海南蓬莱地幔橄榄岩单矿物Sr-Sm-Nd-Lu-Hf同位素组成

海南蓬莱地幔橄榄岩单斜辉石的Sr-Nd同位素组成限定出纯橄岩、方辉橄榄岩和二辉橄榄岩受到的碳酸盐熔体交代介质可能源于碳酸盐沉积物；富单斜辉石二辉橄榄岩再富集介质可能源于上涌软流圈的熔融。单斜辉石和斜方辉石重建的全岩Lu-Hf等时线年龄为1.2Ga。Sr-Nd同位素体系受后期交代作用干扰强烈，并未获得有效等时线年龄。
单斜辉石和斜方辉石的Sr-Sm-Nd-Lu-Hf同位素分析是在中国地质大学（北京）科学研究院同位素地球化学实验室完成，其中Lu-Hf同位素的分析利用同位素稀释法，通过多接收杯电感耦合等离子体质谱仪（MC-ICP-MS）的Aridus II脱溶雾化器（干法进样）进行样品导入和测试，而Sr-Sm-Nd同位素则是通过MC-ICP-MS的雾化室（湿法进样）进行样品导入和测试。该实验方法类似于Shu et al. (2013)的化学实验流程和测试方法。
Lu-Hf和其他基质元素的分离与纯化流程采用的是LN镧系特效树脂，其中斜方辉石需要分为两等份分别过柱子（防止柱子过载），上机前合二为一测试。
通过单斜辉石和斜方辉石重建全岩 Lu-Hf ―假等时线‖的亲石体系方法，限定出海南岛地幔橄榄岩的形成年龄为 1.17 ± 0.09 Ga（1ζ；MSWD = 63，n = 14），该结果与 Re-Os 体系限定出的年龄范围一致，但精度更高。由此可知海南岛岩石圈地幔橄榄岩的形成年龄为晚中元古代（~1.2 Ga）Sr-Nd-Lu-Hf同位素及其含量的分析在Thermo-Finnigan公司生产的Neptune plus型MC-ICP-MS上进行。各类标准样品的实验室长期测定值分别为：87Sr/86Sr = 0.710240 ± 27 （2σ），143Nd/144Nd = 0.512182 ± 16 （2σ），176Lu/175Lu = 0.02656，176Hf/177Hf = 0.282190 ± 15（2σ）。本论文获得的测试结果在误差范围内与上述测定值一致：87Sr/86Sr = 0.710264 ± 20 （2σ，n = 20），143Nd/144Nd = 0.512183 ± 24 （2σ， n = 16），176Lu/175Lu = 0.02657 ± 38（2σ，n = 30），176Hf/177Hf = 0.282190 ± 12（2σ，n = 48）。此外，本论文的各类岩石标准物质BHVO-2、BCR-2的测试与GEOREM推荐值和文献报道值（Kent et al., 2004; Bizzarro et al., 2007）误差范围内一致。

Sr-Nd isotopic compositions of clinopyroxenes from the Hainan Penglai mantle peridotites indicate that the metasomatic carbonate melt agents experienced by dunite, harzburgite, and lherzolite may originate from carbonate sediments; the refertilization agent for clinopyroxene-rich lherzolite may derive from melting of the upwelling asthenosphere. The whole-rock Lu-Hf isochron age reconstructed from clinopyroxene and orthopyroxene is 1.2 Ga. The Sr-Nd isotopic system was strongly disturbed by late-stage metasomatism, and no valid isochron age was obtained. Isotopic analyses of Sr-Sm-Nd-Lu-Hf for clinopyroxene and orthopyroxene were conducted at the Isotope Geochemistry Laboratory, School of Earth Sciences, China University of Geosciences (Beijing). For Lu-Hf isotopic analysis, isotope dilution method was employed, with sample introduction and measurement performed using the Aridus II desolvation nebulizer (dry sample introduction) of multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). For Sr-Sm-Nd isotopes, sample introduction and measurement were carried out via the spray chamber (wet sample introduction) of MC-ICP-MS. This experimental method is similar to the chemical separation and analytical procedures reported by Shu et al. (2013). The separation and purification procedures for Lu-Hf and other matrix elements adopted LN rare earth element (REE) specific resin. Orthopyroxene samples were split into two equal aliquots for column chromatography (to avoid column overloading) and combined into one sample for measurement prior to mass spectrometry analysis. By using the lithophile system "pseudo-isochron" method for whole-rock Lu-Hf dating reconstructed from clinopyroxene and orthopyroxene, the formation age of the Hainan Island mantle peridotites is constrained to 1.17 ± 0.09 Ga (1ζ; MSWD = 63, n = 14), which is consistent with the age range constrained by the Re-Os system but with higher precision. Thus, the formation age of the lithospheric mantle peridotites beneath Hainan Island is late Mesoproterozoic (~1.2 Ga). Analyses of Sr-Nd-Lu-Hf isotopes and their concentrations were performed on a Thermo-Finnigan Neptune plus MC-ICP-MS. Long-term laboratory measured values of various standard reference materials are as follows: 87Sr/86Sr = 0.710240 ± 27 (2σ), 143Nd/144Nd = 0.512182 ± 16 (2σ), 176Lu/175Lu = 0.02656, 176Hf/177Hf = 0.282190 ± 15 (2σ). The analytical results obtained in this study are consistent with the above measured values within error margins: 87Sr/86Sr = 0.710264 ± 20 (2σ, n = 20), 143Nd/144Nd = 0.512183 ± 24 (2σ, n = 16), 176Lu/175Lu = 0.02657 ± 38 (2σ, n = 30), 176Hf/177Hf = 0.282190 ± 12 (2σ, n = 48). In addition, the analyses of rock standard reference materials BHVO-2 and BCR-2 in this study are consistent with the recommended values of GEOREM and previously reported values (Kent et al., 2004; Bizzarro et al., 2007) within error ranges.