Volcanic petrology and geologic history of Northeast Bank, Southern California Borderland.

Basaltic rocks, hyaloclastites, and fossil fragments incorporated in volcanic material, dredged from the flanks of Northeast Bank on the Southern California Borderland, show trace element abundances typical of eastern Pacific basin alkali basalts but enriched (880 ppm) Ba. The fossil fragments, incorporated in breccia, hyaloclastite, and agglomerate, include a fauna which lived in less than 50 m of water, as well as forms from the intertidal zone. Bathymetry of the bank and the depth range of the dredged zone indicate that there has been at least 300 or as much as 500 m subsidence since the volcanism which incorporated the fauna in volcanic material. Isostatic adjustments due to crustal load of the bank can account for this subsidence.