Dating mantle metasomatism: LA‒MC‒ICPMS U‒Pb dating of garnet xenocrysts from the V. Grib kimberlite, Russia

地幔交代作用在很大程度上控制了岩石圈地幔的组成，从而控制了岩石圈地幔的物理和化学性质。因此，它对碱性的岩石成因施加控制（例如，金伯利岩和碳酸岩）板内岩浆，金刚石形成，以及，例如，稀土元素矿床随着时间的推移，成分多样的交代流体反复叠加在亏损的原始地幔围岩上。这就产生了一个复杂的，基本上无处不在的交代岩石圈地幔，在微米到微米的尺度上是不均匀的。通过识别重要的事件和过程来解码这一复杂的记录对于重建岩石圈演化、地球挥发性通量的性质和起源以及深部岩石圈和地壳过程之间的联系是至关重要的。石榴石是表征次大陆岩石圈地幔交代事件的最广泛使用的相，包括大部分厚的岩石圈，深度可达~250 km。然而，对于年龄测定研究，石榴石迄今为止只用于繁琐，昂贵和耗时的传统同位素测年技术。法兰克福同位素和元素研究中心（FIERCE）在分析和数据处理技术方面的最新进展使低铀石榴石首次可以进行原位年龄测定，不仅可以快速通过，而且可以检测矿物尺度的异质性。在这个项目中，现场LA-MC-ICPMS U-Pb测年将被应用于一组良好的特征石榴石捕虏晶从V. Grib金伯利岩调查特定类型的地幔交代和金伯利岩和金刚石形成之间的时间和因果关系。来自V. Grib金伯利岩的石榴石捕虏晶对岩石圈柱进行了采样，深度约为220 km，并为硅酸盐和碳酸盐交代作用提供了证据。研究结果还将提供深入了解岩石圈的演化下的波罗的海盾牌联系深部岩石圈的良好的地壳过程。

Mantle metasomatism largely controls the composition, and thus the physical and chemical properties of the lithospheric mantle. It thereby exerts control over the petrogenesis of alkaline (e.g., kimberlitic and carbonatitic) within-plate magmas, diamond formation, and the generation of, e.g., rare-earth element deposits. Over time, compositionally diverse metasomatic fluids repeatedly overprint variably depleted original mantle wall-rocks. This produces a complex, essentially ubiquitously metasomatised lithospheric mantle, heterogeneous on scales of microns to terranes. Decoding this complex record by identifying significant episodes and processes is essential for reconstructing lithosphere evolution, the nature and origin of Earth’s volatile flux, and the link between deep lithospheric and crustal processes.Garnet is the most widely used phase for characterizing metasomatic events in the subcontinental lithospheric mantle, comprising a large proportion of thick cratonic lithosphere up to ~250 km depth. For age-dating studies, however, garnet has so far only been employed in tedious, costly and time-intensive conventional isotope dating techniques. Very recent advances in analytical and data reduction techniques at the Frankfurt Isotope and Element Research Center (FIERCE) make low-U garnet accessible to in situ age dating for the first time, allowing not only fast through-put but also the detection of mineral-scale heterogeneity. In this project, in situ LA-MC-ICPMS U‒Pb dating will be applied to a set of well-characterized garnet xenocrysts from the V. Grib kimberlite to investigate a temporal and causal link between specific types of mantle metasomatism and kimberlite and diamond formation. Garnet xenocrysts from the V. Grib kimberlite sample the lithospheric column to a depth of ~220 km and provide evidence for silicate and carbonatitic metasomatism. The results will also provide insights into the lithosphere evolution underneath the Baltic shield by linking deep lithospheric to well-dated crustal processes.