Ancient depletion signals in lherzolites from forearc region: Constraints from Lu-Hf isotope compositions
Ancient depletion signals in lherzolites from forearc region: Constraints from Lu-Hf isotope compositions
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弧前区二辉橄榄岩中的古代耗尽信号：Lu-Hf 同位素组成的限制
DOI：
10.1016/j.gsf.2021.101259
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发表时间：
2022
影响因子：
8.9
通讯作者：
Xue-Fa Shi
中科院分区：
文献类型：
--
作者：
Yang Xu;Chuan-Zhou Liu;Wei Lin;Xue-Fa Shi
经历水合熔融的弧下地幔通常以难熔的地球化学成分为特征。然而，来自俯冲带的地幔橄榄岩中也有少量具有可育成分的二辉橄榄岩的报道。二辉橄榄岩的岩石成因和地幔来源仍存在争议。新喀里多尼亚蛇绿岩(橄榄岩推覆体)被认为是弧前岩石圈的异地体。这是由其主要地幔岩石的耐火材料组成支持的。在新喀里多尼亚北部也观察到一些孤立的二辉橄榄岩地块。这些二辉橄榄岩在成分上与深海橄榄岩相似，但与俯冲有关的修改可以忽略不计。本文介绍了二辉橄榄岩的新的综合地球化学组成，特别是高精度的锶-钕-氢同位素数据。初始176Hf/177Hf比值与熔融程度敏感指标(即单斜辉石中橄榄石Fo、全岩Mg#和Yb含量)和全岩初始187Os/188Os比值具有中等相关性。一些样品具有古老的放射性成因的Hf同位素和非放射性成因的Os同位素组成，表明二辉橄榄岩中保存了古老的亏损信号。Nd同位素组成、微量元素和矿物微结构表明，二辉橄榄岩受到了最近的熔岩相互作用事件的叠加。用双辉石稀土测温仪估算了样品的高平衡温度，测得其平衡温度为1066-1315℃。二辉橄榄岩比新喀里多尼亚方辉橄榄岩具有更多的亏损Nd-Hf同位素组成和更高的平衡温度。这表明二辉橄榄岩可能代表了弧前区软流圈地幔的残留物。我们对具有古老亏损信号的新喀里多尼亚二辉橄榄岩的研究表明，在俯冲开始的早期阶段，由于软流层的上涌，对流地幔中的古地幔区域可以侵位到弧前地区。
The sub-arc mantle that experienced hydrous melting is commonly characterized by refractory geochemical compositions. Nevertheless, minor lherzolites with fertile compositions have also been reported for mantle peridotites from subduction zone. The petrogenesis and mantle source of the lherzolites are still controversial. The New Caledonia ophiolite (Peridotite Nappe) has been regarded as an allochthonous body of forearc lithosphere. This is supported by refractory compositions of its dominant mantle rocks. A few isolated lherzolitic massifs have also been observed in the northern part of New Caledonia. Those lherzolites are compositionally similar to abyssal peridotites, with negligible subduction-related modification. Here, we present new comprehensive geochemical compositions, in particular high-precision Sr-Nd-Hf isotope data, for the lherzolites. The initial176Hf/177Hf ratios display moderate correlations with sensitive indicators for the extent of melting (i.e., olivine Fo, whole-rock Mg# and Yb contents in clinopyroxene) and whole-rock initial187Os/188Os ratios. Some samples have ancient radiogenic Hf isotopes and unradiogenic Os isotope compositions, implying the preservation of ancient depletion signals in the lherzolites. The Nd isotope compositions, together with trace elements and mineral micro-textures, suggest that the lherzolites have been overprinted by a recent melt-rock interaction event. The high equilibrium temperatures of the studied samples have been estimated by the two-pyroxene REE thermometer, yielding temperatures of 1066–1315 °C. The lherzolites have more depleted Nd-Hf isotope compositions and higher equilibrium temperatures than the New Caledonia harzburgites. This indicates that the lherzolites may represent the residues of asthenosphere mantle trapped within the forearc region. Our studies on the New Caledonia lherzolites with ancient depletion signals suggest that ancient mantle domains in the convective mantle can be emplaced in forearc region by the upwelling of asthenosphere during the early stage of subduction initiation.
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影响因子：
3.9
作者：
Cassian Pirard;J. Hermann;H. O’Neill
通讯作者：
Cassian Pirard;J. Hermann;H. O’Neill
影响因子：
3.9
作者：
Hellebrand, E;Snow, JE;Hofmann, AW
通讯作者：
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影响因子：
3.9
作者：
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影响因子：
5.3
作者：
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通讯作者：
Jingao Liu;J. Scott;Candace E Martin;D. Pearson
影响因子：
3.5
作者：
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通讯作者：
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