Precambrian geodynamics: models vs. concepts and constrains (Invited)
Abstract
In contrast to modern-day plate tectonics, studying Precambrian geodynamics presents a unique challenge as currently there is no agreement upon paradigm concerning the global geodynamics and lithosphere tectonics for the early Earth. Further progress in this direction requires cross-disciplinary efforts with a special emphasis placed upon quantitative testing of existing geodynamic concepts and extrapolating back in geological time, using both global and regional scale thermomechanical numerical models, which have been validated for present day Earth conditions. Here, we focus on discussing results of recent modeling studies in the context of existing concepts and constraints for Precambrian geodynamics. The three key features of Precambrian Earth evolution are outlined based on combining available observations and thermomechanical models (cf. review by Gerya, 2013): (1) Early Archean pre-subduction geodynamics was dominated by plume tectonics and the development of hot accretionary orogens with low topography, three-dimensional deformation and pronounced gravitational tectonics. Mantle downwellings and lithospheric delamination (dripping-off) processes are likely to have played a key role in assembling and stabilizing the hot orogens on a timescale up to hundreds of millions of years. Both oceanic-like and continental-like lithospheres were rheologically weak due to the high Moho temperature (>800 °C) and melt percolation from hot partially molten sublithospheric mantle (Sizova et al., 2010). (2) Wide spread development of modern-style subduction on Earth started during Mesoarchean-Neoarchean at 3.2-2.5 Ga. This is marked by the appearance of paired metamorphic complexes and oldest eclogite ages in subcontinental lithospheric mantle. Numerical models suggest that the transition occurred at mantle temperatures 175-250 °C higher than present day values, and was triggered by stabilization of rheologically strong plates of both continental and oceanic type (Sizova et al., 2010). Due to the hot mantle temperature, slab break-off was more frequent in the Precambrian time causing more episodic subduction compared to present day. (3) Wide spread development of modern-style (cold) collision on Earth started during Neoproterozoic at 600-800 Ma and is thus decoupled from the onset of modern-style subduction. Cold collision created favorable conditions for the generation of ultrahigh-pressure (UHP) metamorphic complexes which become widespread in Phanerozoic orogens. Numerical models suggest that the transition occurred at mantle temperatures 80-150 °C higher than present day values and was associated with stabilization of the continental subduction (Sizova et al., 2013). Frequent shallow slab break-off limited occurrence of UHP rocks in the Precambrian time. References Gerya, T.V. (2013) Precambrian geodynamics: Concepts and models. Gondwana Research, DOI: http://dx.doi.org/10.1016/j.gr.2012.11.008 Sizova, E., Gerya, T., Brown, M., Perchuk, L.L. (2010) Subduction styles in the Precambrian: Insight from numerical experiments, Lithos, 116, 209-229. Sizova, E.V., Gerya, T.V., Brown, M. (2013) Contrasting styles of Phanerozoic and Precambrian continental collision, Gondwana Research, DOI: http://dx.doi.org/10.1016/j.gr.2012.12.011
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.V31E..04G
- Keywords:
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- 8120 TECTONOPHYSICS Dynamics of lithosphere and mantle: general;
- 8125 TECTONOPHYSICS Evolution of the Earth;
- 8159 TECTONOPHYSICS Rheology: crust and lithosphere;
- 0545 COMPUTATIONAL GEOPHYSICS Modeling