Temporal changes in Nd isotopic composition of Piton de la Fournaise magmatism (Réunion Island, Indian Ocean)
Temporal changes in Nd isotopic composition of Piton de la Fournaise magmatism (Réunion Island, Indian Ocean)
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Piton de la Fournaise 岩浆活动（印度洋留尼旺岛）Nd 同位素组成的时间变化
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发表时间：
2004
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通讯作者：
B. Luais
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作者：
B. Luais
对留尼汪岛Piton de la Fourneise火山最后530 ka火山活动的12个历史样品和57个岩心样品进行了Nd同位素研究，并对历史样品进行了新的锶同位素分析。岩心样品是从RemParts和Langevin Rivers深峡谷(约1000米)的悬崖上获得的。玄武岩(MgO=5~9wt.%)、高镁玄武岩(MgO=10~20wt.%)、富斜长玄武岩和分异样品(SiO_2=48~53wt.%)四种岩石在熔岩段中随机分布。Nd同位素比值的总体变化(0.512751~0.512902)很小，但意义重大。Nd同位素变化的范围比文献中所描述的范围更大，并向更低的值延伸。随着时间的推移，Nd同位素比值增加，并与碱度指数呈广泛的负相关。较老的碱性残留物样品(527~290ka)(平均εND=+3.26)比较年轻的拉斑玄武岩样品(70~40ka)(平均εND=+4.17)和历史熔岩(1901~1956年)(平均εND=+4.74)具有较低的143ND/144ND比值。对同一组样品(RemParts和Langevin系列[Albarède等人，1997年]；历史系列，本研究)的143Nd/144Nd值与可用87Sr/86Sr值的比较表明，锶和钕同位素之间没有相关性。历史拉斑玄武岩样品的高Nd值代表了留尼汪岛热柱的同位素组成。超过530ka的Nd同位素比值的增加反映了随着时间的推移，富集组分对留尼汪岛羽流的贡献减少的影响。这种富集组分将以孤立的斑点形式出现在地幔源区。
A Nd isotopic study of twelve historical samples and fifty‐seven core samples covering the last 530 ka of volcanic activity of the Piton de la Fournaise volcano of Réunion Island was undertaken, with additional new Sr isotopic analyses of historical samples. The core samples were obtained from the cliffs of the deep (ca.1000 m) canyons of the Remparts and Langevin Rivers. Four types of rocks, namely basalts (MgO = 5–9 wt.%), high‐Mg basalts (MgO = 10–20 wt.%), plagioclase‐rich basalts, and differentiated samples (SiO2 = 48–53 wt.%) occur randomly throughout the lava sections. The overall variations in Nd isotopic ratios (0.512751 to 0.512902) are small, but significant. The range of Nd isotopic variations is larger than previously described in the literature, and extends toward lower values. Nd isotopic ratios increase through time and are broadly negatively correlated with the alkalinity index. The older alkaline Remparts samples (527–290 ka) (average εNd = +3.26) exhibit lower 143Nd/144Nd ratios than the younger tholeiitic Langevin samples (70–40 ka) (average εNd = +4.17) and the historical lavas (1901–1956) (average εNd = +4.74). Comparison of 143Nd/144Nd ratios with available 87Sr/86Sr ratios on the same set of samples (Remparts and Langevin series [Albarède et al., 1997]; historical series, this study) shows no correlation between Sr and Nd isotopes. It is suggested that the high Nd isotopic ratios of historical tholeiitic samples would be representative of the isotopic composition of the Réunion plume. The increase in Nd isotopic ratios over 530 ka reflects the effect of decreasing contribution of an enriched component to the Réunion plume through time. This enriched component would occur as isolated blobs in the mantle source.