WINDOWS INTO THE DEEP MANTLE FROM LONG-LASTING EM-1 MANTLE PLUME (Invited Presentation)

Hawai‘i and Kerguelen are the longest lived hotspot tracks in the Pacific and Indian oceans, respectively, spanning 81 and >115 million years of magmatic activity. Basalts on both archipelagoes carry enriched mantle “EM-1” signatures. When projected to the core-mantle boundary, Hawai‘i and Pitcairn overlie the edges of the Pacific large low-shear-velocity province (LLSVP), whereas Kerguelen and Tristan are located on the eastern and western edges, respectively, of the African LLSVP. At Hawai‘i, the LLSVP is proposed to be the repository for enriched components responsible for Loa-trend geochemical enrichment and heterogeneity. For the Kerguelen Archipelago, the enriched component dominates the chemistry of alkalic basalts (25-24 Ma), whereas older (28-26 Ma) tholeiitic-transitional basalts also contain a depleted Southeast Indian Ridge component from when the plume was near the ridge. In isotope plots, Kerguelen compositions form sub-parallel trends that are distinctly more enriched than those from Hawai‘i. Kerguelen and Tristan basalts carry the strongest enriched signature (DUPAL anomaly), whereas Pitcairn and Hawaiian-Loa trend basalts have a distinct, slightly less-pronounced enriched signature. We infer that the Pacific and African LLSVPs store different recycled materials and that the ambient deep mantle is also different beneath the Indian and Pacific oceans. Pacific deep mantle is sampled by Kea trend volcanoes and many other Pacific oceanic plateaus (Ontong-Java, Wrangellia). In Hawai‘i, the EM-1 signature is traced back for at least 5 Ma and appears episodically along the Northwest Hawaiian Ridge as early as 47 Ma. In Kerguelen, it can be traced back until 34 Ma on the archipelago and Northern Kerguelen Plateau, and until 82 Ma along the 5000 km-long Ninetyeast Ridge. This indicates that LLSVPs are long-lived features of the deep mantle, with different compositions and play a significant role in the geochemical signature of strong mantle plumes.