Scott Jess: LL 11.04.24

The ups and downs of extensional tectonics
Abstract: Landscapes shaped in extensional tectonic settings are hard to study. For centuries many have attempted to delineate long-term tectonic histories of these areas through a range of geomorphic, analytical and stratigraphic approaches, all arriving at differing conclusions. These are, in part, down to the limitations inherent in each approach and a lack of combining methods in many studies. For example, the record of surface and rock uplift preserved in an area’s geomorphology over million-year times scales can be difficult to delineate, if it is present at all. Low-temperature thermochronology, frequently used to infer long-term exhumation histories, has limitations that can make it difficult to interpret and model. Offshore, sedimentary fluxes observed in many extensional basins are consistently linked to a tectonically active onshore, even though mechanisms for are hard to find. Using examples from across Eastern Africa, North Atlantic, and the United States, we will explore how these limitations can be overcome or challenged to help reexamine how extensional tectonic system evolve over geological timescales. Rock uplift histories extracted from horst structures across the East African Rift may help to show how extension in the region is older than expected. Thermochronology and offshore sediment packages fluxes across West Greenland are re-examined and reconciled to suggest the margin has experienced little tectonically induced uplift over the last 60 million years. Finally, new thermochronology methods used across the Appalachians show real potential for improving how we can study exhumation across vast extensional settings. These works highlight that studying landscapes shaped by extensional tectonics is challenging, but can be made easier when the entire system is examined, and new methods are implemented.