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Abstract Constraining the long-term evolution of geoid anomalies is essential for unraveling Earth's internal dynamics. While most studies focus on present-day geoid snapshots, we reconstruct the time-dependent evolution of Earth’s strongest geoid depression, the Antarctic Geoid Low (AGL), over the Cenozoic. Unlike geodetic reference frames that place the deepest geoid low in the Indian Ocean, a geodynamic perspective (relative to a hydrostatic ellipsoid) reveals the strongest nonhydrostatic geoid depression actually resides over Antarctica. Using a back-and-forth nudging technique for time-reversed mantle convection modeling, we leverage 3-D mantle density structures derived from seismic tomography and geodynamic constraints. Our results show that the AGL has persisted for at least ~70 Myr, undergoing a major transition in amplitude and position between 50 and 30 Ma. This coincides with abrupt lateral shifts in Earth’s rotation axis at ~50 Ma, validated through paleomagnetic constraints on True Polar Wander. Initially, stable lower mantle contributions dominated the AGL, but over the past ~40 Myr, increasing upper-mantle buoyancy, particularly above ~1300 km depth, amplified the AGL magnitude. This shift stems from the interplay between long-term deep subduction beneath the Antarctic Peninsula and a buoyant, thermally driven upwelling of hot, low-density material from the lowermost mantle. These new results contrast with earlier interpretations, clarifying the crucial role of evolving mantle buoyancy in shaping global geoid anomalies. By incorporating seismic, geodynamic, and mineral-physics data, our reconstructions provide a more comprehensive understanding of mantle flow beneath Antarctica and offer new insights into the dynamic coupling between lower and upper mantle processes that govern Earth’s long-wavelength geoid evolution.
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Mantle dynamics on large spatial and temporal scales
This article provides a review on the studies of large temporal and spatial scale dynamics of the Earth’s mantle. The review focuses on relevant observations and their geodynamic interpretations and implications. These observations include present-day Earth’s plate tectonics, long- and intermediate-wavelength geoid and gravity anomalies, and mantle seismic structures, as well as important tectonism and magmatism that have happened in the last one billion years, associated with the formation and breakup of supercontinents Pangea and Rodinia. Much of the discussion is centered on how these observations have motivated geodynamic studies and modeling that seek to understand and interpret the observations. This review covers four topics. The first is on the primary characteristics of mantle seismic structure and their dynamic origin. The present-day Earth’s mantle is predominated by long-wavelength structures (i.e., degree-2 in the lower mantle and LLSVPs near the core-mantle boundary) and linear structures in subduction zones, both of which can be interpreted as a result of mantle convection modulated by surface plate motion history in the last 100 million years. The second is on the long- and intermediate-wavelength geoid and gravity anomalies and their dynamic interpretation. The geoid anomalies are explained by mantle flow that is driven by buoyancy associated with the mantle structure. Such studies indicate that the upper mantle is at least one magnitude weaker than the lower mantle and strongly suggest the existence of a weak asthenosphere. Third, the cyclic process of formation and breakup of supercontinents Pangea and Rodinia is surface manifestation of time-dependent mantle convection. During supercontinent formation and its early stage, mantle structure is predominately degree-1 with cold downwellings in one hemisphere and hot upwellings in the other hemisphere. However, the degree-1 structure starts to transition to degree-2 mantle structure with two major antipodal upwelling systems (e.g., the present-day Earth) in the late stage of a supercontinent, leading to supercontinent breakup. Abundant observational and dynamic evidence support the 1-2-1 model for supercontinent cycle and mantle structure evolution. The fourth is on the origin of plate tectonics and long-term thermal evolution of the Earth which is a fundamentally important but also controversial topic in the studies of earth science.
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- Award ID(s):
- 1940026
- PAR ID:
- 10317951
- Date Published:
- Journal Name:
- Chinese journal of geophysics
- Volume:
- 64
- Issue:
- 10
- ISSN:
- 0898-9591
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.6038/cjg2021P0530
