On the relative motions of long-lived Pacific mantle plumes

Abstract

Mantle plumes upwelling beneath moving tectonic plates generate age-progressive chains of volcanos (hotspot chains) used to reconstruct plate motion. However, these hotspots appear to move relative to each other, implying that plumes are not laterally fixed. The lack of age constraints on long-lived, coeval hotspot chains hinders attempts to reconstruct plate motion and quantify relative plume motions. Here we provide ⁴⁰Ar/³⁹Ar ages for a newly identified long-lived mantle plume, which formed the Rurutu hotspot chain. By comparing the inter-hotspot distances between three Pacific hotspots, we show that Hawaii is unique in its strong, rapid southward motion from 60 to 50 Myrs ago, consistent with paleomagnetic observations. Conversely, the Rurutu and Louisville chains show little motion. Current geodynamic plume motion models can reproduce the first-order motions for these plumes, but only when each plume is rooted in the lowermost mantle.

Fig. 1

Inter-hotspot distances as a function of age and the geographic locations of the Hawaii and Louisville and Rurutu hotspots. a–c The black lines represent the distance between the two compared model hotspot chains (see Methods) and a dashed purple line displays the modern day inter-hotspot distance. One sigma uncertainties are provided for reconstructed model ages at 1 Ma increments and the gray shading represents distance uncertainties assuming a plume radius of 75 km. The circles represent the distance between a seamount of a given age and the point where a coeval modeled seamount falls geographically on the compared hotspot chain, confirming the estimated uncertainty bounds on the inter-hotspot distances. The inferred center of a seamount was used for the geographic location. a Hawaii compared to Louisville; b Hawaii compared to Rurutu; c Rurutu compared to Louisville. d A digital elevation map (ETOPO1) of the western Pacific showing the modeled reconstructions of the Hawaii-Emperor (orange), Rurutu (blue), and Louisville (green) chains. Stars denote the current hotspot locations presumed at Loihi Seamount, Arago Seamount, and the inferred Louisville hotspot location. Blue hexagons represent the location of seamounts with Rurutu-like geochemical compositions but lack age determinations. Blue triangles represent HIMU seamounts within the Western Pacific Seamount Province (WPSP) that contain ages consistent with belonging to the Rurutu chain^,

Fig. 2

The observed relative inter-hotspot distances through time compared against modeled simulations. The relative motions are from Fig. 1 compared with plume motion model results (colored lines) for both plumes rooted in the D″ above the core mantle boundary (CMB) and at a depth of 660 km at the base of the transition zone (TZ). Black lines and gray uncertainty bounds are the measured inter-hotspot distances as shown in Fig. 1. Individual colored lines represent different buoyancy fluxes (1–9×10³ kg/s) and each line color represents a different starting age of the compared hotspot (from 120 to 150 Ma) with the scale shown in the bottom right. The mantle viscosity model used here is from Steinberger and Calderwood and the tomography model used is TOPOS362d1. The starting age for Hawaii is 130 Ma with a buoyancy of 5×10³ kg/s in panels a, b and d, e with variable Louisville and Rurutu ages and buoyancy, while it is 120 Ma and a buoyancy of 5×10³ kg/s for Louisville in panels c and f with Hawaii and Rurutu being varied. a Hawaii compared against Louisville with mobile roots. b Hawaii compared against Rurutu with mobile roots. c Rurutu compared against Louisville with mobile roots. d Hawaii compared against Louisville with fixed roots. e Hawaii compared against Rurutu with fixed roots. f Rurutu compared against Louisville with fixed roots. Example model results for CMB (red-blue) and TZ (pink-green) hotspot locations through time with a starting age of 150 Ma (Hawaii and Rurutu) and 120 Ma (Louisville) and buoyancy fluxes of 5×10³ kg/s (Hawaii and Rurutu) and 3×10³ kg/s (Louisville) are shown as insets in each graph

Fig. 3

The inter-hotspot distances compared against modeled plume distances. The distances are from Fig. 2 with additional modeled plume motion comparison of a Rurutu plume generated from the transition zone (TZ) while Hawaii and Louisville are generated from the core-mantle boundary (CMB). All examples shown here assume mobile plume roots. a Hawaii compared against Louisville. b Rurutu compared to Louisville. c Hawaii compared to Rurutu. d Rurutu compared against Louisville. Panels a, b use the viscosity model of Steinberger and Calderwood and tomography model TOPOS362d1 with the same age and buoyancy parameters as Fig. 2. Panels c, d use the tomography model SMEAN and the viscosity model of Rudolph et al.. In panel c, Hawaii has an assumed starting age of 150 Ma and buoyancy of 6×10³ kg/s. In panel d, the modeled Louisville plume assumes a starting age of 120 Ma and buoyancy of 4×10³ kg/s