This contribution presents new U-Pb geochronological data and attempts to elucidate the complex evolution history of various garnet types identified from two kimberlite pipes in the Wafangdian diamond mining district, southern Liaoning Province. These calcic garnets are dominated by andradite with relatively low proportions of schorlomite, grossular and pyrope. Abundant euhedral to subhedral, highly brecciated andradite phenocrysts hosted by LN30 “carbonatite-like” kimberlite samples yield a lower-intercept age of 459.3 ± 3.4 Ma, which is in excellent agreement with the previously reported phlogopite Ar-Ar (463.9 ± 0.9 Ma) and Rb-Sr ages (461.7 ± 4.8 Ma). Based on their trace element and C-O isotopic compositions of associated groundmass carbonate, we infer that these primary magmatic andradites probably originated from kimberlitic magmas. By comparison, three compositionally and texturally distinct groups of Ti-bearing andradites from LN42 hypabyssal kimberlites separately define three well-fitted regression lines with lower intercept ages at 581 ± 12 Ma, 414.9 ± 9.3 Ma and 292.0 ± 5.7 Ma, respectively. Relict andradite xenocrysts implies that ancient lower crust of the North China Craton (NCC) might have been affected by a significant but less-known tectonothermal event to varying degrees at ∼ 0.6 Ga. By contrast, fresh grains of magmatic Ti-andradites with chemical zoning produce a relatively young age of ∼ 415 Ma, which can still provide minimum age estimates for the most recent pulses of Paleozoic kimberlite magmatism in this study area. Noteworthily, a yet unrecognized local-scale hydrothermal alteration event at ∼ 292 Ma has been recorded in the texturally distinct population of secondary hydroandradites, whose age reported here for the first time is geologically meaningful. To sum up, this study further highlights andradite U-Pb dating as a potential robust geochronometer for constraining the late-stage evolution of kimberlite magmas as well as post emplacement hydrothermal alteration.

该贡献提供了新的 U-Pb 年代学数据，并试图阐明从辽宁省南部瓦房店钻石矿区的两个金伯利岩管中识别出的各种石榴石类型的复杂演化历史。这些钙质石榴石以钙辉石为主，磷辉石、钙铝榴石和镁铝榴石的比例相对较低。由 LN30“类碳酸盐岩”金伯利岩样品承载的丰富的自面体到半自体、高度角砾化的红柱石斑晶产生了 459.3 ± 3.4 Ma 的较低截距年龄，这与先前报道的金云母 Ar-Ar (463.9 ± 0.9 Ma) 非常吻合和 Rb-Sr 年龄 (461.7 ± 4.8 Ma)。根据伴生基体碳酸盐的微量元素和CO同位素组成，我们推断这些原生岩浆红辉石可能起源于金伯利岩岩浆。相比之下，来自 LN42 次浅海金伯利岩的三个成分和结构不同的含钛红铁矿组分别定义了三个拟合良好的回归线，它们的截距较低，分别为 581 ± 12 Ma、414.9 ± 9.3 Ma 和 292.0 ± 5.7 Ma。残留的钙辉石异晶表明，华北克拉通 (NCC) 的古代下地壳可能在 0.6 Ga 时受到了不同程度的重要但鲜为人知的构造热事件的影响。相比之下，具有化学分带的岩浆钛钙长石的新鲜颗粒产生了~415 Ma的相对年轻的年龄，这仍然可以提供该研究区最近的古生代金伯利岩岩浆作用脉冲的最小年龄估计。值得注意的是，在质地不同的次生水仙岩群中记录了一个尚未识别的~292 Ma的局部尺度热液蚀变事件，其年龄首次在此报道，具有地质意义。综上所述，本研究进一步强调了 andradite U-Pb 测年作为一种潜在的稳健地质年代学，用于约束金伯利岩岩浆后期演化以及侵位后的热液蚀变。