Abstract
Single‐channel and multichannel marine seismic data off the coast of West Antarctica collected during two Nathaniel B. Palmer cruises (NP92‐8 and NP96‐2) in the vicinity of 65°S to 71°S, 220°E to 250°E, reveal a NNW trending graben. We interpret this graben to be part of the paleodivergent plate boundary between the Marie Byrd Land and Bellingshausen plates. This graben coincides with a −520 nT magnetic anomaly to the NNW and a −720 nT anomaly to the SSE, as well as a 20 mGal negative gravity anomaly. Seismic profiles subparallel to the graben (22 km/Ma half‐spreading rate) reveal greater seafloor roughness to the NE, where seafloor spreading was slower, than to the SW (27 km/Ma half‐spreading rate). These data allow the position of the Marie Byrd Land‐Bellingshausen plate boundary to be constrained more precisely than has previously been possible, with a trend of N17°W from 68.52°S, 233.65°E to 68.41°S, 233.56°E. The sediment‐filled graben has normal separation of sedimentary layers varying from 740±30 m to 580±20 m imaged in seafloor of age A33y (74 Ma).
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