ROBUST HOTSPOT ORIGIN FAR FROM LLSVP MARGINS

Walter Alvarez has had a longstanding interest in mantle dynamics, ranging from studies of tectonostratigraphic terranes in western North America (Alvarez et al., 1980; Tarduno and Alvarez, 1985) to studies of sublithospheric mantle flow (e.g., Alvarez, 2001). Herein, I will discuss hotspot motion and how it bears on plume generation and the nature of the lowermost mantle. It has been proposed that hotspots occur on the edges of the African and Pacific large low shear velocity provinces (LLSVP) (Torsvik et al., 2006) and that this has a special significance in terms of plume/hotspot generation. The basis for this proposed global correlation has in turn been challenged (e.g. Austermann et al., 2013; Davies et al., 2015). I will take a different approach by considering hotspots with the greatest buoyancy flux (e.g. King and Adam, 2014) because to be successful, any global model should be able to explain their origin. In all analyses of buoyancy flux, the Pacific’s Hawaiian hotspot stands out above all others. However, paleomagnetic and age-distance relationships indicate that the Hawaiian hotspot originated >1500 km N of the Pacific LLSVP and subsequently drifted to its edge (Tarduno et al., 2003; Bono et al., 2019) where it may have become anchored (Harrison et al., 2017). The hotspot with the highest buoyancy flux in the Atlantic is Iceland, which is far from the African LLSVP. Iceland represents the youngest of three past episodes of extraordinary volcanism affecting the North Atlantic-Arctic region, namely the North Atlantic Tertiary Volcanic Province, the High Arctic Large Igneous Province and the Siberian Traps. This recurrent volcanism spanning more than 250 million years requires either drift of a single pulsing plume, or separate plumes, generated far from the edge of the proposed stationary African LLSVP. Thus, the nature and histories of these robust hotspots in the Pacific and Atlantic imply an origin distinct from LLSVPs.