Abstract
The Earth's biggest magmatic events are believed to originate from massive melting when hot mantle plumes rising from the lowermost mantle reach the base of the lithosphere. Classical models predict large plume heads that cause kilometre-scale surface uplift, and narrow (100 km radius) plume tails that remain in the mantle after the plume head spreads below the lithosphere. However, in many cases, such uplifts and narrow plume tails are not observed. Here using numerical models, we show that the issue can be resolved if major mantle plumes contain up to 15–20% of recycled oceanic crust in a form of dense eclogite, which drastically decreases their buoyancy and makes it depth dependent. We demonstrate that, despite their low buoyancy, large enough thermochemical plumes can rise through the whole mantle causing only negligible surface uplift. Their tails are bulky (>200 km radius) and remain in the upper mantle for 100 millions of years.
Highlights
The Earth’s biggest magmatic events are believed to originate from massive melting when hot mantle plumes rising from the lowermost mantle reach the base of the lithosphere
More than 30 years ago, based on isotopic and trace-element geochemical data, it was suggested that a part of the oceanic crust that subducts to the core-mantle boundary (CMB) is entrained in mantle plumes and transported back to the surface[13]; later this idea was confirmed by numerical models[14,15]
Our modelling shows that a low-buoyancy plumes (LBPs) with parameters similar to the Siberian plume can rise through the entire mantle, if its volume is sufficiently large and the lower mantle is subadiabatic
Summary
The Earth’s biggest magmatic events are believed to originate from massive melting when hot mantle plumes rising from the lowermost mantle reach the base of the lithosphere. Classical models predict large plume heads that cause kilometre-scale surface uplift, and narrow (100 km radius) plume tails that remain in the mantle after the plume head spreads below the lithosphere. Despite their low buoyancy, large enough thermochemical plumes can rise through the whole mantle causing only negligible surface uplift Their tails are bulky (4200 km radius) and remain in the upper mantle for 100 millions of years. The novelty of this study is that the material properties of the plume and the ambient mantle in our model are more Earth-like than what has previously been published These properties, such as plume composition, excess temperature in the upper mantle, density and thermal expansivity, were constrained using geochemical and petrological observations and experimental data. We show that the bulky tails of large and hot LBPs are stable for several tens of millions of years and that their shapes fit seismic tomography data much better than the narrow tails of thermal plumes
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