Element and isotopic signature of re-fertilized mantle peridotite as determined by nanopowder and olivine LA-ICPMS analyses
Element and isotopic signature of re-fertilized mantle peridotite as determined by nanopowder and olivine LA-ICPMS analyses
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通过纳米粉末和橄榄石 LA-ICPMS 分析确定再肥沃地幔橄榄岩的元素和同位素特征
DOI：
10.1016/j.chemgeo.2020.119464
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发表时间：
2020
期刊：
影响因子：
3.9
通讯作者：
Donald Wright
中科院分区：
文献类型：
--
作者：
C. Lawley;D. Pearson;P. Waterton;A. Zagorevski;J. Bédard;S. Jackson;D. Petts;B. Kjarsgaard;Shuangquan Zhang;Donald Wright
岩石圈地幔中的贱金属和贵金属在部分熔融过程中被转移到地壳中，因此应该是贫化的。然而，一些熔融亏损地幔橄榄岩富集这些成矿元素。这可能反映了地幔岩石圈的再肥化和/或残留地幔相对这些元素的螯合作用。这两个过程仍然知之甚少，因为橄榄岩中的不相容元素丰度低，抗消化地幔相的块金状分布，对传统的地球化学方法构成了分析挑战。在这里，我们报告新的主要和微量元素浓度的一套地幔橄榄岩和辉石岩样品从晚二叠世到中三叠世Nahlin蛇绿岩（卡奇克里克，不列颠哥伦比亚省，加拿大）使用激光烧蚀电感耦合等离子体质谱（LA-ICPMS）分析纳米颗粒粉末和橄榄石。相容至中度不相容元素浓度表明Nahlin蛇绿橄榄岩为≥20%熔融萃取后的残留物。辉石岩岩墙和孤立纯橄榄岩带褶皱，紧密夹有残余辉橄榄岩。这些领域的关系，再加上存在的颗粒间贱金属硫化物，单斜辉石和铬尖晶石在微观尺度上，点到criterating熔体，criteriformate熔融亏损地幔橄榄岩。放射成因铅（~（206）Pb/~（204）Pb = 15.402-19.050;~（207）Pb/~（204）Pb = 15.127-15.633;~（208）Pb/~（204）Pb = 34.980-38.434（187 Os/188 Os 0.1143-0.5745;n= 58）同位素组成的一个子集的熔融亏损橄榄岩样品进一步支持交代再受精这些元素。其他成矿元素也牵连在这些交代反应，因为一些熔融亏损橄榄岩样品富集相对于原始地幔，相反的预期行为在部分熔融。新的LA-ICPMS分析的新鲜橄榄石进一步表明，一个显着比例的高度不相容的元素预算的最熔体耗尽的岩石是托管的，和/或发生作为捕获的夹杂物内，富含橄榄石的残留物。从过去的熔融和/或再施肥事件的陷阱阶段的非放射性铅同位素组成和古生代到古元古代再耗尽模型年龄，早于Nahlin蛇绿岩超过10亿年的首选解释。
The lithospheric mantle should be depleted in base- and precious-metals as these elements are transferred to the crust during partial melting. However, some melt-depleted mantle peridotites are enriched in these ore-forming elements. This may reflect re-fertilization of the mantle lithosphere and/or sequestering of these elements by residual mantle phase(s). Both processes remain poorly understood because of the low abundances of incompatible elements in peridotite and the nugget-like distribution of digestion-resistant mantle phases that pose analytical challenges for conventional geochemical methods. Herein we report new major and trace element concentrations for a suite of mantle peridotite and pyroxenite samples from the Late Permian to Middle Triassic Nahlin ophiolite (Cache Creek terrane, British Columbia, Canada) using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS) analysis of nanoparticulate powders and olivine. Compatible to moderately incompatible element concentrations suggest that Nahlin ophiolite peridotites represent residues after ≥20% melt extraction. Pyroxenite dykes and replacive dunite bands are folded and closely intercalated with residual harzburgite. These field relationships, coupled with the presence of intergranular base metal sulphide, clinopyroxene and Cr-spinel at the microscale, point to percolating melts that variably re-fertilized melt-depleted mantle peridotite. Radiogenic Pb (206Pb/204Pb = 15.402–19.050;207Pb/204Pb = 15.127–15.633;208Pb/204Pb = 34.980–38.434;n= 45) and Os (187Os/188Os 0.1143–0.5745;n= 58) isotope compositions for a subset of melt-depleted peridotite samples further support metasomatic re-fertilization of these elements. Other ore-forming elements are also implicated in these metasomatic reactions because some melt-depleted peridotite samples are enriched relative to the primitive mantle, opposite to their expected behaviour during partial melting. New LA-ICPMS analysis of fresh olivine further demonstrates that a significant proportion of the highly incompatible element budget for the most melt-depleted rocks is either hosted by, and/or occurs as trapped inclusions within, the olivine-rich residues. Trapped phases from past melting and/or re-fertilization events are the preferred explanation for unradiogenic Pb isotope compositions and Paleozoic to Paleoproterozoic Re-depletion model ages, which predate the Nahlin ophiolite by over one billion years.
影响因子：
3.5
作者：
J. Warren
通讯作者：
J. Warren
影响因子：
5.3
作者：
Dijkstra, Arjan H.;Dale, Christopher W.;Pearson, D. Graham
通讯作者：
Pearson, D. Graham