Mantle depletion and metasomatism recorded in orthopyroxene in highly depleted peridotites
Mantle depletion and metasomatism recorded in orthopyroxene in highly depleted peridotites
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DOI：
10.1016/j.chemgeo.2016.08.024
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发表时间：
2016-11
期刊：
影响因子：
3.9
通讯作者：
J. Scott;Jingao Liu;D. Pearson;T. Waight
中科院分区：
文献类型：
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作者：
J. Scott;Jingao Liu;D. Pearson;T. Waight
虽然单斜辉石中的微量元素浓度作为一个有用的工具，用于评估地幔橄榄岩的亏损和富集的历史，这是不适用的橄榄岩中的单斜辉石组分已被消耗（~ 25%的部分熔融）。斜方辉石持续在地幔残留物中，直到~ 40%熔融，因此，这种矿物提供了耐火橄榄岩演化的岩石学见解。研究了新西兰两套尖晶石相方辉橄榄岩捕虏体中斜方辉石±单斜辉石的常量和微量元素含量。在查塔姆岛的埃维克角（CLEV）采集的样品中含有微量的单斜辉石（< 2模态%），但从莫阿纳湖（MOA）在南岛的套件是缺乏这种矿物。当比较模拟的斜方辉石微量元素的预算，这是从发表的源模式，熔融模式和元素/熔体分配系数的审查构建，在这两组中测得的斜方辉石稀土元素数据通常表明部分熔融的最小值为25-30%。这些结果与橄榄石（大多为91.4至93.0）和斜方辉石（大多为91.3至93.6）中共存的升高的Mg#、高尖晶石Cr#（通常> 45）和低斜方辉石Al 2 O3（通常< 3.1重量%）一致。然而，建模和测量的斜方辉石组合物的比较表明，所有的样品，即使是最难处理的，都经历了小体积轻稀土元素轴承代理交代。测得的斜方辉石钛浓度表明，交代剂，影响了CLEV套件进行钛，但MOA套件交代是钛贫。因此，在被检查的岩石中的斜方辉石微量元素部分解耦的主要元素丰度，结果表明，即使是高耐火橄榄岩可以记录地幔交代的证据。
Although trace element concentrations in clinopyroxene serve as a useful tool for assessing the depletion and enrichment history of mantle peridotites, this is not applicable for peridotites in which the clinopyroxene component has been consumed (~ 25% partial melting). Orthopyroxene persists in mantle residues until ~ 40% melting and it is therefore this mineral that offers petrological insights into the evolution of refractory peridotites. Major and trace element concentrations in orthopyroxene ± clinopyroxene from two spinel facies harzburgitic xenolith suites from New Zealand are examined. Samples from Cape L'Evique (CLEV) on Chatham Island contain traces of clinopyroxene (< 2 modal %) but a suite from Lake Moana (MOA) in the South Island is devoid of this mineral. When compared with modelled orthopyroxene trace element budgets, which are constructed from a review of published source modes, melting modes and element/melt partition co-efficients, the measured orthopyroxene rare earth element data in both suites generally indicate minimums of 25–30% partial melting. These results are consistent with co-existing elevated Mg# in olivine (mostly 91.4 to 93.0) and orthopyroxene (mostly 91.3 to 93.6), high spinel Cr# (commonly > 45) and low orthopyroxene Al2O3(generally < 3.1 wt%). However, comparison of modelled and measured orthopyroxene compositions shows that all samples, even the most refractory, have undergone metasomatism by small volume light rare earth element-bearing agents. Measured orthopyroxene Ti concentrations show that the metasomatic agent that affected the CLEV suite carried Ti, but that the MOA suite metasomatiser was Ti-poor. Orthopyroxene trace elements in the inspected rocks are therefore partly decoupled from the major element abundances, with the results demonstrating that even highly refractory peridotites can record evidence for mantle metasomatism.