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

地幔交代作用测年：俄罗斯 V. Grib 金伯利岩石榴石异晶的 LAâMCâICPMS UâPb 测年

• 批准号: 497273650
• 负责人: Dr. Leo Jakob Millonig
• 金额: --
• 依托单位: Abteilung Petrologie und Geochemie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2022
• 资助国家: 德国
• 起止时间: 2021-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/497273650?language=en
• 关键词: Dating; mantle; metasomatism; LA; MC

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.

地幔交代作用在很大程度上控制着岩石圈地幔的组成，从而控制着岩石圈地幔的物理化学性质。因此，它控制着碱性(如金伯利岩和碳酸盐岩)板内岩浆的成岩作用、钻石的形成和稀土元素矿床的生成。随着时间的推移，成分多样的交代流体反复地重叠着不同程度地耗尽的原始地幔围岩。这产生了一个复杂的、基本上无处不在的交代岩石圈地幔，在微米到地体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、地球挥发通量的性质和来源以及深部岩石圈和地壳过程之间的联系至关重要。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，它包含了相当大比例的厚克拉通岩石圈，深度可达约250公里。然而，对于年龄测定研究，到目前为止，石榴石只被用于繁琐、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(FAIRE)在分析和数据简化技术方面的最新进展使低U石榴石首次能够进行原位年龄测定，不仅可以快速通过测量，还可以检测矿物尺度的不均一性。在这个项目中，将对一组来自V.Grib金伯利岩的石榴石捕虏晶进行现场LA-MC-ICPMS U-Pb测年，以研究特定类型的地幔交代作用与金伯利岩和钻石形成之间的时间和因果联系。来自V.Grib金伯利岩中的石榴石捕虏晶在岩石圈柱体中取样至约220公里，为硅酸盐和碳酸盐交代作用提供了证据。这些结果还将通过将深层岩石圈与成熟的地壳过程联系起来，深入了解波罗的海地盾下的岩石圈演化。