INTERACTIVE MODELFIELD NOTEGEODYNAMICS

The Plume Pulse Bench

A live model accompanying “A Pulsing Mantle Plume, Timed by the Plate Above It”

Study: Field note
Review: Peer-edited by the club review board
Article: 13 sectionsabout 19 min
Files: LaTeX source20 kB

The field note's central piece of arithmetic is one identity: a spatial wavelength equals an extension rate times a period, because a million years of one millimetre-per-year motion is exactly one kilometre. Set an assumed pulse period below and watch it stretch out at each rift arm's own real extension rate. The shaded bands mark the paper's actually reported cluster spacing for each arm — find a period that lands inside both bands at once and you have reconstructed the club's own reasoning for why one pulsing source, read out on two different plates, is a defensible story.

λ (km) = R (mm/yr) × T (Myr)

Model 1. Stretch a pulse across two rift arms

Assumed pulse period14.0MyrRed Sea Rift extension rate15.0mm/yr

MER wavelength: 72.8 kmRSR wavelength: 210.0 kmMER extension (fixed): ~5.2 mm/yrRSR extension (yours): 15.0 mm/yr

Slide the period until both wavelengths sit inside their shaded bands at once.

MER's extension rate is fixed at the paper's reported ~5.2 mm/yr, the only value given for that arm. RSR's rate is a slider across the paper's full reported range, 10.5–19.5 mm/yr, since the paper gives a range rather than a single number.

Model 2. Why a thicker, slower plate compresses the same pulse

This second panel is a cartoon of the paper's proposed mechanism, not a reconstruction of any of its numbers. A pulse of distinct mantle material is released at the centre and has to flow sideways through the gap between the solid plate above and the rest of the mantle below before it can erupt or freeze in place. Thicken that gap and slow the plate down, and the same pulse has less room and less time to travel before the next one arrives behind it — so the erupted record compresses into a shorter spatial wavelength for the same underlying rhythm.

Overriding plate thickness29km

channel gap: narrowflow speed: slowerupted spacing: condensed

Illustrative only: the animation's channel width and pulse speed are chosen for legibility, not fitted to the paper's numbers. The qualitative direction — thicker, slower plate above, shorter spacing below — is the mechanism the authors themselves propose for why the MER (thicker crust, slower spreading) compresses the pulse record more than the RSR (thinner crust, faster spreading) does.

What pushing the sliders shows

Two things tend to land harder here than in prose. First, the same period can look like two completely different phenomena depending on which plate is doing the stretching — 72 km of spacing and 210 km of spacing are not obviously the same signal until you divide each by its own extension rate. Second, the window where both bands agree is not razor-thin: a fairly wide range of assumed periods, roughly 9.6 to 19.0 million years, is consistent with both rift arms simultaneously, which is a real constraint but not a precise clock. Neither model reproduces the paper's own statistics — the real result comes from k-means clustering on 13 variables across 224 rock samples, not from two sliders — but the arithmetic underneath the club's own reading of it is exactly what you are moving here.