Paleomagnetic Study and Chemistry of Newer Dolerites from Singhbhum, Bihar, India

Abstract

Results of paleomagnetic studies on seventeen dikes sampled from the Newer Dolerites of Singhbhum, between latitude 22°0′N to 22°45′N and longitude 85°48′E to 86°25′E are reported. The dikes are of Precambrian age, probably older than 1000 my. Stable directions of magnetization were obtained for eleven sites by thermal demagnetization in a field free space in temperatures ranging from 250° to 400 °C. These studies showed that the dikes had been reheated by igneous activity of neighboring dikes of a younger age or by regional metamorphism of a younger period. Polished section studies carried out on these dikes showed that the magnetic mineral had been significantly altered as a result of these processes. Reliable virtual geomagnetic poles were obtained for ten different sites. These pole positions can be collected into three different groups which may represent three episodes of igneous activity of the Newer Dolerites. A very tentative polar wandering curve for the Precambrian in India is given.