Isotope geochemistry of Quaternary deposits from the arid lands in northern China
Isotope geochemistry of Quaternary deposits from the arid lands in northern China
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DOI：
10.1016/0012-821x(94)90195-3
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发表时间：
1994-10
影响因子：
5.3
通讯作者：
Cong-Qiang Liu;A. Masuda;A. Okada;S. Yabuki;Z. Fan
中科院分区：
文献类型：
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作者：
Cong-Qiang Liu;A. Masuda;A. Okada;S. Yabuki;Z. Fan
塔里木盆地西南部、北天山、中国东北和黄土高原中部的各种第四纪沉积物（湖相、沙漠砂、河流、黄土和黄土状沉积物）的Nd（0）值范围为− 5 ~ − 12.8，147 Sm 144 Nd值范围为0.110 ~ 0.140。它们的Nd亏损地幔模式年龄介于1.50 ~ 1.92Ga之间，平均值为1.7Ga。Th/Sc比在0.1至2的宽范围内变化。将这些地球化学特征与古老的澳大利亚页岩和现代太平洋尘埃进行比较，表明在地质时期，幔源物质不断输入地壳。北天山地区的矿床具有明显不同的化学和同位素特征，Sm-Nd、143 Nd-144 Nd、87 Sr-86 Sr和La-Lu、Th-Sc比值明显高于其它地区。这表明地质控制的本地源，具有整体年轻和富集的基本组成部分。黄土高原中部两个黄土样品的δ Ce（0）值分别为+1.8和3.9，对应于2.2和3.4Ga的亏损地幔模式年龄。与Rb <$Sr系统一样，由于沉积作用对La Ce的分馏作用，地壳中La <$Ce同位素系统的演化可能与Sm <$Nd系统在一定程度上不耦合。黄土沉积物和沙漠砂在同位素组成上没有区别，但化学组成有所不同。我们的结论是，黄土可以起源于沙漠过程中，沙漠砂和黄土的化学差异可能是由于在沙漠过程中的矿物分选和风成运输。黄土高原中部的黄土沉积物在化学和同位素组成上与塔里木盆地西南部的荒漠黄土沉积物相似，而与北天山的荒漠黄土沉积物不同。因此，高原黄土的源区可能在塔里木盆地，而不是在北天山。
Quaternary deposits of various types (lacustrine, desert sand, river, loess and loess-like deposits) from the southwestern Tarim Basin, North Tianshan, northeast China and the central Loess Plateau exhibit an ϵ Nd (0) range from− 5 to− 12.8 and a 147 Sm 144 Nd range from 0.110 to 0.140. Their Nd-depleted mantle model ages are between 1.50 and 1.92 Ga, with a mean value of 1.7 Ga. Th Sc ratios vary over a wide range from 0.1 to 2. Comparison of these geochemical signatures with those of the old Australian shales and modern Pacific Ocean dust suggests a continuous input of mantle-derived material into the crust over geological time. The deposits from the North Tianshan show clearly different chemical and isotopic features, with significantly higher Sm Nd, high 143 Nd 144 Nd, low 87 Sr 86 Sr, and low La Lu and Th Sc ratios relative to those in the deposits from the other areas. This indicates a geological control on the local source, which has an overall young age and an enrichment of basic components. The ϵ Ce (0) values of two loess samples from the central Loess Plateau are+ 1.8 and 3.9, corresponding to depleted mantle model ages of 2.2 and 3.4 Ga. Like the Rb Sr system, the evolution of the La Ce isotopic system in the crust may be to some extent decoupled from the Sm Nd system, due to La Ce fractionation by sedimentary processes. The loess deposits and the desert sand are not distinguishable in isotopic composition, but show somewhat different chemical compositions. We conclude that the loess can have originated from desert processes, since the difference in the chemistry of the desert sand and loess may result from mineral sorting during desert processes and aeolian transportation. The loess deposits on the central Loess Plateau chemically and isotopically resemble the desert loess deposits in the southwestern Tarim Basin but do not resemble those of the North Tianshan. Accordingly, the loess on the plateau may have a source region in the Tarim Basin but clearly not in the North Tianshan.