IAP2-22-389

Breaking the ice: insights into the evolution of plate tectonics from numerical modelling of Europa’s ice subduction

Subduction is the major driver for plate tectonics, linking present day surface and interior processes, and controlling the Earth’s planetary evolution. However, the style of heat transport for the early Earth remains debated. Horizontal motions for the hot Archean mantle’s lithosphere were likely sluggish and subduction episodic with heat transport mostly controlled by melting (e.g., van Hunen & van der Berg, Lithos, 2008; Foley, Phil. Trans. R. Soc. A., 2018). How does such an Archean Earth evolve into modern tectonics (i.e., from potentially shallow subduction to deep subduction at present day), and what role do fractionation and memory of deformation play in the evolution of plate tectonics?

The answer to this question maybe locked within the icy shell of the Jovian satellite Europa – the only other body in our Solar System to exhibit plate tectonic like deformation (Figure 1; Kattenhorn & Prockter, Nat Geosci, 2014). Similarities in the creep rheology of ice and rocks makes Europa an intriguing analogue for Archean subduction on Earth. Evidence from satellite imagery from Juno’s flyby of Europa suggests that subduction has occurred on Europa in the past. The reworked nature of Europa’s young surface also provides a unique opportunity to understand transient overturns in surface regimes, from stagnant lid to ‘squishy-lid’, to mobile lid convection that approximate plate tectonics. This project will provide new insights into the evolutionary links between these tectonic regimes for a better understanding of planetary evolution and the links between the interior and exterior of planetary bodies, a question that is also fundamental for understanding the deep and surface evolution of our planet from the Archean to present day and has implications for the origin of life.

In this project the student will model convection in a thin ice shell to study localisation of deformation with the aim of answering the following questions:

1. To what extent does grain size evolution and melt generation due to tidal heating assist deformation, lead to the initiation of subduction, and modulate the characteristics of any subducting slabs and surface deformation of the overriding ice?
2. How do these Europa-motivated models compare with numerical models and geological constraints for plate boundary and subduction evolution on Earth?

The project will suit a geologist or (geo-)physicist and is computational in character. Candidates will learn to use, adapt, and extend software written in C++, Python and other programming languages. The candidate will also gain familiarity with high-performance computing systems (HPCs) and gain expertise in geodynamics, planetary geology, ice evolution and dynamics, satellite image analysis and the structure and evolution of the Earth.

Click on an image to expand

Image Captions

Figure 1: Geologic features on Jupiter’s moon Europa suggest that ice dynamics including subduction may help explain the young surface and formation of dark “lenticulae” spots through cryolavas. From Kattenhorn & Prockter (Nat Geosci., 2014).

Methodology

Like plate weakening processes on Earth, the role of grain size evolution, melt generation, and deformation memory are thought to be important for the formation of weak plates boundaries on Europa. However, grain size dynamics and damage have not yet been investigated quantitatively for ocean worlds or ice rheologies.

The student will run thermo-mechanical subduction models using the state of the art, open-source, adaptive mesh refinement, finite element software ASPECT (Heister et al., Geophys. J. Int., 2017) with a free surface, two-phase flow, spatially variable internal heating, and visco-elastic-plastic convection with grain size evolution in 2-D and 3-D.

The project will involve the implementation of the following main components:

1. Melt transport and thin shell geometry for visco-plastic-elastic, internally and bottom heated convection for Europa
2. Modelling the effects of a free surface top boundary condition and elasticity to measure real-time deformation and topographic evolution of the surface
3. Implementing and testing two-phase flow within a numerical subduction set-up
4. Modelling and analysing melt dependent geometry evolution

Project Timeline

Year 1

(1) Literature review,
(2) Familiarisation with code,
(3) Training in HPC techniques, modelling and data analysis
(4) Running of setup and boundary condition tests locally

Year 2

(1) Run simulations of subduction with damage memory and melt transport for the Early Earth,
(2) Implement and run model setups with a thin shell geometry, ice rheologies and internal and bottom heating for Europa
(3) Attend and present research at UK based conferences and workshop
(4) Author a publication

Year 3

(1) Explore melt dependent geometry evolution for both Europa and early Earth models
(2) Compare Europa motivated simulations with numerical models for the Archean Earth and geological constraints for plate boundary and subduction evolution on Earth (including plate reconstructions linked to the mantle record as seen by structural seismology, and sedimentary sequence records)
(3) Attend and present at an international conference e.g., AGU or EGU.
(4) Writing of further manuscript for publication

Year 3.5

Completion of manuscripts for publication and thesis writing

Training
& Skills

The student will receive training in testing, running processing and analysing numerical models. This will include essential skills like good programming practices (including version control), GitHub skills, code development and usage of high-performance computing systems (HPCs)

Training in a wider range of important skills (e.g., networking, presentation skills, paper/thesis writing) will be provided by the College of Science and Engineering and the Research and Innovation Services at the University of Glasgow, and the student will also benefit from cross-disciplinary training provided as part of the IAPETUS DTP.

The student will have opportunities to work with collaborators at the University of Texas at Austin in the US and will attend national and international scientific meetings to present research results. We aim to see all students publish at least two papers in leading scientific journals during their PhD. Upon completion, the student will be well equipped for a career in academia or in a range of industries.

References & further reading

Foley, B. J. (2018). The dependence of planetary tectonics on mantle thermal state : applications to early Earth evolution. In Phil. Trans. R. Soc. A (Vol. 376).

Heister, T., Dannberg, J., Gassmöller, R., & Bangerth, W. (2017). High accuracy mantle convection simulation through modern numerical methods – II: Realistic models and problems. Geophysical Journal International, 210(2), 833–851. https://doi.org/10.1093/gji/ggx195

Howell, S. M., & Pappalardo, R. T. (2019). Europa-style plate tectonics: Extension, convection and the fate of icy slabs. Icarus, 322, 69–79. https://doi.org/10.1016/j.icarus.2019.01.011

Kattenhorn, S. A., & Prockter, L. M. (2014). Evidence for subduction in the ice shell of Europa. Nature Geoscience, 7(10), 762–767. https://doi.org/10.1038/NGEO2245

van Hunen, J., & van den Berg, A. P. (2008). Plate tectonics on the early Earth: Limitations imposed by strength and buoyancy of subducted lithosphere. Lithos, 103(1–2), 217–235. https://doi.org/10.1016/j.lithos.2007.09.016

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