Palaeomagnetism of Sukinda chromites and their geological implications

Abstract

Thirty-eight oriented samples were collected from seven sites over the Precambrian Sukinda chromite ore (between 85°43′E; 21°01′N and 85°50′E; 21°03′N), which is in the form of a plunging syncline. On isolating the primary component of magnetization and affecting the necessary tectonic correction, four sites (A, B, C, F) were found to possess a reverse magnetic polarity (D=210°, I=+22°, with K=122 and α95=6° and one site (E) was found to bear a normal polarity (D=49°, I=-16° with K=474 and α95=2°). The remaining two sites D and G were rejected, the former because of scatter in directions and the latter due to overprinting by a dominant secondary magnetization, induced by lateritization. On comparison of VGPs evaluated for these chromite deposits, with those of other Precambrian rocks almost of a similar age, it is seen that these chromites are probably older than the Gwalior Traps whose age is 1830 ± 200 Ma. From the rock magnetic and microscopic examination it is deduced that the massive chromites of the Sukinda valley have not been affected magnetically to any great extent by serpentinization, though their host rocks are serpentinized ultramafics. Consistent directions of remanent magnetism point to the fact that these deposits crystallized in fairly stable conditions, characteristic of the stratiform type of chromite deposits, therefore, leading us to infer the Sukinda chromites to be of that type. These palaeomagnetic data, when subjected to the fold test, show the primary remanence to pre-date the tectonic disturbance and hence prove these chromites to have consolidated prior to the regional tectonic activity of the area.