B K Galloway and S L Klemperer (Both at: Department of Geophysics, Stanford University, Stanford, CA 94305; 415-725-9907; e-mail: galloway@pangea.stanford.edu) J R Childs and T M Brocher (MS 999, 345 Middlefield Road, Menlo Park, CA 94025) R M Allen (Department of Geological Science, University of Durham, Durham, DH1 3LE, UK) Bering-Chukchi Working Group
We present two deep seismic reflection profiles from the Bering Straits to St. Lawrence Island on the northern Bering Shelf.
The upper and middle crystalline crust, below any sedimentary basins and above about 8 s, has few coherent reflectors. The lower crust has extensive laminar reflectivity, extending from about 8 s to about 11 s. Modelling of coincident refraction data suggests a lower-crustal velocity of about 7 km/s (see Allen et al., this session). The base of this reflectivity, taken to be the reflection Moho, stays fairly constant at around 11 s. North and south dipping upper-mantle reflectors are also seen. A set of mantle reflectors exists just south of the Bering Strait and consists of a band of subparallel reflectors extending from about 11 s to the base of the data (17 s), dipping north at about 0.7 s/km. A single reflector is also visible just north of St. Lawrence, and extends from about 11.8 s to about 15 s, dipping south at about 0.2 s/km.
Extension is believed to have occurred in the Bering Strait region episodically from the Late Cretaceous to the Present (Dumitru, et al., 1995). Extension may be the cause of the lower- crustal reflectivity seen in this dataset, as well as the regional Cretaceous granitic plutons, and Neogene and Quaternary basaltic volcanism mapped in the region. The association of the upper-mantle reflectors with crustal deformation in this area is unknown.