North Singhbhum Mobile Belt [NSMB]

The North Singhbhum Mobile Belt (NSMB) is a multiple folded, low to medium grade meta-sedimentary and meta-igneous rocks of Proterozoic age (1.0–2.4 Ga) sandwiched between the Archaean (>2.4 Ga) Singhbhum Craton in the south, and the Meso/Neo-Proterozoic (0.9–1.7 Ga) Chotanagpur Gneissic Complex (CGC) in the north by north-dipping ductile shear zones.

Clastic sediments with minor volcanics comprising the Singhbhum Group were laid down in rift basin during meso to neo archaean periods. They were subjected to deformation and metamorphosed during the Singhbhum orogeny.

This was followed by a major mafic volcanic event under a rift setting. The volcano-sedimentary sequences are represented by Dalma Group and Dhanjori Group.

Singhbhum Group –

The rock succession lying to the north of Singhbhum shear zone is known as Singhbhum Group.

• The lower Chaibasa formation are exposed in the cores of anticlines, while Dalbhum formation comprising the upper unit occupies the synclnal flexures in northern areas.
• These sequences contains some beds of volcanic flows and tuff containing Fe and Mn ores.

Dalma Group –

The central part of the NSMB has a belt of volcano-sedimentary sequence exposed in Dalma Hills. This sequence is named as Dalma Group. The upper unit of Dalma Group is consisting of ultramafic volcanics. The rocks of Dalma Group have undergone a low grade (greenschist facies) metamorphism.

Dhanjori Group –

The Dhanjori Group is also a volcano-sedimentary sequence and is exposed along the north-eastern edge of Archaean protocontinent. It comprises of basal conglomerate overlain by beds of arkose, quartzite and extensive lava flows.

Simlipal Basin –

Southern extension of these volcanic flows is observed in Simlipal Hills of Keonjhar district and Bonai Hills in sundergarh district of Orissa. Unlike the Dalma and Dhanjori Group, the volcano-sedimentary rocks of Simlipal rocks are undeformed.

REFERENCES –

• https://doi.org/10.1016/j.precamres.2007.07.015
• Lyell collection – ‘Chapter 10 Palaeo-Mesoproterozoic sedimentation and tectonics of the Singhbhum Craton, eastern India, and implications for global and craton-specific geological events’
• Fundamentals of historical geology and stratigraphy of India – Ravindra Kumar