Magma mixing and contamination are among the dominant processes in the building of the isotopic diversity of granite rocks. Felsic microgranular enclaves (FMEs) are remnants of magma mixing and they often carry xenocrysts that also record contamination and assimilation in crystallization fronts disrupted during replenishment events. In addition to isotopic changes, contamination may alter the redox state of the intruding magmas depending on the nature of the country rocks. We investigate the role played by different country-rocks on the redox trajectory of the precursor magmas of two Brazilian occurrences: the Mauá pluton, which intruded sulfide- and graphite-bearing metasediments, and the Salto rapakivi pluton, which intruded orthogneisses. Oxygen fugacity ( f O 2 ) was estimated using Eu 2+ /Eu 3+ ratios retrieved from plagioclase chemistry and literature equation that considers melts chemistry and temperature. The model is demonstrated to replicate the f O 2 from plagioclase-bearing experimental data within a precision usually better than 1 log unit. Results obtained for the Mauá pluton indicate that contaminated plagioclase cores are significantly more reduced (∆QFM − 1.5; 87 Sr/ 86 Sr ~ 0.713) than the xenocryst rims (∆QFM + 0.5; 87 Sr/ 86 Sr ~ 0.710). In contrast, results obtained for the Salto rapakivi pluton vary from ∆QFM + 1.0 to ∆QFM + 2.7 and do not coincide with core to rim variations in 87 Sr/ 86 Sr. MMEs are comparatively more reduced (− 0.1 ≤ ∆QFM ≤ + 0.7). Our results imply that the redox path registered by plagioclase crystals from different geological backgrounds reflects the nature of their country rocks and the processes that affected their precursor magmas The main advantage of using plagioclase trace element data to model redox conditions of equilibrium magmas is the possibility of determining f O 2 paths via spatially controlled trace element analyses of crystals rims and cores. Coupled to the possibility of obtainment of Sr isotope data, the model represents a powerful way to unravel the processes responsible for redox paths of magmatic rocks of varied nature.

中文翻译：

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通过斜长石微量元素特征跟踪形成飞地的花岗岩熔体的氧逸度

岩浆混合和污染是形成花岗岩同位素多样性的主要过程。长英质微粒飞地 (​​FME) 是岩浆混合的残余物，它们通常携带异晶，这些异晶也记录了在补给事件期间中断的结晶前沿中的污染和同化。除了同位素变化外，污染可能会改变侵入岩浆的氧化还原状态，具体取决于围岩的性质。我们研究了不同的乡村岩石对巴西两个矿点的前体岩浆氧化还原轨迹所起的作用：Mauá 岩体侵入了含硫化物和石墨的变质沉积物，而 Salto rapakivi 岩体侵入了正片麻岩。使用从斜长石化学和考虑熔体化学和温度的文献方程中检索到的 Eu 2+ /Eu 3+ 比率估计氧逸度 (f O 2 )。该模型被证明可以在通常优于 1 log 单位的精度内从带有斜长石的实验数据中复制 f O 2。为 Mauá 岩体获得的结果表明，受污染的斜长石岩心比异晶边缘（ΔQFM + 0.5；87 Sr/ 86 Sr ~ 0.710）显着减少（ΔQFM - 1.5；87 Sr/ 86 Sr ~ 0.713）。相比之下，从 Salto rapakivi 岩体获得的结果从 ΔQFM + 1.0 变化到 ΔQFM + 2.7，并且与 87 Sr/86 Sr 的核心到边缘变化不一致。MME 相对减少更多（- 0.1 ≤ ΔQFM ≤ + 0.7）。我们的结果意味着来自不同地质背景的斜长石晶体记录的氧化还原路径反映了其围岩的性质以及影响其前驱岩浆的过程使用斜长石微量元素数据模拟平衡岩浆氧化还原条件的主要优势是通过对晶体边缘和核心进行空间控制的微量元素分析来确定 f O 2 路径。再加上获得 Sr 同位素数据的可能性，该模型代表了一种强大的方式来解开负责不同性质岩浆岩氧化还原路径的过程。