Sea-floor spreading in the easternmost Indian Ocean reveals cyclicity in 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 ocean crust accretion are calculated. The spreading process in this sector of the Southern Ocean is not uniform. A very clear magnetic anomaly profile across the Australian Antarctic plate boundary has allowed a detailed definition of the magnetic anomalies and a fine scale assessment of the spreading rate. Substantial asymmetry of spreading between the 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 instantaneous spreading velocity distribution calculated south the ridge axis along a flow-line shows a general trend with decreasing rates vs. time from 36 Ma to the present, with decrement of 0.022 cm/yr2. The polynomial 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 (1.5cm/yr). These results are in agreement with those obtained computing instantaneous velocities for the conjugate northern flank of the Australian Antarctic ridge segment.