Magnesium Isotopes as a Tracer of Crustal Materials in Volcanic Arc Magmas in the Northern Cascade Arc
Magnesium Isotopes as a Tracer of Crustal Materials in Volcanic Arc Magmas in the Northern Cascade Arc
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DOI：
10.3389/feart.2018.00021
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发表时间：
2018-03
影响因子：
2.9
通讯作者：
A. Brewer;F. Teng;E. Mullen
中科院分区：
文献类型：
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作者：
A. Brewer;F. Teng;E. Mullen
对15个北喀斯喀特弧玄武岩和安山岩进行了镁同位素分析，以研究地壳对该岩浆系统的贡献程度和方式。这些样品的δ 26 Mg值变化范围从洋岛玄武岩（最轻的为-0.33 ± 0.07‰）到较重的组分（最重的为-0.15 ± 0.06‰）。所观察到的化学和同位素组成范围与迄今在环太平洋俯冲带和加勒比地区评估的其他火山弧相似。重镁同位素组成的最好的解释同化和分离结晶内的深陆壳与可能的轻微贡献，除了俯冲板片衍生流体的原始岩浆。大量混合的沉积物进入原始岩浆或地幔源和部分熔融的石榴子石丰富的橄榄岩是不可能产生的Mg同位素组成的观察范围。结果表明，镁同位素可能是一个有用的示踪地壳输入到岩浆，补充传统的方法，如放射性同位素和微量元素数据，特别是在案件中，其中一个高分数的地壳物质已被添加。
Fifteen North Cascade Arc basalts and andesites were analyzed for Mg isotopes to investigate the extent and manner of crustal contributions to this magmatic system. The δ26Mg of these samples vary from within the range of ocean island basalts (the lightest being -0.33 ± 0.07‰) to heavier compositions (as heavy as -0.15 ± 0.06‰). The observed range in chemical and isotopic composition is similar to that of other volcanic arcs that have been assessed to date in the circum-pacific subduction zones and in the Caribbean. The heavy Mg isotope compositions are best explained by assimilation and fractional crystallization within the deep continental crust with a possible minor contribution from the addition of subducting slab-derived fluids to the primitive magma. The bulk mixing of sediment into the primitive magma or mantle source and the partial melting of garnet-rich peridotite are unlikely to have produced the observed range of Mg isotope compositions. The results show that Mg isotopes may be a useful tracer of crustal input into a magma, supplementing traditional methods such as radiogenic isotopic and trace element data, particularly in cases in which a high fraction of crustal material has been added.