This part reviews the development course of Hf technology, Fe Hf isotope analysis, the factors influencing the determination of Fe chemical separation methods and research progress of mass spectrometry. In previous studies, Hf and Fe independent chemical separation method has become increasingly mature, and widely used in domestic and outside of the major laboratory. In addition, MC-ICP-MS has become the mainstream method for the determination of Hf, Fe isotopic compositions. (2) the establishment of "the same" previous research samples for chemical separation of Hf-Fe showed that the main elements of Hf in Fe Analysis will produce huge interference (such as polymer matrix interference effect), how to completely remove the Fe test solution is an urgent problem to be solved in Hf. However, in recent years the Hf-Fe isotope combined analysis of potential value in high temperature geological application has been found. Therefore, we proposed a hypothesis: whether can be separated from the same geological samples, purified Hf and Fe? So, not only can eliminate the interference of Fe to Hf, but also a specimen obtained at the same time their Hf, Fe isotope information, and then reach a combined analysis of Hf-Fe isotopes. Based on the previous independent Hf, Fe separation principle, we design a simple and efficient Hf-Fe multi element chemical separation process. This is the two stage of a combination of ion exchange chromatography and extraction chromatography separation process, from the first through the rock fluid to fully dissolve Bio-Rad AG-MP-1M anion exchange resin Isolated Fe element, then Hf matrix solution containing received by Eichrom LN-Spec resin was further purified by Hf elements. It is worth mentioning that this process in addition to the complete separation of Hf and Fe, can also according to the needs of the purified Lu, Sr, Sm further separation of Rb, Nd, Pb. And other elements, can provide more information on the same isotope samples. (3) establish appropriate Hf isotope reference material Fe isotope standard material accurate and reliable is an important guarantee for technology development of isotopic analysis support. However, Hf, Fe isotope analysis, international standard material in a large extent hindered the popularization of this technology. At the same time, a new Hf, the establishment of Fe international standard, not only is difficult and time-consuming. Therefore, people try to find suitable for isotopic analysis of internal standard elements from existing standard materials "To assist the international standard together with the completion of routine testing. Based on this, we for the first time on the three kinds of national standard substances of igneous rocks (granite GSR-1: GSR-2 andesite; GSR-3 basalt) of the system Hf, Fe isotope analysis, determine whether they are suitable for Hf, Fe isotope analysis of the" internal standard ". The analysis results show that GSR-2 and GSR-3 are suitable for Hf isotopic analysis of the internal standard, the corresponding isotopic composition of recommended values were 176Hf/177Hf=0.282641 + 6 (MSWD=1.5,2 6, n=10) and 176Hf/177Hf=0.282985 (MSWD=0.48,2 + 4 sigma, n=10). However, the GSR-1 granite may be due to inherited zircons show the isotopic composition of the heterogeneity, thus and it is not suitable for Hf isotope reference material. In addition, GSR-1, GSR-2 and GSR-3 are suitable for Fe isotopic analysis of the internal standard, their isotopic recommended value of 657Fe were +0.35 + 0.02 %, +0.22% + 0.05, +0.43 + 0.02% (relative to IRMM-014,2 sigma, n=3). (4) late Cenozoic volcano rock of Tengchong Hf-Fe- (Sr-Nd-Pb) Chinese isotope tracer in southwest Tengchong volcano area distribution of volcano rock many Cenozoic mafic continental intraplate region, the total of 68 cities has obvious volcano cone the mountain volcano, lava distribution area is about 800 square kilometers. According to previous reports, we conducted principal of volcano rock samples fresh 18 in this area, a comprehensive analysis of trace elements and Hf-Fe-Sr-Nd-Pb isotopes, probes into the Tengchong volcano rock source characteristics and magmatic evolution process. The results show that the most of the samples in the volcano rock group experienced fractional crystallization - assimilation effect (AFC). Among them, some of the more obvious contamination samples showed light Fe isotopic characteristics very abnormal, that represents the characteristics of continental crust contamination. On the basis of The main and trace elements, AFC and Hf-Nd isotopic characteristics of the evolution trend of multi evidence, we identified three samples with the characteristics of the initial magma may be directly derived from the mantle source region, Hf-Fe-Sr-Nd-Pb isotope composition (176Hf/177Hf=0.282962, 87Sr, /86Sr=0.705861143Nd/144Nd=0.512675206Pb/204Pb=18.305, 56Fe=0.13%, 207Pb/204Pb=15.642208Pb/204Pb=38.948) to represent the characteristics of China in southwestern Tengchong. Mantle source region through the simulation of melt "experiment, we think that the best model for the origin of Tengchong volcano can be expressed as: by metasomatism of the mantle source region (by the original 95-99% (DMM) and 1-5% depleted mantle subducted sediments (GLOSS) global composition) experienced partial melting of 1-4% after the formation of Tengchong primary magma. These have enriched mantle characteristics. The original magma may be derived from a subduction related metasomatic lithospheric mantle so, The enriched mantle end member of the mantle source region and the former Tengchong volcano rock proposed (such as EM1, EM2 or DUPAUL) have no direct contact with the mantle, they are similar. In addition to the isotopic characteristics of the mantle plume district is the lack of evidence, we speculate that the Tengchong volcano in the background is stretching and reverse stress on the subcontinent of India under the heat of the enriched continental lithospheric mantle upwelled triggered. Due to the metasomatic enriched mantle group prone to melting, Tengchong volcano rock is product divided after the decompression melting of continental lithospheric mantle enrichment group.

【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P597;P588.14
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本文编号：1437078