Quantitative Links Between Mantle Structure, Plate Tectonics and Dynamic Topography Along the Andean and Caribbean Convergent Margins

Date

2021-05

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Abstract

The link between present-day mantle structure and convergent margin plate tectonic histories is increasingly recognized from tectonic analyses of mantle tomographic images. However, it is still unclear how to quantitatively link imaged mantle structure to Earth surface geology at convergent margins. This study is focused on the debated tectonic history of the Andes and the Caribbean. We mapped and unfolded the Nazca slab and other slabs from tomography under South America to build a tomographic plate reconstruction, which was then tested against published geology. We found the current phase of Nazca subduction was established after a 100-80 Ma plate reorganization and progressively propagated southwards from the northern Andes 5ºS at ~80 Ma to the southern Andes 40ºS by ~55 Ma. Contrary to the Andes tectonic paradigm, Nazca subduction was not fully continuous since the Mesozoic and has included episodic divergent phases. Andean compressional initiation and foredeep sedimentation were linked to Nazca anchoring into the lower mantle. At the Caribbean, plate reconstructions from the unfolded proto-Caribbean slab and the unfolded Lesser Antilles slab under the Caribbean shows significant lateral slab dragging of the proto-Caribbean slab from its subduction at 90 Ma until the slab break-off at 30 Ma. The slab dragging might be the cause of the Greater Antilles arc advancement in the Paleocene as well as the Lesser Antilles arc in the Miocene. I quantified Caribbean asthenospheric viscosity under the Caribbean by following a new approach using analytic solutions for Poiseuille-Couette channel flow. We estimated Caribbean dynamic topography and the associated pressure gradient, which, combined with flow velocities estimated from geologic markers and tomographic structure, yield a best-estimate asthenospheric viscosity of (3.0±1.5)*10^18 Pas. This value is consistent with independent estimates for non-cratonic and oceanic regions, and we propose this value to be globally- representative. The tomographic plate models in this study imply significant vertical (i.e., slab anchoring) and lateral (i.e., slab dragging) slab motions in the mantle after subduction that may influence surface geology.

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Keywords

Slab unfolding, Plate tectonics, Seismic tomography, Dynamic topography, Mantle viscosity

Citation

Portions of this document appear in: Chen, Y. W., Wu, J., Suppe, J. (2019). Southward propagation of Nazca subduction along the Andes. Nature, 565(7740), 441-447; and in: Chen, Y. W., Colli, L., Bird, D.E. Wu, J., Zhu, H. (2021) Caribbean plate tilted and actively dragged eastwards by low-viscosity asthenospheric flow. Nat Commun 12, 1603.