Identifying evidence of oxidative weathering in the geological record is essential to trace the evolution of Earth's atmosphere oxygenation. Metamorphosed residues of lateritic weathering have been identified as two rock types in the 2.1‐Ga‐old Cercadinho Formation, Piracicaba Group, Quadrilátero Ferrífero of Minas Gerais. One is tourmaline–hematite–sillimanite–kyanite quartzite; the other is rutile–tourmaline–hematite–muscovite phyllite. Both rocks have abundant tourmaline with δ¹¹B values between about −17‰ and −13‰. The Cercadinho tourmaline is roughly parallel to the povondraite–“oxy‐dravite” join of meta‐evaporitic tourmaline, in its more aluminous segment, offset to higher contents of iron. These compositional and isotopic characteristics of the Cercadinho tourmaline indicate that continental evaporitic brines interacted with aluminium‐ and iron‐rich residues of lateritic weathering. The abundance of disseminated tourmaline, a mineral poorly reported from palaeosols worldwide, implies a boron‐rich brine overprint on the lateritic profile before the onset of metamorphism, reflecting a climatic change from humid to arid conditions in a continental setting. The recognition of lateritic weathering in the Cercadinho Formation contributes to the amount of evidence for increased levels of atmospheric oxygen between 2.22 and 2.06 Ga ago.

中文翻译：

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电气石组成和硼同位素记录了大氧化事件中的红土风化

在地质记录中识别氧化风化的证据对于追踪地球大气氧化的演变至关重要。红土风化的变质残留物已被确认为米纳斯吉拉斯州2.1rac的切尔卡迪尼奥组的Piracicaba组，QuadriláteroFerrífero的两种岩石类型。一种是电气石-赤铁矿-硅线石-蓝晶石石英岩。另一个是金红石-电气石-赤铁矿-白云母千晶石。这两种岩石具有丰富的电气石δ ¹¹B值在大约-17‰和-13‰之间。Cercadinho电气石大致上与含铝蒸发的电气石中的坡辉石-“氧-草酸盐”结合体平行，在其铝含量更高的部分中，被较高的铁含量所抵消。切尔卡迪诺电气石的这些组成和同位素特征表明，大陆蒸发性盐水与红土风化的富铝和铁的残留物相互作用。分布广泛的电气石是世界各地古土壤报道较少的矿物，这意味着在变质作用发生之前，红土剖面上富含硼的盐水叠印，反映了大陆环境从潮湿到干旱的气候变化。对Cercadinho组中的红土风化作用的认识有助于增加2.22至2之间大气中氧气含量的证据。