Evaluating the effect of leaching on trace element and Nd-Pb isotopic systematics in continental basalts
Evaluating the effect of leaching on trace element and Nd-Pb isotopic systematics in continental basalts
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评价淋滤对陆相玄武岩微量元素和 Nd-Pb 同位素系统的影响
DOI：
10.1016/j.sesci.2018.12.001
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发表时间：
2019-03-01
影响因子：
2
通讯作者：
Guan, Yili
中科院分区：
文献类型：
--
作者：
Zhang, Yan;Wei, Xun;Guan, Yili
为了减少或消除海水相互作用对岩浆Sr、Pb同位素特征的二次影响，大多对海底岩石粉末进行淋滤。然而，浸出对微量元素含量的影响相对较差。为了研究这种影响，我们比较了微量元素和Nd-Pb同位素数据酸浸出类似的290马柯坪玄武岩在塔里木大火成岩省（中国西北）与未沥滤数据相同的岩石。浸出样品颗粒（粒径0.6-1.0 mm）的稀土元素（REE）、Y、Th和U含量比同一样品未浸出颗粒低10-65%，而其他微量元素不受影响。Sm/Nd、Lu/Hf、U/Pb和Th/Pb比值在淋溶和未淋溶样品颗粒之间通过酸浸分级。Nd同位素值不受淋溶的影响，但Pb-208/Pb-204和Pb-206/Pb-204值明显低于未淋溶样品。X射线衍射分析结果表明，在酸浸过程中，次生绿帘石的去除会导致稀土元素、Y、Th、U含量、Sm/Nd、Lu/Hf、U/Pb、Th/Pb比值、Pb-208/Pb-204和Pb-206/Pb-204值的分馏。这些结果表明，当样品被强酸（> 1 N HCl）浸出时，其微量元素不能用于示踪来源和岩石成因。如果将沥滤应用于旧的（例如，>100 Ma）大陆玄武岩为了消除样品收集、储存、锯切和破碎过程中的污染，应在相同的浸出样品上获得用于计算初始铅同位素值的Th/Pb和U/Pb比。广州地球化学研究所版权所有（C）2019制作和主办：Elsevier B. V.
Leaching technique was mostly carried out on submarine rock powder to minimize or eliminate secondary effect of seawater interaction on Sr and Pb isotope magmatic signatures. However, the effect of leaching on trace element contents is comparatively poorly established. To investigate such effects, we have compared trace element and Nd-Pb isotopic data for acid leached similar to 290 Ma Keping basalts in the Tarim Large Igneous Province (NW China) with unleached data on the same rocks. Rare earth elements (REE), Y, Th and U contents of leached sample grains (0.6-1.0 mm size) are 10-65% lower than those of unleached grains of the same sample, whereas other trace elements are not affected. Sm/Nd, Lu/Hf, U/Pb and Th/Pb ratios are fractionated by acid leaching between leached and unleached sample grains. Nd isotope values are unaffected by leaching, but Pb-208/Pb-204 and Pb-206/Pb-204 values of leached samples are significantly lower than those of unleached samples. X-ray diffraction results suggest that removal of secondary epidote during the acid leaching process could result in the fractionation of REE, Y, Th and U contents, and Sm/Nd, Lu/Hf, U/Pb and Th/Pb ratios, and Pb-208/Pb-204 and Pb-206/Pb-204 values. These results suggest that when the samples have been leached with strong acid (>1N HCl), their trace element cannot be used to trace the sources and petrogenesis. If leaching is applied to old (e.g., >100 Ma) continental basalts in order to eliminate contamination during sample collection, storage, sawing and crushing, Th/Pb and U/Pb ratios used to calculate the initial Pb isotope values, should be obtained on the same leached samples. Copyright (C) 2019, Guangzhou Institute of Geochemistry. Production and hosting by Elsevier B.V.