Mantle plumes, xenoliths and melt inclusions - heterogeneous deep mantle sources or shallow melt-rock interaction?

在这项研究中，我们将使用加那利群岛作为一个天然的实验室，以检查熔体成分的影响，作为一个被动大陆边缘接近，从底层岩石圈，主要是海洋性的，越来越大陆的性质。特别是，这项研究将使用熔融包裹体，捕获在早期结晶阶段，如橄榄石，在原始熔岩比较熔融组合物之前，与上覆岩石圈的相互作用与最终爆发的产品。熔体包裹体提供了一个快照的原始地幔熔体成分，因此保存在地幔源成分的不均匀性的证据。熔融包裹体，但是，小（亚毫米直径），直到最近，一个熔融包裹体中的地幔源的一个以上的潜在示踪剂的分析一直具有挑战性。该项目使用主要、痕量和挥发性元素与Sr、Nd和Pb同位素测量的强大组合，并使用监督员及其合作者最近开发的方法（见Harvey等人，2009; Reinhard等人，2017年，2018年）将指纹的化学和同位素异质性的性质，在个别熔体包裹体是代表成分，形成熔体形成加那利群岛。这种组合的示踪剂不仅提供了一个独特的视角的规模，规模和分布的地幔柱的地幔不均匀性，这是这个岛屿群岛的基础，但也提供了宝贵的见解，熔体的相互作用与被动的边缘是否可以复制EM-1签名归因于深地幔的异质性。熔融包裹体成分和最终爆发的岩浆之间的差异将揭示接近被动大陆边缘的浅污染性质的任何变化。

In this study we will use the Canary Islands archipelago as a natural laboratory to examine the effects on melt composition as a passive continental margin is approached, transitioning from underlying lithosphere that is dominantly oceanic to increasingly continental in its nature. In particular, this study will use melt inclusions, trapped in early crystallising phases such as olivine, in primitive lavas to compare melt compositions prior to interaction with the overlying lithosphere with the final erupted products. Melt inclusions provide a snapshot of primary mantle melt composition therefore preserving evidence of the compositional heterogeneity in the mantle source. Melt inclusions are, however, small (sub-mm diameter) and, until recently, analysis of more than one potential tracer of mantle source in a melt inclusion had been challenging. This project, using a powerful combination of major, trace and volatile elements with Sr, Nd and Pb isotope measurements, and using methods recently developed by the supervisors and their collaborators (see Harvey et al., 2009; Reinhard et al., 2017, 2018) will fingerprint the nature of the chemical and isotopic heterogeneities in individual melt inclusions that are representative of the ingredients that formed the melts forming the Canary Islands. This combination of tracers will not only provide a unique perspective on the scale, magnitude and distribution of mantle heterogeneities within the mantle plume that has underlain this island archipelago, but also provide valuable insights into whether interaction of a melt with a passive margin can replicate the EM-1 signature attributed to deep-mantle heterogeneity. Differences between melt inclusion compositions and final erupted magmas will reveal any changes in the nature of shallow contamination approaching a passive continental margin.