Abstract
The paleomagnetism of the Deccan Trap lavas in the western Ghats were studied in detail. Several stability tests were performed but the most effective one seemed to be progressive alternating field demagnetization. The direction of stable remanence was determined in 28 Mahabaleshwar and 5 Amboli lavas. It was noted that there is a good correlation between the stability of remanence and certain properties of magnetic minerals. Most rocks with evidence of high temperature oxidation are magnetically more stable than others.
As there is no significant serial correlation nor systematic large movement in directions of NRM in Mahabaleshwar lavas, the directions of the NRM may well represent the secular variation in the geomagnetic field in Eary Tertiary. The present data show a scatter of directions larger than the Quaternary paleomagnetic results, suggesting a bigger secular variation at that time. A statistical method to determine the upper limit of the time interval of volcanism was applied to the Mahabaleshwar section with the result that their activity had not lasted more than 5m.y. at 5% significance level. The mean pole position for all the lavas in this study shows a good agreement with the hypothesis that India moved northward in the Cenozoic era with great speed.
