Table 1.
Mantle plume flux data.
| Plume model | rB (km) | rJ (km) | kmin (km2 yr–1) | kmax (km2 yr–1) | Aspect ratio | Azimuth difference | Geometry factor | Qmin (km2 yr–1) | Qmax (km2 yr–1) |
|---|---|---|---|---|---|---|---|---|---|
| WM89 (28) | 820 | 580 | 0.3 | 1.7 | 1 | – | 1 | 0.5 | 3.5 |
| LM94 (56) | 1260 | 1070 | 0.3 | 2.2 | 1 | – | 1 | 0.7 | 4.6 |
| JW03 (44) | 830 | 780 | 0.1 | 0.4 | 1 | – | 1 | 0.1 | 0.8 |
| MJ06g (18) | 1000 | 670 | 0.4 | 2.8 | 0.42 | 042 | 1.3 | 1.2 | 7.5 |
| MJ06v (18) | 980 | 640 | 0.4 | 2.7 | 0.43 | 054 | 1.7 | 1.5 | 9.7 |
| Nea09 (21) | 870 | 540 | 0.4 | 2.3 | 0.36 | 074 | 2.6 | 2.0 | 12.7 |
Plume model provides reference. rB and rJ are the distances between the model plume centre and the Bressay and Judd sedimentary successions, respectively. The mantle thermal anomaly must have passed Judd before 56.1–55.0 Ma (ref. 36) and Bressay before 55.8–54.8 Ma (ref. 38), implying a time difference of Δt between 0.2 and 1.3 Myr between passage of the thermal anomaly beneath Judd and Bressay37. Hence, plume head parameter k is estimated using (rB − rJ)/Δt (refs. 37,38). Aspect ratio γ (i.e. the ratio of the short and long axes of the ellipse) is specified by the plume model. Azimuth difference θ is the mean of the differences between the forward azimuth from the plume centre to the Judd or Bressay sedimentary records and the azimuth of the long axis of elliptical plume heads. The geometry factor, given by (γ2 cos2θ + sin2θ)/γ, corrects the k value, which implicitly assumes radially symmetrical plume spreading, for an elliptical plume head geometry. Q is the plume head area flux, averaged vertically across the plume head, determined using 2πkγ/3 (ref. 38). It is straightforward to convert Q to plume volume flux, mass flux or buoyancy flux27,38,40. However, area flux is more directly obtained from the stratigraphical data, and can be more directly related to sill intrusion frequency than these other flux measures