Strike‐slip faulting and block rotation along the contact fault system, eastern Prince William Sound, Alaska

The Chugach and Prince William terranes compose a Mesozoic through Paleogene accretionary complex rimming the Gulf of Alaska. In eastern Prince William Sound, we studied the Contact fault system, which juxtaposes flysch of the latest Cretaceous Valdez Group (Chugach terrane) with flysch of the late Paleocene through early Eocene Orca Group (Prince William terrane). Near Valdez, we found three lithotectonic belts separated by right‐lateral strike‐slip faults. Anomalous structural trends between the two faults appear to be the result of clockwise block rotation in response to dextral shear. In a second area, to the east near Cordova, early formed folds were rotated clockwise before burial to depths sufficient to form axial‐planar cleavage. Apparently, synchronous thrusting and dextral‐slip faulting occurred during accretion. The relations above, combined with earlier studies, suggest that the fundamental nature of motion on faults composing the Contact fault system is dextral. Near Cordova, deposition, accretion, and block rotation occurred between early Eocene and early middle Eocene time. Near Valdez, block rotation appears to have occurred prior to accretion of the rocks near Cordova. Current plate tectonic models show that convergence became progressively more oblique during Eocene time, correlating well with the initiation of strike‐slip faulting. The presence of early Tertiary dextral‐slip faults, such as these, helps account for the northward displacement of the Chugach‐Prince William terrane with respect to the Peninsular and Wrangellia terranes suggested by paleomagnetic and geologic studies.