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

点击翻译按钮获取中文摘要

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.