Platinum-group element systematics and petrogenetic processing of the continental upper mantle: A review
Platinum-group element systematics and petrogenetic processing of the continental upper mantle: A review
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DOI：
10.1016/j.lithos.2012.08.017
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发表时间：
2013-04
期刊：
影响因子：
3.5
通讯作者：
J. Lorand;A. Luguet;O. Alard
中科院分区：
文献类型：
--
作者：
J. Lorand;A. Luguet;O. Alard
大陆地幔橄榄岩的铂族元素(PGE)系统学具有很大的变异性，反映了上地幔在部分熔融和岩石圈内熔体/流体渗流过程中的成岩作用。通过去除富Pd-Cu-Ni的硫化物，稳定次大陆地幔岩石圈的部分熔融事件使PPGE(钯组PGE；铂、Pd)相对于IPGE(Ir组PGE；Os、Ir、Ru、Rh)发生了分馏。残留的贱金属硫化物(BMS)以封闭的IPGE富集单硫化物固溶体(MSS)的形式存在，一旦部分熔体变为S不饱和，则分解为富Ru-Os-Ir的难熔铂族矿物(PGMS)。这些微相的小规模非均匀分布可能导致极端的块金效应，正如克拉通橄榄岩中记录的PGE绝对值的巨大变化所示。岩浆流经岩石圈地幔可能会改变熔融事件继承的初始PGE收支，导致次大陆岩石圈橄榄岩中PGE系统学的巨大差异。例如，在增加熔体/岩石比的情况下，熔岩反应作为开放系统熔化过程来运行，去除残留的BMS/PGMS。高渗橄榄岩的特征是PGE极度亏损，再加上逐渐向渗流熔体演化的PGE模式和Os同位素组成。熔岩比降低时的反应(通常被称为“地幔交代”)使富PPGE的BMS沉淀，产生超软体Pd/Ir，偶尔也会影响铂/Ir和Rh/Ir的比值。此外，富挥发分的小体积熔体熔融了相对于Ir的分馏的Os和相对于Se的S，从而形成了具有超软骨石相的Os/Ir和S/Se与超软骨相Pd/Ir和Pt/Ir的岩石。岩石圈-软流圈边界的主要岩浆输入可能使亏损地幔的PGE系统恢复年轻。对全球来源的橄榄岩的综合研究提供了富含PGM的旧哈兹伯里基原岩和新沉积的BMS之间混合的证据。长寿的PGMS将古代熔体枯竭事件的Os同位素组成带入似乎未枯竭的肥沃二辉橄榄岩中。另一个主要参考过程的诊断特征是铂-钯-碲-铋或铂-砷-S微相的模式丰度增加。由于区域尺度的参考作用，岩石圈上部地幔的相当大的(>；100公里)区域现在显著地富含Pd、Au、Cu、Se和其他在PGE成矿事件中相当重要的不相容的亲铜元素。
The platinum-group element (PGE) systematics of continental mantle peridotites show large variability, reflecting petrogenetic processing of the upper mantle during partial melting and melt/fluid percolation inside the lithosphere. By removing Pd–Cu–Ni rich sulfides, partial melting events that have stabilized the sub-continental mantle lithosphere fractionated PPGEs (Palladium-group PGE; Pt, Pd) relative to IPGEs (Iridium-group PGE; Os, Ir, Ru, Rh). Residual base-metal sulfides (BMS) survive as enclosed IPGE-enriched Monosulfide Solid Solutions (Mss), which otherwise decompose into Ru–Os–Ir-rich refractory platinum-group minerals (PGMs) once the partial melts become S-undersaturated. The small-scale heterogeneous distribution of these microphases may cause extreme nugget effects, as seen in the huge variations in absolute PGE concentrations documented in cratonic peridotites. Magmas fluxing through the lithospheric mantle may change the initial PGE budgets inherited from the melting events, resulting in the great diversity of PGE systematics seen in peridotites from the sub-continental lithosphere. For instance, melt–rock reactions at increasing melt/rock ratios operate as open-system melting processes removing residual BMS/PGMs. Highly percolated peridotites are characterized by extreme PGE depletion, coupled with PGE patterns and Os-isotope compositions that gradually evolve toward that of the percolating melt. Reactions at decreasing melt–rock ratios (usually referred to as «mantle metasomatism») precipitate PPGE-enriched BMS that yield suprachondritic Pd/Ir and occasionally affect Pt/Ir and Rh/Ir ratios as well. Moreover, volatile-rich, small volume melts fractionate Os relative to Ir and S relative to Se, thereby producing rocks with supra-chondritic Os/Ir and S/Se coupled with supra-chondritic Pd/Ir and Pt/Ir. Major magmatic inputs at the lithosphere–asthenosphere boundary may rejuvenate the PGE systematics of the depleted mantle. Integrated studies of «refertilized» peridotites with worldwide provenance provide evidence for mixing between old PGM-rich harzburgitic protoliths and newly-precipitated BMS. Long-lived PGMs carry the Os-isotope compositions of ancient melt‐depletion events into seemingly undepleted fertile lherzolites. Another diagnostic feature of major refertilization processes is the increasing modal abundance of Pt–Pd–Te–Bi or Pt–As–S microphases. Due to regional-scale refertilization processes, sizeable (>100km) domains of the upper lithospheric mantle are now significantly enriched in Pd, Au, Cu, Se, and other incompatible chalcophile elements that are of considerable importance in PGE-ore forming events.