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首页> 外文期刊>Contributions to Mineralogy and Petrology >Geochemical constraints on the origin of the Permian Baimazhai mafic-ultramafic intrusion, SW China
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Geochemical constraints on the origin of the Permian Baimazhai mafic-ultramafic intrusion, SW China

机译：中国西南地区二叠系白马寨黑镁质-超镁铁质侵入体的地球化学约束

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The -260 Ma Baimazhai mafic-ultramafic intrusion is considered to be part of the Emeishan large igneous province and consists of orthopyroxenite surrounded by websterite and gabbro. The intrusion is variably mineralized with a massive sulfide ore body (approx 20 vol. percent) in the core of the intrusion. Silicate rocks have Ni/Cu ratios ranging from 0.3 to 46 with majority less than 7 and are rich in LREE relative to HREE and show Nb and Ta anomalies in primitive mantle-normalized trace element patterns, with low Nb/Th (1.0-4.5) and Nb/La (0.3-1.0) ratios. Their e Nd(t) values range from -3.3 to -8.4. Uniform Pd/Pt (0.7-3.5) and Cu/Pd (100,000-400,000) ratios throughout the intrusion indicate that all the sulfides in the rocks were formed in a single sulfide-saturation event. Modeling suggests that the Baimazhai rocks were formed when an Mg-rich magma became crustally contaminated in a deep-seated staging chamber. Crustal contamination (up to approx 35 percent) drove the magma to S-saturation and forced orthopyroxene (Opx) onto the liquidus. The crystal-bearing magma forced out of the staging chamber was migrated by flow differentiation and consequently, the denser sulfide melt and the Opx crystals became centrally disposed in the flowing magma to form the Baimazhai intrusion.
机译：-260 Ma Baimazhai镁铁质-超镁铁质岩体被认为是峨眉山火成岩大省的一部分，由正辉石，韦伯石和辉长岩包围。侵入岩的芯层中有大量硫化物矿体（约占体积的20％），矿化程度可变。硅酸盐岩的镍/铜比范围为0.3-46，多数小于7，并且相对于HREE富含LREE，并且在原始地幔归一化痕量元素模式中显示Nb和Ta异常，而Nb / Th低（1.0-4.5） Nb / La（0.3-1.0）比。它们的e Nd（t）值范围为-3.3至-8.4。在整个侵入过程中，均匀的Pd / Pt（0.7-3.5）和Cu / Pd（100,000-400,000）比表明，岩石中的所有硫化物都是在单个硫化物饱和事件中形成的。建模表明，当富含Mg的岩浆在深处的分期室内被硬壳污染时，形成了Baimazhai岩石。地壳污染（约35％）驱使岩浆达到S饱和状态，并迫使邻苯二茂铁（Opx）进入液相线。从分流腔出来的含晶体岩浆通过流动分异而迁移，因此，较稠密的硫化物熔体和Opx晶体在流动岩浆中居中形成了Baimazhai侵入体。

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