Preferential removal of W relative to other trace elements from zoned, W–Sn–U–Pb-bearing hematite coupled with disturbance of U–Pb isotope systematics is attributed to pseudomorphic replacement via coupled dissolution reprecipitation reaction (CDRR). This hematite has been studied down to the nanoscale to understand the mechanisms leading to compositional and U/Pb isotope heterogeneity at the grain scale. High-Angle Annular Dark Field Scanning Transmission Electron Microscopy (HAADF STEM) imaging of foils extracted in situ from three locations across the W-rich to W-depleted domains show lattice-scale defects and crystal structure modifications adjacent to twin planes. Secondary sets of twins and associated splays are common, but wider (up to ~100 nm) inclusion trails occur only at the boundary between the W-rich and W-depleted domains. STEM energy-dispersive X-ray mapping reveals W- and Pb-enrichment along 2–3 nm-wide features defining the twin planes; W-bearing nanoparticles occur along the splays. Tungsten and Pb are both present, albeit at low concentrations, within Na–K–Cl-bearing inclusions along the trails. HAADF STEM imaging of hematite reveals modifications relative to ideal crystal structure. A two-fold hematite superstructure (a = b = c = 10.85 Å; α = β = γ = 55.28°) involving oxygen vacancies was constructed and assessed by STEM simulations with a good match to data. This model can account for significant W release during interaction with fluids percolating through twin planes and secondary structures as CDRR progresses from the zoned domain, otherwise apparently undisturbed at the micrometre scale. Lead remobilisation is confirmed here at the nanoscale and is responsible for a disturbance of U/Pb ratios in hematite affected by CDRR. Twin planes can provide pathways for fluid percolation and metal entrapment during post-crystallisation overprinting. The presence of complex twinning can therefore predict potential disturbances of isotope systems in hematite that will affect its performance as a robust geochronometer.

相对于其他痕量元素，从带状W-Sn-U-Pb赤铁矿中优先去除W，再加上U-Pb同位素系统的干扰，归因于通过耦合溶解再沉淀反应（CDRR）的假晶置换。已对该赤铁矿进行了纳米级研究，以了解导致晶粒级分组成和U / Pb同位素异质性的机理。高角度环形暗场扫描透射电子显微镜（HAADF STEM）对原位提取的箔进行成像从富W到贫W畴的三个位置显示的晶格尺度缺陷和孪晶面附近的晶体结构修饰。次生双胞胎和相关联的八字组是常见的，但更宽（至约100 nm）的夹杂物痕迹仅出现在富W和贫W域之间的边界处。STEM能量色散X射线映射显示在定义双晶面的2–3 nm宽特征上W和Pb富集；含W的纳米粒子沿花键出现。钨和铅都存在，尽管浓度很低，但在沿径迹的含有Na–K–Cl的夹杂物中。赤铁矿的HAADF STEM成像显示相对于理想晶体结构的修饰。两重赤铁矿上部结构（a = b = c= 10.85Å; α=β=γ= 55.28°）涉及氧空位，并通过STEM模拟评估并与数据良好匹配。该模型可以解释当CDRR从分区域前进时，在与通过双平面和二级结构渗流的流体相互作用期间显着的W释放，否则显然在微米范围内不受干扰。在纳米级证实了铅的迁移，这导致了受CDRR影响的赤铁矿中U / Pb比的扰动。孪晶面可以为结晶后叠印期间的流体渗透和金属截留提供途径。因此，复杂孪晶的存在可以预测赤铁矿中同位素系统的潜在干扰，这将影响其作为稳健的地球计时器的性能。