| Summary: | The Contact fault system has traditionally been viewed as the terrane boundary between the Chugach and Prince William terranes in southern Alaska. It is thought to divide the Campanian-Maastrichtian Valdez Group from the Paleocene-Eocene Orca Group in an arcuate trace across Prince William Sound (PWS). The purpose of this study is to determine whether the Contact fault functions as a terrane boundary by analyzing units on either side of fault segments, which have different names across PWS. In northeastern PWS the high-angle Jack Bay fault is defined as the contact. It merges with the low-angle Landlock fault, defining the Landlock block. In northern PWS the contact is mapped as the Eaglek fault, and in western PWS as the Culross fault. Sandstone samples were collected from either side of the Jack Bay, Landlock, and Eaglet faults between Valdez Arm and Seward. U-Pb ratios were measured for detrital zircons using LA-ICP-MS at the University of Arizona Laserchron Center. Grain-age distributions and maximum depositional ages (MDA) of units across the Jack Bay and Culross faults indicate that these fault segments do not function as a terrane boundary. Our results show that the Eaglek fault in Unakwik Inlet does separate Orca Group from Valdez Group, making it the only Contact fault strand in PWS evidenced to act as the terrane boundary. U-Pb dating of samples across the Landlock faults show that the currently-mapped Landlock block must be revised, as there is no evidence that the fault serves as a boundary between distinct units. Furthermore, grain-age distributions and maximum depositional ages (MDA) of rocks in the Landlock block suggests that it has a similar provenance to Orca Group farther east in PWS on Hinchinbrook Island. Overall, the data suggest that the Contact fault system as currently mapped in PWS is not a major tectonic boundary.
|
|---|