Crustal architecture of North Singhbhum Mobile Belt, Eastern Indian Shield: Constraints from two-dimensional and three-dimensional modelling of Bouguer gravity and aeromagnetic data

The North Singhbhum Mobile Belt (NSMB) that lies in the Eastern Indian Shield between the Chotanagpur Granite-Gneiss Complex (CGGC) and the Singhbhum Craton (SC) provides a unique opportunity to understand the Proterozoic crustal evolution of the Indian shield. In the present study, an integrated interpretation of petrophysical, Bouguer gravity, and aeromagnetic data was carried out to examine the crustal architecture and structural framework of the region. Three-dimensional (3-D) inversion of the aeromagnetic anomalies reveals that the magnetic basement depths range from 0.2 to 9.0 km in the region. The crustal models obtained from two-dimensional (2-D) and 3-D forward modelling of potential field data reveal the Moho at 37-38 km depth beneath the NSMB and at a relatively deeper depth of 39-40 km and 40-44 km beneath SC and CGGC, respectively. Further, the distinct gravity high and the coinciding bipolar magnetic anomalies associated with the Dalma Formation can be attributed to the mafic/ultramafic intrusions. Gravity models across the Singhbhum Shear Zone (SSZ) and South Purulia Shear Zone (SPSZ) exhibit the crustal density inhomogeneity and Moho offset, typical of ancient suture zones of Precambrian terrains. In comparison, the absence of such crustal-scale signatures across the North Purulia Shear Zone represents its intracratonic nature. Further, the Bouguer gravity and aeromagnetic signatures across the SPSZ, together with the crustal architecture and metamorphic ages, suggest that SPSZ marks the eastward continuity of the Gavilgarh-Tan Shear Zone along which the amalgamation of northern and southern Indian cratonic blocks possibly took place at ca. 1.0-0.9 Ga.