CRUSTAL STRUCTURE OF DEXTRAL TRANSPRESSIVE FAULT SYSTEMS: COMPARISON OF THE NORUMBEGA FAULT, MAINE, AND THE CHUGACH METAMORPHIC COMPLEX SHEAR ZONE SYSTEM, ALASKA

The Norumbega Fault (NF) and Chugach Metamorphic Complex shear zone system (CMCSZ) are two geologically-similar, transcurrent, orogen-parallel systems that may provide excellent comparisons for development of mid- to lower-crustal structure during terrane accretion in tectonic settings with lateral components of motion. The dextral transcurrent NF stretches nearly 1200 km from Connecticut to New Brunswick and comprises a zone of crustal weakness extending through the amphibolite-grade rocks of the mid- and lower-crust into the mantle. The dextrally transpressive CMCSZ consists of multiple major fault strands that cut and offset the metamorphosed accretionary prism rocks of the eastern Chugach Terrane during oblique ridge subduction within a tectonic corner structure. Both the NF and CMCSZ have a poly-deformational history—from the Devonian through the Cretaceous for the NF, and from the Late Cretaceous to the Eocene for the CMCSZ. These two fault systems consist of parallel transform fault systems or shear zones that cut and offset high-grade metamorphic rocks, and comparison may help to indicate formation of transpressive restraining bend systems associated with orogenic and structural trend changes. A greater understanding of the accommodation of strain via orogen-parallel transport can be gained through the comparison of these two similar-style deformational systems.