Magnesium isotopic variations in loess: Origins and implications
Magnesium isotopic variations in loess: Origins and implications
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DOI：
10.1016/j.epsl.2013.05.010
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发表时间：
2013-07
影响因子：
5.3
通讯作者：
Kang-Jun Huang;F. Teng;Amira Elsenouy;Wangye Li;Z. Bao
中科院分区：
文献类型：
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作者：
Kang-Jun Huang;F. Teng;Amira Elsenouy;Wangye Li;Z. Bao
黄土沉积物是研究第四纪气候变化和估计上大陆地壳平均化学成分的重要大陆档案。在这里，我们报告了来自中国、阿根廷和欧洲的 19 个黄土样本的高精度镁同位素数据，这些数据以前用于估计上大陆壳的成分。结果表明，全球黄土样品镁同位素组成不均匀，δ26Mg（26Mg/24Mg比值与DSM3标准的每密耳偏差）值范围为-1.64‰至+0.25‰，加权平均值为-0.89‰，比壳和幔硅酸盐都轻。黄土的 MgO 含量和 δ26Mg 与 CaO/Al2O3 比率呈正相关，表明碳酸盐和次生硅酸盐矿物之间存在双组分混合。黄土镁同位素组成的巨大变化是多种因素共同作用的结果，包括来源异质性、黄土运输过程中的风成分选以及黄土矿床形成过程中的化学风化作用。我们的研究结果表明，黄土的镁同位素组成有可能成为表征古气候变化的代理指标，但由于黄土沉积形成过程中同位素不同成分的混合、分选和同位素分馏，可能不能代表上陆壳的平均镁同位素组成。
Loess deposits serve as important continental archives for studying Quaternary climatic variations and for estimating the average chemical composition of the upper continental crust. Here, we report high-precision Mg isotopic data for 19 loess samples from China, Argentina and Europe, which were previously used to estimate the composition of the upper continental crust. The results show that global loess samples have heterogeneous Mg isotopic compositions, with δ26Mg (per mil deviation of the26Mg/24Mg ratio from the DSM3 standard) values ranging from −1.64‰ to +0.25‰ and a weighted average of −0.89‰, which is lighter than both crust and mantle silicates. MgO content and δ26Mg of loess positively correlate with CaO/Al2O3ratio, suggesting a two-component mixing between carbonates and secondary silicate minerals. The large variation in Mg isotopic composition of loess results from a combination of factors, including source heterogeneity, eolian sorting during transport of the loess and chemical weathering during formation of the loess deposit. Our results suggest that Mg isotopic composition of loess has potential to be a proxy indicator to characterize the paleoclimatic change, but may not represent the average Mg isotopic composition of the upper continental crust due to mixing, sorting of isotopically distinct components and isotope fractionation during loess deposit formation.