Rock magnetic signatures of the dalma Formation in the Singhbhum mobile belt, Eastern India

Abstract

Petrography and rock magnetic properties of the Dalma volcanics (DV) and associated meta-sediments of Singhbhum mobile belt (SMB) are presented to describe magnetic grain size and Fe-Ti oxide mineralogy of the volcano-sedimentary sequence. Petrography revealed the presence of Ti-magnetite, hematite, ilmenite and pyrite in quartz-biotite-sericite-muscovite schists, quartzites, and volcanic rocks. The average value of magnetic susceptibility (c) is 5.6 x 10-7 m3/kg, anhysteretic remanent magnetization (ARM) is 2.25 x 10-5Am2/kg, saturating isothermal remanent magnetization (SIRM) is 403.33 x 10-5 Am2/kg, soft IRM is 240.2 x 10-5 Am2/kg, hard IRM is 77.56 x 10-5 Am2/kg, and natural remanent magnetization (NRM) is 54.1 mA/m. The central tendency of the inter-parametric ratio ARM/c is 0.06 kAm-1, SIRM/c is 111.04 kAm-1 and S-ratio is 0.8. Based on results, magnetic mineralogy indicated that the bulk magnetic carrier is stable single domain (SSD) or pseudo single domain (PSD) grains of Fe-Ti oxides with minor iron sulphides such as pyrite, greigite and pyrrhotite. Petrography and rock magnetic studies suggest that the magnetic carriers are chiefly secondary in origin and the NRM is modified over time.