Hafnium isotopic variations in East Atlantic intraplate volcanism
Hafnium isotopic variations in East Atlantic intraplate volcanism
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东大西洋板内火山活动中的铪同位素变化
DOI：
10.1007/s00410-010-0580-5
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发表时间：
2011
影响因子：
3.5
通讯作者：
Schmincke H- U
中科院分区：
文献类型：
--
作者：
Geldmacher J;Hoernle K;Hanan BB;Blichert-Toft J;Hauff F;Gill JB;Schmincke H- U
东大西洋25° ~ 37° N之间的广阔板内火山活动带被认为是由两个相邻的热点轨迹（马德拉和加那利轨迹）形成的，这两个热点轨迹具有系统性的不同同位素特征，反映了不同的地幔源成分。为了检验这一模型，Hf同位素比值从火山岩从所有个别岛屿和所有主要海山在这项研究中。与已发表的Nd同位素变化（6个εNd单位）相比，176 Hf/177 Hf比值范围更大（14个εHf单位）。从拟议的马德拉热点轨道的样品具有最放射性的Hf同位素组成（176 Hf/177 Hfmup至0.283335），横跨整个领域的大西洋中部MORB。它们在Nd与Hf同位素图上形成一个相对狭窄的拉长趋势（延伸超过10 εHf单位），介于亏损的N-MORB样端元和位于Nd-Hf地幔阵列上或略低于Nd-Hf地幔阵列的中等富集成分之间，与Hanan和Graham（1996）提出的“C”地幔成分重叠。相比之下，来自加那利热点的所有样品都位于地幔阵列下方（176 Hf/177 Hfm = 0.282943-0.283067），形成了一个密度更大的星团，成分变化较小（约4个εHf单位）。该集群福尔斯落在（1）低Hf同位素HIMU样端元，（2）更贫化的组成，（3）马德拉趋势的中等富集端之间。新的Hf同位素数据证实了东大西洋加那利和马德拉域的一般地球化学区别。然而，这两个域似乎都有一个共同的、中等富集的端元，具有类似“C”的同位素组成，被认为代表俯冲的、<1 Ga年龄的海洋岩石圈（海洋地壳和可能的少量沉积物添加物）。富集的、类似HIMU的Canary域端元的176 Hf/177 Hf比值较低，表明洋壳岩石圈的贡献较老，其再循环年龄≥ 1Ga。
The broad belt of intraplate volcanism in the East Atlantic between 25° and 37° N is proposed to have formed by two adjacent hotspot tracks (the Madeira and Canary tracks) that possess systematically different isotopic signatures reflecting different mantle source compositions. To test this model, Hf isotope ratios from volcanic rocks from all individual islands and all major seamounts are presented in this study. In comparison with published Nd isotope variations (6 εNd units),176Hf/177Hf ratios span a much larger range (14 εHf units). Samples from the proposed Madeira hotspot track have the most radiogenic Hf isotopic compositions (176Hf/177Hfmup to 0.283335), extending across the entire field for central Atlantic MORB. They form a relatively narrow, elongated trend on the Nd vs. Hf isotope diagram (stretching over > 10 εHf units) between a depleted N-MORB-like endmember and a moderately enriched composition located on, or slightly below, the Nd–Hf mantle array, which overlaps the proposed “C” mantle component of Hanan and Graham (1996). In contrast, all samples from the Canary hotspot track plot below the mantle array (176Hf/177Hfm= 0.282943–0.283067) and form a much denser cluster with less compositional variation (~4 εHf units). The cluster falls between (1) a low Hf isotope HIMU-like endmember, (2) a more depleted composition, and (3) the moderately enriched end of the Madeira trend. The new Hf isotope data confirm the general geochemical distinction of the Canary and Madeira domains in the East Atlantic. Both domains, however, seem to share a common, moderately enriched endmember that has “C”-like isotope compositions and is believed to represent subducted, <1-Ga-old oceanic lithosphere (oceanic crust and possibly minor sediment addition). The lower176Hf/177Hf ratio of the enriched, HIMU-like Canary domain endmember indicates the contribution of oceanic lithosphere with somewhat older recycling ages of ≥1 Ga.
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作者：
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通讯作者：
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DOI：
--
发表时间：
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期刊：
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影响因子：
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作者：
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通讯作者：
D. Graham
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影响因子：
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作者：
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通讯作者：
B. Berning