Mg isotopic composition of carbonate: insight from speleothem formation
Mg isotopic composition of carbonate: insight from speleothem formation
复制标题
DOI：
10.1016/s0012-821x(02)00675-1
复制
发表时间：
2002-07-15
影响因子：
5.3
通讯作者：
O'Nions, RK
中科院分区：
文献类型：
--
作者：
Galy, A;Bar-Matthews, M;O'Nions, RK
采用多接收器电感耦合质谱（MC-ICP-MS）技术，以SRM 980为标准，同时对Mg-24、Mg-25和Mg-26同位素组成进行了高精度测量。本文介绍了四个洞穴（一个在法国阿尔卑斯山，三个在以色列）中的低镁方解石洞穴沉积物及其相关的寄主岩石和沃茨的数据，涵盖了各种气候条件。此外，还介绍了喜马拉雅山三种白云岩和三种石灰岩的资料。δ（26）Mg和δ（25）Mg的总变异分别为4.13 ‰和2.14 ‰。这是测量不确定性的35倍，清楚地表明镁的地球同位素组成并不独特。每个洞穴显示三角洲（26）镁值的特征范围，归因于当地水的同位素组成。钟乳石滴水中Mg同位素组成与现代洞穴沉积物中Mg同位素组成的差异被解释为在4- 18 ℃温度范围内碳酸盐沉淀过程中Mg同位素分馏的结果。低镁方解石轻同位素富集1.35ppm/AMU，对温度的依赖性小于0.02ppm/AMU/℃。尽管地质背景不同，但所研究的白云岩的δ（26）Mg比石灰岩的δ（26）Mg高2.0+/-1.2ppm。总之，这些结果表明，碳酸盐镁同位素组成的矿物控制和弱的温度效应。（C）2002 Elsevier Science B. V.保留所有权利。
Simultaneous high-precision measurement of Mg-24, Mg-25 and Mg-26 isotopic compositions were made by multiple collector inductively coupled mass spectrometry (MC-ICP-MS) relative to the international standard SRM980. Data are presented on low-Mg calcite speleothems and their associated host rocks and waters from four caves, one in the French Alps and three in Israel, covering various climate conditions. In addition, data are presented on three dolostones and three limestones from the Himalaya. The overall variation is 4.13parts per thousand and 2.14parts per thousand in delta(26)Mg and delta(25)Mg, respectively. This is 35 times the uncertainty of the measurements and clearly demonstrates that the terrestrial isotopic composition of Mg is not unique. Each speleothem shows a characteristic range of delta(26)Mg values that are attributed to the isotopic composition of the local water. Differences between the isotopic composition of Mg in the water dripping from stalactites and that of the modern speleothem are interpreted as being due to Mg isotopic fractionation during carbonate precipitation in the temperature range of 4-18degreesC. The low-Mg calcite is enriched in light isotopes by 1.35parts per thousand/AMU and the dependence on temperature has been found to be less than 0.02parts per thousand/AMU/degreesC. Despite various geological settings, the delta(26)Mg of the studied dolostones is 2.0+/-1.2parts per thousand higher than the delta(26)Mg of the limestones. All together, these results suggest a strong mineralogical control and a weak temperature effect on the Mg isotopic composition of carbonate. (C)2002 Elsevier Science B.V. All rights reserved.