To test the potential of deformation twins to record the age of impact events, micrometre-scale size mechanical twins in shocked monazite grains from three impact structures were analyzed by atom probe tomography (APT). Shocked monazite from Vredefort (South Africa; ∼300 km crater diameter), Araguainha (Brazil; ∼40 km diameter), and Woodleigh (Australia; 60 to 120 km diameter) were studied, all from rocks which experienced pressures of ∼30 GPa or higher, but each with a different post-impact thermal history. The Vredefort sample is a thermally recrystallised foliated felsic gneiss and the Araguainha sample is an impact melt-bearing bedrock. Both Vredefort and Araguainha samples record temperatures > 900 °C, whereas the Woodleigh sample is a paragneiss that experienced lower temperature conditions (350 - 500 °C). A combined ²⁰⁸Pb/²³²Th age for common {1$\overline{2}\overline{2}$} twins and shock-specific ($\overline{1}$01) twins in Vredefort monazite was defined at 1979 ± 150 Ma, consistent with the accepted impact age of ∼2020 Ma. Irrational η1 [$\overline{1}\overline{1}$0] shock-specific twins in Araguainha monazite yielded a 260 ± 48 Ma age, also consistent with the accepted 250-260 Ma impact age. However, the age of a common (001) twin in Araguainha monazite is 510 ± 87 Ma, the pre-impact age of igneous crystallisation. These results are explained by the occurrence of common (001) twins in tectonic deformation settings, in contrast to the ($\overline{1}$01) and irrational η1 [$\overline{1}\overline{1}$0] twins, which have only been documented in shock-deformed rocks. In Woodleigh monazite, APT age data for all monazite twins [(001), ($\overline{1}$01), newly identified 102°/<$\overline{4}$23> twin], and host monazite are within uncertainty at 1048 ± 91 Ma, which is interpreted as a pre-impact age of regional metamorphism. We therefore are able to further constrain the poorly known age of the Woodleigh impact to < 1048 ± 91 Ma. These results provide evidence that Pb is expelled from monazite during shock twin formation at high temperature (Vredefort and Araguainha), and also that Pb is not mobilised during twinning at lower temperature (Woodleigh). Our study suggests that twins formed during shock metamorphism have the potential to record the age of the impact event in target rocks that are sufficiently heated during the cratering process.

为了测试变形孪晶记录撞击事件年龄的潜力，通过原子探针断层扫描 (APT) 分析了来自三种撞击结构的冲击独居石晶粒中的微米级机械孪晶。研究了来自 Vredefort（南非；陨石坑直径约 300 公里）、Araguainha（巴西；直径约 40 公里）和 Woodleigh（澳大利亚；直径 60 至 120 公里）的震动独居石，所有岩石都来自经历了约 30 GPa 或更高，但每个都有不同的冲击后热历史。Vredefort 样品是热重结晶的叶状长英质片麻岩，Araguainha 样品是含冲击熔体的基岩。Vredefort 和 Araguainha 样品记录的温度均 > 900 °C，而 Woodleigh 样品是经历了较低温度条件 (350 - 500 °C) 的副片麻岩。一个组合²⁰⁸ Pb/ ²³² Th 普通{1 年龄$\overline{2}\overline{2}$} 双胞胎和电击专用 ($\overline{1}$01) Vredefort 独居石中的双胞胎被定义为 1979 ± 150 Ma，与公认的 2020 Ma 撞击年龄一致。无理数 η1 [$\overline{1}\overline{1}$0] Araguainha 独居石中的冲击特异性双胞胎产生了 260 ± 48 Ma 年龄，也与公认的 250-260 Ma 撞击年龄一致。然而，Araguainha 独居石中常见的 (001) 双胞胎的年龄为 510 ± 87 Ma，这是火成岩结晶的撞击前年龄。这些结果可以通过构造变形环境中常见 (001) 孪晶的出现来解释，而 ($\overline{1}$01) 和无理数 η1 [$\overline{1}\overline{1}$0]双胞胎，仅在冲击变形的岩石中被记录。在 Woodleigh 独居石中，所有独居石双胞胎的 APT 年龄数据 [(001), ($\overline{1}$01), 新确定的 102°/<$\overline{4}$23>孪生]和寄主独居石在 1048±91 Ma 的不确定性范围内，这被解释为区域变质作用的撞击前年龄。因此，我们能够进一步将鲜为人知的伍德利撞击年龄限制在 < 1048 ± 91 Ma。这些结果提供的证据表明，在高温激波孪晶形成过程中（Vredefort 和 Araguainha），Pb 从独居石中被排出，而且在较低温度下形成孪晶过程中，Pb 没有迁移（Woodleigh）。我们的研究表明，在冲击变质过程中形成的双胞胎有可能记录在陨石坑过程中充分加热的目标岩石中撞击事件的年龄。