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1. Do continental lithospheric discontinuities control tectonic plate motion directions

   Kuiper, YD (June 2024, National Association of Geoscience Teachers)

   Plate-tectonic reconstructions use Euler poles about which plates rotate in small circle patterns. These small circle patterns are outlined by oceanic transform faults and contiguous fracture zones. Because oceanic lithosphere older than ~200 Ma is preferentially destroyed by subduction, pre-Mesozoic plate-tectonic reconstructions lack such constraints from oceanic fracture zones. Based on high-resolution bathymetry, geological and geophysical data, some fracture zones are shown to be contiguous with pre-existing discontinuities in adjacent continents. Combined with results from published analog and numerical models, continental rift zones and oceanic spreading ridges that are initially oblique to these discontinuities are demonstrated to evolve into orientations perpendicular to them, while fracture zones and transform faults develop parallel to them. Consequently, oceanic spreading directions, or plate movement directions, are controlled by pre-existing continental lithospheric discontinuities. This hypothesis constitutes a paradigm shift, from the widespread belief that transform fault and fracture zone orientations are controlled by plate motions, to one where they are inherited from pre-existing continental discontinuities, and control plate movement directions. If so, identifying such discontinuities in ancient continental lithosphere may constrain plate motions in deep geologic time. 

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2. Magmatism controls global oceanic transform fault topography

   https://doi.org/10.1038/s41467-024-46197-9  

   Tian, Xiaochuan; Behn, Mark D; Ito, Garrett; Schierjott, Jana C; Kaus, Boris_J P; Popov, Anton A (December 2024, Nature Communications)

   Abstract Oceanic transform faults play an essential role in plate tectonics. Yet to date, there is no unifying explanation for the global trend in broad-scale transform fault topography, ranging from deep valleys to shallow topographic highs. Using three-dimensional numerical models, we find that spreading-rate dependent magmatism within the transform domain exerts a first-order control on the observed spectrum of transform fault depths. Low-rate magmatism results in deep transform valleys caused by transform-parallel tectonic stretching; intermediate-rate magmatism fully accommodates far-field stretching, but strike-slip motion induces across-transform tension, producing transform strength dependent shallow valleys; high-rate magmatism produces elevated transform zones due to local compression. Our models also address the observation that fracture zones are consistently shallower than their adjacent transform fault zones. These results suggest that plate motion change is not a necessary condition for reproducing oceanic transform topography and that oceanic transform faults are not simple conservative strike-slip plate boundaries. 

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3. Generation of Evolving Plate Boundaries and Toroidal Flow From Visco‐Plastic Damage‐Rheology Mantle Convection and Continents

   https://doi.org/10.1029/2023GC011179  

   Becker, Thorsten W.; Fuchs, Lukas (December 2023, Geochemistry, Geophysics, Geosystems)

   Earth's style of planetary heat transport is characterized by plate tectonics which requires rock strength to be reduced plastically in order to break an otherwise stagnant lithospheric lid, and for rocks to have a memory of past deformation to account for strain localization and the hysteresis implied by geological sutures. Here, we explore ∼10⁷Rayleigh number, visco‐plastic, 3‐D global mantle convection with damage. We show that oceanic lithosphere‐only models generate strong toroidal‐poloidal power ratios and features such as a mix of long‐wavelength tectonic motions and smaller‐scale, back‐arc tectonics driven by downwellings. Undulating divergent plate boundaries can evolve to form overlapping spreading centers and microplates, promoted and perhaps stabilized by the effects of damage with long memory. The inclusion of continental rafts enhances heat flux variability and toroidal flow, including net rotation of the lithosphere, to a level seen in plate reconstructions for the Cenozoic. Both the super‐continental cycle and local rheological descriptions affect heat transport and tectonic deformation across a range of scales, and we showcase both general tectonic dynamics and regionally applied continental breakup scenarios. Our work points toward avenues for renewed analysis of the typical, mean behavior as well as the evolution of fluctuations in geological and model plate boundary evolution scenarios. 

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4. Strike‐Slip Enables Subduction Initiation Beneath a Failed Rift: New Seismic Constraints From Puysegur Margin, New Zealand

   https://doi.org/10.1029/2020TC006436  

   Shuck, Brandon; Van Avendonk, Harm; Gulick, Sean P. S.; Gurnis, Michael; Sutherland, Rupert; Stock, Joann; Patel, Jiten; Hightower, Erin; Saustrup, Steffen; Hess, Thomas (May 2021, Tectonics)

   Abstract Subduction initiation often takes advantage of previously weakened lithosphere and may preferentially nucleate along pre‐existing plate boundaries. To evaluate how past tectonic regimes and inherited lithospheric structure might lead to self‐sustaining subduction, we present an analysis of the Puysegur Trench, a young subduction zone with a rapidly evolving tectonic history. The Puysegur margin, south of New Zealand, has experienced a transformation from rifting to seafloor spreading to strike‐slip, and most recently to incipient subduction, all in the last ∼45 million years. Here we present deep‐penetrating multichannel reflection and ocean‐bottom seismometer tomographic images to document crustal structures along the margin. Our images reveal that the overriding Pacific Plate beneath the Solander Basin contains stretched continental crust with magmatic intrusions, which formed from Eocene‐Oligocene rifting between the Campbell and Challenger plateaus. Rifting was more advanced to the south, yet never proceeded to breakup and seafloor spreading in the Solander Basin as previously thought. Subsequent strike‐slip deformation translated continental crust northward causing an oblique collisional zone, with trailing ∼10 Myr old oceanic lithosphere. Incipient subduction transpired as oceanic lithosphere from the south forcibly underthrust the continent‐collision zone. We suggest that subduction initiation at the Puysegur Trench was assisted by inherited buoyancy contrasts and structural weaknesses that were imprinted into the lithosphere during earlier phases of continental rifting and strike‐slip along the plate boundary. The Puysegur margin demonstrates that forced nucleation along a strike‐slip boundary is a viable subduction initiation scenario and should be considered throughout Earth's history. 

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5. Microseismicity Indicates Atypical Small‐Scale Plate Rotation at the Quebrada Transform Fault System, East Pacific Rise

   https://doi.org/10.1029/2021GL097000  

   Gong, Jianhua; Fan, Wenyuan; Parnell‐Turner, Ross (February 2022, Geophysical Research Letters)

   Abstract Closely spaced, multi‐strand ridge transform faults (RTFs) accommodate relative motions along fast spreading mid‐ocean ridges. However, the relations between RTFs and plate spreading dynamics are poorly understood. The Quebrada system is one of the most unique RTF systems at the East Pacific Rise, consisting of four transform faults connected by three short intra‐transform spreading centers (ITSCs). We use seven‐months of ocean bottom seismograph data to study the Quebrada system, and find abundant earthquakes unevenly distributed among three active faults. We identify two deep, diffuse seismicity clouds at the inside corners of the ITSC‐transform fault intersections, and one seismically active fracture zone. The observations suggest a complex regional plate‐motion pattern, including possible heterogeneous rotations within the Quebrada system. Evolution of multi‐strand RTFs may have resulted from a strong three‐dimensional local thermal and fluid effects, while the RTFs may have also regulated regional tectonics, forming an intricate feedback system. 

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