Tracing the origin of continental HIMU-like intraplate volcanism using magnesium isotope systematics
Tracing the origin of continental HIMU-like intraplate volcanism using magnesium isotope systematics
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DOI：
10.1016/j.gca.2016.01.007
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发表时间：
2016-07
影响因子：
5
通讯作者：
Shui‐Jiong Wang;F. Teng;J. Scott
中科院分区：
文献类型：
--
作者：
Shui‐Jiong Wang;F. Teng;J. Scott
分别来自新西兰南岛和新西兰Antipodes群岛的11个橄榄岩捕虏体和21个HIMU型板内玄武岩的Mg同位素组成，为大陆板内碱性玄武岩的成因提供了新的证据。橄榄岩中的橄榄石和斜方辉石显示出非常有限的镁同位素变化（橄榄石为−0.28‰至−0.17‰;斜方辉石为−0.24‰至−0.14‰）。单斜辉石的Mg同位素组成（−0.37‰至−0.10‰）比共存的橄榄石和斜方辉石稍轻。橄榄岩的全岩δ 26 Mg值为-0.27 ‰ ~-0.16 ‰，属于正常地幔范围（-0.25 ± 0.07‰）。而大陆板内熔岩的δ 26 Mg值变化范围为-0.47 ‰ ~-0.06 ‰，与（Gd/Yb）N比值呈负相关。橄榄岩和板内玄武岩之间的Mg同位素系统学的差异表明，前者不能是唯一的岩浆源，后者，和一个岩性与较轻的Mg同位素组成，如碳酸榴辉岩也必须作出贡献。因此，具有HIMU样源特征的板内熔岩可能代表来自橄榄岩和再循环碳酸榴辉岩的熔体混合的产物。因此镁同位素可能是板内火山活动地幔来源的一个有用的示踪剂。
The Mg isotopic compositions of 11 peridotite xenoliths and 21 HIMU-like intraplate basaltic lavas from New Zealand’s South Island and Antipodes Islands, respectively, provide new evidence bearing on the origin of continental intraplate alkaline basalts. Olivine and orthopyroxene in the peridotites display very limited Mg isotopic variations (−0.28‰ to −0.17‰ for olivine; −0.24‰ to −0.14‰ for orthopyroxene). The clinopyroxenes have Mg isotopic compositions (−0.37‰ to −0.10‰) slightly lighter than coexisting olivine and orthopyroxene. Calculated whole rock δ26Mg values of the peridotites vary from −0.27‰ to −0.16‰, falling within the normal mantle range (−0.25 ± 0.07‰). By contrast, the δ26Mg values of continental intraplate lavas vary from −0.47‰ to −0.06‰ and negatively correlate with (Gd/Yb)Nratios. The difference in Mg isotopic systematics between peridotites and intraplate basalts reveals that the former cannot be the sole magma source to the latter, and a lithology with a lighter Mg isotopic composition such as carbonated eclogite must also have contributed. Thus, the intraplate lavas with HIMU-like source signatures likely represent the product of mixing of melts derived from peridotite and recycled carbonated eclogite. Magnesium isotopes may therefore be a useful tracer of mantle sources to intraplate volcanism.