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Generation and Evolution Of Transform-Ridge Interaction and Behavior on Earth

Periodic Reporting for period 1 - GEOTRIBE (Generation and Evolution Of Transform-Ridge Interaction and Behavior on Earth)

Période du rapport: 2018-04-01 au 2020-03-31

Surface of the Earth is divided into a jigsaw of plates that move relative to each other. While surface tectonics and mechanics of the plate processes influence the mantle dynamics, the deep mantle forces in the interior of the Earth are at the origin of its tectonic manifestations at the surface. Coupling Earth mantle dynamics with its surface response is critical for understanding of some fundamental features on Earth such as sea level change over time or postglacial rebound. Plate tectonics is a key process in linking the deep Earth to its surface. The theory of plate tectonics is successful in explaining multiple geophysical and geological phenomena. Yet, the fundamental scientific questions about the mechanics of plate tectonics and formation of new plate boundaries is still largely debated and remain unresolved. The goals of this project are to unravel how the interaction between the deep forces and lithospheric mantle shape the evolution of plate tectonics and to explain how new plate boundaries are generated in global context taking into account surface and deep forces within the mantle. To quantify the conditions under which the new plate boundaries are formed and characterize their long-term evolution, the fellow used the state-of-the-art numerical models. The synthetic results obtained using high resolution massively parallel numerical code StagYY were confronted with data retrieved from plate tectonic reconstructions.
This project relied heavily on high resolution, massively parallel, state-of-the-art numerical simulations of mantle convection with plate-like surface. The numerical models were used to understand how plate boundaries form and how they evolve in time. The numerous aspects of plate tectonics were addressed and diverse tectonic settings were explored including rifting in divergent setting, birth of new subduction zones in convergent setting, and connection of mid ocean ridges with shear plate boundaries in extensional setting. A study deciphering the dynamics of rifting was published in Geophysical Research Letters journal. The work unravels for the first time four distinct phases of rifting: an initially slow phase, a speed-up phase featuring an abrupt increase of extension rate, the breakup phase with formation of new ocean basin, and a deceleration phase where extensional velocities decrease. The speed-up during rifting can trigger the formation of new plate boundaries elsewhere on Earth, even at large distances to the rift. This work illustrated new links between local rift dynamics, plate motions, and subduction kinematics during times of continental separation.

The work further focused on the locations of new subduction initiation to answer questions such as where new subduction zones preferentially form, where they endure and where they stop living. A study that predicts locations of new subduction zones was published in the Earth and Planetary Science Letters. The models showed that the position of subduction initiation is largely controlled by the strength of the lithosphere and by the length of continental margins. The results of the models were confronted with subduction histories retrieved from plate tectonic reconstructions. Both approaches agree that subduction initiation on Earth is not a random process within the oceans, and more subduction zones stop and die in the vicinity of continental margins compared to subduction initiation. The models also suggest that intra-oceanic subduction initiation is more prevalent during times of supercontinent assembly (e.g. Pangea 220 My ago) compared to more recent continental dispersal.

One of the least understood plate boundaries on Earth are transform faults where two tectonic plates slide past each another. The work analyzed the influence of free deformable surface on the formation of detachment faults and transform boundaries. Advanced numerical methods were implemented and new rheology was developed in the convection code to assess the influence of localization of deformation on plate boundary formation. The models showed that lithospheric strength and deformation history play a key role on the surface tectonics and controls the formation of new shear plate boundaries.
Studying surface tectonics in the global convection models is a state-of-the-art research direction. During the fellowship, the researcher designed and run cutting-edge 2D and 3D fully spherical high resolution massively parallel numerical models to further unravel the fundamental mechanisms lying behind the plate tectonic processes. In addition to numerical modelling, the fellow performed an analysis of geological observations and geophysical data contained in the plate reconstructions. A new approach of combining information from plate tectonic reconstructions with synthetic data from numerical simulations was developed. The results of this project have important implications for our knowledge on how plate boundaries operate on Earth. The project provides guidance to the geodynamics community as well as tectonics/geology/seismology communities and fill an important gap in understanding how large-scale dynamics shapes the Earth’s surface.