Can a sheet‐like low‐velocity region form an elongated Large Igneous Province?

Abstract

[1] High-resolution tomography of the lower mantle has revealed the existence of another chemically distinct region with low-velocity and a sheet-like structure beneath the western Pacific. On the other hand, Large Igneous Provinces (LIPs) sometimes have elongated shapes. If a sheet-like upwelling reaches the Earth's surface while maintaining its shape, an elongated LIP may form. In order to test this hypothesis, we perform a series of experiments and investigate the stability of a buoyant sheet. The experimental results show that the buoyant fluid accumulates at the top of the sheet to form a buoyant cylinder. The gravitational instability divides the cylinder into several plume heads. We develop a model to explain the growth of the buoyant cylinder and the time scale until instability begins. Our model shows that a thin sheet-like upwelling with a width of 200 km, a small density difference from the ambient mantle, 10 kg m À3, and a high supply rate of buoyant fluid, 0.1 m yr À1, can reach the Earth's surface while maintaining its shape. We thus infer that LIPs with an elongated shape can be generated by sheet-like upwellings. The width of the observed sheet-like low-velocity region beneath the western Pacific is 500 km and is marginally sufficient to form an elongated LIP.

Komatiites From Mantle Transition Zone Plumes

“…Recent years have seen significant advances in the quality of mantle plume imaging, the sophistication of numerical models for the upwellings themselves and their interaction with tectonic plates (Mittelstaedt and Ito, 2005;Bredow et al, 2017;Nelson and Grand, 2018). A wide range of plume types have been suggested, including shallow and deep types (Courtillot et al, 2003), sheetlike and pulsating varieties (Mjelde et al, 2010;Namiki et al, 2013) that only rarely define simple symmetrical upwellings (Zhao, 2007). Without the capacity for the direct measurement of Archean plume features, the literature on Archean geodynamics and crustal growth has not witnessed a comparable in-depth re-assessment of the purported craton-forming upwellings from the core -mantle boundary.…”