On the relative motions of long-lived Pacific mantle plumes

2021-02-21 地球物理

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 Kevin Konrad from Oregon State University in Corvallis, Oregon, and his team 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, they 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.

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 

Reference:
Kevin Konrad, Anthony A. P. Koppers, Bernhard Steinberger, Valerie A. Finlayson, Jasper G. Konter, Matthew G. Jackson. On the relative motions of long-lived Pacific mantle plumes. Nature Communications, 2018; 9 (1) DOI: 10.1038/s41467-018-03277-x 

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