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 initial ¹⁷⁶Hf/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 initial ¹⁸⁷Os/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.

经历过含水熔融的亚弧地幔通常以难熔的地球化学成分为特征。尽管如此，也有报道称俯冲带的地幔橄榄岩中含有少量的橄榄岩。辉长岩的成因和地幔来源仍存在争议。新喀里多尼亚蛇绿岩（橄榄岩推覆岩）被认为是弧前岩石圈的外来体。这是由其主要地幔岩石的耐火成分支持的。在新喀里多尼亚北部也观察到一些孤立的黑方岩地块。这些橄榄岩在成分上与深海橄榄岩相似，与俯冲相关的改变可以忽略不计。在这里，我们提出了新的综合地球化学成分，特别是高精度 Sr-Nd-Hf 同位素数据，为锂辉石。最初的¹⁷⁶ Hf/ ¹⁷⁷ Hf 比值与熔融程度敏感指标（即橄榄石 Fo、单斜辉石中全岩 Mg# 和 Yb 含量）和全岩初始¹⁸⁷ Os/ ¹⁸⁸显示出中等相关性操作系统比率。一些样品具有古老的放射成因 Hf 同位素和非放射成因 Os 同位素组成，这意味着在二镁橄榄岩中保留了古老的耗尽信号。Nd 同位素组成，连同微量元素和矿物微结构，表明近期发生的熔岩相互作用事件已经叠加了三辉石。研究样品的高平衡温度已通过双辉石 REE 温度计估计，产生的温度为 1066–1315 °C。与新喀里多尼亚方辉石相比，锂辉石具有更贫化的 Nd-Hf 同位素组成和更高的平衡温度。这表明二镁橄榄石可能代表了被困在弧前区域内的软流圈地幔的残余物。