TECTONIC GEOMORPHOLOGY INSIGHTS TO FRONTIER RESEARCH IN PLATE TECTONICS WITH EXAMPLES FROM PLATE BOUNDARY AND PLATE INTERIOR SETTINGS

The Earth’s surface is a boundary condition for the plate tectonic processes that deform the lithosphere while also providing an interface where those processes dynamically interact with the hydrosphere, atmosphere, and biosphere. The three types of plate boundaries, together with relatively stable continental interiors, are immediately recognizable in topography and bathymetry and we now know that rates of crustal deformation in these settings are throttled by the efficacy of surficial processes to redistribute mass. Tectonic geomorphology, which emerged within a decade of plate tectonic theory, hinges on geomorphic and stratigraphic markers such as river channels, terraces, and growth strata to provide geologic geodetic and paleo-geodetic data with plate-scale spatial and temporal dimensions. When paired with other geologic, geophysical, and thermochronologic datasets, these markers help identify the deformation processes. The research frontier of plate tectonic theory that can be explored with tectonic geomorphology includes syn-orogenic crustal shortening and extension at plate boundaries, intraplate seismicity along passive margins, and intraplate orogenesis in continental interiors. For example, strain partitioning on syn-convergent and extensional faults and intrinsic vs extrinsic controls on fault slip along the Apennine (Italy) plate boundary is revealed using rock-magnetic based cyclostratigraphy applied to river terraces and correlative basin growth strata. In contrast, combinations of growth strata, channel profiles, and river terrace geomorphic markers are revealing the nature of transpressional rejuvenation of long-dead orogens in the Mongolian Altai of the central Asian continental interior. Similarly, river terraces and anomalously steep river channel profiles document crustal deformation in zones of historic seismicity for the mid-Atlantic passive margin. This deformation is embedded into regional dynamic topography epeirogenesis, which ironically was predicted by long-term landscape evolution paradigms before plate tectonics. Tectonic geomorphology contributions to plate tectonic theory will continue to evolve as field observations are used to elucidate the physical underpinnings and linkages between geomorphic and geodynamic numeric models.