New Seismic Reflection Images of the Continent-Ocean Transition across the Exmouth and Cuvier Margins, off Northwestern Australia

We present new multi-channel seismic reflection results obtained during R/V MAURICE EWING cruise 0113 that investigated the development of the adjacent Exmouth and Cuvier rifted margins, northwestern Australia. We have processed the 480-channel data through post-stack migration using ProMAX. The transition from faulted blocks of pre-existing continent to normal oceanic crust occurs across a wide zone of basement highs and troughs on the southern Exmouth margin. In contrast, this transition on the Cuvier margin occurs beneath a smooth slope that is only half as wide. Strong reflections from the Moho are observed at 9-10 seconds beneath most of the Exmouth margin, but only rarely beneath Cuvier. Units of seaward-dipping reflectors (SDRs) appear at the seaward edge of the continent-ocean transition on the Exmouth margin, and the thickness of oceanic crust adjacent to this margin is greater than that of normal oceanic crust. The sizes of the SDR units are similar in both margins, suggesting that both margins are moderately volcanic. Previous studies suggest that the final breakup was contemporaneous between the two margins (around magnetic anomaly M10 time). However, the shape of magnetic anomalies identified as M5-M10, and their location over the basement highs and troughs on the outer Exmouth margin, call into question this interpretation. The final breakup of the southern Exmouth margin possibly occurred later (around M4 time) than that of the Cuvier margin, or a ridge crest jump transferred M5-M10 to the Indian plate.