Magnesium isotopic variation of oceanic island basalts generated by partial melting and crustal recycling
Magnesium isotopic variation of oceanic island basalts generated by partial melting and crustal recycling
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部分熔融和地壳循环产生的洋岛玄武岩的镁同位素变化
DOI：
10.1016/j.epsl.2017.01.040
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发表时间：
2017-04
影响因子：
5.3
通讯作者：
Zeng Gang
中科院分区：
文献类型：
--
作者：
Zhong Yuan;Chen Li-Hui;Wang Xiao-Jun;Zhang Guo-Liang;Xie Lie-Wen;Zeng Gang
洋岛玄武岩(OIB)的放射性同位素在地球化学上具有多样性，这一特征通常被归因于记录其深部地幔来源的化学不均一性，其中显著的成分变化与不同数量的古代再循环地壳物质有关。尽管镁是地幔的主要成分，但OIB的镁同位素是否主要对应于深部地幔来源的不均一性或部分熔融等过程仍不清楚。在这里，我们介绍了夏威夷群岛、路易斯维尔海山和南太平洋蚀变洋壳样品的大洋界面镁同位素和微量元素组成数据。这些OIB的δ2 6 mg值范围为−0.2 9±0.0 7‰(2SD，n=17)，这一变化大约是已知的橄榄岩地幔成分变化(−0.2 3±0.0 4‰，2SD)的两倍。此外，碱性玄武岩(−0.31±0.04‰，2SD，n=12)比拉斑玄武岩(−0.24±0.02‰，2SD，n=5)相对富镁。与玄武岩和橄榄岩地幔相比，本研究所分析的蚀变洋壳具有较重的镁同位素组成(−0.18±0.08‰，2SD，n=13)。对我们和已发表的数据的评估表明，大多数OIB的δ26 mg值与熔融敏感的微量元素比率负相关，但它们与来源敏感的元素比率无关。这表明大多数油气田的镁同位素变化在很大程度上受不同程度的部分熔融作用的控制，而不受物源非均质性的控制。Nb/Zr(或La/Sm)与δ26 mg的负相关表明，镁同位素组成较重的蚀变洋壳更适合于常见的OIBs。然而，对于给定的熔融程度，路易斯维尔玄武岩的δ值比其他OIB低26 mg值，这表明有不同的来源，例如橄榄岩地幔。模拟计算表明，石榴石辉石岩(再循环洋壳蚀变)和石榴石橄榄岩的熔融都可以产生具有低δ26 mg特征的熔体，为低程度部分熔融。因此，如果部分熔融的程度能够独立地约束母岩浆的产生，就可以估算其源区的镁同位素组成，以研究深部地幔的化学不均质性。
Ocean island basalts (OIBs) are geochemically diverse in radiogenic isotopes, a feature that is commonly ascribed to record the chemical heterogeneity of their deep-mantle source, where significant compositional variation relates to variable amounts of ancient recycled crustal material. Although Mg is a major constituent of the mantle, it is still unclear whether Mg isotopes of OIBs predominantly correspond to deep-mantle source heterogeneity or processes such as partial melting. Here, we present Mg isotopic and trace-element compositional data for OIBs from the Hawaii islands, the Louisville seamounts, and for altered oceanic crust samples from the South Pacific. The δ 26 Mg value range of these OIBs is− 0.29±0.07‰(2SD, n= 17), which is a variation approximately twice as large as the known compositional variation of the peridotitic mantle (− 0.23±0.04‰, 2SD). Moreover, alkaline basalt (− 0.31±0.04‰, 2SD, n= 12) is relatively enriched in light Mg isotopes compared to tholeiitic basalt (− 0.24±0.02‰, 2SD, n= 5). In contrast, altered oceanic crust analyzed in this study has heavier Mg isotopic composition (− 0.18±0.08‰, 2SD, n= 13) relative to the basalts and to the peridotitic mantle. An evaluation of our and published data shows that the δ 26 Mg values of most OIBs negatively correlate with melting-sensitive trace-element ratios, but that they are uncorrelated with source-sensitive elemental ratios. This implies that Mg isotopic variation in most OIBs is largely controlled by variable degrees of partial melting and not by source heterogeneity. Negative correlation between Nb/Zr (or La/Sm) versus δ 26 Mg suggests that altered oceanic crust with heavier Mg isotopic composition is a more suitable source candidate for common OIBs. However, for a given melting degree, Louisville basalts have lower δ 26 Mg values than other OIBs, suggesting a different source, eg a peridotitic mantle. Modeling calculations suggest that melting of both garnet pyroxenite (recycled altered oceanic crust) and garnet peridotite can generate melts with low-δ 26 Mg signature for low-degree partial melting. Therefore, if the degree of partial melting can be independently constrained for the generation of parental OIB magma, the Mg isotopic compositions of their source can be estimated to investigate the chemical heterogeneity of the deep mantle.
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影响因子：
5.3
作者：
P. V. Strandmann;K. Burton;R. James;P. Calsteren;S. Gíslason;B. Sigfússon
通讯作者：
P. V. Strandmann;K. Burton;R. James;P. Calsteren;S. Gíslason;B. Sigfússon
DOI：
10.1146/annurev-earth-040809-152450
发表时间：
2010-04
影响因子：
14.9
作者：
W. White
通讯作者：
W. White
影响因子：
12.1
作者：
C. Timm;K. Hoernle;R. Werner;F. Hauff;P. Bogaard;J. White;N. Mortimer;C. Garbe-Schönberg
通讯作者：
C. Timm;K. Hoernle;R. Werner;F. Hauff;P. Bogaard;J. White;N. Mortimer;C. Garbe-Schönberg
DOI：
10.1029/gm043p0283
发表时间：
2013-03
期刊：
Geophysical monograph
影响因子：
--
作者：
Q. Cheng;K. Park;J. Macdougall;A. Zindler;G. Lugmair;H. Staudigel;J. Hawkins;P. Lonsdale
通讯作者：
Q. Cheng;K. Park;J. Macdougall;A. Zindler;G. Lugmair;H. Staudigel;J. Hawkins;P. Lonsdale
影响因子：
5
作者：
Shui‐Jiong Wang;F. Teng;J. Scott
通讯作者：
Shui‐Jiong Wang;F. Teng;J. Scott