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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Grand Comore Island: A well-constrained 'low He-3/He-4' mantle plume
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Grand Comore Island: A well-constrained 'low He-3/He-4' mantle plume

机译：大科莫尔岛：受约束的“低He-3 / He-4”地幔柱

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摘要

We report He isotope (He-3/He-4) variations in samples from alkali basaltic and basanitic lava flows from Grande Comore Island complemented by existing[1,2] [C. Class, S.L. Goldstein, Plume-lithosphere interactions in the ocean basins: constraints from the source mineralogy. Earth Planet. Sci. Lett., 150 (1997) 245-260, C. Class, S.L. Goldstein, R. Altherr, P. Bachechlery, The process of plume-lithosphere interaction in the ocean basins-the case of Grande Comore. J. Petrel., 39 (5) (1998) 881903] and new Sr-Nd-Pb isotope ratios and major and trace element abundances. He isotope data in samples from Tristan da Cunha and Gough islands and the Huri Hills in Kenya are reported also. Grande Comore He-3/He-4 ratios vary between 5.05 and 7.08 R-A (He-4/He-3 approximate to 141,000-101,000). Chemical and Sr-Nd-Pb isotopic variations of Grande Comore lavas were previously shown to reflect melts derived from the deep mantle plume and the shallow lithospheric mantle[1-3] [C. Class, S.L. Goldstein, Plume-lithosphere interactions in the ocean basins: constraints from the source mineralogy. Earth Planet. Sci. Lett., 150 (1997) 245-260, C. Class, S.L. Goldstein, R. Altherr, P. Bachechlery, The process of plume-lithosphere interaction in the ocean basins-the case of Grande Comore. J. Petrol., 39 (5) (1998) 881-903, C. Claude-Ivanaj, B. Bourdon, C.J. Allegre, Ra-Th-Sr isotope systematics in Grande Comore Island: a case study of plume-lithosphere interaction. Earth Planet. Sci. Lett. 164 (1998) 99-117]. The lithosphere-dominated end-member (La Grille volcano) shows uniform He-3/He-4 ratios within error of 6.75-7.08 R-A (He-4/He-3 approximate to 106,000-101,000) over a range of [He]=36-428 x 10(-9) ccSTP/g. The plume end-member (of the Karthala volcano suite), as constrained by Sr, Nd, Pb isotope ratios, shows uniformly lower He-3/He-4 ratios with 5.05-5.41 R-A (He-4/He-3 approximate to 141,000-132,000) over a range of [He]= 11-136 x 10(-9) ccSTP/g. All samples show good correlations between Sr-Nd-He isotope ratios, indicating that the Grande Comore He-3/He-4 ratios are not significantly influenced by crustal contamination and reflect recent mixing between plume- and lithosphere-derived melts. The lithosphere beneath Grande Comore has retained its MORB-like helium isotopic composition, which suggests that the previously identified amphibole-forming metasomatism of the lithospheric mantle [1] [C. Class, S.L. Goldstein, Plume-lithosphere interactions in the ocean basins: constraints from the source mineralogy. Earth Planet. Sci. Lett., 150 (1997) 245-260] occurred prior to the arrival of the Comoro plume. The well-constrained He-3/He-4 = 5.2 +/- 0.2 R-A (He-4/He-3 approximate to 137,000 +/- 5000) of the Comoro plume confirms the existence of "low He-3/He-4" mantle plumes. A global compilation of OIB shows that OIB from "low He-3/He-4" plumes form one "side" of the roughly triangular distribution of the global OIB data set in Nd-143/Nd-144 versus Pb-206/Pb-204 and Pb-208/Pb-204, encompassing the lowest Nd to the highest Pb isotope ratios. It is also shown that "low He-3/He-4" plumes are more enriched in Th and U relative to other plumes. (C) 2005 Elsevier B.V All rights reserved.
机译：我们报告了来自格兰德·科莫尔岛的碱性玄武岩和玄武岩熔岩流样品中的He同位素（He-3 / He-4）变化，并辅以现有的[1,2] [C。 S.L.班戈德斯坦，海盆中的羽-岩圈相互作用：源矿物学的限制。地球行星。科学Lett。，150（1997）245-260，C.Class，S.L. Goldstein，R。Altherr，P。Bachechlery，海洋盆地中的羽流与石圈相互作用的过程，以Grande Comore为例。 J. Petrel。，39（5）（1998）881903]和新的Sr-Nd-Pb同位素比率以及主要元素和痕量元素的丰度。还报告了Tristan da Cunha和Gough岛以及肯尼亚Huri Hills的样品中的He同位素数据。 Grande Comore He-3 / He-4比率在5.05至7.08 R-A之间变化（He-4 / He-3约为141,000-101,000）。先前显示，格兰德·科莫尔熔岩的化学和Sr-Nd-Pb同位素变化反映了来自深地幔羽和浅岩石圈地幔的熔体[1-3] [C． S.L.班戈德斯坦，海盆中的羽-岩圈相互作用：源矿物学的限制。地球行星。科学Lett。，150（1997）245-260，C.Class，S.L. Goldstein，R。Altherr，P。Bachechlery，海洋盆地中的羽流与石圈相互作用的过程，以Grande Comore为例。 J. Petrol。，39（5）（1998）881-903，C。Claude-Ivanaj，B。Bourdon，C.J。Allegre，大科莫尔岛的Ra-Th-Sr同位素系统：羽-岩圈相互作用的案例研究。地球行星。科学来吧164（1998）99-117]。在[He]范围内，以岩石圈为主的端构件（La Grille火山）显示出均匀的He-3 / He-4比，误差在6.75-7.08 RA（He-4 / He-3约为106,000-101,000）范围内＝ 36-428×10（-9）ccSTP /克。受Sr，Nd，Pb同位素比率限制，（卡尔塔拉火山组的）羽状末端构件显示出均匀的较低的He-3 / He-4比率和5.05-5.41 RA（He-4 / He-3近似等于141,000-132,000），范围为[He] = 11-136 x 10（-9）ccSTP / g。所有样品均显示出Sr-Nd-He同位素比率之间的良好相关性，表明Grande Comore He-3 / He-4比率不受地壳污染的显着影响，并且反映了羽状和岩石圈衍生的熔体之间最近的混合。 Grande Comore下方的岩石圈保留了其MORB状的氦同位素组成，这表明先前确定的岩石圈地幔形成闪石的交代作用[1] [C． S.L.班戈德斯坦，海盆中的羽-岩圈相互作用：源矿物学的限制。地球行星。科学Lett。，150（1997）245-260]发生在科摩罗羽流到来之前。受到严格约束的科摩罗羽流的He-3 / He-4 = 5.2 +/- 0.2 RA（He-4 / He-3约为137,000 +/- 5000）证实了“低He-3 / He- 4英寸地幔柱。 OIB的全球汇编显示，来自“低He-3 / He-4”羽的OIB构成了Nd-143 / Nd-144与Pb-206 / Pb中的全球OIB数据集的大致三角形分布的“一侧” -204和Pb-208 / Pb-204，涵盖了最低的Nd与最高的Pb同位素比。还显示出“低He-3 / He-4”羽相对于其他羽更富集在Th和U中。 （C）2005 Elsevier B.V保留所有权利。

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