IMPACT TECTONICS; BEYOND THE CRATERS

After decades of mapping and characterizing tectonic structures of the Eastern North American seaboard, I am beginning to understand how large-bolide (asteroid or comet) impacts have far-reaching strain effects that extend well beyond the craters that are a fundamental aspect of plate tectonics. 3D computer models of impact-tectonic, far-field (ITFF) crustal and lithospheric strains resulting from the Chicxulub (~66 Ma) and Chesapeake (~35 Ma) bolide impacts on the North American Plate (NAP) were developed, and then used to help identify other suspected, large-impact sites on Earth and Mars. The modelled strain fields have geometric shapes constrained by seismic-wave geometry that reflect rapid tectonic upheavals occurring thousands of kilometers away from the craters where the ground energy is introduced suddenly, then dissipates remotely as seismic disturbances. Bench-top impact tests using glass spheres show that different impact-incidence angles produce differently shaped strain fields. Current plate-tectonic theory ignores ITFF secondary structures or any impact-induced plate fragmentation and reorganizations stemming from planetary accretion, and therefore doesn't fully capture the set of causative agents behind such enigmatic geological features like diatremes, hot-spots, kimberlites, and epeirogenic uplifts. A plate-tectonic paradigm that excludes ITFF strains simply cannot explain the composite set of driving forces behind terrestrial plate mechanics. Besides contributing to our differentiation of geological time on Earth, such large impacts also spur plate breakups and subsequent shifts to drive tectonic systems towards new equilibriums. Modern, remotely sensed Earth data are fundamental to the formulating these hypotheses that show that not only do periodic, large-bolide impacts profoundly alter Earth's ecosystems, but also produce tectonic shifts and upheavals, with demonstrable ties to such ill-explained epeirogenic episodes in the North American plate as the Laramide orogeny, Adirondack and Llano uplifts, and Cincinnati Arch. A big challenge in accepting and integrating shock dynamics into plate-tectonic theory is the prospect of having periodic tectonic episodes of rapid mountain building. The 3D strain-field models are available at www.impacttectonics.org.