SEA-FLOOR SPREADING IN THE EASTERNMOST INDIAN-OCEAN REVEALS CYCLICITYIN OCEAN CRUST ACCRETION (0-36 MA)

A new map of chrons (C1-C20) from the easternmost Australian-Antarctic ridge segment to the western Ross Sea is presented, and rates of ocea n crust accretion are calculated. The spreading process in this sector of the Southern Ocean is not uniform. A very clear magnetic anomaly p rofile across the Australian-Antarctic plate boundary has allowed a de tailed definition of the magnetic anomalies and a fine scale assessmen t of the spreading rate. Substantial asymmetry of spreading between th e northern and southern flanks of the ridge axis has been revealed in the 2.15-4.29 Ma time interval. The linear regression of the instantan eous spreading velocity distribution calculated south the ridge axis a long a flow-line shows a general trend with decreasing rates vs. time from 36 Ma to the present, with decrement of 0.022 cm/yr(2). The polyn omial regression shows two-maxima of 20 Ma (4.8 cm/yr) and 31 Ma (6.1 cm/yr); the minimum coincides with 21.5 Ma (1.5 cm/yr). These results are in agreement with those obtained computing instantaneous velocitie s for the conjugate northern flank of the Australian-Antarctic ridge s egment.