Collaborative Research: Reactivation of Continental Margin Fracture Zones: Insights From Seismicity, Strain Patterns, and Numerical Modeling of Modern and Ancient Orogens

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The overall goal of this project is to understand how along-strike variations in crustal architecture associated with rift-related continental margin fracture zones affect the evolution of collisional orogenic belts. Data will be collected from the ongoing Taiwan and early Paleozoic Taconic collisional orogenic belts because of the opportunities afforded by modern and ancient orogens for understanding kinematics at lower upper-crustal levels. Short-term brittle deformation will be characterized in the region of the partially subducted fracture zone in Taiwan from brittle faults and earthquake focal mechanisms through the application of micropolar continuum theory to invert for strain. Long-term ductile deformation resulting from the reactivation of continental margin fracture zones will be quantified through finite and incremental strain analysis of slates exposed in the Taconic allochthon of Vermont and New York. Kinematic and mechanical modeling will be undertaken to integrate the results obtained from the two orogenic belts. In addition to testing the viability of kinematic models, the mechanical modeling will be used to put limits on the boundary conditions and rock rheology.Although the high topography of mountain chains develops on the overriding tectonic plate at collisional zones, the geometry of the downgoing tectonic plate can exert a fundamental control on the pattern of deformation within and uplift history of mountainous regions. Fracture zones, which form during precollisional rifting and lie at a high angle to the continental margin, are a general feature of downgoing continental crust. Their reactivation during collision is expected to produce complex, three-dimensional deformation. This project, therefore, will contribute to ongoing research in the field aimed at (1) describing how crustal-scale heterogeneities result in strain partitioning in both the horizontal and vertical directions in a deforming body of rock and (2) fully characterizing the three-dimensional nature of deformation of Earth?s crust. Moreover, the integration of results from modern and ancient collisional zones will enable the development of a global model to aid in the interpretation of other ancient collisions. Ultimately, this project will advance understanding of the factors influencing the topographic development of mountain chains and the distribution of earthquakes within them.