PALEOMAGNETIC STUDY OF RAJMAHAL TRAP IN INDIA : DISCUSSION OF GEOMAGNETIC DIPOLE MOMENT AND RECONSTRUCTION OF GONDWANALAND
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A paleomagnetic study was conducted on the Rajmahal trap in northeastern India. The age of the trap was determined by ^<40>Ar/^<39>Ar dating as 125 to 130 Ma (H. SAKAI et al., J. Geol. Soc. Jpn., 103,192,1997). The VGP (vitual geomagnetic pole) of the Rajmahal trap was studied and compared with the APWP (apparent polar wander path) of India (J. E. BESSE and V. COURTILLOT, J. Geophys, Res., 96,4029,1991). The VGP is situated slightly apart from the position of 120 Ma in Indian APWP, which suggests that the Rajmahal trap is older than 120 Ma. That is, paleomagnetic study supports the ^<40>Ar/^<39>Ar age of 125-130 Ma. This result suggests that the Rajmahal trap was formed around the age of rifting of India from Antarctica. Thelliers' paleointensity experiment was applied to the Rajmahal basalt and the paleointensity of 31.4±5.8 μT was determined. The geomagnetic dipole moment in Mesozoic was summarized using formerly reported paleointensities and data in this study. We can identify that the dipole moment from 180 Ma to 125 Ma before the period of Cretaceous quiet zone, oscillates between 30% and 70% of the present moment.
- Proceedings of the NIPR Symposium on Antarctic Geosciences
Proceedings of the NIPR Symposium on Antarctic Geosciences 10, 68-78, 1997-09