Geophysical Evidence for the Origin of the Aleutian Basin

The crust of the Aleutian Basin, in the eastern deep-sea Bering Sea Basin, is concealed beneath 1 to 5 km of sediment, and its origin is poorly known. In the past 5 years, a multichannel seismic cruise, a new compilation of marine magnetic anomalies, and re-analysis of legacy multichannel and single-channel seismic data have provided insights into the formation of the Aleutian and adjacent basins. Ocean bottom seismometer refraction results indicate that the seismic structure near the center of the Aleutian Basin is typical of oceanic crust elsewhere, although it is slightly ( 1 km) thicker than the global average. Marine magnetic data show two distinct magnetic fabric domains, one characterized by north-south-oriented lineations and the other characterized by higher-amplitude and more spatially-variable magnetic anomalies. The lineated fabric does not correlate with basement topography in most places; thus, we interpret its origin as remnant magnetization variations of the upper crust, consistent with being formed by seafloor spreading. We also explore whether some of these anomalies might arise from fracture-zone structures. The main basement structure of the Aleutian Basin is a broad high termed the Vitus Arch. Numerous multichannel seismic reflection profile crossings of the Vitus Arch show no evidence of uparching after sediment deposition, nor is there any evidence in these profiles of igneous intrusions into the sediments. We agree with prior interpretations the Vitus Arch is a broad, structural uplift that formed as a result of mild NW-SE-oriented compressional strain accompanying plate convergence early in the history of the Aleutian Basin. In this study, we evaluate the evidence for an autochthonous (e.g. back-arc spreading) versus an allochthonous (e.g. plate capture during subduction change) origin of the Aleutian Basin.