Abstract Oxygen fugacities (fO2) $\left( {{f}_{{{\text{O}}_{2}}}} \right)$of mantle-derived mafic magmas have important controls on the sulfur status and solubility of the magmas, which are key factors to the formation of magmatic Ni-Cu sulfide deposits, particularly those in convergent margin settings. To investigate the fO2 ${{f}_{{{\text{O}}_{2}}}}$of mafic magmas related to Ni-Cu sulfide deposits in convergent margin settings, we obtained the magma fO2 ${{f}_{{{\text{O}}_{2}}}}$of several Ni-Cu sulfide-bearing mafic-ultramafic intrusions in the Central Asian Orogenic Belt (CAOB), North China, based on the olivine-spinel oxygen barometer and the modeling of V partitioning between olivine and melt. We also calculated the mantle fO2 ${{f}_{{{\text{O}}_{2}}}}$on the basis of V/ Sc ratios of primary magmas of these intrusions. Ni-Cu sulfide-bearing mafic-ultramafic intrusions in the CAOB include arc-related Silurian-Carboniferous ones and post-collisional Permian-Triassic ones. Arc-related intrusions formed before the closure of the paleo-Asian ocean and include the Jinbulake, Heishan, Kuwei, and Erbutu intrusions. Post-collisional intrusions were emplaced in extensional settings after the closure of the paleo-Asian ocean and include the Kalatongke, Baixintan, Huangshandong, Huangshan, Poyi, Poshi, Tulaergen, and Hongqiling No. 7 intrusions. It is clear that the magma fO2 ${{f}_{{{\text{O}}_{2}}}}$values of all these intrusions in both settings range mostly from FMQ+0.5 (FMQ means fayalite-magnetite-quartz oxygen buffer) to FMQ+3 and are generally elevated with the fractionation of magmas, much higher than that of MORBs (FMQ-1 to FMQ+0.5). However, the mantle fO2 ${{f}_{{{\text{O}}_{2}}}}$values of these intrusions vary from ~FMQ to ~FMQ+1.0, just slightly higher than that of mid-ocean ridge basalts (MORBs) (≤FMQ). This slight difference is interpreted as the intrusions in the CAOB may have been derived from the metasomatized mantle wedges where only minor slab-derived, oxidized components were involved. Therefore, the high-magma fO2 values of most Ni-Cu sulfide-bearing mafic-ultramafic intrusions in the CAOB were attributed to the fractionation of magmas derived from the slightly oxidized metasomatized mantle. In addition, the intrusions that host economic Ni-Cu sulfide deposits in the CAOB usually have magma fO2 of >FMQ+1.0 and sulfides with mantle-like δ34S values (–1.0 to +1.1‰), indicating that the oxidized mafic magmas may be able to dissolve enough mantle-derived sulfur to form economic Ni-Cu sulfide deposits. Oxidized mafic magmas derived from metasomatized mantle sources may be an important feature of major orogenic belts.

中文翻译：

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会聚边缘环境中镁铁质-超镁铁质侵入体的岩浆氧逸度：关于岩浆氧化态对岩浆镍铜硫化物矿化作用的见解

摘要 地幔基性岩浆的氧逸度 (fO2) $\left( {{f}_{{{\text{O}}_{2}}}} \right)$ 对硫的状态和溶解度有重要的控制岩浆，这是形成岩浆镍铜硫化物矿床的关键因素，特别是在会聚边缘环境中的那些。为了研究收敛边缘环境中与镍铜硫化物矿床有关的基性岩浆 fO2 ${{f}_{{{\text{O}}_{2}}}}$，我们得到了岩浆 fO2 ${{ f}_{{{\text{O}}_{2}}}}$ 在华北中亚造山带 (CAOB) 中几个含 Ni-Cu 硫化物的镁铁质-超镁铁质侵入体，基于橄榄石-尖晶石氧气压计和橄榄石和熔体之间 V 分配的建模。我们还根据这些侵入体的原生岩浆的 V/Sc 比计算了地幔 fO2 ${{f}_{{{\text{O}}_{2}}}}$。CAOB中含Ni-Cu硫化物的镁铁质-超镁铁质侵入体包括与弧相关的志留纪-石炭纪侵入体和碰撞后二叠纪-三叠纪侵入体。与弧相关的侵入体形成于古亚洲洋闭合之前，包括金布拉克、黑山、库韦和尔布图侵入体。碰撞后侵入体在古亚洲洋闭合后进入伸展环境，包括喀拉通克、白心滩、黄山东、黄山、坡伊、波什、图拉尔根和红旗岭7号侵入体。很明显，两种环境中所有这些侵入体的岩浆 fO2 ${{f}_{{{\text{O}}_{2}}}}$ 值大多在 FMQ+0.5 范围内（FMQ 表示铁橄榄石-磁铁矿-石英氧缓冲液）至 FMQ+3 并且一般随着岩浆的分馏而升高，远高于 MORB（FMQ-1 至 FMQ+0.5）。然而，这些侵入体的地幔 fO2 ${{f}_{{{\text{O}}_{2}}}}$ 值从 ~FMQ 到 ~FMQ+1.0 不等，仅略高于洋中脊玄武岩 (MORB) (≤FMQ)。这种细微的差异被解释为 CAOB 中的侵入体可能来自交代地幔楔，其中仅涉及少量板片衍生的氧化成分。因此，CAOB 中大多数含 Ni-Cu 硫化物的镁铁质-超镁铁质侵入体的高岩浆 fO2 值归因于来自轻度氧化交代地幔的岩浆的分馏。此外，在中亚盆地拥有经济镍铜硫化物矿床的侵入体通常具有 >FMQ+1.0 的岩浆 fO2 和具有类似地幔的 δ34S 值（–1.0 至 +1.1‰）的硫化物，这表明氧化的镁铁质岩浆可能能够溶解足够的地幔衍生的硫，形成经济的镍铜硫化物矿床。来自交代地幔源的氧化镁铁质岩浆可能是主要造山带的一个重要特征。