Sedimentary evidence for moderate mantle temperature anomalies associated with hotspot volcanism

Abstract

One of the characteristics of deep-rooted mantle plume models, and the hotspot volcanism with which they are associated is the presence of anomalously buoyant asthenosphere underlying the lithospheric plate. The presence of hot, upwelling, lowdensity asthenosphere causes shallowing of the seafloor over the plume center. It is commonly assumed that as the plume mantle disperses, greater subsidence occurs compared to normal oceanic crust. However, in this paper analysis of the sedimentary cover from a range of hotspot-related seamounts, plateaus, and ridges of various ages from all major ocean basins shows either no subsidence anomalies or only moderate ones that can be linked to hot asthenosphere during hotspot magmatism. Assuming that all the uplift is caused by excess mantle heat, temperature anomalies rarely exceed 100 °C for a plume head ~100 km thick and could be somewhat lower if dynamic flow or composition are important causes of uplift. On the Ontong-Java Plateau, Mid-Pacific Mountains, Emperor Seamounts, Hess Rise, and MIT Guyot, subsidence is slower than for normal oceanic lithosphere, suggesting either colder than normal mantle temperatures or, more likely, the formation of a buoyant lithospheric root under the hotspot province at the time of its formation.

Are ‘hot spots’ hot spots?

“…This does not explain, however, why the picrite cumulates that are often assumed to represent original melts, are common. The absence of plateau subsidence predicted by cooling models has been attributed to post-eruption magmatic underplating causing continuous crustal growth and bathymetric support [Clift, 2005] or to support from buoyant, depleted mantle residuum remaining after melt extraction, e.g., at the Ontong Java plateau [Robinson, 1988] and the Hawaiian swell [Phipps- Morgan et al, 1995]. On the other hand, the lack of such support in the North Atlantic has been explained by the suggestion that vigorous convection removed the residuum there.…”

“…Bathymetry, and the history of sea-floor subsidence in the North Atlantic has been used to estimate asthenosphere temperature [Clift, 2005;Clift et al, 1998;Ribe et al, 1995]. The sea floor is anomalously shallow in the North Atlantic, and it has been suggested that this results from support by thermally buoyant plume-head material.…”

“…Mantle temperature beneath plateaus, ridges and seamounts, has been studied using their subsidence histories (Figure 27) [Clift, 2005]. The results can be divided into four categories (Figure 28): a.…”

“…Faster subsidence than mid-ocean ridges (MORs) indicates higher initial mantle temperatures, and slower subsidence than MORs indicates lower initial mantle temperatures [from Clift, 2005].…”

Vertical tectonics of the High Plateau region, Manihiki Plateau, Western Pacific, from seismic stratigraphy

“…They explained this by invoking late stage underplating and proposed that the formation of the Manihiki Plateau was related to a hotspot. The more recent analysis by Clift (2005) argues that the subsidence is less than typical for normal oceanic lithosphere, similar to that reconstructed for the Ontong-Java Plateau.…”