Abstract This study uses selected granite samples to evaluate the effect of redox conditions expressed as molar ferric-ferrous iron oxide ratio, Fe3+# [=Fe2O3/(FeO + Fe2O3)], on estimation of crystallization pressure (P) of granites using the Qtz-geobarometer. The results indicate that calculated P decreases significantly with increasing Fe3+# for calc-alkaline, metaluminous and peraluminous granites, but much less so for peralkaline and evolved granites. For a calc-alkaline, metaluminous or peraluminous granite sample of a fixed silica content, the calculated P values are a polynomial function of Fe3+#. The difference in P for Fe3+# between 0.1 (reduced) and 1.0 (oxidized) is as high as 437 MPa (or 4.37 kb), much higher than the uncertainty of the geobarometer. However, peralkaline and evolved granite samples display much less difference in P for Fe3+# between 0.1 and 1.0, essentially within the uncertainty. Therefore, redox conditions need to be considered when using Qtz-geobarometry to estimate P of calc-alkaline, metaluminous and peraluminous granites, particularly those bearing hornblende with relatively low silica contents, but such corrections may not be required for peralkaline and highly evolved granites. A practical procedure is proposed to calculate Fe3+# from whole-rock geochemical data to obtain improved P estimation, and a Microsoft Excel spreadsheet program is provided. In addition to constraining the emplacement depth, the program can also be used to evaluate the redox conditions using ferric-ferrous iron oxide ratios, both of which are important for mineralization associated with granite intrusions.

中文翻译：

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三价铁-亚铁氧化铁比率：通过 Qtz-geobarometry 估计对花岗岩结晶压力的影响

摘要 本研究使用选定的花岗岩样品来评估氧化还原条件对使用 Qtz 估算花岗岩结晶压力 (P) 的影响，以摩尔三价铁-亚铁氧化铁比 Fe3+# [=Fe2O3/(FeO + Fe2O3)] 表示。 -地理气压计。结果表明，对于钙碱性、金属铝和过铝质花岗岩，计算出的 P 随 Fe3+# 的增加而显着降低，但对于过碱性和演化花岗岩，则下降幅度较小。对于具有固定二氧化硅含量的钙碱性、金属铝或过铝花岗岩样品，计算的 P 值是 Fe3+# 的多项式函数。Fe3+# 在 0.1（还原）和 1.0（氧化）之间的 P 差异高达 437 MPa（或 4.37 kb），远高于地球气压计的不确定性。然而，过碱性和演化的花岗岩样品在 0.1 和 1.0 之间显示 Fe3+# 的 P 差异要小得多，基本上在不确定性范围内。因此，当使用 Qtz 地压法估算钙碱性、金属铝和过铝质花岗岩的 P 时，需要考虑氧化还原条件，特别是那些含有相对较低二氧化硅含量的角闪石的花岗岩，但对于过碱性和高度演化的花岗岩，可能不需要这种校正。提出了一种从全岩地球化学数据计算 Fe3+# 的实用程序，以获得改进的 P 估计，并提供了 Microsoft Excel 电子表格程序。除了限制就位深度外，该程序还可用于使用三价铁-二价铁氧化物比率来评估氧化还原条件，