The direct dating of gem-quality garnet mineralization has been extremely limited, even though it has been known for decades that garnet may be dated by the U–Pb method. Here, we demonstrate the application of in situ laser U–Pb geochronology on gem-quality tsavorite to determine the timing of mineralization from two localities in the Mozambique Belt, Tanzania.

U–Pb dating of tsavorite from Merelani and Umba provides ages of 569.5 ± 6.8 Ma and 540.0 ± 5.8 Ma, respectively. Due to the high closure temperature of the U–Pb system in garnet, we argue that these ages correspond to tsavorite mineralization. These ages postdate the East African Orogeny (650–620 Ma), the most significant metamorphic episode recorded in the Mozambique Belt, which had been previously considered to be the main tsavorite mineralization event. Instead, these dates correspond to the later Kuungan orogenic episode (570–530 Ma), associated with the final amalgamation of Gondwana. The mineralization of tsavorite tens of millions of years after the East African Orogeny in the Mozambique Belt illustrates the benefits of direct dating of gem-quality garnet to determine mineralization timing and style.

尽管几十年来人们就知道可以通过 U-Pb 法对石榴石进行测年，但对宝石级石榴石矿化的直接测年却极为有限。在这里，我们展示了原位激光 U-Pb 地质年代学在宝石级沙弗莱石上的应用，以确定坦桑尼亚莫桑比克带两个地点的成矿时间。

对 Merelani 和 Umba 的沙弗莱石进行 U-Pb 测年，其年龄分别为 569.5 ± 6.8 Ma 和 540.0 ± 5.8 Ma。由于石榴石中 U-Pb 系统的闭合温度较高，我们认为这些年龄对应于沙弗莱石矿化。这些年龄是东非造山运动（650-620 Ma）之后的，这是莫桑比克带记录的最重要的变质事件，之前被认为是主要的沙弗莱石成矿事件。相反，这些日期对应于后来的昆干造山期（570-530 Ma），与冈瓦纳大陆的最终合并有关。东非造山运动后几千万年，莫桑比克带沙弗莱石的矿化说明了直接对宝石级石榴石进行测年以确定矿化时间和类型的好处。