Investigating large-scale mantle flow and its surface expression: a tale of multiscale dynamic interaction shaping earth’s tectonics

Li, Yanchong

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https://hdl.handle.net/2142/129861 Copy

Description

Title

Investigating large-scale mantle flow and its surface expression: a tale of multiscale dynamic interaction shaping earth’s tectonics

Author(s)

Li, Yanchong

Issue Date

2025-07-13

Director of Research (if dissertation) or Advisor (if thesis)

Liu, Lijun

Doctoral Committee Chair(s)

Lundstrom, Craig

Committee Member(s)

• Gregg, Patricia
• Maguire, Ross

Department of Study

Earth Sci & Environmental Chng

Discipline

Geology

Degree Granting Institution

University of Illinois Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Geodynamics
• Plate Tectonics
• Numerical Modeling
• Driving Force
• Global Mantle Convection

Abstract

Surface tectonics are fundamentally driven by mantle convection. Understanding this lithosphere-mantle coupled system in three dimensions and over time is crucial but challenging due to Earth's spherical geometry, complex rheology, and limited observational data. Most data either provide present-day depth information or past surface records, constrained by our inability to probe deep into the mantle. Given these limitations, geodynamic modeling serves as a vital tool to synthesize data and reconstruct a coherent, time-evolving picture of mantle dynamics. Only recently have global, time-dependent geodynamic models with sufficient resolution to capture lithosphere-mantle coupling become available. This study leverages such models to revisit fundamental tectonic processes and develop quantitative analysis techniques to deepen our understanding of mantle convection. We begin by exploring the kinematic links between surface tectonics and mantle convection. Traditionally, past surface tectonic history is inferred from seismic tomography by directly mapping imaged slabs to the surface using an assumed sinking rate, forming the basis of "tomotectonic" plate reconstructions. We quantitatively assess the geodynamic and tectonic implications of three global reconstructions by focusing on North American subduction. These reconstructions vary in their dependence on tomotectonic constraints, leading to different trench retreat histories, plate motions, and subduction geometries. Using sequential data-assimilation modeling, we simulate subduction since 200 Ma and compare the resulting slab structures. Our results show that the reconstruction without explicit tomotectonic constraint best matches seismic tomography and Mesozoic paleotopography, supporting the idea of differential lithosphere motion relative to the mantle. Conversely, the explicit tomotectonic reconstruction provides the poorest match. This geodynamic modeling exercise evaluates the tectonic implications of different plate reconstructions and suggests that an iterative geodynamic-tomographic-tectonic workflow could enhance tomotectonic reconstructions. Building on this kinematic understanding, we investigate the mantle driving forces behind the Cenozoic India-Asia collision, one of Earth's most significant tectonic events. Despite extensive studies, the force sustaining India's northward motion and the rise of Tibetan Plateau remains elusive. Our global geodynamic models reveal that a prominent upper-mantle flow, originating from the northward rollover of the detached Neo-Tethyan slab and sinking slabs below East Asia, pushes the thick Indian lithospheric root. The resulting mantle drag is comparable in magnitude to slab pull (~10¹³ N m⁻¹). The thick Indian craton enhances both lithosphere-asthenosphere coupling and upper-plate compression, sustaining Tibetan Plateau topography. Furthermore, our calculations show that the resistive force at the India-Asia plate boundary aligns with the gravitational potential energy of the plateau. This mantle-driven force thus plays a crucial role in the evolution of the Tibetan Plateau and is part of a hemispheric convergent flow centered on Central Asia. As a counterpart to this hemispheric convergence, we hypothesize a divergent mantle flow in the East Pacific, approximately 180° apart, potentially influencing the formation of mid-ocean ridge (MOR), boundaries that accommodate most plate divergence. Our statistical analysis shows that most MORs form and persist in the regions including East Pacific, a pattern unlikely to be coincidental. While the traditional view attributes MOR formation to passive plate separation driven by distant subduction, the remarkable stability of MOR locations suggests deeper control. Our global geodynamic models indicate that broad-scale mantle upwellings, rooted in the lower mantle and pumped like a “fountain” by sinking slabs, actively shape MOR distribution. Unlike localized plumes, these upwellings are broad in scale and correlate with stable, deep-seated structures such as Large Low Shear Velocity Provinces (LLSVPs) in the Pacific and Pan-African regions. These results suggest that mantle convection exerts a fundamental influence on MOR dynamics, with ridges tracing deep mantle fountains extending from the core-mantle boundary to the surface. In conclusion, understanding the lithosphere-mantle system requires a global, time-dependent perspective. Our study reveals that fundamental mantle convection patterns—degree-1 and degree-2 flows—govern a broad range of tectonic processes, many of which were previously underappreciated. As data synthesis and modeling techniques advance, we anticipate further discoveries in deep-shallow, cross-scale interactions, including the origin of the lithospheric net rotation, the tectonic equator, and other regional tectonic processes. We are at the cusp of a new era in geodynamics, bridging deep Earth dynamics with surface evolution in unprecedented ways.

Graduation Semester

2025-08

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/129861

Copyright and License Information

Copyright 2025 Yanchong Li

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