SKEWNESS OF MARINE MAGNETIC-ANOMALIES CREATED BETWEEN 85-MA AND 40-MA IN THE INDIAN-OCEAN

We have performed a detailed analysis of the skewness of marine magnetic anomalies in Indian Ocean basins created between 85 and 40 Ma as a result of the northward motion of India. Visual and semiautomated methods of skewness determination were applied to the data. Both provide consistent results, but the visual method is preferred for its ability to deal with noisy data. Plots of apparent effective remanent inclination (or skewness corrected for present geomagnetic field inclination) versus time for conjugate basins display the combination of three effects: a gradual increase with time, related to the northward motion of the ridges attached to India in the geomagnetic reference frame; a gap between conjugate curves, which represents anomalous skewness sense stricto; and short-period fluctuations, which represent the sequence effect, i.e., the effect of neighboring magnetic sources on the skewness of a given anomaly. The anomalous skewness decreases with faster spreading rate and completely disappears above 50 km/m.y., an observation which negates geomagnetic field behavior as a possible cause of the observed anomalous skewness.