Abstract:
The present study deals with the alternating field (AF) demagnetization of the volcanic rocks and meta-sediments from the
North Singhbhum Mobile Belt (NSMB) within a field of 2.5 to 100 mT. All the three rock types encountered were subjected
to AF demagnetization and the behavior during demagnetization was noted. As the rocks of the NSMB have variable
potential to record remanences, the samples to demagnetize were sorted based on their feasibility to record characteristic
remanent magnetization (ChRM). A gradual decrease in the magnetic intensity of the quartzites during AF demagnetization
yielded two stable palaeomagnetic vectors recorded in them. Two palaeomagnetic poles are determined from these stable
vectors. The palaeomagnetic poles thus obtained from the quartzites lie on a hairpin bend in the Proterozoic apparent polar
wandering path (APWP) of the Indian subcontinent. This is significant towards the ~ 1850 Ma initiated Satpura orogeny
which developed the regional mesoscopic as well as the magnetic fabrics in the NSMB. Thus, these palaeomagnetic poles
are useful in relating the regional tectonics and magneto-tectonics of the NSMB. However, the magnetic intensity of the
schists and volcanic rocks continues to decrease with increasing applied AF up to a certain extent, and then again continues
to increase, which proves that these samples are affected by the acquisition of gyro remanent magnetization (GRM), which is
a magnetic vector component acquired by certain rocks during AF demagnetization of their natural remanent magnetization
(NRM). As GRM is an imperfection commonly associated with AF demagnetization of the rocks, the samples with such
features are not considered for tectonics-related palaeomagnetic studies in the NSMB.
