Plate Tectonics Beyond Plate Boundaries: The Role of Ancient Structures in Continental Lithosphere on Intraplate Orogenesis

English Abstract:

The development of orogens that occur at a distance from plate boundaries (i.e., ‘intraplate’ deformation) infers a more complex argument for lithospheric and mantle interaction than the conventional plate tectonic theory allows. One hypothesis is the amalgamation of continental micro-plates leaves inherent scars on the crust and mantle lithosphere. Previous studies into continent-continent collisions identify a number of scenarios from accretionary tectonics that affect the crust and mantle (namely, the development of a Rayleigh-Taylor instability, lithospheric underplating, lithospheric delamination, and lithospheric subduction). Any of these processes may weaken the lithosphere allowing episodic reactivation of faults within continental interiors. Hence, continental convergence at a time after continental collision may cause the already weakened crust and mantle lithosphere to produce intraplate deformation. In order to better understand tectonic processes away from plate boundaries, we present suites of numerical models to identify the preferred style of deformation during continental shortening. Ancient structures are modeled by applying weak subduction scarring, changing the rheological conditions, and modifying the thermal structure within the lithosphere. The effect of climate-driven erosion and deposition on the tectonic structure of intraplate deformation is also addressed. We explore the relevance of the models to previously studied regions of intraplate orogenesis (including the Pyrenees in Europe, the Laramide and Eurekan orogenies in North America, Tien Shan orogen in Central Asia, and Central Australia). Our findings indicate that there exists a number of tectonic environments that can be produced relating to continental accretion, and that specific observational constraints to the local area (e.g., geological, geophysical, geodetic) are required to be integrated directly into the analyses for better interpretation. The models show that although rheological changes to the lithosphere can produce a range of deformation during continental convergence (i.e., crustal thickening, thinning, and folding), mantle weak zones from ancient subduction can generate more localized deformation and topography.