【作者】 宋佳瑶；

【导师】 袁洪林；

【作者基本信息】 西北大学 ， 地球化学， 2011， 硕士

【摘要】 长石是常见的造岩矿物之一,普遍存在于各类岩石中。长石的铅同位素组成是示踪岩石形成和演化历史的重要途径,通过铅同位素地球化学研究,不仅可以确定成矿时代或模式年龄,而且还可判断成矿物质来源、矿床成因等。然而,传统的整体分析方法得到的铅同位素组成是整个矿物或一些矿物的混合物,可能不具有实际地质意义。这就需要具有微区Pb同位素分析功能的分析技术。激光剥蚀多接收等离子体质谱(LA-MC-ICPMS)技术是进行原位微区分析微量元素和同位素的重要设备之一,然而,由于该技术属于相对分析,即分析过程中实际样品的分析数据是在与标准样品分析信号对比基础上获取的,标准样品与实际样品基体的匹配程度将直接影响分析结果的准确度,与样品具有类似基体的标准物质就成为影响该技术成功应用的关键影响因素。因此,研制与基体相近的长石玻璃标准也是利用LA-MC-ICPMS进行微区Pb同位素组成分析的关键问题。本论文利用高温炉对天然钾长石粉末(加入了单硅酸铅)进行熔融的实验条件研究,研制出钾长石玻璃,并利用LA-Q-ICPMS和LA-MC-ICPMS技术分别就其中的主、微量元素和Pb同位素组成进行详细的均一性研究,经过反复试验和对比,获得如下结论：1.熔融实验之前需要将初始钾长石粉末研磨至1300目以上；2.确定钾长石标准玻璃的合成条件为：熔融温度1680℃、熔融时间2小时,采用液氮淬火；3.经检验合成的钾长石标准玻璃具有很好的均一性。其主量元素RSD%优于5%,微量元素RSD优于10%,内部Pb同位素比值为1.90779±0.00009 (208Pb/206Pb,2s), 0.75899±0.00004(207Pb/206Pb,2s),20.909±0.002(206Pb/204Pb,2s),15.871±0.002(207Pb/204Pb,2s)和39.888±0.005 (208Pb/204Pb,2s),相应的RSD分别为0.007%,0.008%,0.016%,0.016%和0.021%。4、利用合成的钾长石标准玻璃作外标,对地质样品中长石的铅同位素开展了原位分析,结果与前人利用传统化学方法分析得到的结果在误差范围内完全吻合。更多还原

【Abstract】 The feldspar is one of the common rock forming minerals. The Pb isotopic composition of feldspar could be used as tracer of the rock formation and the history evolution. Based on lead isotope geochemistry research, one may not only determine the metallogenetic epoch or the modle age, but judge the origination of mineralization material metallogenesis. The traditional bulk rock analysis of lead isotopic composition can only obtain the mixed lead isotopes and may not have practical significance. This requires the in situ analytical techniques. The laser ablation coupled with multiple-collector inductively coupled plasma mass spectrometer (LA-MC-ICPMS) is one of the most important in situ micro analytical techniques for lead isotopic coposition measurement. However, all kind of in situ micro analycial techniques need external standard materials to calibrate instrumental fracationation and other obstacles to get elemental and isotopic compositions of samples. The matrix matched external calibration standards are the short cut way to obtain the geochemical information of relative geological samples in most applications. There is no feldspar standards for precise lead isotope analysis of K-feldspar using in situ analytical techniques, such as LA-MC-ICPMS. We tried to synthesize K-feldspar glasses using high temperature furnace with monosilicate lead dopted K-feldspar powder and evaluated the homogeneity of trace elements and lead isotopic compositions.1. The grinding step prior to melting is one of the key step for homogenized glasses synthesion. The K-feldspar need to be grinded to 1300mesh instead of 200mesh to get final homogenized glasses due to high viscosity melt;2. The experimental coditions for K-feldspar glasses synthesion are:heating temperature 1680℃,heating duration time 2 hours and liquid nitrogen quenching;3. The homogeneity of the synthesized K-feldspar glasses are:RSD% of major and trace elements are less than 5% and 10%, respectively. Lead isotopic compositions are 1.90779±0.00009 (208Pb/206Pb,2s),0.75899±0.00004 (207Pb/206Pb,2s),20.909±0.002 (206Pb/204Pb,2s),15.871±0.002 (207Pb/204Pb,2s)和39.888±0.005 (208Pb/204Pb,2s),while the relative RSD of these ratios are 0.007%,0.008%,0.016%,0.016% and 0.021%, respectively.更多还原