Hawaiian hot spot dynamics as inferred from the Hf and Pb isotope evolution of Mauna Kea volcano
Hawaiian hot spot dynamics as inferred from the Hf and Pb isotope evolution of Mauna Kea volcano
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从莫纳克亚火山的 Hf 和 Pb 同位素演化推断夏威夷热点动态
DOI：
10.1029/2002gc000340
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发表时间：
2003
期刊：
影响因子：
3.7
通讯作者：
F. Albarède
中科院分区：
文献类型：
--
作者：
J. Blichert‐Toft;D. Weis;C. Maerschalk;A. Agranier;F. Albarède
本工作报告的多个收集电感耦合等离子体质谱（MC‐ICP‐MS）测量的Hf和Pb的同位素组成的前3公里的深芯检索的夏威夷科学钻探项目。测量涵盖了标准地球化学参考集的所有样品、深孔的玻璃和先导孔的复制品。与莫纳克亚山相比，莫纳罗亚山的Hf和Pb的放射成因较少。在深核中，εHf和208 Pb/204 Pb的变化是渐进的，但208 Pb */206 Pb * 的变化是明显的不连续。样品的碱度与同位素组成之间没有相关性。具体而言，先导孔样品的Hf同位素组成与HSDP-2岩芯中从相似深度提取的样品的Hf同位素组成并不完全相同，这表明在侵位时存在陡峭的地形或记录了不同的喷发序列。208Pb ~*/206Pb ~* 与3He ~*/4He（M. D. Kurz等人（来自夏威夷科学钻探项目的莫纳克亚火山盾状熔岩中的快速氦同位素变化，提交给地球化学地球物理学地球系统公司，2002年））要求偶尔掺入一种类似于基拉韦厄或洛伊希喷发中心喷发的玄武岩的成分（该成分称为K/L）。这些数据表明，大约50万年前，莫纳克亚火山正在挖掘一个地幔源，与今天基拉韦厄挖掘的地幔源相似。铅和他的同位素变异不能占在一个封闭的系统中的放射性向内生长，但需要混合的地幔源成分与不同的脱气历史。莫纳克亚火山样品中同位素和浓度数据的时间序列跨越了大约35万年的历史，表明熔融柱中地球化学模式的重现。忽略最新的碱性样品，我们发现εHf和207 Pb/204 Pb的主导波动对应于50，000年的周期。对于La/Yb、Zr/Nb、87 Sr/86 Sr、206 Pb/204 Pb、207 Pb/206 Pb和208 Pb/206 Pb，存在一个约为1000 μ m的优势周期。18，000年已获得。一旦考虑到谐波的存在，导向孔和HDSP-2堆芯的同位素谱之间的一致性非常好。K/L分量的输入似乎不是周期性的。我们使用这些复发间隔结合推导出的浮力通量和地震证据的散射体的最大尺寸的上升流率约束的夏威夷羽状管道的半径在10-50公里的范围内，上升流速度在0.13-3米/年的范围内。管道中不均匀性的合理垂直长度尺度为6.5-160 km。
The present work reports multiple collector inductively coupled plasma mass spectrometry (MC‐ICP‐MS) measurements of the isotopic compositions of Hf and Pb in the first 3 km of the deep core retrieved by the Hawaii Scientific Drilling Project. The measurements cover all the samples from the standard geochemical reference set, glasses from the deep hole, and replicates from the pilot hole. Both Hf and Pb are less radiogenic in Mauna Loa compared to Mauna Kea. The transition between Mauna Kea and Mauna Loa lavas in the deep core is progressive for εHf and 208Pb/204Pb, but a sharp discontinuity is observed for 208Pb*/206Pb*. There is no correlation between the alkalinity of the samples and isotopic composition. In detail, the Hf isotope compositions of samples from the pilot hole are not all identical to those of the HSDP‐2 core for samples retrieved from a similar depth, suggesting that steep topography existed at the time of emplacement or that a different eruptive sequence was recorded. The strong correlation between 208Pb*/206Pb* and 3He/4He (He data from M. D. Kurz et al. (Rapid helium isotopic variability in Mauna Kea shield lavas from the Hawaiian Scientific Drilling Project, submitted to Geochemistry Geophysics Geosystems, 2002)) requires the episodic incorporation of a component that resembles the basalts erupted by either Kilauea or the Loihi eruptive centers (this component is referred to as K/L). The data suggest that some 500 kyr ago, Mauna Kea was tapping a mantle source similar to that tapped by Kilauea today. Isotopic variability of Pb and He cannot be accounted for by radiogenic ingrowth in a closed system, but requires the mixing of mantle source components with distinct outgassing histories. The time series of isotopic and concentration data in Mauna Kea samples spanning about 350,000 years of age indicate the recurrence of geochemical patterns in the melting column. Ignoring the most recent alkalic samples, we find that the dominant fluctuations of εHf and 207Pb/204Pb correspond to a period of 50,000 years. For La/Yb, Zr/Nb, 87Sr/86Sr, 206Pb/204Pb, 207Pb/206Pb, and 208Pb/206Pb, a dominant period of ca. 18,000 years is obtained. Once provision is made for the existence of harmonics, the consistency between the isotopic spectrum of the pilot hole and the HDSP‐2 core is very good. The input of the K/L component does not seem to be periodic. We use these recurrence intervals in conjunction with the upwelling rate deduced from buoyancy flux and seismic evidence of the maximum dimension of scatterers to constrain the radius of the Hawaiian plume conduit to be in the range of 10–50 km and the upwelling velocity to be in the range of 0.13–3 m/yr. Plausible vertical length scales of heterogeneities in the conduit are 6.5–160 km.