Chalcophile element geochemistry and petrogenesis of high-Ti and low-Ti magmas in the Permian Emeishan large igneous province, SW China
Chalcophile element geochemistry and petrogenesis of high-Ti and low-Ti magmas in the Permian Emeishan large igneous province, SW China
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DOI：
10.1007/s00410-010-0529-8
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发表时间：
2011-02
影响因子：
3.5
通讯作者：
C. Wang;Mei‐Fu Zhou;L. Qi
中科院分区：
文献类型：
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作者：
C. Wang;Mei‐Fu Zhou;L. Qi
阜宁地区贫硫化物镁铁质层状侵入体、岩床/岩墙和熔岩流是峨眉山大火成岩省的一部分。它们属于具有高Ti/Y比（351- 1，018）的高Ti组（TiO 2 = 1.6- 4.4wt%）或具有低Ti/Y比（133-223）的低Ti组（TiO 2 <1.2wt%）。本文研究了富宁高钛组和低钛组岩石中橄榄石、铬铁矿和硫化物的分馏作用对Ni、Cu和PGE亲铜元素分布的影响。高钛组岩石中Pt + Pd含量为1.6- 5.3ppb，Ir含量为0.06- 0.43ppb，Ru含量为0.01- 0.13ppb，（Cu/Pd）PM比值为4.0-9.7，Ni/Pd与Cu/Ir比值呈负相关。高Ti组岩石的IPGE/PPGE分异特征和Ru的负异常，以及橄榄石的低Fo值（59- 62mol%），表明高Ti岩浆可能在硫不饱和条件下经历了橄榄石和铬铁矿的分异作用。根据PGE含量，低Ti组岩石可进一步分为两个亚组：高PGE低Ti亚组和低PGE低Ti亚组。高PGE低Ti组岩石富含MgO（10- 20wt%），但橄榄石的Fo值较低（74- 76mol%）。岩石中的铂族元素（Pt + Pd = 1.7-88 ppb，Ir = 0.05-1.3 ppb）、镍（179 - 1，380 ppm）和铜（59-568 ppm）含量变化很大。它们的Cu/Zr比>1，（Y/Pd）PM比低（0.2-7.1），（Cu/Pd）PM比接近恒定（1.5-3.8）。高PGE低Ti亚组岩石的亲铜元素分布均匀平行，可能是S-欠饱和条件下橄榄石主导分馏作用的结果。低PGE低Ti组岩石具有低MgO（4.5- 8.9wt%）和非常差的PGE（Pt + Pd 0.5- 1.6ppb，Ir 0.004- 0.02ppb），具有低Cu/Zr比（0.1-0.5）、高（Y/Pd）PM（26-70）和可变（Cu/Pd）PM比（2.8-14）。低PGE低Ti亚群岩石的槽状亲铜元素配分模式表明岩浆已被硫化物饱和，并有硫化物熔体从岩浆中提取出来。富宁地区深部硫化物熔体可能是潜在的镍铜硫化矿。
Sulfide-poor mafic layered intrusions, sills/dykes and lava flows in the Funing region, SW China, are part of the ~260 Ma Emeishan large igneous province. They belong to either a high-Ti group (TiO2= 1.6–4.4 wt%) with elevated Ti/Y ratios (351–1,018), or a low-Ti group (TiO2< 1.2 wt%) with low Ti/Y ratios (133–223). This study investigates the role of fractionation of olivine, chromite and sulfide on the distributions of chalcophile elements, Ni, Cu and PGE, of the high-Ti and low-Ti group rocks at Funing. The high-Ti group rocks contain 1.6–5.3 ppb Pt + Pd, 0.06–0.43 ppb Ir and 0.01–0.13 ppb Ru, and show relative constant (Cu/Pd)PMratios (4.0–9.7) and a negative correlation between Ni/Pd and Cu/Ir ratios. Fractionated IPGE/PPGE patterns and very negative Ru anomalies of the high-Ti group rocks, together with low Fo values (59–62 mol%) of olivine, indicate that the high-Ti magmas may have experienced fractionation of olivine and chromite under S-undersaturated condition. Based on the PGE concentrations, the low-Ti group rocks can be further divided into two subgroups; a high-PGE low-Ti subgroup and a low-PGE low-Ti subgroup. The high-PGE low-Ti group rocks are rich in MgO (10–20 wt%), but Fo values of olivine from the rocks are low (74–76 mol%). The rocks contain highly variable PGE (Pt + Pd = 1.7–88 ppb, Ir = 0.05–1.3 ppb), Ni (179 –1,380 ppm) and Cu (59–568 ppm). They have Cu/Zr ratios >1, low (Y/Pd)PMratios (0.2–7.1) and nearly constant (Cu/Pd)PMratios (1.5–3.8). The even and parallel chalcophile element patterns of the high-PGE low-Ti subgroup rocks are likely a result of olivine-dominated fractionation under S-undersaturated condition. The low-PGE low-Ti group rocks have low MgO (4.5–8.9 wt%) and very poor PGE (Pt + Pd 0.5–1.6 ppb, Ir 0.004–0.02 ppb) with low Cu/Zr ratios (0.1–0.5), high (Y/Pd)PM(26–70) and variable (Cu/Pd)PMratios (2.8–14). The trough-like chalcophile element patterns of the low-PGE low-Ti subgroup rocks indicate that the magmas were sulfide saturation and sulfide melts were extracted from the magmas. The extracted sulfide melts might be potential Ni–Cu sulfide ores at depth in the Funing region.