Caribbean plate tilted and actively dragged eastwards by low-viscosity asthenospheric flow

Abstract

The importance of a low-viscosity asthenosphere underlying mobile plates has been highlighted since the earliest days of the plate tectonics revolution. However, absolute asthenospheric viscosities are still poorly constrained, with estimates spanning up to 3 orders of magnitude. Here we follow a new approach using analytic solutions for Poiseuille-Couette channel flow to compute asthenospheric viscosities under the Caribbean. We estimate Caribbean dynamic topography and the associated pressure gradient, which, combined with flow velocities estimated from geologic markers and tomographic structure, yield our best-estimate asthenospheric viscosity of (3.0 ± 1.5)*1018 Pa s. This value is consistent with independent estimates for non-cratonic and oceanic regions, and challenges the hypothesis that higher-viscosity asthenosphere inferred from postglacial rebound is globally-representative. The active flow driven by Galapagos plume overpressure shown here contradicts the traditional view that the asthenosphere is only a passive lubricating layer for Earth’s tectonic plates.

High 3 He/ 4 He in central Panama reveals a distal connection to the Galápagos plume

“…Importantly, a slab-derived origin of the high 3 He/ 4 He in the CAM is highly implausible because, 1) unlike other elements, He is lost from the slab to the surface during the earliest stages of subduction, and it does not accumulate or laterally migrate beneath the arc, and 2) no known hotspot track component subducts directly beneath central Panama (see plate tectonic reconstruction, Movie S1 ). As such, we argue that the 3 He-rich mantle source beneath central Panama likely represents direct evidence for the influx of Galápagos mantle through the Panama slab window ( 49 ).…”

Ongoing tectonic subsidence in the Lesser Antilles subduction zone

“…Finally, mantle flow at the scale of lithospheric plates may also contribute to long-term vertical motions of subduction arcs. For instance, Chen et al (2021) show that the westward flow of mantle material from the Galapagos plume through the Panama subduction slab window underneath the Caribbean plate to induces a tilting of the Caribbean plate, resulting in 100s of meters of negative dynamic topography at the Lesser Antilles arc. Although dynamic topography models do not provide, to our knowledge, vertical motion rates that could be directly compared to our observations, the fact that they predict a signal comparable to observed long-term vertical deformation indicates that they also contribute to current vertical rates at subduction volcanic arcs.…”

Asthenospheric flow through the Izanagi-Pacific slab window and its influence on dynamic topography and intraplate volcanism in East Asia

“…Consequently, the inflowing Pacific material cannot flow far west enough during the late Cenozoic. A larger viscosity drop in the asthenosphere, making it compatible with the new constraints of ~10 18 -10 19 Pa•s (e.g., Chen et al, 2021), would also increase asthenospheric flow velocities (assuming the same pressure gradient) and may help to reconcile this issue. These limitations are highlighted by the low ~3 cm/year velocity of this influx, when compared to recent inferences of ~15 cm/year pressure-driven asthenospheric flow velocities (Hartley et al, 2011;Colli et al, 2014;Parnell-Turner et al, 2014;Chen et al, 2021).…”

“…A larger viscosity drop in the asthenosphere, making it compatible with the new constraints of ~10 18 -10 19 Pa•s (e.g., Chen et al, 2021), would also increase asthenospheric flow velocities (assuming the same pressure gradient) and may help to reconcile this issue. These limitations are highlighted by the low ~3 cm/year velocity of this influx, when compared to recent inferences of ~15 cm/year pressure-driven asthenospheric flow velocities (Hartley et al, 2011;Colli et al, 2014;Parnell-Turner et al, 2014;Chen et al, 2021). Taken together, it becomes clear that the implementation of refined viscosity profiles in the next generation of exascaleenabled mantle convection codes (e.g., TerraNeo, Bauer et al, 2020) could plausibly allow the influx of hot material reach further into East Asia during the late Cenozoic.…”