Structure and crustal balance of the Herald Arch and Hope Basin in the Chukchi Sea, Alaska

The Herald Arch is a structural high bounded by the Herald Thrust fault to the northeast and by a normal, or possibly strike-slip, fault to the southwest in the Chukchi Sea, off the northwest coast of Alaska. The thrust continues for approximately 60 kilometers from the northwest tip of the Lisburne Peninsula into the Chukchi Sea. Its dip varies from nearly 60 degrees in the east, to 20 degrees in the west before terminating on the available seismic data. Closer to the shore, the detachment of the Herald Thrust occurs at the edge of a Devonian rift basin containing the Franklinian Sequence. Moving towards the northwest, the rift diminishes along with the detachment of the Herald Thrust. Northeast of the Herald Thrust in the Colville Basin, the anticlines and thrust faults of the Brookian layers diminish in magnitude and displacement from the Lisburne Peninsula to the northwest. The depth to the reflection Moho decreases from approximately 37 km beneath the Colville Basin to 28 km under the Hope Basin to the south. Estimates for the amount of extension required to produce the present day crustal thickness are at least 20% less than the amount of Tertiary stretching that has been documented by restoration of supracrustal normal faults. The thinning of the crust could be attributed to differential spreading where the upper crust was stretched less then the lower crust and mantle, or due to and older, mid Cretaceous, extensional event that has gone unrecognized on the seismic data. A magnetic high that corresponds closely to the Herald Arch could be evidence of magmatic material brought up during the mid-Cretaceous spreading event