Heterogeneity and evolution of the Miocene Iceland mantle plume

• Main Author: Martin-Roberts, Emma L.
• Other Authors: Stuart, Fin, Fitton, Godfrey, Kirstein, Linda, Natural Environment Research Council (NERC)
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: The University of Edinburgh 2020
• Subjects: mantle plume evolution; West Greenland; geochemical analysis; isotope ratio variations; helium isotopes; North Atlantic Igneous Province; core-mantle boundary; Greenland; Iceland; North Atlantic
• Online Access: https://hdl.handle.net/1842/38092; https://doi.org/10.7488/era/1363

The North Atlantic Igneous Province (NAIP) is unique in that it presents a complete magmatic history from ~62 Ma to today. This provides an unrivalled opportunity to study the geochemical and thermal evolution of a mantle plume through time. Despite the wealth of geochemical data available for Iceland, our knowledge of mantle heterogeneity beneath Iceland during the mid-Miocene remains sketchy. The oldest basalts (15-16 Ma) on Iceland are preserved in several ~1 km thick sequences in Vestfirdir in Northwest Iceland. Each sequence contains a hiatus in volcanism, marked by a laterite-lignite horizon, that is likely the result of the relocation of a spreading axis. The basalt geochemistry from above and below this horizon provide an insight into the heterogeneity of the Iceland mantle plume during the mid-Miocene. The Vestfirdir basalts are also characterised by the highest 3He/4He (~40 Ra) on Iceland requiring the involvement of deep mantle. Incompatible trace element and Nd-Sr-Pb isotope data indicate that there are two enriched components (NWE1 and NWE2) and one depleted component (NWD1) within the mantle beneath Iceland during the Miocene. Both enriched components have low 143Nd/144Nd and high 87Sr/86Sr, that are comparable with the most enriched modern Iceland basalts. The two components are differentiated by the relative enrichment in the more incompatible trace elements and their Pb-isotope compositions. Component NWE1 is similar to the modern Iceland mantle plume composition, while NWE2 is closer in composition to modern depleted Iceland rift-zone basalts. The depleted component identified in the Vestfirdir basalts (NWD1) is distinct from modern North Atlantic N-MORB and the depleted component in the neovolcanic rift zones by, for instance, higher incompatible trace element concentrations and a more negative ∆207Pb composition. These observations allow the identification of a depleted mantle component present at 15-16 Ma that is no longer sampled in the modern Iceland plume setting and argue for a distinct ...