Title: The Structural Evolution of the Calabrian Forearc
Description: This dissertation investigates the temporal and spatial variations in deformation of the Calabrian forearc during the evolution of the subduction-rollback system. In addition to contributing new data to the area, I develop three strategies for understanding recent and active deformation by linking long-term structural data with short-term geomorphological data. First, setting a “baseline” of deformation is important when studying plate boundaries. Through the structural mapping of an uplifted forearc basin, I conclude that rapid rollback is characterized by tectonic quiescence in the Calabrian forearc when it is located far from collision (from ~12 Ma – ~5 Ma). This “baseline” provides a framework from which I interpret younger phases of deformation. In the middle Pliocene (~5-4 Ma), an arc-parallel shortening event characterizes the first stage of forearc collision in my field area. These folded sediments are later tilted, but structural data from the field cannot constrain the age or structure responsible for this youngest phase of deformation.

The Neto River dissects this tilted surface opening up the possibly of linking structural data with geomorphic data from river erosion. I collected a transect of river sediment samples for 10Be analysis to determine variation in catchment-wide erosion rates through the modern day deformation. I, then, developed a numerical model that describes changes in erosion rate through time with the structural growth of the tilted surface. The model is the first of its kind to use catchment-wide erosion rates to constrain a structural model. The model results constrain the age of the beginning of deformation to 850 ka and suggest that a fold with a migrating hinge caused tilting of the surface. The model provides the basis for my hypothesis that the forearc is experiencing an arc-perpendicular shortening strain, which contradicts conclusions from GPS data and the well-documented extension in the western part of the forearc. To further investigate surficial deformation, I carry out geomorphic analyses of 87 river drainages.

I interpret my findings in terms of structural framework and find that surficial deformation varies tremendously from east to west. The rivers draining eastward are characterized by low concavities and higher erosion rates, consistent with shortening. While just 50 km away, the westward-draining rivers are characterized by high concavities and lower erosion rates, consistent with extension. Overall, the drainages are shifting from east-draining to west-draining, likely due to the topographic growth that decreases concavities on the eastern side. Although a new interpretation, this finding is consistent with previous structural, paleomagnetic, and seismological datasets. In each of the chapters, I interpret the structural and geomorphic data in a regional framework. This extra step is critical in interpreting deformation along active plate boundaries because it is highly variable and can be seemingly contradictory. In my final chapter, I present a cross section of the plate boundary that incorporates my data and interpretations from the geomorphic results and the most recent structural event as well as data from multiple other sources (GPS, seismological, paleomagnetics, structural, tomographic, geomorphic, etc.).

This approach confirms the importance of boundary conditions on deformation in a subduction-rollback system. More intriguingly, the cross-section highlights the spatial variations along the surface and with depth suggesting that there is significant interplay between active structures.