Abstract

“Tectonic escape” is strike-slip-dominated motion of colliding continental or arc crust in the direction of subductable oceanic crust. I describe four examples of large transtensional basins in Cenozoic zones of tectonic escape and propose that these basins formed along newly formed, transtensional faults formed between the collided and escaping parts of the plate. The reoriented direction of the escaping plate, split along the new transtensional fault zone, is determined by the presence of a “free face,” or subductable oceanic crust. Continued subduction toward the free face is driven by the force of gravity acting on dense oceanic crust (“slab pull”). The four examples presented here show that a variety of transtensional deformational styles can be generated within this specific type of divergent tectonic setting. These transtensional styles include pull-apart basins at fault stepovers, more asymmetrical, rift-like basins thought to be formed under conditions of fault-normal extensional stresses, and single or multiple short spreading ridges. Transtensional styles may be controlled more by the type and age of crust present than the angle of reorientation of the escaping plate.

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