Analogue Modeling of Plate Rotation Effects in Transform Margins and Rift‐Transform Intersections

Transform margins are first‐order tectonic features that accommodate oceanic spreading. Uncertainties remain about their evolution, genetic relationship to oceanic spreading, and general structural character. When the relative motion of the plates changes during the margin evolution, further structu...

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Veröffentlicht in:Tectonics (Washington, D.C.) D.C.), 2019-03, Vol.38 (3), p.823-841
Hauptverfasser: Farangitakis, G.‐P., Sokoutis, D., McCaffrey, K. J. W., Willingshofer, E., Kalnins, L. M., Phethean, J. J. J., Hunen, J., Steen, V.
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Sprache:eng
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Zusammenfassung:Transform margins are first‐order tectonic features that accommodate oceanic spreading. Uncertainties remain about their evolution, genetic relationship to oceanic spreading, and general structural character. When the relative motion of the plates changes during the margin evolution, further structural complexity is added. This work investigates the evolution of transform margins and associated rift‐transform intersections, using an analogue modeling approach that simulates changing plate motions. We investigate the effects of different crustal rheologies by using either (a) a two‐layer brittle‐ductile configuration to simulate upper and lower continental crust, or (b) a single layer brittle configuration to simulate oceanic crust. The modeled rifting is initially orthogonal, followed by an imposed plate vector change of 7° that results in oblique rifting and plate overlap (transpression) or underlap (transtension) along each transform margin. This oblique deformation reactivates and overprints earlier orthogonal structures and is representative of natural examples. We find that (a) a transtensional shift in the plate direction produces a large strike‐slip principal displacement zone, accompanied by en‐echelon oblique‐normal faults that accommodate the horizontal displacement until the new plate motion vector is stabilized, while (b) a transpressional shift produces compressional structures such as thrust fronts in a triangular zone in the area of overlap. These observations are in good agreement with natural examples from the Gulf of California (transtensional) and Tanzania Coastal Basin (transpressional) shear margins and illustrate that when these deformation patterns are present, a component of plate vector change should be considered in the evolution of transform margins. Plain Language Summary Tectonic plate boundaries on our planet are categorized by their relative motion with respect to each other. The three main categories are those moving away, toward, and parallel to one another. We study the processes occurring when two tectonic plates moving parallel begin to rotate and move away or toward each other. Currently, this is occurring in the Gulf of California, and in the past, it occurred in areas such as the Southern Atlantic, creating the segmented pattern along its midocean ridge. To study these tectonic plate boundaries, we use sandbox modeling. We make miniature models of the Earth's crust with silicone putty and sand and recreate the same mo
ISSN:0278-7407
1944-9194
DOI:10.1029/2018TC005261