PALAEOMAGNETIC RESULTS ON A DOLERITIC SILL OF DECCAN TRAP AGE IN THE SONHAT COAL BASIN, INDIA*

Abstract

Klootwijk, C.T., 1974. Palaeomagnetic results on a doleritic sill of Deccan Trap age in the Sonhat Coal Basin, India. Tectonophysics, 22: 335-353. Palaeomagnetic research was carried out on a thick doleritic sill of Late Deccan Trap age (60.0 * 3.0 m.y.) in the Sonhat Coal Basin, Central India. The samples, 104 in all, showed a magnetization with normal polarity. The characteristic mean-site direction for this sill, obtained after treatment in alternating fields and by thermal methods, becomes coincident with the mean Upper Deccan Trap direction of the Western Ghats, after application of a correction for the slight dip of the adjacent strata. This indicates that the tectonic disturbances are of post-intrusional age. The present results do not support earlier palaeomagnetic arguments in favour of the hypothesis of a prolonged magmatic activity on the Indian subcontinent, lasting from the Rajmahal Trap effusion (100-105 m.y.) till the Deccan Trap effusion (60-65 m.y.). During thermal treatment of the specimens, evidence for a partial self-reversal of magnetization was found.