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唐波, 王景腾, 付勇. 不同地质储库中的镁同位素组成及碳酸盐矿物形成过程中的镁同位素分馏控制因素[J]. 岩矿测试, 2020, 39(2): 162-173. DOI: 10.15898/j.cnki.11-2131/td.201908120122
引用本文: 唐波, 王景腾, 付勇. 不同地质储库中的镁同位素组成及碳酸盐矿物形成过程中的镁同位素分馏控制因素[J]. 岩矿测试, 2020, 39(2): 162-173. DOI: 10.15898/j.cnki.11-2131/td.201908120122
TANG Bo, WANG Jing-teng, FU Yong. Magnesium Isotope Composition of Different Geological Reservoirs and Controlling Factors of Magnesium Isotope Fractionation in the Formation of Carbonate Minerals-A Summary of Previous Results[J]. Rock and Mineral Analysis, 2020, 39(2): 162-173. DOI: 10.15898/j.cnki.11-2131/td.201908120122
Citation: TANG Bo, WANG Jing-teng, FU Yong. Magnesium Isotope Composition of Different Geological Reservoirs and Controlling Factors of Magnesium Isotope Fractionation in the Formation of Carbonate Minerals-A Summary of Previous Results[J]. Rock and Mineral Analysis, 2020, 39(2): 162-173. DOI: 10.15898/j.cnki.11-2131/td.201908120122

不同地质储库中的镁同位素组成及碳酸盐矿物形成过程中的镁同位素分馏控制因素

Magnesium Isotope Composition of Different Geological Reservoirs and Controlling Factors of Magnesium Isotope Fractionation in the Formation of Carbonate Minerals-A Summary of Previous Results

  • 摘要: 镁同位素在低温地球化学过程中显著的分馏效应,是其示踪地球表生环境演化及物质循环的基础。本文在前人研究的基础上,对地球上不同地质储库中的镁同位素组成及碳酸盐矿物形成过程中的镁同位素分馏控制因素进行了总结:火成岩的镁同位素组成较均一;风化产物总体富集重的镁同位素,且变化较大;碳酸盐岩中灰岩相对白云岩富集轻的镁同位素,但总体上富集轻的镁同位素;岩石类型、风化强度以及植被等因素对河流地表水的镁同位素组成影响较大,导致地表水的镁同位素组成总体变化较大;海水的镁同位素组成均一,平均值约为-0.83‰;低温条件下,控制碳酸盐矿物无机成因过程中镁同位素分馏的因素有矿物相、沉淀速率和温度,其中矿物相是主要控制因素;生物成因碳酸盐矿物镁同位素组成与生物体对含镁碳酸盐矿物的利用形式有关,除了需考虑与无机碳酸盐沉淀类似的控制因素外,还需考虑不同物种对轻、重镁同位素的选择性吸收能力;因生物成因海相碳酸盐矿物几乎都是由最初的无定形相碳酸盐转变而来,故生物成因海相碳酸盐矿物的镁同位素特征不能代表生成无定形相碳酸盐的流体的镁同位素特征。镁同位素在低温条件下具有良好的分馏效应,随着分析测试技术的发展及不同地质储库中镁同位素组成数据的积累和完善,有关表生环境中镁同位素分馏机制的许多问题将逐步得到解决,镁同位素在揭示地球表生环境演化及物质循环方面将发挥更大的作用。

     

    Abstract:
    BACKGROUNDMagnesium isotope fractionation effect during low-temperature geochemical processes is the foundation of tracing supergene evolution and material cycle of the earth.
    OBJECTIVESTo summarize the magnesium isotope composition of different geological reservoirs and investigate the controlling factors of the magnesium isotope fractionation during the formation of carbonate minerals.
    METHODSSystematic collection and summary of previous research results.
    RESULTSMagnesium isotope compositions of igneous rocks were relatively homogeneous. The weathering products were relatively enriched in heavy isotopes of magnesium with significant variation. Carbonate rocks showed enrichment in light isotopes of magnesium in general. The large variation of magnesium isotope composition of river water was affected by lithology, weathering degree and vegetation. Magnesium isotope composition of seawater was homogeneous with an average of -0.83‰. At low temperature, the factors controlling the fractionation of magnesium isotopes in the inorganic process of carbonate minerals were mineral phase, precipitation rate and temperature, of which mineral phase was the main controlling factor. The factors influencing the magnesium isotope composition of biogenic carbonate minerals were forms of utilization of magnesium carbonate minerals by organisms. In addition to considering the mechanisms that were similar to inorganic carbonate precipitation, the selective absorption of light and heavy magnesium isotopes by different species should be considered. Almost all biogenic marine carbonate minerals were transformed from the original amorphous phase carbonate precursor, and their original magnesium isotope composition was masked by the later magnesium isotope composition during transformation. Therefore, the magnesium isotope composition of biogenic marine carbonate minerals cannot represent the fluid isotope composition from which the original amorphous carbonate precursor formed.
    CONCLUSIONSMagnesium isotopes have a good fractionation effect at low temperature. With the development of analytical technology and the accumulation and improvement of magnesium isotope composition data in different geological reservoirs, many problems related to the mechanism of magnesium isotope fractionation in the supergene environment will be solved gradually. Magnesium isotopes will play a greater role in revealing the evolution of the supergene environment and the material cycle of the earth.

     

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