Fig. 7
From: Iron diapirs entrain silicates to the core and initiate thermochemical plumes
Conduit stability. a Conduit constriction time for seven experiments which vary μ2. Constriction time, tc (see Results), is defined by the time interval from the opening of a conduit when a diapir is fully formed (Rstart) to the time when the conduit radius stops changing after the metal diapir reaches the base of the tank base (Fig. 2d). Solid line shows theoretical prediction, tc, for a smooth metal diapir. b Theoretical prediction for diapir descent time versus conduit constriction time18 (filled circles) for diapir radii (rm) 200–500 km using Eqs. (2) and (5) and previous theoretical analysis18. Each line represents the descent of a diapir in time and distance from the base of the magma ocean to the CMB after onset of the metal pond instability (assuming ρ1 = 2850 kg/m3, ρ2 = 4500 kg/m3, μ2 = 1023 Pa ⋅ s, average hc = 300 km, and θ = 55°). Filled black circles indicate the time for conduit collapse for each diapir. An average onset time, tonset of 1.0 My is used for a 1 km deep metal pond. Increasing tonset will only prolong final diapir descent times but does not change the depth to which conduits stay open, as conduit constriction times are referenced to the beginning of conduit formation after tonset. Conduit radius, represented by θ, reduces drag around a diapir and is one of the most important factors controlling the depth of conduit closure showing that conduits stay open to deeper depths for increasing θ and higher ρ1. Constriction times, tc, are multiplied by 2, consistent with our laboratory observations (Fig. 7a). Once the conduit closes, diapirs are assumed to descend according to classical Stokes velocity (slope change). Interior mantle depth is defined from the base of a 400 km deep magma ocean. The total times estimated for metal plume descent and thermochemical plume ascent is 2–60 My for μ2 ranging from 1019 to 1023 Pa ⋅ s (see Supplementary Fig. 3), diapir radius of 500 km, and a soliton radius of 50 km
